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Measurement of internal intervertebral disc strain is paramount for understanding the underlying mechanisms of injury and validating computational models. Although advancements in noninvasive imaging and image processing have made it possible to quantify strain, they often rely on visual markers that alter tissue mechanics and are limited to static testing that is not reflective of physiologic loading conditions. The purpose of this study was to integrate high-frequency ultrasound and texture correlation to quantify disc strain during dynamic loading. We acquired ultrasound images of the posterior side of bovine discs in the transverse plane throughout 0-0.5 mm of assigned axial compression at 0.3-0.5 Hz. Internal Green-Lagrangian strains were quantified across time using direct deformation estimation (DDE), a texture correlation method. Median principal strain at maximal compression was 0.038±0.011 for E1 and -0.042±0.012 for E2. Strain distributions were heterogeneous throughout the discs, with higher strains noted near the disc endplates. This methodological report shows that high-frequency ultrasound can be a valuable tool for quantification of disc strain under dynamic loading conditions. Further work will be needed to determine if diseased or damaged discs reveal similar strain patterns, opening the possibility of clinical use in patients with disc disease. [ABSTRACT FROM AUTHOR]

The transition in the mechanical behavior of heat-treated intact rock samples and rock samples containing joints with different types of infill materials was investigated at varying strain rates. Both dynamic compression [using split-Hopkinson pressure bar (SHPB)] and static uniaxial compressive strength (UCS) tests were carried out. A series of 114 SHPB tests were conducted on preheated samples under different temperatures (i.e., 30°C–300°C) for 5 h, under different strain rates (i.e., 53–130 s−1), along with static 57 UCS tests (at 10−4 s−1). Fracture initiation and progression in the samples during loading were continuously observed through high-speed imaging. The evolution of strain was assessed using digital image correlation analysis. Rate dependency existed in the strength behavior of all samples, with a general trend of increasing strength as strain rate increased. However, the rate dependency in the mechanical response of samples significantly depended on treatment temperature. Intact and epoxy-grouted samples showed higher rate dependency than unfilled and cement-grouted samples for temperatures lower than the transition temperature. With increasing temperature, the rate dependency in intact and epoxy-grouted samples reduced significantly and eventually aligned with that of ungrouted and cement-grouted samples. The fracture mechanism transitioned from being tensile-dominated to shear-dominated with increasing temperature in all samples, with crack-initiation and propagation showing significant dependence on the treatment temperature. The damage at the macroscopic level generally increased in all samples with increasing strain rates at all temperatures. More macrolevel cracks were observed in the samples at lower temperatures than those above the transition temperatures. Practical Applications: Rocks can be subjected to high-temperature conditions in different structures, such as nuclear waste repositories or during open fires. Further, these rocks could also be subjected to dynamic loading, such as blast loading or rapid transport. The dual effects of temperature and loading rate can change the chemophysical characteristics of rocks, resulting in premature failure of rock-supported structures during service. The present experimental study captures the failure mechanism in rock under high strain rate loading and temperature variation. The obtained data from experiments could be used to analyze the response of rock structures and improve the design of support systems in the field with more accuracy and confidence. Further, the knowledge of the efficiency of grouts in improving the mechanical response of low-quality rocks under high-temperature and high-loading rate conditions is of utmost importance for the practical design of rock structures in the field. This is important because the mechanical behavior of grouts depends on the existing temperature of rocks and the loading rate, as observed in this study. [ABSTRACT FROM AUTHOR]

Blast loading is associated with relatively short duration and high amplitude of forces, which when comes in contact with the reinforced concrete (RC) slabs results in the strong vibrations that yields high internal stresses and relatively larger deflections within the slabs. In this study, behaviour of a typical residential RC slab, when subjected to indoor confined blast, was investigated numerically using the conventional weapons (CONWEP) model available in the finite element software ABAQUS. For this purpose, the blast effect produced due to the gas leakage in a pipe was considered for studying the influence of different parameters which include concrete compressive strength, thickness of the slab, reinforcement ratio and spacing, the standoff distance and the boundary conditions of the RC slab. It was observed that the behaviour of the RC slabs, when subjected to blast loading, significantly differ from that observed under static loading as the latter was found to be associated with the overall bending of the slab, whereas for the case of blast loading the behaviour is characterized by both local damage in the direct contact zone of the slab and detonation and overall bending response. Maximum deflections were found to be more affected by concrete compressive strength, slab thickness and standoff distance. A relationship was proposed for the estimation of central deflection which correlates well with the values obtained from nonlinear FE analysis. [ABSTRACT FROM AUTHOR]

Shallow soils are highly vulnerable to the combined impacts of various factors, including vehicle loading, precipitation, and groundwater. The slope soil at the roadside is inevitably subjected to long-term cyclic loading from traffic. Previous studies have demonstrated that ecological engineering measures can effectively mitigate soil deformation and reduce pore water pressure development, thereby preventing soil erosion and landslides. This study aims to investigate the influence of root distribution patterns on the elastic deformation and pore water pressure development trends in root reinforced soil by simulating cyclic traffic loading through dynamic triaxial tests. The study findings demonstrate that the presence of roots significantly enhances the soil's resistance to deformation. When the vertical root accounts for 25% (while the horizontal root accounts for 75%), experimental results indicate that the soil reinforced by roots exhibits minimal deformation and slower pore water development. Moreover, a parameter D is introduced to enhance the existing pore water pressure models with the increased coefficients of determination, thereby improving the applicability in root-reinforced soils. These findings provide valuable insights for enhancing strength and liquefaction resistance in root reinforced soils while providing guiding research for the mechanical effects of root reinforcement of soil for ecological restoration of highway slopes. [ABSTRACT FROM AUTHOR]

The frequent or occasional impact loads pose serious threats to the service safety of conventional concrete structures in tunnel. In this paper, a novel three-dimensional mesoscopic model of steel fiber reinforced concrete (SFRC) is constructed by discrete element method. The model encompasses the concrete matrix, aggregate, interfacial transition zone and steel fibers, taking into account the random shape of the coarse aggregate and the stochastic distribution of steel fibers. It captures microscopic-level interactions among the coarse aggregate, steel fibers, and matrix. Subsequently, a comprehensive procedure is formulated to calibrate the microscopic parameters required by the model, and the reliability of the model is verified by comparing with the experimental results. Furthermore, a coupled finite difference method-discrete element method approach is used to construct the model of the split Hopkinson pressure bar. Compression tests are simulated on SFRC specimens with varying steel fiber contents under static and dynamic loading conditions. Finally, based on the advantages of DEM analysis at the mesoscopic level, this study analyzed mechanisms of enhancement and crack arrest in SFRC. It shed a light on the perspectives of interface failure process, microcrack propagation, contact force field evolution and energy analysis, offering valuable insights for related mining engineering applications. [ABSTRACT FROM AUTHOR]

Freeze–thaw action is a key factor in the deterioration of the dynamic mechanical behavior of rocks in cold regions. This study used yellow sandstone, which is prevalent in the seasonally cold region of Xinjiang, China. The yellow sandstone samples were subjected to various temperatures and a range of freeze–thaw cycles. Impact mechanical tests were performed using a Split Hopkinson Pressure Bar (SHPB) system on the treated samples. The effects of freezing temperature and changes in impact load on the mechanical properties of frozen–thawed sandstone were examined. Additionally, the damage fractal characteristics of the sandstone were analyzed using fractal theory. The results indicate that as the freezing temperature decreases, the stress–strain curves of frozen–thawed specimens exhibit a clear initial compaction stage. The dynamic strength of the specimens decreases with lower freezing temperatures and shows a logarithmic relationship with the loading strain rate; however, the dynamic deformation modulus exhibits no significant correlation with the strain rate. The fractal dimension is positively correlated with the strain rate, indicating that lower freezing temperatures correspond to a higher rate of increase in the fractal dimension. These findings offer valuable insights into the damage deterioration characteristics of frozen–thawed rocks under varying temperature conditions. [ABSTRACT FROM AUTHOR]

The deterioration of the US transportation highway network and the onset of new technologies in the freight industry are expected to cause changes in the axle load magnitude and distribution, further exacerbating the reduction in the service life of flexible pavements. In this study, a reviewed framework to incorporate roughness-induced dynamic wheel loading into tire–pavement contact stress prediction is presented. The response to nonfree-rolling conditions, usually overlooked, was considered. State-of-the-art numerical models were used to account for pavement unevenness, vehicle dynamics, and 3D and nonuniform contact stresses. In this framework, for a given target international roughness index, an artificial multitrack roughness profile was converted into a dynamic loading profile based on the mechanical properties of a Class 9 vehicle. Upon discretization of the dynamic loading profile into a finite number of loads based on percentile distributions, a 3D finite element model of a dual-tire assembly was used to predict the contact stress distribution over a rigid surface. The performed numerical simulations allowed us to analytically quantify the variation of vertical and in-plane contact stress distribution. Hence, changes in the stress/strain field distribution and peak values under various axle loading scenarios were determined. The findings reveal that disregarding the effect of road roughness and vehicle maneuvering could result in considerable underestimation of the net forces and contact stress distribution developed at the tire–pavement interface. These considerations are particularly impactful on in-plane contact stresses, which, in turn, are associated with near-surface distresses. Practical Applications: The distribution of contact stresses at the tire–pavement interface influences the likelihood of failure near the surface and is greatly affected by driving behavior (braking, cornering, and acceleration). Truck electrification is likely to modify driving behavior due to the instant torque availability provided by electric powertrains, and the incorporation of battery packs is likely to alter the distribution of axle loading. The impact of these variables on the applied load to a pavement system could be further exacerbated by road conditions. In that regard, this paper aims to quantify the changes in the contact stress distribution when roughness, driving behavior, and axle loading are compounded. Because these considerations are not taken into account by current pavement analysis procedures, pavement engineers can use the results to assess the importance of each parameter on load characterization, a controlling variable on the prediction of pavement responses. [ABSTRACT FROM AUTHOR]

Container transport is one of the most promising modes of international freight transport. Railway container transport is mainly carried out using flat cars. Container cars can be damaged under the most unfavorable operating load conditions of a 1520 mm track gauge, i.e., shunting collisions. In this context, an improvement to the supporting structure of flat cars is proposed to ensure their strength, involving the installation of special superstructures in their cantilever parts to limit the movement of the containers. The choice of the superstructure profiles was made on the basis of the section modulus of their components. Mathematical modeling of the dynamic loading of a flat car with containers in the event of a shunting collision was carried out. The determined value of acceleration was taken into account in the calculation of the strength of the load-bearing structure of the flat car. It was found that the maximum stresses were 24% lower than the allowable stresses. Therefore, the strength condition of the flat car was met. The results of this study will contribute to reducing damage to container transport vehicles in service, to the formulation of recommendations for their construction and to an increase in their profitability, including in international transport. [ABSTRACT FROM AUTHOR]

AbstractThis study introduces a novel hybrid tetra-chiral honeycomb (NHTCH) structure achieved by combining a tetra-chiral honeycomb and its inverse configuration. The honeycomb prototype was created through 3D printing, and a quasi-static compression experiment was conducted in the opposite direction. Utilizing Abaqus/Explicit, we developed a finite element numerical model and verified its accuracy. The mechanical properties of the proposed structure, denoted as NHTCH, were compared with those of traditional tetra-chiral honeycombs (TCH). Results indicated that NHTCH exhibits superior mechanical properties compared to TCH, and its plastic deformation displays a noticeable negative Poisson’s ratio effect. Furthermore, we analyzed the in-plane mechanical response of NHTCH under varying impact velocities and conducted parametric studies on the angle between chiral elements and the radius of the node circle. Our findings reveal that, under high-speed impacts, NHTCH demonstrates higher energy-absorbing and load-carrying capacities compared to the other two configurations. Simultaneously, optimizing the clamping angle and nodal circle radius of NHTCH efficiently enhances the mechanical properties within a specific range, without causing significant changes to the plastic deformation of the structure. [ABSTRACT FROM AUTHOR]

Bone behaves as a complex composite material, and is highly heterogenous and anisotropic in nature due to its hierarchical structure. The effect of the location and orientation of bone specimens on the viscoelastic properties of bovine femoral cortical bone was examined in this study. The bone samples were extracted from different locations i.e., proximal, central and distal along the direction of longitudinal and transverse and underwent sinusoidal loading. The longitudinal orientation shows more values of loss tangent and loss modulus in comparison to transverse orientation bone samples. Across locations reveal no significant difference in the storage modulus, loss tangent, loss modulus and complex modulus. The trends in the complex and storage moduli remain consistent within both types of orientations. Significant differences were observed across the locations for both storage and recovered energy, with no variance in the hysteresis loss. The findings from the study shall help in a deep understanding of the bone biomechanics, offering insights for material design and orthopedic interventions in biomechanical engineering. [ABSTRACT FROM AUTHOR]

The structural optimization of trusses is a complex problem that can be affected by many different factors. In this research, the authors investigated the optimization of trusses performing a geometric nonlinear analysis under dynamic loading, using two different metaheuristic algorithms: the Genetic Algorithm (GA) and Particle Swarm Optimization (PSO). The objective function was to minimize the weight of the structure. A number of benchmark test problems for spatial trusses considering a geometric nonlinear analysis, and dynamic loading are analyzed to verify the performance of the optimization algorithms. The results showed that both algorithms were able to find efficient solutions to the optimization problem and suggest that the choice of the optimization algorithm can have a significant impact on the performance of the optimization process. [ABSTRACT FROM AUTHOR]

Purpose: Limited nutrient transport is hypothesized to be involved in intervertebral disc (IVD) degeneration. It is widely recognized that the dominant mode of transport of small molecules such as glucose is via diffusion, rather than convection. However, recent findings suggest a role for convection-induced by fast (motion-related) and slow (diurnal) dynamic loading in molecular transport of even such small solutes. The aim of this study was to investigate whether fluid exchange induced by simulated physiological loading (composed of both fast cyclic or slower diurnal loading) can influence the molecular transport of a small molecule through the cartilage endplate (CEP) into the nucleus pulposus (NP) of IVDs. Methods: The molecular transport of fluorescein through the CEP and into the NP was studied in a bovine CEP/NP explant model and loading was applied by an axial compression bioreactor. The loaded explants (convection and diffusion) were compared to unloaded explants (diffusion alone). Results: In the initial 24 h, there were no differences between loaded and unloaded explants, indicating that convection did not enhance molecular transport of small solutes over diffusion alone. Notably, after 48 h which corresponds to two complete diurnal cycles of tissue compression, fluid exudation/imbibing and redistribution, the fluorescein concentration was significantly increased in the top and bottom layer of the explant, when compared to the unloaded explant. Conclusions: Slower diurnal cyclic compression of the IVD might enhance the transport of small molecules into the IVD although it could not be discerned whether this was due to diffusion/convection or a combination. [ABSTRACT FROM AUTHOR]

Despite the significant research on the seismic stability of earth structures, critical gaps remain in understanding the dynamic response of soil slopes with varying reinforcements. These gaps were addressed in this study by using a small shake table to investigate the dynamic behavior of soil slopes under different conditions. The research examines responses at various frequencies, the effect of reinforcement methods, and the impact of slope height. Results indicate that the higher frequencies and amplitudes lead to increased displacements, while reinforcement reduces crest displacement by 21 to 45%. Steeper slopes (35° and 40°) also show increased displacements by 9 to 65%, compared to a 30° slope. The importance of reinforcement in improving the seismic resilience of soil slopes is highlighted in this study, offering practical insights for engineering design. [ABSTRACT FROM AUTHOR]

The examination of electrical potential (EP) response characteristics in flawed coal and its correlation with mechanical behavior can establish a theoretical foundation for enhancing safety and stability in deep underground engineering under extreme loading conditions. This study employs the Split Hopkinson pressure bar (SHPB) to conduct dynamic testing on coal samples containing defects, while simultaneously recording the EP. Using continuous wavelet transform, the time–frequency characteristics of the EP are analyzed and correlated with the mechanical behavior of the coal. Digital image correlation (DIC) technology is employed to reveal the deformation characteristics of the samples and their relationship with EP parameters. The intrinsic connection between the EP response mechanism and coal fracture is examined. The results suggest a strong correlation between the time–frequency characteristics of the EP and both the stress level and fracture mode exhibited by the samples. The cumulative EP increases as strain accumulates, while transient EP magnitude is determined by strain rate. Crack propagation generates free charges, where cumulative charge increases proportionally with crack length; similarly, crack propagation rate determines release rate of free charges. In terms of energy evolution, absorbed energy exhibits a linear correlation with EP energy. These findings provide valuable theoretical guidance for applying EP testing technology in monitoring underground engineering stability. Highlights: The dynamic load EP test was carried out by the SHPB-EP-DIC experimental system. The time–frequency evolution of the EP response of the specimens under dynamic loading was investigated. Correlation expressions between mechanical parameters and EP parameters are analyzed. The internal connection between crack expansion and free charge is discussed. The transformation relationship between absorption energy and EP energy is explored. [ABSTRACT FROM AUTHOR]

Abstract The frequent or occasional impact loads pose serious threats to the service safety of conventional concrete structures in tunnel. In this paper, a novel three-dimensional mesoscopic model of steel fiber reinforced concrete (SFRC) is constructed by discrete element method. The model encompasses the concrete matrix, aggregate, interfacial transition zone and steel fibers, taking into account the random shape of the coarse aggregate and the stochastic distribution of steel fibers. It captures microscopic-level interactions among the coarse aggregate, steel fibers, and matrix. Subsequently, a comprehensive procedure is formulated to calibrate the microscopic parameters required by the model, and the reliability of the model is verified by comparing with the experimental results. Furthermore, a coupled finite difference method-discrete element method approach is used to construct the model of the split Hopkinson pressure bar. Compression tests are simulated on SFRC specimens with varying steel fiber contents under static and dynamic loading conditions. Finally, based on the advantages of DEM analysis at the mesoscopic level, this study analyzed mechanisms of enhancement and crack arrest in SFRC. It shed a light on the perspectives of interface failure process, microcrack propagation, contact force field evolution and energy analysis, offering valuable insights for related mining engineering applications.

Abstract Accurately predicting rock tensile strength under varying strain rates is crucial for tunnel construction, as rock often fails in tension. This study examines the effect of rock mesostructure on tensile strength using a breakable grain-based model (GBM) implemented within the UDEC software. The Brazilian disk model was established to simulate the quasi-static and dynamic tensile behaviors of rocks under varying mineral average grain sizes, grain size distributions, and grain roundness, respectively. Simulation outcomes indicate that mesostructure significantly influences rock tensile strength. The breakable GBM effectively captures the tensile failure process under high strain rates, revealing the role of grain structure heterogeneity in strain rate effects. Additionally, the study evaluates the applicability of different dynamic increase factor (DIF) models, confirming the effectiveness of the normalized DIF model for predicting the dynamic tensile strength of granite. These findings underscore the importance of considering rock mesostructure for accurate prediction and enhancement of rock performance under dynamic loading conditions.

Two-phase immersion cooling has emerged as a promising solution for efficient and effective thermal management in high-performance computing applications. This study presents the results of detailed experimental investigations on two-phase immersion cooling via pool boiling employing single-fluid and multi fluids in the system. In the proposed multi-fluid system, two immiscible fluids are stacked in series without a solid interface separating them. NOVEC 7100 is used as the boiling fluid where the heater is fully immersed, and deionized water serves as the condensing fluid. The results show that both single and multi-fluid immersion cooling systems are able to effectively cool high-power electronic devices. However, the multi-fluid system demonstrates superior cooling performance compared to the single-fluid system, owing to its enhanced heat transfer capabilities. The multi-fluid system has a superior overall heat transfer coefficient with an average increase of 33.3% compared to the single-fluid system. The findings of this study contribute to the understanding and optimization of future multi-fluid two-phase immersion cooling systems. [ABSTRACT FROM AUTHOR]

This study investigates the mechanical, biodegradation, and microstructural performance of cementitious composites reinforced with Corn Straw Ash (CSA) and Corn Straw Fiber (CSF) for applications in bio-inspired materials and sustainable engineering. CSA, a pozzolanic material, enhances matrix densification, while CSF provides crack-bridging and toughness improvement. Dynamic mechanical testing under cyclic loading demonstrated that CSA-CSF composites exhibit superior fatigue resistance, retaining 85% of their initial compressive strength after 1000 cycles. Biodegradation studies in simulated body fluid (SBF) and acidic environments revealed that the composites maintain 75% compressive strength in SBF over 28 days, highlighting their potential for bioactive scaffolds. Scanning electron microscopy (SEM) and quantitative porosity analysis showed that CSA-derived Calcium Silicate Hydrate (C-S-H) gel effectively filled voids, while CSF enhanced fiber-matrix bonding, mimicking the hierarchical structure of biological systems. The results emphasize the dual benefits of CSA-CSF composites in dynamic environments and their alignment with sustainable and bio-inspired design principles. This research provides insights into the development of materials for biomechanical applications, including tissue engineering scaffolds and earthquake-resistant structures. [ABSTRACT FROM AUTHOR]

ObjectiveThis study aims to simulate the actual forces applied to drill rods during the borehole drilling for gas drainage from underground coal mines to satisfy the requirements of drill rods’ fatigue tests. MethodsThis study designed a dynamic loading system for full-size drill rods in coal mines. This system consists of a drill rod loading platform, a hydraulic pump unit with power recovery, and a measurement and control system, allowing for the composite loading of dynamic torque, axial force, and radial displacement on drill rods of different specifications. In this system, torque is loaded to drill rods using the hydraulic power recovery method. Specifically, two identical hydraulic motors, acting as loads mutually, are mechanically connected to the tested drill rod. The active motor drives the drill rod and the loading motor to rotate, while the loading motor returns the output flow to the active motor, thus achieving torque loading and power recovery. The energy loss of the closed-loop system is compensated by two hydraulic compensating pumps. The loading of axial force and radial displacement is controlled based on the electro-hydraulic proportion. Based on various variables collected by sensors, the programmable logic controller (PLC) performs closed-loop adjustment of the force and displacement of the loading cylinder to achieve precise control. During tests, various operating parameters and power recovery efficiency are acquired using the measurement and control system and then displayed in the upper computer in real time. The loading capacity of the dynamic loading system was verified using a round drill rod measuring ø127 mm×3 000 mm. Results and ConclusionThe results indicate that the torque and rotational speed of the dynamic loading system can be adjusted by changing the flow or pressure of hydraulic compensating pumps, the displacement relationship between the active and loading motors, and the gearbox gear, thereby meeting various operation conditions of the tests. In the case of the same displacement between the active and loading motors, the power recovery efficiency can reach the theoretical maximum (77%). Under the operating condition of a low rotational speed combined with a high torque, the measured torque loaded to the drill rod reached the maximum (35080 N∙m), corresponding to a rotational speed of 28 r/min, motor power of 50.7 kW, and power recovery efficiency of 66.2%. This suggests an effective reduction of the installed power of the dynamic loading system. Overall, the proposed dynamic loading system for drill rods in coal mines overcomes the limitations of existing devices for fatigue tests, such as insufficient loading capacity and high energy consumption, providing strong equipment support for drill rod tests and being of great application value.

Blasting excavation and cavity filling are the core means of filling mining in underground metal mine. As the core load-bearing unit of cavity, the backfill is inevitably subjected to the blasting dynamic load perturbation of adjacent ore body, which in turn induces some structural changes in the internal structure of matrix and affects its re-bearing capacity and stability, which is related to the safety of mine production. Therefore, in this paper, the dynamic damage filling body considering the magnitude of impact amplitude is prepared based on the split Hopkinson press bar system (SHPB), and the simulation of filling body blasting disturbance is realized. The mesoscopic structural response characteristics of the filling body under dynamic loading are investigated, the mechanical behavior and crack extension mechanism of the dynamically damaged filling body are revealed, and the instability over-warning of the dynamically damaged filling body is realized. The results show that: the degradation of meso-structure of the dynamically damaged filling body increases with the increase of impact amplitude, corresponding to the increase of porosity by 34.48%, the decrease of wave velocity by 44.48%, and the intensification of the initial damage degree. With the increased impact amplitude, the uniaxial compressive strength and elastic modulus of the dynamically damaged filling body show a three-stage trend of slow decrease, then rapid decrease and then slow decrease, with the maximum decrease rate of 54.15% and 69.02%, respectively. Meanwhile, the compaction stage of the stress-strain curve of the dynamically damaged filling body is significantly prolonged with the increase of the damage degree. The peak strain increases by 78.35%, and the filling body changes from brittle ductile to ductile. The characteristic parameters of acoustic emission (AE) are closely related to the rupture behavior of the filling body. Due to the difference in the initial damage degree, the rate, number and scale of cracks sprouting, expanding and propagating within the matrix of the dynamically damaged filling body are significantly different. The activity and sparsity of the AE signal initially decrease, then increase, and finally decrease again with the increase in impact amplitude. The AE ib value exhibits a pattern of “fluctuating increase”, “sharp decrease”, and “large fluctuation”. As the impact amplitude increases, there is an increase in the area of sharp decline in AE ib values and a shift to the pre-peak stage. The area of sharp decline in ib value is judged to be the precursor information of instability, and the dynamic damage filling body reaches the critical value of instability at a smaller stress. Increasing the impact amplitude has no significant effect on the failure mode of the dynamically damaged filling body, but the area of the surface collapse zone is increased and the degree of failure is significantly enhanced.

Abstract The study of mechanical properties and failure mechanism of propellants under impact loads is crucial for analyzing structural integrity of propellant charges. An experimental investigation was conducted on NEPE propellant using a separated Hopkinson pressure bar to conduct high strain rate uniaxial impact tests. Deformation and failure processes of the propellant under impact conditions were recorded with a high-speed camera. The microscopic failure forms of the propellants were observed using a scanning electron microscope and an optical microscope. Stress-strain curves and high-speed images revealed that the damage behavior and failure mechanism of NEPE propellants are significantly influenced by strain rate. As the strain rate increases, there is a notable increase in the deformation degree of the propellant specimens, with a more pronounced shear effect. This leads to an earlier occurrence of failure and a more severe degree of failure. The predominant failure forms observed in NEPE propellants include transgranular failure, matrix tearing, and cavity merging. A nonlinear visco-hyperelastic constitutive model with damage at high strain rates was established to provide a precise account of the mechanical response of NEPE propellant under high strain rates.

ABSTRACT This work examines the effect of loading rate (K·$$ \overset{\cdotp }{K} $$) on the mode III fracture behavior of sandstone. Edge‐notched diametrically compressed (ENDC) disc sandstone specimens were tested under different static and dynamic mode III fracture loadings, revealing a clear loading rate effect on both mode III and mode I fractures. Specifically, the peak load and fracture toughness (KIIIC, KIC) increase as the K·$$ \overset{\cdotp }{K} $$ increases across both static and dynamic scales. At the static scale, the KIIIC is about 1.28–1.38 times of the KIC, whereas at the dynamic scale, the KIIIC is less than the KIC. The relationship between KIIIC and KIC is affected by the loading scale and the shape of the specimen, but the data collected thus far indicate that the origin and type of rock have minimal effect on this relationship. In addition, the fracture surface morphology characteristics were quantitatively analyzed. [ABSTRACT FROM AUTHOR]

In this manuscript, a rate-sensitive plasticity-based damage model for concrete subjected to dynamic loads is presented. The developed rate-sensitive damage model incorporates the key experimental evidence related to strain rate and damage rate. With increasing strain rates, the model is able to predict a decrease in the rate of damage evolution due to artificial stiffening effects together with a final higher level of damage. The major contribution of the work is to include the effect of damage rate, strain rate and also to consider all the physical mechanisms of damage. This is achieved by using a power law model to relate the rate of damage to the equivalent plastic strain rate. The damage parameter considers hydrostatic, tension and compression damage. Such a damage definition helps in the prediction of pulverized damage due to a loss in cohesive strength at increased hydrostatic stress, shear-induced compressive damage and tensile microcracking. Strong volumetric deformation of the material that includes hydrostatic and compaction damage is also considered in the model. Because hydrostatic damage accounts for the reduction in stiffness and compaction damage accounts for the increase in stiffness under pure compressive loading. A strain rate-dependent failure surface is considered and with increasing strain rate there is an increase in the size of the failure surface which is capped at an upper limiting value. The incremental effective stress-strain relationship is defined in terms of rate of damage, accumulated damage and viscosity parameters reflecting the inherent inertial, thermal and viscous mechanisms respectively. The stress-strain relationship in the model also accounts for stress reversals that occur due to interference of an incident and reflected wave, by including a Heaviside function. The developed model is implemented in LS-DYNA using vectorized UMAT. Verification, validation and parameterization of the developed model have been made through several numerical analyses. Highlights: From the SHPB analysis, the developed model can predict the key finding of a decrease in the rate of damage evolution and a higher damage level with an increasing strain rate. Un-confined and confined compression test demonstrate that the concrete subjected to increased hydrostatic stress will lose its cohesive strength and undergoes pulverized damage. Dynamic compressive and tensile test shows that the role of viscosity parameter and damage rate becomes predominant with increasing strain rate. The developed model is able to get the material characteristic, structural response, damage and evolution of damage. [ABSTRACT FROM AUTHOR]

The transportation sector is responsible for significant greenhouse gas (GHG) emissions, with medium- and heavy-duty trucks (MHDTs) being major contributors. In response, medium- and heavy-duty electric trucks (MHDETs) are being explored as zero-emission alternatives. However, the weight of high-capacity batteries needed for long-haul trips and heavy loads could increase the axle loads as well as the gross vehicle weight (GVW) of heavy-duty electric trucks (HDETs), leading to extra damage on flexible highway pavements. This study simulated the GVW increment of HDETs and assessed its effects on pavement damage, environmental impacts, and life-cycle costs of four typical highway pavement structures in Illinois (known as thick–weak, thick–strong, thin–weak, and thin–strong). The utilisation of electric trucks resulted in significant reductions in diesel combustion related global warming potential (GWP) emissions and costs (in $2022) by 73% and 11.5%, respectively. However, the results demonstrated that with a 100% penetration of HDETs carrying an additional weight of 8 kips per truck, the pavement deterioration accelerated compared to traffic with conventional trucks. As a consequence, GWP and costs were reduced by 69% and 10.6%, respectively. [ABSTRACT FROM AUTHOR]

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This study investigates the impact of tightening torque (preload) and the friction coefficient on stress generation and fatigue resistance of a Ti-6Al-4V abutment screw with an internal hexagonal connection under dynamic multi-axial masticatory loads in high-cycle fatigue (HCF) conditions. A three-dimensional model of the implant–abutment assembly was simulated using ANSYS Workbench 16.2 computer aided engineering software with chewing forces ranging from 300 N to 1000 N, evaluated over 1.35 × 107 cycles, simulating 15 years of service. Results indicate that the healthy range of normal to maximal mastication forces (300–550 N) preserved the screw's structural integrity, while higher loads (≥800 N) exceeded the Ti-6Al-4V alloy's yield strength, indicating a risk of plastic deformation under extreme conditions. Stress peaked near the end of the occluding phase (206.5 ms), marking a critical temporal point for fatigue accumulation. Optimizing the friction coefficient (0.5 µ) and preload management improved stress distribution, minimized fatigue damage, and ensured joint stability. Masticatory forces up to 550 N were well within the abutment screw's capacity to sustain extended service life and maintain its elastic behavior. [ABSTRACT FROM AUTHOR]

In the present study, an effort was made to determine the effects of a porous matrix with different viscosities on the dynamic and static behaviors of rough short journal bearings taking into account the action of a squeezing film under varying loads without journal rotation. The micropolar fluid was regarded as a lubricant that contained microstructure additives in both the porous region and the film region. By applying Darcy's law for micropolar fluids through a porous matrix and stochastic theory related to uneven surfaces, a standardized Reynolds-type equation was extrapolated. Two scenarios with a stable and an alternating applied load were analyzed. The impacts of variations in viscosity, the porous medium, and roughness on a short journal bearing were examined. We inspected the dynamic and static behaviors of the journal bearing. We found that the velocity of the journal center with a micropolar fluid decreased when there was a cyclic load, and the impact of variations in the viscosity and porous matrix diminished the load capacity and pressure in the squeeze film and increased the velocity of the journal center. [ABSTRACT FROM AUTHOR]

Articular cartilage injuries in the knee can lead to post-traumatic osteoarthritis if untreated, causing debilitating problems later in life. Standard surgical treatments fail to ensure long lasting repair of damaged cartilage, often resulting in fibrotic tissue. While there is a vast amount of research into cartilage regeneration, integrating engineered implants with cartilage remains a challenge. As cartilage is a load bearing tissue, it is imperative to evaluate tissue repair strategies and their ability to integrate under mechanical loading. This work established a dynamically loaded ex vivo model of cartilage repair using human cartilage explants. The model was used to assess the efficacy of a stem cell therapy delivered in a bioadhesive hydrogel comprised of photocrosslinkable gelatin methacryloyl (GelMA) and microbial transglutaminase to repair the model defect. Extensive neocartilage production and integration were observed via histology and immunohistochemistry after 28 days chondrogenic culture. Analysis of culture media allowed monitoring of glycosaminoglycan and type II collagen production over time. A mechanical assessment of integration via a push out test showed a 15-fold increase in push out strength over the culture duration. The model was successful in exhibiting robust chondrogenesis with transglutaminase or without, and under both culture conditions. The work also highlights several limitations of ex vivo models and challenges of working with bioreactors that must be overcome to increase their utility. This ex vivo model has the potential to delay the need for costly pre-clinical studies and provide a more nuanced assessment of cartilage repair strategies than is possible in vivo. [ABSTRACT FROM AUTHOR]

Laminar flow offers significant potential for increasing the energy efficiency of future transport aircraft. At the Cluster of Excellence SE2A—Sustainable and Energy-Efficient Aviation—the laminarization of the wing by means of hybrid laminar flow control (HLFC) is being investigated. The aim is to maintain the boundary layer as laminar for up to 80% of the chord length of the wing. This is achieved by active suction on the leading edge and the rear part of the wing. The suction panels are constructed with a thin micro-perforated skin and a supporting open-cellular core structure. The mechanical requirements for this kind of sandwich structure vary depending on its position of usage. The suction panel on the leading edge must be able to sustain bird strikes, while the suction panel on the rear part must sustain bending loads from the deformation of the wing. The objective of this study was to investigate the energy absorption properties of a triply periodic minimal surface (TPMS) structure that can be used as a bird strike-resistant core in the wing leading edge. To this end, cubic-sheet-based gyroid specimens of different polymeric materials and different geometric dimensions were manufactured using additive manufacturing processes. The specimens were then tested under quasi-static compression and dynamic crushing loading until failure. It was found that the mechanical behavior was dependent on the material, the unit cell size, the relative density, and the loading rate. In general, the weight-specific energy absorption (SEA) at 50% compaction increased with increasing relative density. Polyurethane specimens exhibited an increase in SEA with increasing loading rate, as opposed to the specimens of the other investigated polymers. A smaller unit cell size induced a more consistent energy absorption, due to the higher plateau force. [ABSTRACT FROM AUTHOR]