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Longitudinal joints are the most vulnerable parts of prefabricated utility tunnels, susceptible to damage from external forces and foundation settlement. Currently, the shear mechanical properties of prefabricated double-cabin utility tunnel joints are unclear, preventing the evaluation of the structural or joint safety of utility tunnels. The shear mechanical response and failure characteristics of the joints of prefabricated double-cabin utility tunnels are investigated by combining model testing with numerical simulation. The results indicate that the shear deformation of utility tunnel joints can be categorized into elastic, crack propagation, and damage stages. In the course of joint-shear deformation, the middle utility tunnel sustains centrosymmetric failure. The degree of deformation of the large cabin is greater than that of the small cabin, while the damage to the small cabin is more severe. When the utility tunnel is subjected to the same load, the joint dislocation under the gravelly sand foundation is the smallest, but the damage range is the largest and the cracks are the most. Local strengthening and protection are needed at the chamfer, near the bolt hole, and the top and bottom. The stratum conditions have little effect on the shear stiffness of the joint during the elastic stage, but they have a significant impact during the crack propagation and damage stages. Finally, the joint damage area is approximately 15% of the total utility tunnel, and the deformation region of the longitudinal connectors is approximately 16% of its length. [ABSTRACT FROM AUTHOR]

This paper systematically investigates the dynamic mechanical response and fragment characteristics of sandstone with asymmetrical conjugate fissures subjected to preexisting static stress based on the split Hopkinson pressure bar apparatus. The cross-fissured sandstone exhibits significant variations in mechanical behavior when exposed to higher dynamic strain rates under identical static pre-stress. The cross-fissured sandstone with a higher dynamic strain rate is characterized by a greater coupled strength under the same static pre-stress; for a given dynamic load, the highest coupled strength occurs under the static pre-stress of 60% UCS. The failure mode of the cross-fissured sandstone is predominantly governed by the dynamic strain rate, independent of static pre-stress variations considered in this investigation. At lower dynamic strain rates, the specimens typically exhibit a mixed tensile-shear failure mode, characterized by the dominance of larger fragments in the broken specimens. In contrast, under high dynamic impacts, the sandstone tends to fail in a shear-dominated manner, resulting in smaller fragments with a more uniform size distribution. Furthermore, the study explores how varying dynamic strain rates and static pre-stress influence the fragment characteristics of the cross-fissured sandstone. Higher dynamic strain rates and increased static pre-stress generally lead to smaller mean fragment sizes. This phenomenon is quantitatively described by fitting fragment size distributions using the Generalized Extreme Value (GEV) distribution, revealing a decrease in the location parameter (μ) and an increase in fractal dimension. These metrics indicate that higher dynamic strain rates and static pre-stress result in sandstone specimens breaking into smaller fragments with a more homogeneous size distribution. These findings contribute to a deeper understanding of rock dynamics, with potential implications for engineering applications involving similar geological configuration under dynamic loading conditions. [ABSTRACT FROM AUTHOR]

In this study, a novel debris flow resisting structure is proposed that incorporates negative Poisson's ratio (NPR) cables to unite a flexible net and a rigid barrier; this structure is referred to as the NPR barrier. The NPR barrier attempts to utilize the mechanical properties of the NPR cable—the constant resistance and large deformation—to convert the impact into particle friction resistance and support force. NPR cables can effectively improve the performance of the resisting barrier. To investigate the mechanical response of an NPR barrier, physical experiments are conducted on a debris flow impacting an NPR barrier at two distances with four volume fractions. The experimental results reveal that the impact model of a debris flow with an NPR barrier is a hybrid model that simultaneously incorporates both runup and pileup mechanisms. During the buffering, run-up, and backflow-depositional stages of the debris flow, the NPR cables correspondingly demonstrate a sharp increase in resistance, slight decrease in resistance, and constant resistance, respectively, effectively transforming the impact into resistance. The relationship between the buffer force and impact force exhibits an inverse correlation as the material volume fraction increases. When the material volume fraction increases from 40 to 70%, the buffer force significantly increases by 73.4%, and the impact force substantially decreases by 35.6%. Finally, the calculation methods for the impact force, NPR cable tension, and buffer force are discussed. This study represents an attempt to generate novel insights into the structural optimization of debris flow control systems. Highlights: A novel debris flow barrier, which incorporates Negative Poisson's ratio (NPR) cables, a flexible net, and a rigid barrier, is proposed and referred to as the NPR-anchored barrier (NPR barrier). The impact model of a debris flow with an NPR barrier is a hybrid model that simultaneously integrates both run-up and pile-up mechanisms. The NPR barrier utilizes the constant resistance and large deformation properties of the NPR cable to achieve a sustained equilibrium of impact load and to enhance the efficiency of dissipating impact energy. The mechanical response properties of the NPR barrier have been validated through physical experiments and mechanical calculation analyses. [ABSTRACT FROM AUTHOR]

This study aims to develop an analytical model based on the curve beam theory to capture the mechanical response of a multihelix cable considering the internal contact displacements. Accordingly, a double-helix cable subjected to axial tension and torsion is analyzed, and both the line and point contacts between the neighboring wires and strands are considered via an equivalent homogenized approach. Then, the proposed theoretical model is extended to a hierarchical multihelix cable with mutual contact displacements by constructing a recursive relationship between the high- and low-level multihelix structures. The global tensile stiffness and torsional stiffness of the double-helix cable are successfully evaluated. The results are validated by a finite element (FE) model, and are found to be consistent with the findings of previous studies. It is shown that the contact deformations in multihelix cables significantly affect their equivalent mechanical stiffness, and the contact displacements are remarkably enhanced as the helix angles increase. This study provides insights into the interwire/interstrand mutual contact effects on global and local responses. [ABSTRACT FROM AUTHOR]

The stick-slip action of strike-slip faults poses a significant threat to the safety and stability of underground structures. In this study, the north-east area of the Longmenshan fault, Sichuan, provides the geological background; the rheological characteristics of the crustal lithosphere and the nonlinear interactions between plates are described by Burger's viscoelastic constitutive model and the friction constitutive model, respectively. A large-scale global numerical model for plate squeezing analysis is established, and the seemingly periodic stick-slip action of faults at different crust depths is simulated. For a second model at a smaller scale, a local finite element model (sub-model), the time history of displacement at a ground level location on the Longmenshan fault plane in a stick-slip action is considered as the displacement loading. The integration of these models, creating a multi-scale modeling method, is used to evaluate the crack propagation and mechanical response of a tunnel subjected to strike-slip faulting. The determinations of the recurrence interval of stick-slip action and the cracking characteristics of the tunnel are in substantial agreement with the previous field investigation and experimental results, validating the multi-scale modeling method. It can be concluded that, regardless of stratum stiffness, initial cracks first occur at the inverted arch of the tunnel in the footwall, on the squeezed side under strike-slip faulting. The smaller the stratum stiffness is, the smaller the included angle between the crack expansion and longitudinal direction of the tunnel, and the more extensive the crack expansion range. For the tunnel in a high stiffness stratum, both shear and bending failures occur on the lining under strike-slip faulting, while for that in the low stiffness stratum, only bending failure occurs on the lining. [ABSTRACT FROM AUTHOR]

During perfusion culture, the growth of bone tissues in the scaffold was closely related to the locations of initial adhered cells and their density. In this study, the fluid mechanical responses of Voronoi-lattice scaffolds and initial adhered cells on scaffolds were quantitatively investigated. Multiphase fluid-structure interaction (FSI) model was verified by comparing with the results of Diamond scaffolds culture in the literature. Fluid mechanical responses of Voronoi-lattice scaffolds and cells were analyzed by multiphase FSI model. Regression equations were established by response surface method (RSM) to determine relationships between structural design factors of Voronoi-lattice scaffolds and fluid mechanical response parameters of scaffolds and cells. The results showed that the percentage of adhered cells and the locations of initial adhered cells obtained by multiphase FSI model of Diamond scaffolds had the same trend with that obtained by perfusion culture. Regression equations established based on RSM could well predict the fluid mechanical response parameters of Voronoi-scaffolds and cells. The multiphase FSI model closely related the densities of cells and the locations of adhered cells to bone tissue growth. The model could provide a certain theoretical basis for constructing and culturing engineered bone tissues in vitro perfusion. [ABSTRACT FROM AUTHOR]

Biochar (BC) is a by-product rich in carbon, from the pyrolysis of biomass, and therefore, it has great appeal to be used in several applications. In the present work, the use of biochar from poultry litter waste (PLW) as a filler for composites with epoxy resin is evaluated regarding its performance in the thermal, mechanical and dynamic mechanical properties. The BC was produced from the pyrolysis of the PLW, and the composites were produced from concentrations of 2.5, 5.0 and 10.0 wt% of BC, in relation to the epoxy resin mass. The composites were characterized in terms of micrography (MEV), infrared spectroscopy with Fourier transform (FTIR), thermogravimetric analysis (TGA), mechanical properties (tension and impact) and dynamic mechanical analysis (DMA). From the dynamic mechanical point of view, there was a considerable increase in parameters such as storage modulus at both glassy (≈ 23%) and rubbery regions (≈ 43%) and loss modulus (≈ 32%). However, a decrease at the glass transition temperature, in loss modulus, (≈ 19 °C) was reported, comparing the neat epoxy with those composites with 10 wt% of BC. This behavior was mainly related to the poor dispersion of BC into the composites, especially those with 10 wt% of reinforcement. [ABSTRACT FROM AUTHOR]

Deep-buried tunnels with weak surrounding rock are frequently encountered issues in traffic engineering. It plays an important role in the excavation process and the project operation. This paper applies the theoretical analysis and laboratory test related to four different conditions in terms of their thickness to determine the mechanical response of deep-buried tunnel lining. Then, the energy dissipative structure theory is employed to explain the experimental results. This paper has made the following achievements: firstly, it is found that the toughness of the secondary lining was found to be often the most important indicator of tunnel safety, with better-toughness linings having higher tensile strength and crack resistance. Secondly, it suggests that the inclusion of steel reinforcement in the concrete lining can effectively improve the secondary lining toughness. Finally, it proves that the more ductile liner had more energy, higher load-carrying capacity, and was better able to maintain the overall stability of the structure. [ABSTRACT FROM AUTHOR]

Aiming at roadway rockbursts induced by near-field dynamic disturbances, this study explored the mechanical response and failure mechanism of anchored roadway surrounding rocks under this condition through the similarity simulation experiment and theoretical modeling analysis. Results show that the greater the disturbance energy is, the stronger mechanical response of surrounding rocks while the faster its attenuation. The starting acceleration amplitude is relatively smaller while the braking acceleration amplitude is larger in the bolt densification area, which has a better self-stabilizing ability. Anchored roadway surrounding rocks exhibit local impact failure characteristics, and the region facing disturbance is most seriously damaged. The bolt-mesh-cable support structure shows the good resistance to low-energy disturbances, while the impact failure is induced with damages inside support structure increasing abruptly under high-energy disturbances. The impact resistance of local surrounding rocks can be improved by bolt densification. Based on the failure criterion, the surrounding rocks only undergo impact failure in the region facing disturbance, while quasi-static failure occurs in remaining regions. The experimental and theoretical research results have been verified through in-situ measurements, which can provide an important reference for the mechanism and prevention of roadway rockburst under near-field dynamic disturbance. [ABSTRACT FROM AUTHOR]

The demand for 3D-printed high-performance polymers (HPPs) is on the rise across sectors such as the defense, aerospace, and automotive industries. Polyethyleneimine (PEI) exhibits exceptional mechanical performance, thermal stability, and wear resistance. Herein, six generic and device-independent control parameters, that is, the infill percentage, deposition angle, layer height, travel speed, nozzle temperature, and bed temperature, were quantitatively evaluated for their impact on multiple response metrics related to energy consumption and mechanical strength. The balance between energy consumption and mechanical strength was investigated for the first time, contributing to the sustainability of the PEI material in 3D printing. This is critical considering that HPPs require high temperatures to be built using the 3D printing method. PEI filaments were fabricated and utilized in material extrusion 3D printing of 125 specimens for 25 different experimental runs (five replicates per run). The divergent impacts of the control parameters on the response metrics throughout the experimental course have been reported. The real weight of the samples varies from 1.06 to 1.82 g (71%), the real printing time from 214 to 2841 s (~ 1300%), the ultimate tensile strength from 15.17 up to 80.73 MPa (530%), and the consumed energy from 0.094 to 1.44 MJ (1500%). The regression and reduced quadratic equations were validated through confirmation runs (10 additional specimens). These outcomes have excessive engineering and industrial merit in determining the optimum control parameters, ensuring the sustainability of the process, and the desired functionality of the products. [ABSTRACT FROM AUTHOR]

The dynamic mechanical behavior of frozen rock with a flaw is essential for plateau alpine region mining. However, the freezing temperature's strengthening and damage mechanism on dynamic strength is still unclear. Drop weight impact tests (single factor) and orthogonal tests (3 factors and 5 levels) were used to examine the influence of flaw dip angle (β), impact height (H), and freezing temperature (T) on the dynamic response of frozen sandstone in plateau alpine region. Different factors' effect on peak strain and failure mode was compared, as well as a significant analysis of three factors' influence on peak strain. The results reveal that with the increase of β, the ultimate strain (εu) of sandstone shows a 'M' type variation, while the linear increase of εu occurs with the increase of H and the decrease of T. At the same time, β and T have a substantial effect on εu, and T has a significant influence on the occurrence time of εu. In addition, tensile failure is the failure mode of sandstone with tensile cracks mainly parallel to the direction of impact. Moreover, a two-dimensional particle flow code was used to supply the stress–strain curve, cracking process, and energy absorption characteristics. The obvious rebound phenomenon can be observed, and the peak stress increases with the increase of H and decreases as β and T increase. Furthermore, the energy usage rate has a linear relationship with β and T, but it decreases first and then increases as impact energy increases. At the end, the effect of the strengthening mechanism of T on single-flaw sandstone dynamic strength and the damage evolution was discussed. The effect of pore ice is primarily responsible for the strength enhancement of frozen sandstone, but the frost heave damage at a certain T (− 20 °C) will inhibit the strength growth. The damage constitutive model based on logistic function can accurately describe the stress–strain properties of single-flaw frozen sandstone before εu. Highlights: The dynamic mechanical responses of single flaw frozen sandstone were studied by drop weight impact tests and numerical simulation. The influence of flaw dip angle, impact height and freezing temperature on peak strain, stress, and energy consumption were revealed. The strengthening mechanism of freezing temperature on dynamic strength was discussed. The frost heave damage formed at a certain freezing temperature (– 20 °C) will inhibit the growth of strength. [ABSTRACT FROM AUTHOR]

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Cavities under roads are one of the main reasons for early structural damage to pavements. It is necessary to conduct a structural analysis of road sections with cavities and evaluate the possibility of pavement cracking caused by different cavity sizes. In this study, an analysis method for evaluating the possibility of pavement cracking based on the load-mechanical response is proposed. An example library of the mechanical response of asphalt concrete (AC) pavements was established by numerical simulation. Based on the tensile cracking characteristics of pavements in the mechanical response research, the tensile strain at the bottom of the AC layer was selected as the key analysis parameter. Sensitivity analysis of the tensile strain was conducted, and the main factors controlling pavement cracking were determined. A tensile strain response prediction model was established using multiple linear regression, and its reliability was verified. The cavity influence coefficient (CIC) and pavement cracking factor (PCF) were constructed to analyze the cracking possibility. The variation in PCF with the cavity size and pavement structure parameters was studied. A quantitative relationship between the depth and length of the cavity for a given PCF was obtained. This law conforms to a power function. The possibility of pavement cracking can be determined by measuring the cavity size. Compared to the existing cavity management system, the proposed method provided analysis results of the cracking possibility that were more consistent when the cavity depth was small and the length was long. The findings of this study provide new insights for evaluating the possibility of pavement cracking. [ABSTRACT FROM AUTHOR]

In this research, the rockbolt mechanism of a jointed rock mass under uniaxial tension was systematically revealed with a laboratory test and a numerical simulation. It was found that the rockbolt rock mass experienced five stages under uniaxial tension, the densification stage, elastic stage, plastic deformation stage, progressive debonding stage, and complete debonding stage. The stress-strain curve and ultimate tensile strength of a rockbolt rock mass were analyzed by taking the rockbolt spacing and rockbolt angle as variables. It was found that the improvement effect of the reduction of the rockbolt spacing on the ultimate tensile strength was limited. When the rockbolt spacing was reduced to a certain limit, the stress concentration area between adjacent rockbolts was connected and destroyed, resulting in the increase of the rockbolt rock strength becoming smaller, and even having a downward trend. The increase of the rockbolt angle led to the change of the stress mode and failure mode of the whole structure, and the ultimate tensile strength first increased and then decreased. The optimal rockbolt angle was between 60° and 70°. It is worth noting that there was an obvious mechanical occlusion between the thread on the rockbolt surface and the rock mass, resulting in the multi-stage step-down characteristic of the stress-strain curve in the complete debonding stage. The results of this study can provide a reference for the design and construction of similar projects. [ABSTRACT FROM AUTHOR]

Many practical engineering experiments show that the structural plane effect plays an important role in the rockburst development process. The mechanical response of the surrounding rock and the distribution and evolution law of rockburst risk zones during the excavation of tunnels with different structural plane shapes were investigated in the article. Based on FLAC3D numerical program and introducing the numerical analysis index, we analyzed the distribution of the stress field and displacement field after the tunnel excavation containing different structural plane shapes. Furthermore, we visualized the distribution of risk zone by using the Fish function for secondary programming to study the distribution of rockburst risk zones and its evolution process. The results are drawn as follows: When the tunnel contains the unexposed structural plane, the development process of the rockburst is concealed and lagged compared to the exposed structural plane. However, the rockburst risk zone will be expanded once the unexposed structural plane is activated. The exposed part of the exposed structural plane releases much energy and has a strong rockburst impact tendency. The vertical structural plane in the sidewall will make the rockburst risk zone expand in the direction of the structural plane and eventually form the rockburst risk zone, similar to a pan between the structural plane and the excavation boundary. The research results can provide a reference for excavation design and construction of similar underground engineering. [ABSTRACT FROM AUTHOR]

Based on the Euler–Bernoulli beam element theory, a nonlinear finite element method is proposed to solve the mechanical response of functionally graded shape memory alloys (FG-SMAs) three-point bending beam considering the tension–compression asymmetry under the loading process. The Auricchio's shape memory alloy (SMA) constitutive model was used to describe the phase transformation relationship of SMA. The constitutive model of the power exponent distribution law of FG-SMA was developed by using the theory of composite mechanics. Using the virtual work principle, the bending beam equilibrium equation of FG-SMA was developed. The finite element method and Newton–Raphson method were used to solve the equilibrium equation of the three-point bending beam of FG-SMA. The accuracy of the proposed method was verified by comparing the present results obtained by the nonlinear finite element method with the existing literature. Then three-point bending beam analysis of FG-SMA was carried out. The results show that the increase in the graded index and tensile asymmetry coefficient increases the stiffness of the beam. When the SMA enters phase transformation, the increase in temperature will reduce the deflection of the beam. In addition, the strain variation in the mid-span section near pure shape memory alloy layer is more obvious than that near pure ceramic layer due to temperature. The compressive axial load is more likely to cause beam bending than tensile axial load. [ABSTRACT FROM AUTHOR]

Clarifying the geomechanical properties and inherent heterogeneity of layered rocks is essential for predicting fracture morphology and designing hydraulic fracturing pumping schemes. Grid nanoindentation combined with high-resolution scanning electron microscopy and energy-dispersive spectroscopy (SEM–EDS) techniques were used to investigate mechanical differences between the sandstone layer and the mudstone layer for the downhole thinly interbedded core rocks (layered core rocks). Subsequently, the indent impressions and mechanical responses of individual minerals and multiple minerals were quantified. On this basis, the bulk mechanical properties and failure modes of the layered core rocks are investigated under confining pressures. Results indicate that quartz exhibits the highest hardness and Young's modulus with the smallest indent impression, whereas kaolinite exhibits the opposite in each layer. When the indenter covers multiple minerals simultaneously, the mechanical responses of which are determined by the softer phases. Moreover, minerals exhibit diverse deformations and cracking patterns in different layers. Quartz shows elastic-dominated deformation in the sandstone layer, whereas medium-plastic deformation in the mudstone layer. Since the unstable sheet structures, kaolinite exhibits plastic-dominated deformation in each layer. Shear cracks and radical cracks are prone to occur in elastic-dominated minerals, while chipping damage is induced in plastic-dominated minerals. In addition, the failures of the layered core rocks tend to create along the mudstone layer since the lower mechanical properties. With the increasing of confining pressure, the compressive strength of layered core rocks gradually grows and the failure changes from tensile splitting to tensile–shear mixed failure mode and shear failure mode. The key findings of this paper can provide reliable input data for multiscale geomechanical modeling in understanding proppant embedment mechanisms and designing hydraulic fracturing treatments in coal measure strata. Highlights: The mechanical responses and indent impressions of individual minerals and multiple minerals are quantified and compared in different layers. Quartz shows elastic-dominated deformation in the sandstone layer, whereas medium-plastic deformation in the mudstone layer. The mechanical responses of multiple minerals are determined by the softer phases and irregular indent impressions are generated. The failure of the layered rocks changes from tensile splitting to shear failure with the increase of confining pressure in a macro-scale. [ABSTRACT FROM AUTHOR]

The finite-discrete element method (FDEM) can be used to simulate brittle materials such as polycrystalline ice with specific geometric information. However, most previous studies treat ice as intact and nonporous, ignoring the effect of internal porosity. In this study, an FDEM model of polycrystalline ice with specific porosity is built by using the cohesive interface element and the method of randomly deleting elements. Comparison with experimental results confirms that the model can capture the strength properties and deformation patterns of polycrystalline ice. The fracture failure patterns and mechanical responses of ice specimens and their relationships with porosity are investigated by uniaxial compression tests and Brazilian splitting tests. The results show that with increasing porosity, the fracture failure patterns of the specimens in the uniaxial compression test evolve into three types: global shear failure, local shear failure and local tensile‒shear failure. There is no obvious difference in the failure patterns of the specimens in the Brazilian splitting test. In addition, as the porosity increases, the material exhibits a transition from brittleness to ductility, and the porosity also affects the local fragmentation characteristics inside the polycrystalline ice, significantly weakening the strength of the specimens. [ABSTRACT FROM AUTHOR]

Rock indentation and fragmentation behavior under dynamic and quasi-static loads have significant impacts on the exploration drilling for oil, gas, and geothermal energy. In this study, the mechanical response of rock indentation subjected to dynamic and quasi-static loads was investigated in terms of the interaction between the button and the rock in percussion drilling. The effect of rock type, grain size, and mineralogical composition on rock fragmentation and penetration response was compared, and the cracking characteristics of the rock and crack propagation paths were analyzed. The results show that the damage characteristics of rocks under quasi-static load are similar to those under dynamic load, but the penetration performance under dynamic load is better than that under quasi-static load. The brittleness index can be used to assess the fragmentation performance of different rocks. When the brittleness index of the rock is less than 20, the rock fragmentation performance is particularly sensitive to the brittleness index. The mineral grain size will affect the period of rock failure, when the mineral grain size is less than 900 µm, there is no significant difference in crater depth or volume. The mineralogical composition has a significant effect on the penetration characteristics. When the content of feldspar is more than 5 times that of quartz, the fragmentation performance will not be much different. The relationship between the axial force and the penetration depth follows the power-law relationship, which can be used to describe the dynamic mechanical response of bit and rock in the process of percussion drilling. Highlights: The mechanical response of rock indentation subjected to dynamic and quasi-static loads was investigated and compared. The influence of rock type, grain size, and mineralogical composition on rock fragmentation was evaluated. The rock fragmentation process under quasi-static load can be regarded as a slow motion of rock fragmentation under dynamic load. The relationship between the axial force and the penetration depth in the elastic deformation stage follows a power-law relationship. [ABSTRACT FROM AUTHOR]

Fault slip will directly affect the technical performance of solid expandable tubular (SET). However, there are few researches on the mechanical behavior of shear failure when SET crosses the slip fault. In response to the above problems, this paper builds a three-dimensional dynamic tube-rock system numerical model that considers nonlinear frictional contact and fault slip based on the SET material constitutive model, Coulomb friction, and shale layer rock. The purpose is to reveal the influence of fault slip on the mechanical behavior of SET and to analyze the risk point of SET failure. The results of the study show that as the amount of fault slip increases, the maximum value of the Mises stress of SET appears in the direction perpendicular to the amount of fault slip (90°). With the increase in the number of faults, the shear stress distribution on the cross section hardly changes, and the shear stress distribution on the fault plane presents a "8" shape. When the included angle is 60°, the shear stress on the shear plane is the largest and the shear distribution is the most uneven. The research results of this paper provide a theoretical basis for the slip shear of SET. [ABSTRACT FROM AUTHOR]

Tunnels crossing active faults can be severely damaged by fault dislocation. Based on a freeway tunnel crossing an active fault, a three-dimensional numerical model is established to investigate the influences of the friction coefficient and position of the dislocation surface on the tunnel response under the action of right-lateral strike-slip reverse fault dislocation. The results show that the friction coefficient of the dislocation surface has little effect on the deformation characteristics in the tunnel but has a slight effect on the stress distribution. As the friction coefficient increases from 0.3 to 1.0, the stress distribution shape in the tunnel basically remains unchanged, while the maximum absolute values of the principal stresses decrease. The dislocation position has a significant effect on the deformation and stress distribution in the tunnel. When the fault moves along the interface between the fracture zone and the intact rock mass in the hanging wall or footwall, the deformation of the tunnel is the most severe, and the local stress concentration is also the most severe. In view of the local damage, amongst the conditions studied here, the condition of fault dislocation occurring along the interface between the fracture zone and the intact rock mass is the most dangerous and the condition of dislocation occurring along the fracture zone is safest. Under fault dislocation, the tunnel deformation is the most obvious in the fracture zone and tends to decrease to both sides; the principal stress in the tunnel peaks in the fracture zone and decreases to the two sides. The tunnel may be seriously damaged in the fracture zone and fault walls within 5 m of both sides of the fracture zone, and the tunnel fortification length is 3.39 times the fault width of 90 m. Disaster mitigation measures should be adopted for the tunnel design within the fortification range. [ABSTRACT FROM AUTHOR]

The conductor on round core (CORC) cables are fabricated with multilayer high-temperature superconductor tapes, which are helically wound around a circular central former. The large Lorentz force will be generated by the transport current in CORC cables under high magnetic field, which will affect the stress and strain distributions of tapes in the cables and the performance of superconducting tape. This paper establishes a two-dimensional axisymmetric model to analyze the mechanical response of CORC cables subjected to the Lorentz force and analyzes the influence of air gaps on stress and strain distributions inside the cables. The T-A method is used to calculate the distributions of current density, magnetic field and the Lorentz force in CORC cables. The mechanical response of CORC cables is analyzed by applying the Lorentz force as an external load in the mechanical model. The direction of electromagnetic force is analyzed in CORC cables with and without shielding current, and the results show that the shielding current can lead to the concentration of electromagnetic force. The maximum stress and strain occur on both sides of the superconducting tapes in the cables with shielding current. Reducing the size of air gaps can reduce the stress and strain in the superconducting layers. The analysis of mechanical response of CORC cables can play an important role in optimizing the design of CORC cables and improving transmission performance. [ABSTRACT FROM AUTHOR]

An analytical model based on complex variable theory is proposed to investigate ground responses due to shallow tunneling in multi-layered ground with an arbitrary ground surface load. The ground layers are assumed to be linear-elastic with full-stick contact between them. To solve the proposed multi-boundary problem, a series of analytic functions is introduced to accurately express the stresses and displacements contributed by different boundaries. Based on the principle of linear-elastic superposition, the multi-boundary problem is converted into a superposition of multiple single-boundary problems. The conformal mappings of different boundaries are independent of each other, which allows the stress and displacement fields to be obtained by the sum of components from each boundary. The analytical results are validated based on numerical and in situ monitoring results. The present model is superior to the classical model for analyzing ground responses of shallow tunneling in multi-layered ground; thus, it can be used with assurance to estimate the ground movement and surface building safety of shallow tunnel constructions beneath surface buildings. Moreover, the solution for the ground stress distribution can be used to estimate the safety of a single-layer composite ground. [ABSTRACT FROM AUTHOR]

This paper aims to evaluate the effect of propylene pre-polymerization on the crystalline structure and mechanical response of HDPE resin. It was deduced from the PLM and DSC outcomes that the pre-polymerization with isotactic homo-polypropylene resulted in the formation of an in-reactor blend of the HDPE/iPP, in which the concentration and molecular weight of the iPP as the minor phase were heterogeneous within the HDPE powder particles of various sizes as the major phase. On the other hand, the presence of the iPP pre-polymer in the HDPE matrix led to significant phase separation. The results highlighted that the ultra-high molecular weight chains in the iPP acted as the nuclei for the formation of the shish-like structure, resulting in enhanced oriented α-type spherulites during the melt stretching fields. Moreover, in the molding processes involving the elongational fields, the similarity of the crystallization temperature of HDPE resin and the ultra-high molecular weight of the iPP led to the replication of stretch-induced molecular orientation caused by the iPP to the HDPE matrix. The crystalline structure consisted of highly ordered lamellae in the flow direction, causing reinforcement of the mechanical properties in the flow direction and weakening the mechanical properties in the counter-flow direction. Nevertheless, in the compression molding process, the ultra-high molecular weight iPP only acted as the nucleation agent for polyethylene, which caused the fine crystalline texture. Besides, more crystalline boundaries, a low degree of bonding between the whole crystalline domains, and inadequate bonding between the iPP and HDPE crystalline domains diminished the mechanical properties. Furthermore, a comparison between ambient and low-temperature impact strength exhibited that the pre-polymerized sample had a higher low-temperature impact strength, which may be attributed to the resin's finer crystalline texture. [ABSTRACT FROM AUTHOR]

Solar pavements are a new type of pavement structure that harvest energy from the sun and have been widely investigated in recent years. A critical step toward the acceptance and development of solar pavement structures is investigating their mechanical response, which is conducted in this study. Here, a typical pavement structure with functional photovoltaic, cement concrete, base, subbase, and subgrade layers was selected. This is one of the most acceptable forms of the solar pavement structure. A numerical simulation of the solar pavement was conducted by establishing a 3D model using the finite element software ABAQUS. The effects of the vehicle critical load position, elastic modulus, geometric size, linear expansion coefficient of the photovoltaic panel (PVP), and cement concrete slab (CCS) thickness on the mechanical response of the solar pavement under vehicle and temperature loadings were investigated. The results indicated that the critical load position of the solar pavement in the middle of the long side of the concrete slab was the same as that of the traditional concrete pavement. The PVP parameters influenced the mechanical response in the following order: elastic modulus, linear expansion coefficient, and geometric size. By increasing the CCS thickness from 0.20 to 0.28 m, the CCS load stress decreased by 15%; however, the curling stress increased significantly from 0.85 to 1.97 MPa. An increase in the PVP linear expansion coefficient caused the curling stress of the solar pavement to first decrease and then increase. A linear expansion coefficient of 1 × 10–5 resulted in minimum curling stresses of 0.42 and 1.70 MPa for PVP and CCS, respectively. [ABSTRACT FROM AUTHOR]

The mechanical response of polyethylene nano-fibers with the same chain length but different chain numbers are studied by using steered molecular dynamics simulations. The shrinking or stretching forces acted on the chain ends are investigated according to the chain-end distance and temperature under isothermal or continuous warming-cooling conditions, respectively. An inflection point is found in the Force-Distance response when temperature is below 500 K. This inflection point is related to the balance between entropy force and inter-monomer interaction and it reflects the strong effect of crystallization on the mechanical response of the nano-fibers. The force at inflection point is also affected by the buckling effect due to increased stiffness when crystallization occurs. The two stages found in the Force-Temperature response and the difference between the shrinking and stretching forces indicate the hysteresis of crystallization and melting. The forces at different shrinking and stretching rates reveal the entropy contribution upon the mechanical response, indicated by the Ramachandran plot of dihedrals. The chain-conformation entropy is majorly contributed by dihedrals and is quantified by the information entropy of dihedrals, which has a highly similarity to the mechanical Force-Temperature response. The enlarged forces in multiple chains over a single chain are attributed to the enhanced dihedral-conformation entropy. Our study provides a new insight to the dynamically mechanical response of polymer nano-fibers according to the effect of crystallization and entropy contribution. [ABSTRACT FROM AUTHOR]

Silt is often selected as the filling soil in Northwest and North China. "Pot cover effect" or rainfall infiltration are easily to cause localized wetting during the service period of airport. The response characteristics of pavement derived from aircraft loading under wetting condition are the basis to explore the evolution law of pavement damage. To investigate this response characteristics for different parameters of pavement under wetting condition, a self-developed model test system was developed, and the verified numerical model was then established. The interaction mechanisms of pavement slabs, and the influence of wetting on mechanical response in loading area of pavement under different pavement parameters were analyzed. The results showed that the increased vertical deformation depends on water-holding capacity of silt, and the vertical deformation under loading is little affected by pavement parameters. The peak shear stress and the increased peak shear stress derived from wetting at the bottom of pavement layers are largely influenced by elastic modulus of base course. For cement concrete pavement, the increase in load transfer capacity of joints cannot decrease the increase of peak stress, including horizontal stress and shear stress, derived from wetting. The increase in load transfer capacity of joints can decrease the stress concentration in surface layer, while the elastic modulus of surface layer has little influence. For bituminous pavement, optimal parameters of base course can be obtained to decrease the peak stress and the increase of peak stress derived from wetting in subgrade. The research can provide technical basis for the structure design, optimization, and disease treatment of pavement in airport engineering. [ABSTRACT FROM AUTHOR]

In the process of geothermal energy exploitation, granites undergo cyclic heating and water cooling due to the heat conduction from distant rock mass to the cooled rock. The mechanical response, deformation and acoustic emission (AE) characteristics of granite treated by cyclic heating (150–300 °C) and water cooling (1–15) under the coupling action of compressive and shear stress were analyzed by preset angle shear tests in three preset angles (45°, 55°, 65°) at macroscopic level. Given that the peak strength of granite shows an accelerating downward trend with the increase of heating temperature and cycle times. The cohesion of granite declines, and the internal friction angle increases in general. AE activities are active throughout the loading process, which shows ductile failure characteristics of granite obviously. The accumulative AE events decrease by 69.3% with increasing heating temperature (150–600 °C), and 82.4% with increasing cycle times (1–15). The crack initiation area gradually shifts from the two ends of sample to the middle area with the increasing thermal damage. Shear behaviors inside the granite start earlier and last for a longer period, which results in the complex fracture network distribution of turtle shape and the shearing failure of "Z" shape on the surface of 600-1 sample. Scanning electron microscopy (SEM) was conducted to reveal the microscopic mechanism of thermal damage. Given that the intergranular and transgranular cracks induced by the uneven expansion of particles connect with each other and form a complex crack network as the thermal damage increasing. The continuous heating with high temperature causes minerals to melt and deform, resulting in the decrease of bonding strength between particles. All above results can provide references for the analysis and prediction of rock stability of granite in Enhanced Geothermal Systems (EGS) project. [ABSTRACT FROM AUTHOR]

Bioplotting has high potential for the 3D printing of scaffolds and cellular structures. Medical-grade poly(ε-caprolactone) (PCL) is characterized by low 3D printing temperatures and strengths compared to those of common polymers. Thus far, research on PCL in bioplotting has mainly focused on improving its performance through the development of composites. In this study, the quantitative impact of six common 3D plotting settings on the engineering strength of PCL parts was evaluated. Three modeling approaches were implemented: linear regression modeling (LRM), reduced quadratic regression modeling, and quadratic regression modeling. The LRM results were not as accurate as those obtained using the other two approaches. The difference between the tensile strength results for parts fabricated applying certain control factor ranges reached a remarkable 600%, indicating the impact of appropriate 3D plotting settings on the workpiece response. Prediction models were compiled and validated experimentally. The results possess engineering and industrial value for establishing the best control parameters during manufacturing, thus achieving the intended functionality of the end products. The findings can be used as a roadmap for optimum parameter selection and prediction of mechanical property metrics, leading to more robust and efficient parts.Graphical Abstract: Bioplotting has high potential for the 3D printing of scaffolds and cellular structures. Medical-grade poly(ε-caprolactone) (PCL) is characterized by low 3D printing temperatures and strengths compared to those of common polymers. Thus far, research on PCL in bioplotting has mainly focused on improving its performance through the development of composites. In this study, the quantitative impact of six common 3D plotting settings on the engineering strength of PCL parts was evaluated. Three modeling approaches were implemented: linear regression modeling (LRM), reduced quadratic regression modeling, and quadratic regression modeling. The LRM results were not as accurate as those obtained using the other two approaches. The difference between the tensile strength results for parts fabricated applying certain control factor ranges reached a remarkable 600%, indicating the impact of appropriate 3D plotting settings on the workpiece response. Prediction models were compiled and validated experimentally. The results possess engineering and industrial value for establishing the best control parameters during manufacturing, thus achieving the intended functionality of the end products. The findings can be used as a roadmap for optimum parameter selection and prediction of mechanical property metrics, leading to more robust and efficient parts. [ABSTRACT FROM AUTHOR]

The deterioration of mechanical properties and structural instability of coal–rock system under water–rock interaction seriously affect the efficient mining of coal and the safety of workers. The interlayer weak zone between coal seam and rock strata in coal–rock system is the main area of fracture distribution. The existence of fractures speeds the process of water–rock interaction, accounting for aggravating the damage of coal–rock system. Considering penetrating fractures and water–rock interaction, five kinds of coal–rock combined body with different fracture widths were prefabricated, and uniaxial compression tests under different soaking time were carried out. The research shows that: (1) The larger the fracture width and the longer the soaking time, the more obvious the compaction stage and the plastic stage, the less obvious the elastic stage, and the slower the damage. (2) With the increase of fracture width, the compressive strength, elastic modulus, pre-peak energy, post-peak energy and impact energy index decrease gradually, and there is a linear relationship between fracture width and each parameter. With the increase of soaking time, the compressive strength, elastic modulus, pre-peak energy, post-peak energy and impact energy index all decrease gradually, but there is a non-linear relationship between soaking time and each parameter. (3) The crack evolution law of coal–rock combined body under the influence of fracture width and soaking time is analyzed. It is found that the fracture width and soaking time have a certain influence on the wing crack, secondary inclined crack, secondary coplanar crack, inclined crack, secondary derivative crack, wing crack derivative crack, far field crack and flake phenomenon. (4) With the increase of fracture width and soaking time, the cohesion and internal friction angle decrease gradually. (5) Considering the influence of fracture width and soaking time, the D–P criterion is modified. Two parameters c(k,t)\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$c{\,}_{(k,t)}$$\end{document} and φ(k,t)\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\varphi {\,}_{(k,t)}$$\end{document} are introduced into the Drucker–Prager criterion, and the strength criterion considering fracture width and soaking time is constructed and verified. The error range of all samples is 2.48–9.30%, which indicates that the modified D–P strength criterion has high accuracy and good rationality. (6) The energy migration model of fractured coal–rock combined body is constructed, and the energy migration mechanism of intact and fractured coal–rock combined body is compared and analyzed. The two ends of the fracture are the main energy accumulation areas. When the fracture end of the coal component is destroyed, a part of the energy is transported from the coal component to the fracture end of the rock component, and released in the form of deformation or failure of the rock component. (7) The deterioration mechanism of mechanical properties of coal–rock combined body under water–rock interaction is analyzed. The physical, chemical and mechanical effects between water and coal–rock combined body lead to the damage inside the coal rock, and the continuous accumulation of damage leads to the macroscopic damage of the sample. The deterioration effect of mechanical properties under water–rock interaction is a process of continuous accumulation of damage. [ABSTRACT FROM AUTHOR]

Metal—organic framework-derived materials have attracted significant attention in the applications of functional materials. In this work, the rod-like nickel-based metal—organic frameworks were first synthesized and subsequently employed as the hard templates and nickel sources to prepare the whisker-shaped nickel phyllosilicate using a facile hydrothermal technology. Then, the nickel phyllosilicate whiskers were evaluated to enhance the mechanical, thermal, flammable, and tribological properties of epoxy resin. The results show that adequate nickel phyllosilicate whiskers can disperse well in the matrix, improving the tensile strength and elastic modulus by 13.6% and 56.4%, respectively. Although the addition of nickel phyllosilicate whiskers could not obtain any UL-94 ratings, it enhanced the difficulty in burning the resulted epoxy resin nanocomposites and considerably enhanced thermal stabilities. Additionally, it was demonstrated that such nickel phyllosilicate whiskers preferred to improve the wear resistance instead of the antifriction feature. Moreover, the wear rate of epoxy resin nanocomposites was reduced significantly by 80% for pure epoxy resin by adding 1 phr whiskers. The as-prepared nickel phyllosilicate whiskers proved to be promising reinforcements in preparing of high-performance epoxy resin nanocomposites. [ABSTRACT FROM AUTHOR]

Because of favorable mechanical properties, deformation resistance and being conducive to environmental protection, honeycomb fabricated plastic pavement slabs are highly recommended these years. At present, most studies focus on the performance of plastic materials, however, the dimension optimization of fabricated plastic pavement slab is rarely mentioned. In this paper, an optimized geometry of the honeycomb pavement slab was determined through finite element analysis. Mechanical response of honeycomb slabs with different internal dimensions and external dimensions were explored. Several dimension factors were taken into consideration including the side length, rib thickness, the thickness of both top and bottom slabs of honeycomb structure and the length, the width and the thickness of the fabricated plastic slab. The results showed that honeycomb pavement slab with 6 cm bottom slab, 12 cm top slab,18 cm side length and 6 cm rib thickness is recommended, additionally, an external dimension of 4 m × 4 m × 0.45 m is suggested. Then, the mechanical responses of this optimized fabricated plastic slab were further investigated. Significance of different influencing factors, including wheel load, elastic modulus of plastic material, base layer thickness, soil foundation modulus and base layer modulus were ranked. [ABSTRACT FROM AUTHOR]

This paper presents a study of closely spaced double tunnels in Taizhou, China. One is Xiabei Mountain No. 2 four-line super-span high-speed railway tunnel (HRT), and the other is Xiabei Mountain double-line large-span subway tunnel (ST). The excavation spans of HRT and ST are 26.3 and 14 m, respectively. The two tunnels are located at different levels, and their separating distance is 17.2 m. Due to the short construction period, the HRT excavation was completed earlier than ST. The structural design of the HRT, taking account of the disturbance by the ST construction, was analyzed by a numerical simulation. It was found that the "yielding principle" design was more feasible than the "resistance principle" design when considering the safety and durability of the HRT secondary lining. The mechanical responses of the HRT during ST construction were comprehensively monitored and analyzed, including the vault settlement, horizontal convergence, surrounding rock pressure, and the internal stress in shotcrete and steel arch. Results show that the longitudinal influence range of the ST construction on the HRT was approximately 0.6–1.1 times the ST outer diameter; the disturbance was mainly generated in the ST upper bench excavation; and the final axial force of the HRT shotcrete was approximately 9–16 times that of the steel arch, which indicated that the shotcrete was the main bearing structure. The safety status of the HRT was assessed based on the monitoring data, and the minimum safety factors of the HRT shotcrete and steel arch were 1.61 and 1.89, respectively. Parametric studies were performed to show how the lining stress of HRT was affected by the relative angle, pillar width, ST excavation method and excavation footage. Finally, the design and construction optimization were proposed according to the monitoring data and parameter analysis results. This study might provide practical reference for similar projects. [ABSTRACT FROM AUTHOR]

The mechanical response of CFRP laminates under low-velocity oblique impact was investigated using finite element simulation and experimental test in this paper. Based on the 3D Hashin failure criterion, bilinear cohesive constitutive model and progressive failure theory, a finite element model of CFRP laminate with hemispherical cylindrical impactor under low-velocity oblique impact was established, by using finite element simulation software ABAQUS. A clamp for multi-angle impact was designed and manufactured. A low-velocity oblique test platform was built based on the clamp. Several groups of experiments with different impact angles and impact energy were carried out. It was found that the damage morphology and energy absorption caused by normal impact and oblique impact is quite different. For normal impact, the main damage mode on the front of the laminate is indentation, while for oblique impact, the main damage mode on the front surface is scratch due to the sliding of the impactor on the laminate. The damage caused by normal impact on the back of the laminate is always more significant than that caused by oblique impact. The simulation results of the contact force and the residual velocity of impactor are compared with the experimental results, and the good agreement verifies the reliability of the simulation model. The mechanical response is studied by simulation, and it is found that the mechanism of normal impact is different from that of oblique impact. The contact force and residual kinetic energy of the impactor decrease with the increase of impact angle, while the contact time and the energy consumed by friction increase are the opposite. The energy absorbed by the laminate is not negatively related to the impact angle. [ABSTRACT FROM AUTHOR]

An iron ore mine at Anhui Province of China is in the transition from open pit to underground mining. The closed open pit of this mine will be filled with mine waste for land reclamation. This is conducive to the sustainable development of the mine. However, filling the open pit may affect the exploitation of lower mineral resources. Therefore, the influence of the filling of the pit on the underground mining operation should be investigated. A numerical model is thus established to study the mechanical response of the pit and underground stope to the open pit filling. The strain–time evolution of backfill with binder content and stress–strain data of backfill with curing time are investigated and thus used to compare with the relevant outcomes predicted by the developed model. The comparison results can prove the validity and applicability of the developed model. The validated model is then applied to study the evolutions of stress and displacement of the pit and stope during the filling process. The simulation results indicate that stress concentration of the slope, pit bottom and underground stope evolves during the filling process. The displacement of the stope roof is affected by the horizontal distance between the stope and the pit bottom. Filling the open pit can reduce the maximum stress on the stope roof. The obtained results can be combined with the field monitoring data in the future, which will provide guidance for the better production arrangement of the open pit filling and underground stope mining. [ABSTRACT FROM AUTHOR]

Rock masses that undergo a long and complex geological tectonic process contain widely distributed parallel and intersecting flaws. These two types of flaws have different inclinations with the rock layer, resulting in a significant deterioration of the mechanical properties of the rock mass and complex fracture evolution characteristics. However, the effects of flaw inclination and the coupling effect between the two types of flaws on the dynamic response characteristics of rock masses are still unclear. In this paper, both qualitative and quantitative analysis methods are adopted to systematically analyze the influence of flaw inclination on the dynamic properties and fracture evolution mechanisms of rock masses containing both parallel and intersecting flaws via a modified split Hopkinson pressure bar (SHPB) apparatus, a high-speed camera, and digital image correlation (DIC) technology. The test results show that the peak stress and peak strain decrease initially and then increase with increasing flaw inclination from 0° to 90°. The origin of specimen failure and the proportion of energy are dominated by the flaw inclination. Furthermore, flaw tips are prone to strain concentration, which promotes and guides the crack propagation. The major cracks in flawed specimens always occur along flaws, and their failure modes can be classified into three categories: tensile failure along flaws, tensile‒shear composite failure along flaws, and tensile failure perpendicular to flaws. Additionally, fractal feature analyses indicate that the degree of fragmentation of the flawed specimens tends to increase and then decrease as the flaw inclination increases from 0° to 90°. [ABSTRACT FROM AUTHOR]

Reflective cracks in asphalt pavement are major distresses in semi-rigid pavement. To date, grouting and jointing filling are commonly used to solve this problem. However, the grouting materials cannot be filled with cracks that have not propagated to the surface of base. Thus, these measures are limited to reducing the potential cracks in the base. This paper presents a comprehensive treatment measure of base regeneration by preset cracking and grouting (BRPCG) to repair the semi-rigid pavement with severe reflective cracks. The effect of BRPCG on the crack resistance of pavement was investigated by a linear elastic model. The dynamic load and the dynamic load–temperature coupling programs were designed to obtain the mechanical responses of pavement. Furthermore, mechanical indexes based on fatigue and yield failures of pavement materials and crack coefficients were proposed to evaluate the crack resistance and safety of pavement. The results showed that the temperature difference and aging of the original pavement are two factors that should be considered when simulating the pavement structure in service. The temperature of the coupling effect has a greater influence on the tensile stress of the structure layer compared to the dynamic load. The overload conditions only increased the value of the mechanical indexes without changing the variation trend of these indexes. [ABSTRACT FROM AUTHOR]

The viscoelastic deformation of cement emulsified asphalt mortar (CA mortar) can lead to gaps between the mortar and track slab, thereby adversely affecting the mechanical capability and deformation behavior of the track structures. According to the time hardening rate method, a solid model of the China Railway Track System I (CRTS-I) slab track was established to study the viscoelastic characteristics of mortar. What's more, this paper also analyzed the influence of viscoelastic deformation of mortar on the mechanical responses of track structures. The results obtained indicate that the viscoelastic deformation of CA mortar under train loading occurs mainly in the area from the track slab end to the third fastener, which is about 1.5 m long. Its viscoelastic deformation can reach nearly 0.6 mm. The maximum mortar stresses under passenger train and freight train loads with considering the viscoelastic deformation of mortar 0.6 mm, are 0.382 MPa and 0.566 MPa, respectively, which are both 2 to 3 times greater than those under normal conditions (without CA mortar failure, namely none vertical deformation of mortar). Besides, the vertical accelerations of rail and track slab are also significantly larger than those under normal conditions when the viscoelastic deformation of CA mortar is taken into account. And these values under the freight train load are greater than those under the passenger train load. Therefore, we suggest that future research should take the adverse impact of viscoelastic deformation of CA mortar into account when studying the mechanical responses of track structures. Furthermore, for the shared passenger and freight railway lines, the passage of freight trains should be strictly controlled. [ABSTRACT FROM AUTHOR]

Despite the economic and ecological importance of corals' skeletal structure, as well as their predicted vulnerability to future climate change, few studies have examined the skeletal mechanical properties at the nanoscale. As climate change is predicted to alter coral growth and physiology, as well as increase mechanical stress events (e.g., bioerosion, storm frequency), it is crucial to understand how skeletal mechanical properties change with environmental conditions. Moreover, while material properties are intimately linked to the chemical composition of the skeleton, no previous study has examined mechanical properties alongside carbonate geochemical composition. Using Porites coral cores from a wide range of reef environments (Thailand, Singapore, Taiwan), we correlated coral's micro-mechanical properties with chemical composition. In contrast to previous mechanical measurements of reef-building corals, we document unprecedented variability in the hardness, stiffness, and micro-cracking stress of Porites corals across reef environments, which may significantly decrease the structural integrity of reef substrate. Corals from environments with low salinity and high sedimentation had higher organic content and fractured at lower loads, suggesting that skeletal organic content caused enhanced embrittlement. Within individual coral cores, we observed seasonal variability in skeletal stiffness, and a relationship between high sea surface temperature, increased stiffness, and high-density. Regionally, lower Sr/Ca and higher Mg/Ca coincided with decreased stiffness and hardness, which is likely driven by increased amorphous calcium carbonate and skeletal organic content. If the coral is significantly embrittled, as measured here in samples from Singapore, faster erosion is expected. A decrease in skeletal stiffness will decrease the quality of reef substrate, enhance the rate of bioerosion by predators and borers, and increase colony dislodgement, resulting in widespread loss of structural complexity. [ABSTRACT FROM AUTHOR]

Quench and mechanical behaviors are critical issues in high temperature superconducting coils. In this paper, the quench characteristics in the rare earth barium copper oxide (REBCO) pancake coil at 4.2 K are analyzed, and a two-dimensional (2D) axisymmetric electro-magneto-thermal model is presented. The effects of the constituent materials, background field, and coil size are analyzed. An elastoplastic mechanical model is used to study the corresponding mechanical responses during the quench propagation. The variations of the temperature and strain in superconducting layers are compared. The results indicate that the radial strain evolutions can reflect the transverse quench propagation and the tensile hoop and radial stresses in superconducting layers increase with the quench propagation. The possible damages are discussed with the consideration of the effects of the background field and coil size. It is concluded that the high background field significantly increases the maximum tensile hoop and radial stresses in quenching coils and local damage may be caused. [ABSTRACT FROM AUTHOR]

Granular impact phenomena have implications in many areas. A fundamental problem deals with the mechanical response of a granular medium under external loads, such as those derived from the impact of a rigid object on the top of the medium. Here, the load changes its magnitude and intensity during the impact, being also applied in much shorter intervals than those of a static load, where the Boussinesq model is usually valid. This dynamic has been poorly addressed in the literature, a void to which this study aims to contribute, where we measure the pressure distribution transmitted at the bottom of a uniform, dry granular layer under the action of gravitational impacts of a steel sphere of fixed diameter. Exploring different bed thicknesses and drop heights, it is found that the structure of this distribution follows a similar form to the Boussinesq model, which was proposed initially for static conditions. This surprising result opens up several questions and future research challenges that could help validate or refute this model in other scenarios. [ABSTRACT FROM AUTHOR]

To investigate the temporal–spatial temperature field and mechanical response of an orthotropic steel bridge deck during paving with gussasphalt concrete (GAC), in situ monitoring of the Cuntan Yangtze River Bridge in China was conducted during GAC paving, and a finite element method model of the temperature field was established. The test and model show the following: (1) The maximum temperature occur at the paving area mid-span on the steel bridge deck, and the temperature stress of the ribs is non-negligible. (2) The deck in the paving and non-paving areas is mainly subjected to compressive and tensile stresses, respectively. (3) The beam end of the steel box expanded outward, and the deck bulge upward. (4) Based on the analysis of the construction parameters, the paving temperature and width have a greater influence than the paving speed on the stress and deformation fields. In bridge design, the temperature-stress problem caused by high-temperature pavement and the pavement thickness problem caused by the temperature deformation of the deck must be considered. The longitudinal elongation should meet the allowable limits of the corresponding telescopic device. These results can provide a reference for construction workers and maintenance personnel of bridge deck pavement. [ABSTRACT FROM AUTHOR]

The feasibility of a cost-efficient method to produce carbon coated Al-foams in a single-step heating process is investigated. In this context, a dissolution-sintering process for manufacturing metal foams is developed using raw cane sugar as both the space holder material and the carbon generating medium. The structural characteristics of the produced carbon coated Al-foams were evaluated by XRD, Raman and SEM analyses. Static compression tests were conducted to determine the mechanical response of the produced carbon coated Al-foams. The produced carbon coated Al-foams were fully covered with an external carbon layer having a relatively uniform thickness, despite the inherent complex 3D surface of the foam. The carbon deposition process led to a significant increase of the compression strength of the Al-foam. A strain softening behavior was observed for the carbon coated Al-foams attributed to micro-cracking of aluminum carbides. The produced carbon coated Al-foams can potentially be used as a catalyst support structure. [ABSTRACT FROM AUTHOR]

Cemented paste backfill (CPB), which is prepared by mixing tailings, binder and water, is widely used in underground mines for waste management and ground control. Since the CPB is delivered into mined-out areas in the form of fluid, a barricade needs to be constructed for retaining it during the process of its filling and hardening. Therefore, the barricade should have enough mechanical stability to ensure the safety of the backfill operation. The behavior of CPB, which is influenced by the thermal, hydraulic, mechanical and chemical (THMC) coupled processes, acts on the barricade and thus affects its mechanical response. In the present study, a numerical model is developed to predict and analyze the barricade mechanical performance in response to the coupled THMC behavior of CPB. The validity of the proposed model is then verified against two field case studies. Acceptable agreement between the model prediction results and in situ monitoring data proves the capability of the developed model in simulating the barricade pressure and displacement. Then, the validated model is used to investigate the effect of filling strategy on the barricade displacement. The obtained results can contribute to a better understanding of the barricade performance under various backfill conditions. [ABSTRACT FROM AUTHOR]

The current study presents the physical and mechanical properties of municipal solid waste (MSW) with different ages of new and old Tabriz landfill. Although there are several theoretical and laboratory methods to investigate the shear strength parameters of MSW, field methods provide more accurate results due to the minimum MSW disturbance and changes, so in this study the shear strength parameters of MSW Tabriz landfill were evaluated using the "Large Scale in Situ Direct Shear Device" with the cross-sectional dimensions 122 × 122 cm. In spite of difficulties related to conducting tests such as potential exposure to various contaminations and the lack of specific equipment in the beginning, it provided more realistic results of the geotechnical behavior of municipal solid waste compared to other methods. Moreover, the in situ unit weight, physical analysis, moisture and organic content at different ages were evaluated to better understand the mechanical response with increase in the age of MSW. The results showed the cohesion and friction angle of 5- and 16-year-old MSW was estimated as 1.17, 2.215 kPa and 31.51°, 21.51°, respectively; According to the results, the shear strength of 5- and 16-year-old MSW is mainly controlled by the friction angle which seems due to the MSW composition as a function of the consumption pattern. The physical analysis of fresh MSW from 2005 to 2017 showed an increase in the fiber content including plastics and textiles. Moreover, studies on MSW mechanical responses over the time revealed a decrease in the shear strength because of the raise in the fiber and plastic content. [ABSTRACT FROM AUTHOR]

Effect of size and shape of the additively manufactured Nickel-Titanium (NiTi) alloys on their thermomechanical properties is experimentally studied. Although additive manufacturing is shown as a solution to the difficulties of machining of NiTi shape memory alloys (SMAs), our understanding of the effect of various processing (e.g., laser power, scanning pattern, etc.) and part characteristics (e.g., part geometry) on the resulting properties is not complete. During the SLM fabrication process, various factors influence the properties of the final product. In this study, we investigated the effect of size and shape of the SLM samples on the thermomechanical behavior of the parts. Tensile specimens with different thicknesses and shapes were fabricated for this investigation. The accuracy of fabrication is discussed for all of the specimens. Differential scanning calorimetry (DSC) measurements were conducted to compare the transformation temperatures of specimens with different size and shape. Moreover, tensile tests including loading, unloading, and heating were done for all of the specimens and the mechanical responses were compared with each other. Digital image correlation (DIC) was used for strain measurements as a more accurate strain measurement tool. The transformation temperatures of the fabricated parts were similar for parts with different shapes and sizes. From the mechanical tests, higher strength was observed for the thinner parts in both rectangular and oval specimens. Also, from the mechanical behavior of different shapes, it was observed that the rectangular showed higher critical stress than their equivalent oval specimens. [ABSTRACT FROM AUTHOR]

In order to improve the energy density of polytetrafluoroethylene/aluminum (PTFE/Al), titanium hydride (TiH2) was added as a high-energy additive, and thermogravimetry–differential scanning calorimetry (TG-DSC), quasi-static compression and Split-Hopkinson pressure bar (SHPB) tests were conducted to investigate the chemical reaction mechanism and mechanical response of PTFE/Al/TiH2. The results of TG-DSC indicate that TiH2 first decomposes to form titanium and hydrogen, and titanium reacts with PTFE to produce TiF3, and then with the temperature rising, titanium reacts with carbon and excessive aluminum to generate TiC and Al3Ti. Under quasi-static compression, the strength of PTFE/Al/TiH2 specimens can reach 108.8 Mpa, 14.2% higher than that of PTFE/Al, the special burning flames during the reaction and XRD patterns of the reaction residues consistently indicate that TiH2 has participated in the reaction and react completely, achieving its purpose as a high-energy additive. Under dynamic compression tests, PTFE/Al/TiH2 composites show obvious strain hardening and strain rate hardening effects, and the yield strength and compressive strength are sensitive to strain rates; the established Johnson-Cook (JC) constitutive model can describe the mechanical response of PTFE/Al/TiH2 material well. In addition, the ignition threshold of PTFE/Al/TiH2 drops to 22.78 m/s, less than that of PTFE/Al (23.74 m/s), and the ignition delay time is advanced from 650-700 to 100-150 μs as the impact velocity increase. [ABSTRACT FROM AUTHOR]

In this paper, a simple phenomenological model describing the macroscopic mechanical response of electrospun nanofibrous structures is proposed. Motivated by the experimental observation, the model development starts from the description of membrane response at fiber scale in order to capture individual fiber response and irreversible inter-fiber interactions using hyperelastic and large strain elasto-plastic frameworks, respectively. The macroscopic response is subsequently obtained by integrating the fiber responses in all possible fiber orientations. The efficiency of the proposed model is assessed using experimental data of PVDF electrospun nanofibrous membranes. It is found that the model is qualitatively in good agreement with uniaxial monotonic and cyclic tensile loading tests. Two other deformation modes, i.e., equibiaxial extension and pure shear (planar extension), are simulated to further evaluate the model responses. Finally, the deformation-induced fiber re-orientation is investigated for different modes of deformations. [ABSTRACT FROM AUTHOR]

The disposal of scrap rubber tires has induced critical environmental issue worldwide due to the rapid increase in the number of vehicles. Recycled scrap tires as a construction material in civil engineering have significant environmental benefits from a waste management perspective. A systematic study that deals with strength and microstructure characteristics of the rubber-sand mixtures is initiated, and mechanical response of the mixtures is discussed in this investigation. Experiments were conducted to evaluate the effects of rubber fraction on the basic properties including mass density (ρ), stress-strain characteristics, shear strength, and unconfined compression strength (qu) of the rubber-sand mixtures. Additionally, scanning electron microscopy (SEM) was carried out to reveal the microstructure characteristics of the mixtures with various rubber fractions. A discussion on the micromechanics of the mixtures also was conducted. This study demonstrates that the ρ, friction angle, and qu decrease linearly with an increase in rubber fraction, whereas shear strain at peak increases. The stress-strain characteristics of the rubber-sand mixtures shift from brittle to ductile as the rubber fraction increase. These changes are attributed to remarkably lower stiffness and higher compressibility of the rubber particle compared with those of the conventional mineral aggregates. With an increase in the rubber fraction, the mechanical response of rubber-sand mixtures exhibits two types: sand-like material and rubber-like material. Rubber particle possesses the capacity to prevent the contacted sand particles from sliding at lower rubber fraction, whereas it transmits the applied loadings as the rubber fraction increased. This outcome reinforces the practicability of using recycled rubber tire-sand mixtures as a lightweight backfill in subbase/base applications. [ABSTRACT FROM AUTHOR]

Shear spring compliance was adopted to simulate interlayer bonding conditions between semi-rigid base layer and asphalt layer. The parametric sensitivity of the thickness and modulus of base layer and surface layer, and the horizontal force on deflection, tensile stress, shear stress was analyzed by orthogonal method under different interlayer bonding conditions. The effects of different interlayer bonding conditions and asphalt layer thicknesses on shear stress, tensile stress were further studied. The results show that when interlayer contact conditions change from the full bonding to half bonding or full slipping condition, the variation amplitude of interlayer maximum shear stress is the largest and its value is 0.48 MPa, and tensile stress is the second, and the variation of deflection is the smallest. When the pavement structure is affected by horizontal force, pavement mechanics index is sensitive to asphalt layer thickness, and 12 cm is the unfavorable thickness for mechanical response of pavement structure. When the interlayer horizontal shear coefficient is between 107 N/m³ and 1011 N/m³, the interlayer between semi-rigid base layer and asphalt pavement layer is in half bonding condition, and the variation of each pavement mechanics index is very prominently. [ABSTRACT FROM AUTHOR]