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Stress concentrations in a new type of reduced-beam-section (RBS) connection were investigated. Experimental and numerical results of RBS connections with semilunar web (SW) and holed tubular webs (HTW) were compared with connections with tubular webs (TW). For the SW, two semi-circular plates were used in place of a flat web in the beam. For the HTW, a steel tube was used instead of part of the beam web and holes were created in the beam web. For the TW, a steel tube was used instead of part of the beam web but without holes. The connections had adequate shear capacity but made little contribution to flexural stiffness and capacity. Semi-deep beam specimens were fabricated and tested under cyclic loading. The results showed that the beam connections with SWs and HTWs had 30% and 20% less fatigue damage respectively than those with TWs. The story drift capacity was also increased to 7%, much more than that stipulated by current seismic codes. The specimens were modelled using finite-element software to validate the experimental results.

We studied the microstructure evolution of Mg-4Y-3Nd-2Sm-0.5Zr alloy by quasi-in-situ electron backscatter diffraction (EBSD) along with several strains under compression tests, which provided direct evidence for the influence of different twin-twin geometric structure on the twinning behavior. The results showed that the mechanical properties of the alloy were higher than traditional magnesium alloys (the maximum compressive strength reaches 402.5 MPa) due to the strengthening effect of Sm and Nd elements addition on solution strengthening, precipitation strengthening, and grain refinement. Combined with the quasi-in-situ EBSD technique, two different twin-twin geometric structures, ‘parallel structure’ and ‘cross structure’, were observed directly in the alloy. In the later stage of deformation, for ‘parallel structure’, residual stress and a large number of dislocations mainly existed in the twin boundary and tip position. For the ‘cross structure’, there was a lot of dislocation density in the interior of twins after fusion. The twin growth rate of ‘parallel structure’ was much faster than that of ‘cross structure’ because the stress of twins was mainly concentrated on the tip of twin. When the movement for the tip of twin was blocked, the growth rate of twin would be obviously decreased. Moreover, the ‘cross structure’ was easy to produce closed space. Due to the constraints of surrounding twins, the confined space was easy to stress concentration, thus inhibiting the growth of twins. At the same time, the ‘cross structure’ of twins needed a more external force to continue to deform, which also served as a strengthening structure.

This paper offers the use of stress concentration factor in determining the critical fracture stress and fracture toughness of polymeric composite materials at various crack length ratios. The stress intensity factor has been turned into a function of the stress concentration factor derived from the maximum stress occurring at the notch tip and the tip stress generated by the force applied to the sample. This conversion allowed the use of a fixed theoretical radius (1.2732 mm) instead of the actual radius of the notch or crack. On the edge cracked three-point bending and tensile samples, the specified method detects the three point bending fracture stresses with a maximum error rate of 1.2%. This study also establishes a relationship between the clamped end and the pin-loaded tensile specimens and states that the underlying mechanism of the stress intensity factor of the clamped end tensile specimen is based on the normalization of the stress intensity factor of the pin-loaded conditions with the geometric correction factor.

To design a steel shear wall, dynamics of stress concentration on the columns and beam under lateral loads is essential. Therefore, it has been suggested that the thickness of plates should be reduced as much as possible. In cases where a plate with low thickness is not available, this is compensated by using either low-yield-stress plate or by preparing some holes in the structure. Two objectives are pursued in this study, namely, the formulation of a new time integration method for evaluating structural seismic behaviour, and to discover the influences of the yield strength of the steel plate and openings on the wall. The results obtained indicate that the proposed scheme can accurately assess the seismic performance of structures. In addition, in the shear wall with low yield stress, where the steel plate has 5% and 10% openings, there are no significant differences between the outputs of widespread and concentrated openings. The behaviours of these two kinds of shear walls are approximately the same.

Low dimensional sp3 carbon nanostructures have attracted increasing attention recently, due to their unique properties and appealing applications. Based on in silico studies, this work exploits the impacts from functional groups on the tensile properties of carbon nanothreads (NTH) – a new sp3 carbon nanostructure. It is found that functional groups will alter the local bond configuration and induce initial stress concentration, which significantly reduces the fracture strain/strength of NTH. Different functional types lead to different local bond re-configurations, and introduce different impacts on NTH. Further studies reveal that the tensile properties decreases generally when the content of functional groups increases. However, some NTHs with higher content of functional groups exhibit higher fracture strain/strength than their counterparts with lower percentage. Such observations are attributed to the synergetic effects from the sample length, self-oscillation, and distribution of functional groups. Simulations show that the tensile behaviour of NTH with the same functional percentage differs when the distribution pattern varies. Overall, ethyl groups are found to induce larger degradation on the tensile properties of NTH than methyl and phenyl groups. This study provides a comprehensive understanding of the influence from functional groups, which should be beneficial to the engineering applications of NTH.

Based on the use of a multi-level mathematical model, this paper estimates the stressed-strained state of a cylindrical reservoir in the mounting joint and considers the concentration of stresses in the joint zone. The correctness of the selected mathematical model was verified to show that for an engineering assessment of the stressed-strained state of the wall of a cylindrical tank with variable thickness, it is possible to use the ratios for a cylindrical shell with a constant wall thickness. The spread of values is no more than 1 %, which indicates the proper selection of the mathematical model. A numerical assessment of the stressed-strained state in the zone of the mounting joint proved the assumption of significant stress concentrations in the zone and indicated the determining effect exerted on the concentration of stresses by its geometric dimensions. The concentration of stresses in the joint zone of the tank wall was investigated at various sizes in the ANSYS programming environment. The result of calculating the stressed-strained state of the reservoir for various values of the dent parameters f/t and is the constructed polynomials that approximate the stress concentration coefficient Kσ. As a result of the calculations, an interpolation polynomial and an approximating stress concentration coefficient were derived, which could be used to assess the strength, durability, residual life of the tank and to normalize the limiting dimensions of the imperfection of the joint. This paper reports comparative results of the calculations of the stress concentration coefficient depending on the geometric dimensions of the imperfection of the mounting joint in the ANSYS software package, as well as using an interpolation polynomial. The results could be used to assess the strength and residual life of such structures., На основі використання багаторівневої математичної моделі оцінено напружено-деформований стан циліндричного резервуару в монтажному стику та вивчено концентрацію напружень у зоні стику. Проведено верифікацію правильності обраної математичної моделі, і показано, що для інженерної оцінки напружено-деформованого стану стінки циліндричного резервуару зі змінною товщиною можна скористатися співвідношеннями для циліндричної оболонки з постійною товщиною стінки. Розкид значень становить трохи більше 1 %, що свідчить про правильність обраної математичної моделі. Проведена чисельна оцінка напружено-деформованого стану в зоні монтажного стику довела припущення про значні концентрації напруги в зоні та вказала на визначальний вплив на концентрацію напружень її геометричних розмірів. Досліджено концентрацію напруг у зоні стику стінки резервуара в середовищі ANSYS при різних розмірах. В результаті розрахунків напружено-деформованого стану резервуару для різних значень параметрів вм’ятин f/t і побудовані поліноми, що апроксимують коефіцієнт концентрації напруг Kσ. В результаті розрахунків отримано інтерполяційний поліном та апроксимуючий коефіцієнт концентрації напруг, які можуть використовуватися для оцінки міцності, довговічності, залишкового ресурсу резервуару та для нормування граничних розмірів недосконалості стику. Наведено порівняльні результати розрахунків коефіцієнта концентрації напруг від геометричних розмірів недосконалості монтажного стику в програмному комплексі ANSYS, а також із застосуванням інтерполяційного полінома. Отримані результати можуть бути використані для оцінки міцності та залишкового ресурсу подібних конструкцій.

Tectonism often plays an important role in the mineralization process, which is generally thought to be the main controlling factor in the accumulation of economic materials (e.g., gold, coal, oil and gas) through deformation. However, numerous experimental and theoretical studies have suggested that tectonic stress not only causes deformation (physical changes) in rocks and minerals but also promotes their chemical changes by acting directly on chemical bonds and causing bond scission or regeneration, called tectonic stress chemistry (TSC). In recent years, TSC actions caused by tectonic activities have provided new ideas and evidence for explaining the chemical structural evolution of coal, hydrocarbon formation, organic (coal-derived) and inorganic graphitization and hydrothermal mineralization under shear stress. These background studies have provided incentives and insights into how tectonic stress affects the chemical structures of minerals, rocks and even ore-forming fluids in the process of mineralization. In this paper, we briefly review: (1) the concept of TSC; (2) the TSC process in the formation of shear zone type gold deposits from stress concentration, brittle fracturing, sudden reduction of fluid pressure, and flash vaporization to gold precipitation; (3) mechanisms of the macromolecular structural evolution of coal and gas generation under shear stress from deformation experiments and molecular dynamic simulations; (4) coal-derived graphitization caused by preferred orientation and extension of the basic structural units (BSUs) under shear stress; and (5) some preliminary experimental explorations on inorganic graphitization in carbonate-hosted shear zones. In addition, some existing problems and possible solutions for these processes are also discussed. Finally, we propose additional potential TSC processes in extensive geological processes, e.g., the relationship between deformation and metamorphism and trigger mechanisms of slow-slip earthquakes. To further explore these processes, a combination of experiments and molecular dynamic simulations should be undertaken by researchers.

Abstract Zirconia-based shape memory ceramics (SMCs) exhibit anisotropic mechanical response when undergoing elastic deformations as well as during austenite–martensite phase transformation. This behavior results in different types of strain incompatibility at grain boundaries, which we study here using a micromechanical model. A single-crystal model is implemented to provide a full mechanistic three-dimensional description of the anisotropic elastic as well as martensitic transformation stress–strain response, including non-Schmid behavior caused by the significant volume change during martensitic transformation. This model was calibrated to and validated against compression tests of single-crystal zirconia micro-pillars conducted previously, and then used to model bi-crystals. Upon the introduction of a grain boundary, the simulation provides detailed information on the nucleation and evolution of martensite variants and stress distribution at grain boundaries. We identify bi-crystal configurations which result in very large stress concentrations at very low deformations due to elastic incompatibility, as well as others where the elastic incompatibility is relatively low and stress concentrations only occur at large transformation strains. We also show how this approach can be used to explore the misorientation space for quantifying the level of elastic and transformation incompatibility at SMCs grain boundaries. Graphical abstract Micromechanics models provide insights on grain boundary elastic and phase transformation strain incompatibility in shape memory zirconia

An equiatomic VNbTi medium-entropy alloy with outstanding tensile properties and unique deformation behavior is reported. The screw dislocation glide, deformation twinning, and dislocation accumulation induced kink bands are identified as three deformation mechanisms that contribute to a large elongation above 20%. The {112} twins are activated at the beginning of the yield stage accompanied by sudden stress-drop and pronounced acoustic emission. Dislocations dominate subsequent tensile deformation, and the prevalent multiplanar dislocation slip promotes the formation of complex dislocation configurations (e.g., debris, dipoles, and loops) and dense dislocation networks. The twin bands and kink bands can further impede the dislocation motion meanwhile effectively alleviate stress concentration. The synergistic activation of these deformation mechanisms provides new opportunities to design ductile refractory medium- and high-entropy alloys.

The failure mechanisms of Oxide-Oxide ceramic matrix composites AS-N610 were studied at both room temperature and high temperature using tensile and fatigue tests with and without lateral and laminar notches. The unnotched coupons had an average tensile strength of 423 MPa with elastic modulus of 97 GPa at room temperature showing a perfect elastic behaviour whereas the laminar notched samples shown similar strength of 425 MPa with elastic modulus (98 GPa) revealing pseudo-ductile behaviour. A reduction in tensile strength of the oxide ceramic matrix composites was observed at high temperatures. Thermal shock experiments revealed that the retained strength of the samples quenched from 1100 °C deteriorated by ∼10 % (395 ± 15 MPa). In all samples fracture origin was observed on the mid plane showing a higher degree of fiber pull-out, delamination and pseudo ductile behaviour. FEA confirmed higher stress concentration on the areas of failures.

Slip is one of the most critical components for the frac plug, which would lodge into the casing and lock the frac plug in place during the setting and anchoring process. However, fracture failure of slip significantly affects the hydraulic fracturing effects and has attracted tremendous attention. In this paper, a three-dimensional contact model is applied to explore the setting process of slip. The effects of key structural parameters such as apex angle, inclination angle, and wedge angle on the contact characteristics of slip are systematically investigated. Numerical results indicate that the maximum contact stress appears at the contact area between slip tooth and the casing's inner wall. Besides, the maximum contact stress generally increases with the increase of apex angle and inclination angle, while decrease linearly with the rise in the wedge angle. Experimental results show that the slip teeth get blunt and appear severe plastic deformation, which arises from stress concentration. Comparison of biting area indicates that the experimental results are about 21.3% larger, which still have a reasonable agreement with the numerical results. These obtained results can guide the parametric selection of plug slip and other similar components.

Surface structure of C/C composites has been regulated through electrochemical corrosion at room temperature to modify the residual stress and improve the joining strength when brazed to Nb. The unique crevice corrosion in C/C composites is investigated to reveal the change of corrosion depth and fiber size. The interlacing zone of carbon fiber reinforced brazing alloy replaces the reaction layer in the original joint. Joining area is increased dramatically and the continuous crack will be hindered. The interlacing zone eliminates the stress concentration and relieves the residual stress through reducing the property mismatch. All advantages contribute to the joining quality of C/C Nb. Shear strength of C/C Nb joint with 80 μm depth reached 37.7 MPa, which was 1.2 times higher than that of original joint. Surface structure design of C/C composites not only expands the application in structure component, but also exhibits the promising application in energy field.

A multi-level mathematical model was used to estimate the stressed-strained state of a cylindrical reservoir with a defect in the wall shape in the form of a dent; the concentration of stresses in the defect zone was studied. The proper choice of the mathematical model was verified; it has been shown that the engineering assessment of the stressed-strained state of the wall of a cylindrical tank with the variable thickness could employ ratios for a cylindrical shell with a constant wall thickness. The spread of values is 2‒10%. This indicates the proper choice of the mathematical model, as well as the fact that it is possible, for an engineering assessment of the stressed-strained state of the wall of a cylindrical tank with variable thickness, to use the ratios for a cylindrical shell with a constant wall thickness. The stressed-strained state of the dent zone in the tank wall was numerically estimated, which proved the assumption of significant stress concentrations in the dent zone and indicated the determining effect on the concentration of stresses in the dent zone exerted by its geometric dimensions and its depth in particular. The concentration of stresses in the zone of dents in the tank wall was investigated in the ANSYS programming environment at different sizes of dents on the tank wall, for which two dimensionless parameters were introduced: the dimensionless radius of the dent and the dimensionless depth of the dent. Based on the results of a numerical study into the stressed-strained state of the dent zone in the tank wall, graphic dependences were derived of the stress concentration coefficient on the dimensionless depth of the dent for various values of the dimensionless radius of dents, which does not exceed 2% of the indicator. Based on fitting the stress concentration curves on the dimensions of the dent and tank, a formula was derived for calculating the stress concentration coefficient as a function of the dimensionless radius ξ and the dimensionless depth ς of the dent. The resulting formula makes it possible, with known dimensionless parameters of the depth and radius of the dent, to determine the coefficients of stress concentration in the dented zone of the tank wall.

Two types of MgO-C refractories with tight particle grading and non-tight particle grading were prepared according to Andreasen's continuous packing theory. Fracture behaviors were investigated using wedge splitting tests combined with digital image correlation method and acoustic emission techniques. The results indicated that MgO-C refractory with non-tight particle grading treated at 1400 ℃ had more in situ phases (e.g., AlN and MgAl2O4) and exhibited less brittleness than specimens with tight particle grading even though they had similar nominal tensile strengths. In contrast, specimens with non-tight particle grading had greater horizontal strain under various loading stages, reflecting their better ability to resist rupture deformation. In addition, more microcracks were initiated earlier in the pre-peak region, and more energy was consumed. The decrease in coarse particles and corresponding increase in fine powder content increased the interface between particles, benefiting for reducing the local stress concentration and improving the thermal shock resistance of refractories.

A special structure named tetrahedral twin was found in a cold-drawn CoCrFeNi high-entropy alloy. Crystallographic characterization using convergent beam electron diffraction indicated that the three-dimensional (3D) tetrahedral twins were achieved through the intersection of each couple of twin layers in four {111}FCC planes, which was caused by the low stacking fault energy and the special plane strain state during deformation. The calculation results revealed that the tetrahedron-morphological twins could result in significant stress concentration, thereby considerably deteriorating the plasticity of the high-entropy alloy.

In this study, a substrate was surface textured using a femtosecond laser to prolong the service life of thermal barrier coatings (TBCs). The selected texture showed linear and diamond shapes. The effect of the texture shape on the thermal shock resistance of the TBCs was investigated by subjecting them to thermal shock cycles. The microstructure and composition of the TBCs were investigated using various characterisation methods. The mechanical properties of the TBCs were measured using the microindentation method. Based on the theory of elastoplastic mechanics, a three-dimensional finite element numerical model was established to analyse the effect of the two textures on the stress distribution of the TBCs. The results revealed that the linear-textured TBCs showed improved stress concentration at the coating interface when the coatings expanded or shrank, which resulted in an improvement in their thermal shock resistance. Therefore, the linear-textured TBCs showed excellent oxidation resistance, fracture toughness, and heat resistance as compared to the diamond-textured TBCs.

Natural gas hydrate (NGH) reservoirs consist of the types of sediments with weak cementation, low strength, high plasticity, and high creep. Based on the kinetics and thermodynamic characteristics of NGH decomposition, herein a heat-fluid-solid coupling model was established for studying the wellbore stability in an NGH-bearing formation to analyze the effects of the creep characteristics of NGH-bearing sediments during long-term drilling. The results demonstrated that the creep characteristics of sediments resulted in larger plastic yield range, thus aggravating the plastic strain accumulation around the wellbore. Furthermore, the creep characteristics of NGH-bearing sediments could enhance the effects induced by the difference in horizontal in situ stress, as a result, the plastic strain in the formation around the wellbore increased nonlinearly with increasing difference in in situ stress. The lower the pore pressure, the greater the stress concentration effects and the higher the plastic strain at the wellbore. Moreover, the lower the initial NGH saturation, the greater the initial plastic strain and yield range and the higher the equivalent creep stress. The plastic strain at the wellbore increased nonlinearly with decreasing initial saturation.

Joining of Al2O3 ceramic to Cu has been conducted with Ag-26.7Cu-4.5Ti braze and refractory metal (W or Ta) foil. The interfacial microstructure in the joint with W foil is similar to that with Ta foil. The joining region in the joint consists of a reaction zone, braze zone I, refractory metal layer and braze zone II. The reaction zone of Cu3Ti3O with a thickness of about 5 μm develops close to Al2O3 side due to the reactions of Ti and Cu in the braze with Al2O3 substrate. The braze zones I and II are mainly composed of Ag- and Cu-based solid solutions. For the joint with W foil, the adsorption of Ti at the braze/W interfaces followed by the Ti diffusion into W foil occurs, whilst slight dissolution and diffusion of Ta into the brazes take place in the joint with Ta foil. The average shear strengths of joints with W and Ta foils are much higher than those without refractory metal foil, indicating the contribution of the refractory metal foil to the improvement of joint mechanical strength. Introduction of refractory metal foil in Al2O3/Cu joining is beneficial for the shift of joint residual stress distribution and the decrease of stress concentration in the joint since the coefficient of thermal expansion (CTE) of refractory metal layer approximately approaches that of Al2O3. Furthermore, a slight thickness increase of the Cu3Ti3O reaction zone in the joint with refractory metal foil may also give rise to the joint strength promotion.

This work aims to present a methodology to model Functionally Graded Material (FGM) in Finite Element Method (FEM) based software ANSYS and to reduce the stress concentration by applying the FGM ring around the rounded rectangular slot subjected to far field tensile loading. The effects of power law FGM parameters are analysed on stress concentration. From the analysis, it is observed that by applying the FGM ring around a rounded rectangular slot the stress concentration is reduced significantly in comparison to the homogeneous material case. The amount of reduction can be controlled by the FGM ring parameters.

Three steel beams were made-up and tested to study the effect of CFRP (Carbon Fiber Reinforced Polymer) laminates with and without end anchorage plates on the behavior of flexural strength of steel beams. Tested steel specimens are equal in clear span length, gross sectional area, and strengthened by intermediate stiffeners. Three types of specimens were made, the first specimen was considered as a reference one, while the other two were reinforced by CFRP laminates with and without end anchorage plates respectively. From the experimental outcomes, it was found that, the load deflection curve and load strain responses for specimens strengthened by CFRP strips became stiffer in comparison with the reference beam. On the other hand, it was found that, the deflection values for strengthened beams by CFRP without and with end anchorage plates were decreased to 58.33% and 79.95%, while, the strain values were decreased to 63% and 85.55% respectively, in comparison with the reference beam at yielding stage at load (Py = 20 kN) while, at failure stage at load (Pu = 45 kN) for reference beam, the deflection values for strengthened beams by CFRP without and with end anchorage plates were decreased to 81.19% and 88.13%, while, the strain values were decreased to 88.6% and 97.14% respectively, in comparison with the reference beam. Also, the percentages of increasing in yielding -load for strengthened beams by CFRP without and with end anchorage plates were increased to 100 % to 225 %, while, the percentages of increasing in ultimate-load for strengthened beams by CFRP without and with end anchorage plates were increased to 38.88 % to 111.11 %, respectively, in comparison with the reference. Finale the failure mode for reference beam was flexural failure type (plastic hinge), while, the failure mode for strengthened beams by CFRP without and with end anchorage plates was sudden; because of the de-bonding at the end of the CFRP strips and at the end of carbon fibre that due to the stress concentration at the ends of the CFRP.

The aero engine turbine rotors are under strong centrifugal load and the highest thermal load. The ventilation openings on the rotors are inevitable, because air flow need to pass through them to cool the temperatures down and keep the air pressure balanced in internal aero engine. The ventilation openings will lead to stress concentration effect. In this paper, the stress concentration factor of elliptical opening on rotating disc is deduced by superposition method. How to define the optimal location and shape of the elliptical opening on rotating disc to decrease the stress concentration effect has been investigated specifically. The reliability and accuracy of the theoretical deviation process is verified by Finite Element Method (FEM). The process of how to obtain the optimal location of the elliptical ventilation opening with particular shape on turbine sealing disc is described as an engineering application case. The investigation provides sufficient theoretical support for optimal location and shape definition of elliptical ventilation opening on aero engine rotors with stress concentration effect by pure mechanics consideration.

The application of the step lap joint has been increased due to its good characteristics such as lightweight, high stiffness, and good fatigue durability. Moreover, it has a wide application in the aerospace, automotive and marine sector because of its efficient strength and less stress concentration. The present study is concentrated on the effect of the kind of joint used for lap joint like the adhesive joint, riveted joints, and bolted joints. In addition, the length of the steps has been changed to study the behavior of adhesive lap joint in detail. Also, the hybrid joint such as a bolted-adhesive and riveted-adhesive joint is examined in the current study. The variation in the number of bolts and rivets are made for detailed analysis. The main objective of this project is to analyze the step lap joint with different length, different material for adherend and adhesive and also compare it with different mechanical fasteners such as rivets and bolts considering hybridization of it with and without the adhesive, Finite Element Analysis (FEA) is carried out in ANSYS Workbench for analysis and SolidWorks software is used for 3-D modelling.

The effect of varying abrasion pressure and nanographene on two body abrasive wear behavior of Glass – Epoxy (GE) composites under multipass condition was studied. These composites: Epoxy (EP), Glass –Epoxy (GE), GE/1 wt% nanographene (GE1) and GE/2 wt% nanographene (GE2) were developed using autoclave molding. The experimentation has been carried out by varying the abrasion load of 2.5, 5, 7.5 and 10 N under the influence of 180 Grit SiC abrasives through an abrading velocity of 0.5 m/s as per ASTM G99 method. It is observed that the wear volume loss of these composites is a linear function of abrasion load and their composition. Further, inclusion of 1 wt% nanographene showed better abrasion wear resistance than higher loading of the same nano filler. This may be due to the structural integrity of Glass Epoxy composites. Higher loading of nanographene localized the stress concentration which leads to poor tribological response. Further, hardness, good mechanical properties and improved degree of crystallanity made the GE1 composites to exhibit good abrasion wear behavior. The frictional study suggested that coefficient of friction (COF) decreases initially as an effect of adding nanographene under lower pressure whereas the reverse action has been exhibited by the composites under the influence of higher pressure. The morphology of the abrasion worn surface was studied using SEM images. It was found that microcuttng, microploughing and fatigue were some of the mechanisms responsible for the failure.

To investigate the degradation mechanism of static tensile mechanical behaviors of marble containing dynamic damage, multiple impact loading tests were performed on the disc marble samples, and then static Brazilian tests were conducted for the damaged samples. Besides, coupling modeling technology of finite difference method (FDM)—discrete element method (DEM) was used to carry out the numerical investigation. The results show that after multiple impacts, more white patches appear on the surface, and some microcracks, macro-fractures as well as pulverized grains are found by optical microscopic. The static tensile strength decreases with the increase of the dynamic damage variable characterized by the ultrasonic wave velocity of sample. The interaction between grains in the damaged sample becomes intense in the subsequent static loading process, causing a relatively large strain. The volume of the fragments falling off around the loading points becomes larger as impact number increases. As the dynamic damage increases, the absorbed energy of sample during the static loading first decreases and then tends to be stable. Both the stress concentration and the breakage of the force chains are the root causes of the degradation of the static tensile strength.

The stress concentration factor (SCF) is one of the most important parameters in the fatigue reliability analysis of tubular offshore structures. This parameter exhibits remarkable scatter which calls for more emphasis in accurately computing the SCFs for determining the fatigue life. As per the authors’ knowledge, no study has been conducted on the probability distribution of SCFs in tubular joints with FRP. Therefore, in this study, results of performing 288 FE analyses on 96 T/Y-joints with FRP have been used to propose a probability distribution model for SCFs in the FRP-reinforced joints subjected to axial, IPB, and OPB loads. According to the T/Y-connection FE models which were validated with several experimental tests, a set of SCF sample databases was generated. 11 various probability density functions (PDFs) were fitted to the relative frequency histograms of the SCF samples. For determining the parameters of every distribution, the maximum likelihood method was applied. Evaluating the goodness-of-fit according to the Chi-squared and Kolmogorov-Smirnov tests indicated that the Weibull distribution is the best one for the maximum SCF values in tubular T/Y-connections retrofitted with FRP under axial load. Also, the Gamma distribution was set as the governing probability function for T/Y-joints with FRP under IPB and OPB loads. In the final step, five fully defined PDFs were proposed for the maximum weld SCFs of in T/Y-joints with FRP under three different types of loadings.

SiC nanowires reinforced C/(PyC-SiC)n multilayered matrix composites (SM-CS for short) were prepared by combined with sol-gel and chemical vapor infiltration (CVI) method. Firstly, (PyC-SiOC)n multilayered structure was formed by cycles of impregnation and deposition. Then SiOC was transformed into SiC by heat-treatment, and (PyC-SiC)n multilayered structure would be obtained. At the same time, the PyC layer which was designed as the outmost layer could decrease gas supersaturation to form in-situ tubular SiC nanowires on the surface of multilayered structure. The results of three-point bending test showed that the maximum force of SM-CS composites was increased by the number of cycles of the preparation process, which were up to enhanced by 74.38% compared with C/C composite materials. The fracture surface showed that the improvement was due to the multiscale reinforcing system of (PyC-SiC)n multilayered structure and SiC nanowires. Multilayered structure can protect carbon fibers and release stress concentration by induction of cracks. And the mechanical interlocking effect of SiC nanowires could reinforce bonding force of the remaining matrix.

The response of crystalline materials to elasto-plastic cyclic loading is reviewed and analyzed. The important parameters characterizing the cyclic plastic response of single crystals, polycrystals, and multiphase materials are presented and related to the internal dislocation structure. Cyclic plastic strain localization is shown to be the characteristic feature of cyclic plastic straining which leads to surface relief formation and fatigue crack initiation. Recent models of fatigue crack initiation are presented. The mechanisms and kinetics of early crack growth are reviewed and the analysis of the relation of the crack growth kinetics and fatigue life curves is suggested.

The paper studies effective elastic properties of foam or cellular materials modeled by a set of Gibson-Ashby open cells with regular or irregular structures. Currently, there are many papers that present results of studying cellular materials using theoretical, numerical and experimental methods. However, these papers consider either regular lattices, or a single cell, or representative volume models based not on the Gibson-Ashby models. In this paper, in addition to the regular lattice, irregular structures were numerically studied. A mathematical formulation of the homogenization problem based on the energy equivalence of a foam-like material and on a homogeneous comparison medium is described. Formulations of six boundary value problems are presented. The solutions of these problems allow us to determine a complete set of effective stiffness modules for foams with different types of physical and geometric anisotropies. All stages of the numerical study were implemented in the ANSYS finite element package. Two algorithms for forming solid-state and finite-element models of irregular Gibson-Ashby lattices with small and large porosity are described in detail. As an example, numerical calculations are carried out for polycarbonate foams. The values of the effective elastic modules for regular and irregular lattices and for the Gibson-Ashby analytical model are compared. The results of numerical experiments showed that the Gibson-Ashby model describes the behavior of highly porous materials quite well (for porosity more than 75%), but this model gives a less satisfactory prediction in case of lower porosity. It is noted that for a large number of cells, regular and irregular lattices statistically give similar results for effective modules. However, for individual structures of irregular lattices, especially with strongly differing cells in individual directions, the effective moduli can have significantly different values, and the effective homogeneous medium can have pronounced anisotropic properties. These effects are due to geometric anisotropy and stress concentration in long connecting beams and at the joints of beams of various sizes in highly irregular Gibson-Ashby lattices. Examples of such lattices are given. We analyze the scatter of value for relative modules, which characterizes the anisotropy of such structures.

Cutouts are widely used to accommodate windows, openings for access purposes, or fasteners in the primary structural parts of airplanes. The presence of cutouts in composite panels results in stres...

Mg–Al–Zn–Ca–Y alloys with excellent ignition and corrosion resistances—termed SEN alloys (where the letters “S,” “E,” and “N” stand for stainless, environmentally friendly, and non-flammable, respectively)—have been developed recently. In this study, the microstructure, tensile properties, and high-cycle fatigue properties of an extruded Mg–9.0Al–0.8Zn–0.1Mn–0.3Ca–0.2Y (SEN9) alloy are investigated and compared with those of a commercial Mg–9.0Al–0.8Zn–0.1Mn (AZ91) alloy extruded under the same conditions. Both the extruded SEN9 alloy and the extruded AZ91 alloy have a fully recrystallized structure comprising equiaxed grains, but the former has a smaller average grain size owing to the promoted dynamic recrystallization during extrusion. The extruded AZ91 alloy contains coarse Mg17Al12 discontinuous precipitate (DP) bands parallel to the extrusion direction, which are formed during its cool down after extrusion. In contrast, the extruded SEN9 alloy contains relatively fine undissolved Al2Ca, Al8Mn4Y, and Al2Y second-phase particles, which are formed during the solidification stage of the casting process. The tensile strength of the extruded SEN9 alloy, which has finer grains and more abundant particles, is slightly higher than that of the extruded AZ91 alloy. However, the difference in their strengths is relatively small because the stronger solid-solution hardening and precipitation hardening effects in the extruded AZ91 alloy offset the stronger grain-boundary hardening and dispersion hardening effects in the extruded SEN9 alloy to some extent. The tensile elongation of the extruded AZ91 alloy is significantly lower than that of the extruded SEN9 alloy because the large cracks formed in the DP bands in the former cause its premature fracture. Although the extruded SEN9 alloy has higher tensile properties than the extruded AZ91 alloy, the high-cycle fatigue life and fatigue strength of the former are shorter and lower, respectively, than those of the latter. The DP bands in the extruded AZ91 alloy do not act as fatigue crack initiation sites, and therefore, fatigue cracks initiate on the specimen surface at all stress amplitude levels. In contrast, in most of the fatigue-fractured specimens of the extruded SEN9 alloy, fatigue cracks initiate on the undissolved Al2Ca and Al2Y particles present on the surface or subsurface of the specimens because of the high local stress concentration on the particles during cyclic loading. This particle-initiated fatigue fracture eventually decreases the high-cycle fatigue resistance of the extruded SEN9 alloy.

Due to the complex effects of combined loadings on complete steel structures, the combined effects of high-velocity projectile impact and heat radiation due to a pool-fire on a vertical Q345 steel tank have not been generally considered. In this study, a consecutive coupling approach is established. The combined effects of projectile perforation and heat radiation on the failure modes and fire resistance of a vertical steel tank are investigated. Additionally, the effects of the projectile size, projectile shape, and separation distance are analyzed. The results indicate that compared with a fixed-roof tank without impact, the perforation results in stress concentrations in the plastic deformation zone. The stress level of the perforated tank is higher, and the fire resistance of the perforated tank is lower. Additionally, as the perforation size increases, the stress level triggering the thermal buckling of the perforated tank decreases outside of the plastic deformation zone. Additionally, the fire resistance decreases. Moreover, as the separation distance decreases, the stress level of the cylindrical shell increases. The fire resistance of the perforated tank decreases dramatically. By understanding the failure mode, this study is able to suggest fire and explosion protection measures in petrochemical industries to decrease or eliminate the domino effect risk and incident damage. Additionally, the fire resistance data can help improve guidelines and understanding for fire and rescue services, which would undoubtedly play a vital part in emergency response and rescue, and enhance the process safety level overall.

Investigating the fatigue performance of high-strength bolt is essential to prevent related accidents. An axial-tensile fatigue test under a stress ratio of 0.5 was performed on 21 specimens of high-strength bolts to investigate the constant-amplitude fatigue performance of grade 8.8 M24 high-strength bolts. Based on experimental results, S–N curves were obtained through regression analysis, and fractographic analysis was conducted on typical specimens. Moreover, the results were compared with the existing fatigue experimental results and standards. Further, a finite element model was established to analyze the stress distribution of the bolts. It was found that the fatigue strength of the high-strength bolt at 2 × 106 cycles under a stress ratio of 0.5 was 89.76 MPa, which is 1.60 to 1.87 times greater than the values specified in the current standards. Through the comparison of the fatigue tests under stress ratios of 0.3, 0.5, and 0.8, the fatigue strength decreased as the stress ratio increased. Additionally, two main fatigue failure modes were found, with most bolts fracturing at the root of the first loaded thread; this is confirmed by the stress concentration location obtained from finite element analysis. The fracture morphology of the bolts exhibited a single-point fatigue source and possessed obvious fatigue fracture characteristics. It was concluded that the area of the fatigue propagation region was basically inversely proportional to stress ratio.

The aim of this paper is to assess the stress concentration zone (SCZ) of a circular smooth specimen at an early stage. Following the detection of the stress concentration zone, the specimen residual life was calculated and compared to the experimental result. Uniaxial loading on the servo-hydraulic testing machine was used for the laboratory testing. The stress concentration tester was used to detect the SCZ on the specimen, based on spontaneous surface micro magnetic signals on the ferromagnetic surface. In addition, cyclic testing for fatigue characteristics was conducted at 70% and 75% of ultimate tensile stress (UTS). The results indicated that the estimated residual life for the 70% UTS was nearly identical to the experimental value, based on two magnetic parameters, i.e, Kmax and the contraction value. Meanwhile, the estimated residual life for the 75% UTS was equivalent to the experimental findings. The minimum and maximum error values for life estimation using both parameters were 0.47% and 24.35%, respectively, for the contraction value. The correlation value, R2, between the estimated life using MMM and experimental life was 0.95, showing good estimation. All the estimated life data using this method was distributed within the range of a 95% to 90% confidence interval. Hence, the proposed method can be used to predict the fatigue life of ferromagnetic components through magnetic flux leakage signals, especially in the stress concentration region.

In this study, a new approach is presented to determine the stress and displacement field of a shallow buried circular tunnel subject to gravity and arbitrary lateral stress based on the complex variable method. The soil mass and lining are conformally mapped onto two ring regions. A more effective method than the power series method is used to solve the undetermined coefficients of complex potential functions. The interaction mechanism between the lining and the soil mass is fully considered. The boundary conditions along the inner boundary of the lining and the ground surface and the stress and displacement continuity conditions along the excavation line are used in the analytical derivation. In the verification, the stress and displacement distributions obtained in the semi-analytical solution agree with the numerical results and satisfy the boundary and continuity conditions. Using examples, the stress distributions along the inner boundary of the lining and interface are presented to examine the influence of key parameters including the Young's modulus and buried depth. The effect of the lining in reducing stress concentration and restricting tunnel convergence is quantitatively analyzed.

Unreinforced masonry (URM) structures exhibit high vulnerability in the moderate or strong earthquakes. The door- or window-type opening would further increase the seismic vulnerability, in which there is a weak area in the structures with stress concentrations. To improve the seismic behavior of perforated URM wall, a reinforcement of engineered cementitious composites (ECC) overlay was used on the both sides of the wall. Two 1/2-scale H-shaped specimens were prepared and tested under cyclic lateral loads. The damage patterns, hysteretic curves, envelope curves, stiffness degradation and energy dissipation of specimens were analyzed and discussed. The ECC effect can be observed as an increase of lateral resistance (maximum lateral force from 87.5 kN to 255.2 kN), and energy dissipation capacity (the cumulative energy dissipation up to ultimate state from 10.6 kJ to 21.5 kJ). Moreover, ECC overlay was able to control the crack initiation and propagation. The wide cracks along mortar joints observed in the spandrel of control specimen became multiple flexural cracks in the masonry piers after ECC reinforcement. The final failure of strengthened wall was dominated by the bending of piers, which was beneficial to improving the collapse resistance of masonry structures in the strong earthquake excitation.

Strength of a unidirectional composite along the fibers is the most important characteristic for the design calculation of composite products, being, however most difficult for correct determination in the experiment. The main problem is attributed to the shape and methods of fixing the specimen, providing the minimum impact of the stress concentration near the grips on the strength. The impossibility of direct use of standard self-tightening grips due to lateral crushing of the sample led to the necessity of using either samples with glued pads, or special grips with a constant transverse force. Specimens with fillets should not be used for unidirectionally reinforced plastics. When using standardized specimens in the form of rectangular strips with abruptly varying shear stresses applied to their lateral surface which results a significant concentration of tensile stresses, the incorrect result can be gained. We present the calculated values of the stress concentration factor (SCF) near the grips using a simplified model of shear analysis and the finite element method (FEM). Since the strength reduction factor is always less than the theoretical stress concentration factor, a phenomenological parameter of the material with the dimension of length, as a characteristic size of the stress averaging zone should be introduced to assess the strength value. Three methods are proposed to find this characteristic size according to the results of testing specimens of different kind: 1) smooth with various thicknesses; 2) smooth with various thicknesses and with holes in which the failure occurs at the hole, away from the grips; 3) with a series of holes with a decreasing radius, to find that small radius, the influence of which on the strength decrease is equivalent to the influence of grips. Proceeding from the experimentally determined characteristic size, the dependences of the strength on the specimen thickness, on the ratio of Young’s and shear modulus, on the length of the grips and the working zone, and on the degree of stress smoothing near the grip edges are calculated. The proposed calculation and experimental technique provided more accurate assess of the «true» tensile strength of the composites, which can be approximately 10 % higher than that determined on the specimens of large thickness. Taking this correction for the effect of grips into account, it appeared possible to reduce the safety factor, and, hence, to reduce the mass of composite structures.

Roughening of the free surface in micro-forming results in the local necking and subsequent fracture, which seriously affects the formability of sheet metals. In this work, laser pre-shocking (LPS) was introduced into microscale laser dynamic flexible bulging (μLDFB) to reduce surface roughening in terms of reducing the surface roughness and refining the internal grains. In LPS experiments, when the laser energy is 447 mJ, the rebound of the copper foils can be negligible. LPS can be expected to suppress the surface roughening by reducing the initial roughness R0, increasing the N value and decreasing the rate of surface roughening. The copper foils subjected by 447 mJ LPS were used for the μLDFB experiments. The 50 μm T2 copper foils with four different grain sizes were used in μLDFB under different laser pulse energies. When laser pulse energy ranges from 325 mJ to 575 mJ, compared with μLDFB without LPS, the surface roughness on the bottom surface of the bulging sample is decreased. And the nano-hardness, elastic modulus and forming uniformity are significantly improved. In μLDFB experiments without LPS, for fine-grained samples, the cracks initiate in the bulging transition zone under 725 mJ laser energy due to surface roughening. As laser energy increases to 1050 mJ, the cracks initiate in the mold entrance zone due to the strong stress concentration. For coarse-grained samples, cracks initiate under 575 mJ laser energy, and the propagations of the cracks are difficult to predict due to non-uniform distribution of grain size and the difference of grain orientation. The experimental results suggest that LPS can reduce the possibility of the premature fracture caused by the local necking, and alleviate the uncertainty in the fracture mode.

An analytical approach is established to analyze the mechanical behavior of a unidirectional (UD) composite subjected to an in-plane shear. The effects of the interface debonding on the in-plane shear strength and plasticity of the composite are evaluated respectively. The volume-averaged internal stresses of the fiber and matrix are calculated through Bridging Model. Owing to the stress fluctuation in the matrix caused by other phases (such as the imbedded fiber and interface crack), the homogenized matrix stresses must be converted into true values based on a stress concentration factor (SCF). A new in-plane shear SCF of a composite with debonded interface is derived and applied to the predictions of strain and strength in this paper. Moreover, the contribution of the relative slippage between fiber and matrix to the non-linear shear deformation of the composite is analyzed. Finally, the efficiency and accuracy of our theory are verified with a series of examples. The approach is very efficient because the calculation can be achieved with explicit expressions mainly based on the constituent material properties. The comparisons between predicted strength and deformation with the experimental results show that our analytical approach can give out reliable underlying data for multi-scale analysis. Moreover, this theoretical method can tell if and how much the interface of a composite needs to be modified for a given load environment.

Water inrush disasters are extremely prone to occur if the coal seam floor contains a confined aquifer. To find out the failure behavior of coal seam floor of paste filling working face, a beam-based theoretical model for the floor aquifuge was built, and then, the water inrush risk was evaluated based on the thickness of floor aquifuge. Next, the floor failure characteristics of the paste filling face was numerically studied and the effects of the filling interval and long-term strength of the filling body on the floor failure depth, stress and displacement distributions, and plastic zone were explored. The results showed that the theoretical model for evaluating the safety of the floor of the paste filling face based on the empty roof distance is proved to be consistent with that of the empirical formula judged based on the assumption that the paste filling working face was regarded as a cut hole with a certain width. The filling interval has a significant effect on the stress concentration of the surrounding rock, failure depth of floor, and roof-floor convergence. The smaller the filling interval is, the smaller their values are. When the filling rate is 98%, the long-term strength of the filling body is 5 MPa, and the floor failure depth is not more than 4 m. In contrast, the strength of the filling body has no obvious influence on the floor failure depth, but it has a certain impact on the roof-floor convergence. From the perspective of reducing floor failure depth, there is no need to increase the long-term strength of backfill, but it is necessary to increase the early strength of backfill so as to reduce the width of the equivalent roadway.

The possibility that pressure-loaded natural fractures in naturally fractured formations may contribute to wellbore instability merits further investigation. The present study analyzes in detail the state of stress around a wellbore with pressurized natural fractures nearby. Synthetic examples are given of unanticipated well instability when pressure-loaded natural fractures occur in the vicinity of the wellbore at the time of first penetration of the naturally fractured formation. The locations of shear failure are controlled by the stress field distortion due to the fluid pressure in the natural fractures. Various shear failure criteria are used to quantify where and when the critical stress for shear is reached. Rather than shear failure, tension failure may also occur at the wellbore. For example, wellbore stability is jeopardized by unintended circulation loss when the mud load causes unexpected hydraulic fracturing during drilling operations. The method of solution is a recently developed linear superposition method (LSM) of elastic displacements. The LSM models show static solutions of the stress state, and a dynamic version of the method (TLSM) uses time-stepped superposition to model fracture propagation processes. Time-stepped solutions show how fluid pressure-loaded natural fractures near a newly drilled well may alter the fracture propagation paths. The study also includes examples of stress concentrations near boreholes prepared with slotted perforations commonly used during fracture treatment operations in both conventional and unconventional fields.

Актуальность. В настоящее время более 75 % проводимых подземных горных выработок поддерживаются при помощи анкерного крепления. В процессе длительной эксплуатации выработок возникают деформации приконтурного массива пород и элементов крепи. Актуальной научно-практической задачей представляется выявление типовых форм деформаций пород и элементов крепи с целью разработки проектных решений и обоснования параметров крепи при производстве текущего ремонта или восстановления подземных выработок. Цель: разработка проектных решений и обоснование параметров анкерного крепления при ремонте и восстановлении подземных горных выработок. Методы: натурные исследования, статистическая обработка результатов экспериментальных исследований. Результаты. Приведено описание, причины возникновения и формы проявления геомеханических процессов в приконтурном углепородном массиве горных выработок, закрепленных анкерной крепью. На основе длительных натурных наблюдений установлено шесть форм типовых деформаций приконтурного массива. Процесс сводообразования в кровле выработок начинается с разуплотнения приконутрного слоя, которое служит причиной расслоения пород под действием гравитационных сил, а также образования полостей. Отжим угля из боков выработок и вывалы угля происходят в связи с образованием вокруг выработки зон неупругих деформаций, где уголь и породы находятся в несвязанном состоянии и удерживаются в равновесии за счёт сил трения и отпора крепи. Ширина зоны неупругих деформаций зависит от многих факторов. Существенное влияние оказывают ширина выработки и угол внутреннего трения. При увеличении ширины выработки увеличивается коэффициент концентрации напряжений в боках. Разработаны проектные решения по усилению крепления или полной перекрепке поврежденных участков горных выработок при геомеханических процессах локального вывалообразования. Они включают в себя: схему установки, обоснование параметров и номенклатуру применяемых элементов крепи-усиления, технологию работ, список применяемого оборудования. Relevance. More than 75 % of underground mine workings are supported by anchorage nowadays. In the case of long-term mine workings maintenance the deformations of surrounding rock massif and anchoring elements occur. The surrounding rock massif typical forms deformations determination in order to develop the design solutions and substantiate anchorage parameters is currently urgent scientific and practical task. Especially it is important in case of mine workings support repair or recovery stages. The main aim is mine working anchorage design solutions and parameters substantiate during the repair and recovery stages. Methods: field measurements, statistical processing of results. Results. The paper introduces the description, causes of occurrence and manifestation forms of geomechanical processes in surrounding rock massif supported by anchorage. Based on the long-term field measurements six forms of rock massif typical deformations have been established. The roof bridging begins with decompaction of rocks, which causes rocks stratification under the influence of gravity. This results in cavities formation and lower layers separation from upper ones. Because of formation of the plastic deformation zone around mine workings the extraction and dumping coal from walls occur. Coal and rocks are in an unbound state and are kept in balance due to the forces of friction and resistance of the support in the zones of plastic deformations. Its width depends on many factors such as the working width and the internal friction angle. The coefficient of stress concentration in the walls rises up due to growth of mine working widht.

Stainless steel is used as a new generation of long-span metal roof systems with continuous welding technology, which exhibits many unknown behaviors during temperature action. This study focuses on the temperature effect of a continuous welded stainless steel roof (CWSSR) system and analyzes the stress distribution of plate rib (PR), plate surface (PS), and support (SU), and the horizontal and vertical displacement. Furthermore, the thermal action of the CWSSR system is comprehensively analyzed considering different loading rates, constant temperature time, and the cycle number. Research results show that the stress concentration and thermal expansion of the CWSSR system are obvious, and fatigue damage occurs under long-term temperature action. The responses of the CWSSR system are greatly influenced by the loading rate and the cycle number but are less influenced by the constant temperature time. Loading rate and the cycle number mainly affect the plate surface stress and vertical displacement. The plate surface stress and vertical displacement peak increased by 34.6% and 29.6% with the loading rate, and changed by 32.4% and 42.5% with the cycle number. Cyclic loading reduces support tensile capacity by 4.4%. The research results can provide reference for the design and application of temperature field resistance of the CWSSR system.

Two methods (i.e., direct tensile test and the Brazilian test) are commonly adopted to measure the tensile strength of rock, but the tensile strengths obtained by the two methods are obviously different. Taking Beishan granite as physical background, this study systematically investigates the discrepancies between the Brazilian test and direct tensile test with the use of three-dimensional Flat-joint model (FJM3D) simulation. Simulation results indicate that the Brazilian disc is under a complex three-dimensional stress state, and produce some shear cracks, which is significantly different from direct tensile test. By assigning different micro parameters to the FJM, the influences of the heterogeneity of the microstructure (particles size and pre-existing cracks) and micro-strength (bond strength) on the direct tensile strength (DTS) and the Brazilian tensile strength (BTS) are investigated. The heterogeneity of particles size, pre-existing cracks, and bond strength have negatively effects on both DTS and BTS, and that the ratio between DTS and BTS decreases with the increase of heterogeneity of pre-existing cracks and bond strength. The statistical analyses reveal that in the Brazilian disc, the contact normal stresses obey the normal distribution, but in the direct tensile specimen, the contact normal stresses obey the log-normal distribution. The three heterogeneities have minor effects on the dip direction of cracks, but significantly affect the dip angle of cracks. The heterogeneity of microstructure affects the local stress concentration, which reduces the tensile strength, and changes the orientation of cracks.

This paper investigates the high stress concentration zone for fatigue crack estimation on the damaged tower crane pulley by measuring magnetic flux leakage. Fatigue crack analysis is important to prevent any component failure that could harm workers. Precautions must be taken to locate the possibilities of failure region on a tower crane pulley. For this study, magnetic flux leakage signals were measured using metal magnetic memory method to predict the high stress concentration area. The respective signals were collected for 30 scanning lines on the tower crane pulley surface and merged to provide a better graphical view to estimate the irregularities or defect location more accurately. The metal magnetic memory polar mapping was compared with the finite element analysis results for validation. The highest von Mises stress value obtained through the finite element analysis is 167.84 MPa using three-dimensional tetrahedral mesh for the size of 3 mm. Thus, the comparison revealed the similarities of stress concentration zone between the results and will produce more accurate prediction for the actual irregularity or defect location on the failed component.

Ribs in aircraft wings maintain the airfoil shape of the wing under aerodynamic loads and also support the resulting bending and shear loads that act on the wing. Aircrafts are designed for least weight and hence the wings are made of hollow torsion box and the ribs are designed with cut-outs to reduce the weight of the aircraft structure. These cut-outs on the ribs will lead to higher stresses and stress concentration that can lead to failure of the aircraft structures. The stresses depend on the shape of the cut-outs in the ribs and thus in the present work, the commercial software ANSYS was used to evaluate the stresses on the ribs with different shapes of cut-outs. Four different shapes of cut-out were considered to study the effect of cut-out shape on the stresses in the ribs. It was found that the best shape for the cut-outs on the ribs of wings to reduce weight is elliptical.

Electronics are becoming smaller and more versatile, and the size of solder joints has decreased to tens of microns, inducing obvious inhomogeneity among the phases in the solder matrix microstructure. In this study, the influence of phase inhomogeneity on the mechanical behavior of microscale Cu/Sn–58Bi/Cu solder joints was studied. Sn and Bi single-phase solid solution samples with the same composition as the Sn and Bi phases in the Sn58Bi microstructure were prepared, and their mechanical performances, elastic constants, and power-law constitutive models were measured, calculated, and identified. Based on the obtained mechanical performances, elastic constants, and power-law constitutive models, a three-dimensional finite element model of line-type Cu/Sn58Bi/Cu microscale solder joints, including their microstructure, was established. The results demonstrate that phase inhomogeneity increases the maximum value of von Mises stress, leading to stress concentration. When the Sn58Bi solder matrix transfers from the elastic deformation stage to the plastic deformation stage, the high σeq zone of the matrix gradually shifts from the Sn phase to the Bi phase. In addition, a study of the anisotropy reveals that the elastic anisotropic mechanical properties of Sn58Bi solder matrix are mainly affected by the anisotropic effect of Sn. The stress concentration is the lowest when the crystal orientation is π/2.

Toe formation is a phenomenon resulting from unconnected cracks between blastholes, which occurred during blasting excavation of the abutment slot at Baihetan hydropower station. Analysis of crack development has tended not to focus on the high in-situ stress environment at the slope corner. Therefore, this study aimed to explore the toe formation process through theoretical analysis and numerical simulation. Firstly, a three-blasthole model was established to analyze the effects of blasting load and in-situ stress on crack extension. Then, a finite-element model of the abutment slot was built to simulate crack propagation under different in-situ stress environment. Finally, optimization measures for avoiding toe were proposed. The results demonstrate that cracks grow preferentially in the direction of the maximum tangential tensile stress and are influenced by the blasting load and in-situ stress. On the lateral side of the abutment slot, the crack initiation and extension occur far from the centerline due to the deviation of the maximum tangential tensile stress. The deviation increased as the in-situ stress. Consequently, cracks between blastholes not being able to connect with each other results in toe formation. Increment of the linear density of the charge and optimization of the excavated profile are both effective in reducing the impact of the stress concentration caused by in-situ stress and preventing toe formation.

The severe electric and thermal environments may cause localized deterioration of the contact behavior of thermoelectric devices. The contact responses of the thermoelectricity under the joint effect of the finite size and the friction are analyzed. The law of the Coulomb friction is adopted. The obtained Fredholm kernel functions reveal the influence of the thickness and the friction. The known Jacobi polynomials are employed to discretize the obtained singular integral equation. The effects of the thermoelectric loadings (the total electric current and the total energy flux), friction coefficient, the thermoelectric strip thickness, and the elastic and thermoelectric material constants on the distribution of the normal traction and the surface in-plane stress are demonstrated in detail. The smaller thermal expansion coefficient and shear modulus will contribute to the lower stress concentration at both contact edges. The surface in-plane tensile stress behind the trailing edge can be alleviated as the thermoelectric strip becomes thinner.