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Ice fractures when subject to stress that exceeds the material failure strength. Previous studies have found that a von Mises failure criterion, which places a bound on the second invariant of the deviatoric stress tensor, is consistent with empirical data. Other studies have suggested that a scaling effect exists, such that larger sample specimens have a substantially lower failure strength, implying that estimating material strength from laboratory-scale experiments may be insufficient for glacier-scale modeling. In this paper, we analyze the stress conditions in crevasse onset regions to better understand the failure criterion and strength relevant for large-scale modeling. The local deviatoric stress is inferred using surface velocities and reanalysis temperatures, and crevasse onset regions are extracted from a remotely sensed crevasse density map. We project the stress state onto the failure plane spanned by Haigh–Westergaard coordinates, showing how failure depends on mode of stress. We find that existing crevasse data are consistent with a Schmidt–Ishlinsky failure criterion that places a bound on the absolute value of the maximal principal deviatoric stress, estimated to be 158±44 kPa. Although the traditional von Mises failure criterion also provides an adequate fit to the data with a von Mises strength of 265±73 kPa, it depends only on stress magnitude and is indifferent to the specific stress state, unlike Schmidt–Ishlinsky failure which has a larger shear failure strength compared to tensile strength. Implications for large-scale ice flow and fracture modeling are discussed. [ABSTRACT FROM AUTHOR]

The UK High Temperature Power Plant Forum have completed a long term cross-weld creep test programme on a Grade 92 steel pipe. This paper describes an analysis of the creep test data. The weld strength factor (WSF), i.e. the ratio of cross-weld strength to base material strength for a specified rupture time and temperature, is shown to be a unique function of a dimensionless parameter S, the creep test stress divided by ultimate tensile strength at the test temperature. The key practical finding is that, since a single universal cross-weld creep life parametric is applicable to all temperatures, long-term behaviour at service temperatures should reliably be predictable from short-term tests at accelerated temperatures. [ABSTRACT FROM AUTHOR]

The assumption of an isotropic material behaviour is still common practice for tunnel design. Strictly speaking, this assumption is only valid if the influence of directional dependencies on the resulting deformations and stresses is marginal. In lithologies that have a high degree of anisotropy, such as shales and phyllites, the orientation characteristics of material properties such as strength and stiffness should be taken into account in order to avoid serious misinterpretations of the bearing capacity and deformation characteristic of the surrounding rock and the tunnel lining. The main focus is to accurately distinguish between the different types and terminology of anisotropy. [ABSTRACT FROM AUTHOR]

During the operation of certain structures, two questions arise: about the stress-strain state (SSS) at a point and in its neighborhood on the surface of the object under study and in its bulk, and about the remaining material strength in the considered area. The values of stresses and strains not at a point, but in a neighborhood, make it possible to use the results of the proposed research to test existing numerical and analytical calculation schemes, to find the direction of growth or decrease of the quantities under consideration, and to predict catastrophic events. It is proposed to assess the state of the material using classical formulations and methods of solid mechanics, which guarantee the existence and uniqueness of the solution and continuous dependence on the input data. To determine the SSS of the material in the neighborhood of the point, we start with the full unload of the latter in order to determine the unloading displacements at the boundary. The SSS within the area, including stresses at the boundary, is found from the known boundary displacements. When studying the SSS inside the body, it is proposed to install elongated reference elements with their ends reaching the surface. To measure unloading displacements, the existing optical, mechanical, and tensometric systems are used. The uniqueness of the proposed approach is in considering not only radial displacements, but also tangential ones. The aim of the work is experimental and analytical determination of the SSS at any point of the structure and at any time of its non-stop operation. [ABSTRACT FROM AUTHOR]

Bituminous pavement layers are composite in nature, consisting of binder, filler, and aggregates. Understanding the mechanical behaviour of bituminous layers demands investigation of their different material scales, such as the binder, mastic, and mixture scales. While substantial investigation has been carried out on binder and mixture related to fatigue damage, not much research is carried out on mastic. Of the methods used to characterise fatigue damage, energy dissipation is widely used; however, it is complicated due to the presence of other modes of dissipation, such as viscous dissipation. In this study, an attempt is made to separate viscous dissipation and dissipation due to damage for both binder and mastic using a nonlinear viscoelastic fluid model. For this purpose, six types of materials were tested at temperatures of 20 $^\circ$ ∘ C and 25 $^\circ$ ∘ C, 10 Hz frequency, and five different strain levels spanning the linear and non-linear regimes, for 20,000 cycles. Material parameters for the non-linear White-Metzner model incorporated with the Williamson model were determined for an initial cycle and using these parameters, the viscous component of energy dissipation was determined. Dissipation due to damage was estimated by separating viscous dissipation from total dissipation at every 2000th cycle and based on the evolution of viscous and damage dissipation across cycles, three trends were observed. Based on the trends observed, the influence of strain amplitude, temperature and modifiers on the fatigue resistance of the materials was ascertained. [ABSTRACT FROM AUTHOR]

A method is developed for predicting creep and long-term strength based on the behavior of a previously tested sample (leader sample, prototype) in the case of ductile fracture. It is assumed that a loaded material does not undergo instantaneous plastic deformation and the first stage of creep. The incompressibility hypothesis is fulfilled in this case. It is shown that, if a constant-stress creep curve and the time to fracture are known for a leader sample, then obtaining a diagram of rheological deformation and long-term strength of the material at other stress values requires knowing only the initial (at the initial time) minimum creep strain rate of the samples for these stress values. The relevance of the developed method is checked with experimental data in two types of tests. The first type is tension tests of 12Kh18N10T corrosion-resistant steel samples at a temperature of 850°C and titanium alloy samples at a temperature of 600°C and the second type is tension and torsion tests of D16T alloy samples at a temperature of 250°C. It is shown that the prediction results are independent of the choice of a leader sample from many samples tested at different stresses. The possibility of using the developed method in experimental studies of creep of materials until their fracture is discussed. [ABSTRACT FROM AUTHOR]

Bituminous pavement layers are composite in nature, consisting of binder, filler, and aggregates. Understanding the mechanical behaviour of bituminous layers demands investigation of their different material scales, such as the binder, mastic, and mixture scales. While substantial investigation has been carried out on binder and mixture related to fatigue damage, not much research is carried out on mastic. Of the methods used to characterise fatigue damage, energy dissipation is widely used; however, it is complicated due to the presence of other modes of dissipation, such as viscous dissipation. In this study, an attempt is made to separate viscous dissipation and dissipation due to damage for both binder and mastic using a nonlinear viscoelastic fluid model. For this purpose, six types of materials were tested at temperatures of 20 $^\circ$ ∘ C and 25 $^\circ$ ∘ C, 10 Hz frequency, and five different strain levels spanning the linear and non-linear regimes, for 20,000 cycles. Material parameters for the non-linear White-Metzner model incorporated with the Williamson model were determined for an initial cycle and using these parameters, the viscous component of energy dissipation was determined. Dissipation due to damage was estimated by separating viscous dissipation from total dissipation at every 2000th cycle and based on the evolution of viscous and damage dissipation across cycles, three trends were observed. Based on the trends observed, the influence of strain amplitude, temperature and modifiers on the fatigue resistance of the materials was ascertained. [ABSTRACT FROM AUTHOR]

Retaining walls are a part of the geotechnical construction industry for the support of structures from soil erosion. Granular materials are conventionally used as backfill behind retaining walls. Instead of the conventional compacted granular fill, other industrial by-products are also used nowadays. The utilisation of these industrial by-products for Civil engineering applications helps to build a sustainable environment by reducing the waste depositions. In this paper, an experimental study was conducted to evaluate the properties of coal ash-based Controlled Low Strength Materials (CLSM) for backfill applications. The properties of pond ash-based CLSM mixes were studied to identify the effectiveness in utilising CLSM for backfill applications. Further, numerical analysis using PLAXIS 2D was carried out to evaluate the stresses and displacements developed in retaining walls for different backfilling materials. It was observed that CLSM mixes exhibit the properties required for utilising it as a backfill material. The stresses and deformations developed in situations where CLSM was used were found to be negligible compared to the normal compacted backfill materials. Thus, the studies on CLSM mixes showed that pond ash can be used as a replacement to natural aggregates which can be used as a backfill for retaining wall applications. [ABSTRACT FROM AUTHOR]

In this paper, experimental investigations are carried out to assess the weld strength of S700 steel during and after fire. Standard and nonstandard tensile coupons were tested during fire and postfire stages at temperatures ranging from 500°C to 800°C. In this experiment, all the standard specimens failed at the base material without any distinct yield plateau in the stress–strain relationship. The postfire specimens display yield strength reduction from ∼70% at 500°C to ∼55% at 800°C; while the ultimate strength reduced by ∼20%–30%. The slower cooling process (cooling in air) show lower ultimate strength regain than the quicker cooling process (cooling in water). The heat treatment does not affect the elastic modulus. As compared to the postfire residual ultimate strength of the parent material is not affected by heat treatment, the strength of air-cooled weld specimens display considerable (∼30% less) strength reduction. The S700 weld connection display lower strength as compared to most of the lower grade steel at elevated temperature. The ultimate strength of the S700 weld at elevated temperature display slightly lower strength than the Eurocode prediction. The weld material displays higher strength than the base material during and after fire. [ABSTRACT FROM AUTHOR]

Creep deformation and creep rupture is essential for the safety of steels working at high temperatures. Considering the practical creep rate curves and classical theta projection method, a generalized creep constitutive model with two critical creep time points and six stress-dependent parameters has then been proposed to describe typical creep curve styles. P92 and T92 steels are taken as the examples to verify that this model can represent and predict creep behaviors in a unified and smooth way. By means of interpolation functions for eight creep parameters, it is found that fitting functions should be separated by a critical creep stress, which is smaller than yield strength of material. Based on creep damage model, two creep-life calculation methods have been established corresponding to considering the creep deformation or not. Comparisons between two creep-life methods illustrate that creep deformation speeds up creep damage accumulation by increasing the true stress. Moreover, critical creep stress is also the turning point in the bilinear graph of creep-life curve, which means that damage accumulation styles are different for stress larger and smaller than critical stress. [ABSTRACT FROM AUTHOR]

An explicit failure model for ceramics undergoing a solid–solid phase transition under shock compression is developed and tested on silicon carbide and aluminum nitride. This model enhances the applicability of our failure model recently developed for boron carbide. Smoothed particle hydrodynamics simulations of ceramics under shock loading are performed to optimize the model parameters using the velocity profiles obtained in available shock-wave experiments. It is demonstrated that the inclusion of a phase transition with hysteresis is essential for agreement between simulations and experiments. Evolution of damage spreading in samples with propagation of the failure wave front is discussed. We show that it changes from a homogeneous damage pattern to regular structures of failure bands, where growth is guided by distributions of equivalent stress and shear strength of material within the band tips. [ABSTRACT FROM AUTHOR]

Large-scale, high-strength aluminum alloy forgings are essential components in the aerospace industry, with benefits including increasing strength and decreasing weight. Accurate shape-property control is the secret to forging quality. This study uses the alloy 7050 to experimentally evaluate the parametric influence of cold compression on residual stress and mechanical characteristics. The evolutions of mechanical properties, microstructure and residual stress are theoretically studied using various cold compression strains from 1% to 5% on an equivalent part, of which the results are further applied on a complicated rib-structured die forging. It is demonstrated that increasing the compression strain reduces the tensile strength of the material, but has little impact on conductivity and fracture toughness. According to the TEM results, compression also encourages the precipitation and growth of precipitated phases, particularly in positions with high dislocation densities after aging. Cold compression significantly reduces residual stress; nevertheless, as compression strain increases, residual stress first decreases and then increases. With the use of rib-structured forging, it is observed that the compression strain for 7050 aluminum alloy ranges from 2% to 4%, and the combined pressing method of the rib and web improves the uniformity of residual stress. [ABSTRACT FROM AUTHOR]

The rheology of rocks transitions from a cataclastic brittle behaviour to plastic flow with increasing pressure and temperature. This brittle-plastic transition is empirically observed to occur when the material strength becomes lower than the confining stress, which is termed Goetze's criterion. Such a criterion works well for most silicates but is not universal for all materials. We aim to determine the microphysical controls and stress–strain behaviour of rocks in the brittle-plastic transition. We use a micromechanical approach due to Horii and Nemat-Nasser, and consider representative volume elements containing sliding wing-cracks and plastic zones. We find solutions for frictional slip, plastic deformation and crack opening at constant confining pressure, and obtain stress–strain evolution. We show that the brittle-plastic transition depends on the confining stress, fracture toughness and plastic yield stress but also critically on the friction coefficient on pre-existing defects. Materials with low friction are expected to be more brittle, and experience transition to fully plastic flow at higher pressure than anticipated from Goetze's criterion. The overall success of Goetze's criterion for the brittle-plastic transition in rocks is likely arising from the low toughness, high strength and medium friction coefficient character of most rock forming minerals. [ABSTRACT FROM AUTHOR]

The purpose of this work is to analyze the stress-raisers that affect the tensile strength and fatigue resistance of GFRP parts using the point and line methods of the theory of critical distances (TCD) to obtain a quantitative measure of the defect size that can be tolerated by the composite before it fails. In the course of the work, a method combining TCD and the Weibull function was developed. In the course of the work, GFRP structural fiberglass for electrical purposes was tested under uniaxial quasi-static and cyclic loading with digital image correlation (DIC) and acoustic emission (AE), as well as a numerical simulation of deformation. The studied specimens were plain (without a stress-raiser) and notched (V-shaped) with different notch root radii and depths. The results were used to determine the material critical distances. In this case, two approaches to TCD were used: line (LM) and point (PM) methods. To analyze the experimental results, finite element modeling was applied using the ANSYS software package. As a result, the linearized maximum principal stresses were obtained on the central line passing through the top of the stress raiser. Thus, the values of the critical distances of the material were determined by PM and LM. Based on the data obtained, the sizes of permissible defects in the studied fiberglass were established that do not affect the tensile and fatigue strength of the material. The paper illustrates the cumulative energy, peak amplitudes, and distributions of the frequency of the spectral maximum of acoustic emission signals obtained after the destruction of specimens by fatigue test. Evolutions of deformation fields on the specimen surface were recorded using a Vic-3D contactless optical video system and the DIC. [ABSTRACT FROM AUTHOR]

Triaxial tests are generally conducted to establish the mechanical behaviour of cement-treated clays. Numerical simulations of these tests involve selection of the correct constitutive model, which can capture the key features of the stress–strain response of the geomaterial. However, as cement-treated clays behave differently to untreated clay in its natural state, the classic constitutive models may not give reasonable results and the failure envelope has been found to be non-linear. An attempt was made in this work to simulate the behaviour of cement-treated clays using the Hoek–Brown model and the experimental and numerical simulation results were compared. [ABSTRACT FROM AUTHOR]

In view of the fact that the threshing gap of combine harvester can only be controlled by adjusting gravure screen and it is time-consuming and laboring, a kind of variable-diameter threshing drum with movable radial plates is developed by changing the diameter of threshing drum to adjust the threshing gap concentrically. All parts of the threshing drum were designed and checked by mechanical design principle, and the statics and modal analysis of the whole structure were carried out by ANSYS Workbench. The results show that the maximum deformation of the variable-diameter threshing drum with movable radial plates is 0.29 mm under boundary conditions. The maximum allowable deformation of the threshing drum in use is 3 mm, which meets the requirements of use. The equivalent stress of the threshing drum with variable diameter is up to 100 MPa, which is less than the yield strength of the material, and will not cause structural damage. According to the modal analysis, the natural frequency of the threshing drum does not cause resonance phenomenon. The field test of wheat was carried out after the processing of the variable-diameter threshing drum with movable radial plates was installed, and the working performance was compared with that of the ordinary drum. The results showed that the threshing performance was the best when the forward speed was 1 m/s, the grain entrainment loss rate was 0.53%, and the grain un-threshed rate was 0.065%. The grain breakage rate is 0.54%, and the performance is more than 50% higher than that of ordinary rollers. It lays a foundation for the adaptive adjustment of threshing gap in combine harvester. [ABSTRACT FROM AUTHOR]

The failure characteristics of geotechnical materials are quite complex, among which there are obvious differences between soil materials and rock materials. In order to describe the failure characteristics of soil materials and rock materials uniformly, a new failure and yield criterion, called VML criterion, is proposed in this paper. This strength criterion has the following characteristics. (1) On the deviatoric plane, the criterion can be expressed as a power parameter expression of von Mises criterion and spatial mobilized plane (SMP) criterion, so it can be used to describe cohesive materials such as metals or frictional materials such as sand. (2) On the meridian plane, another power parameter expression can be used to consider tensile stress strength. On the meridian plane, the material strength envelope can be expressed as a curve, so the hydrostatic pressure effect of soil material can be reasonably considered. (3) In order to consider the volumetric compression yield properties of soil materials under isotropic compression, a yield criterion considering the volumetric compression yield properties is also proposed on the deviatoric plane. Since geotechnical materials are often in plane strain condition in engineering, a VML criterion expression considering plane strain condition is proposed in this paper. The criterion shows that the internal friction angle of soil under plane strain is usually 1.1 times of that under conventional triaxial compression. The comparison between the predicted and tested data shows that the VML criterion proposed in this paper can be widely applied to the failure simulation of rock and soil materials, and the plane strain VML criterion can also be applied to the failure prediction with plane strain state. [ABSTRACT FROM AUTHOR]

Despite the limitations imposed by their composition, natural materials overcome the trade-off between strength and ductility through their unique structural features. Inspired by the crossedlamellar structure of conch shells, SS316L-IN625 heterostructured materials were designed and fabricated by laser directed energy deposition (LDED). Interestingly, this bionic heterostructured material (BHM) breaks the strength-ductility trade-off of the constitutive material with a tensile strength of 731.74 MPa and a uniform elongation of 34.98%. This particular with multi-scale and periodic distributions and interfaces with crossed-lamellar deliver the BHM superior performance combinations beyond the rules of mixtures. The strain gradient induced by heterogeneous deformation activates additional slip systems, and this unique slip band delays premature necking in the SS316L region and hinders crack propagation. The BHM takes full advantage of the intrinsic strength of IN625 and the toughness of SS316L to stimulate multiple enhancement and toughening mechanisms. [ABSTRACT FROM AUTHOR]

The influence of additives on the structural behaviour of cement-stabilised rammed earth was investigated through an experimental programme based on 13 different mixes with varying cement contents (6, 8 and 10% by earth weight) and three different types of additives (superplasticiser, air-entraining agent (AEA) and hardening accelerator). In total, 156 specimens were fabricated and tested at 7 and 28 days in order to compare their compressive strength and other properties such as stress–strain relationships, shrinkage and workability. The results highlighted the essential role of cement in increasing the compressive strength of the material. Specifically, cement contents of 6%, 8% and 10% corresponded, respectively, to strength increases of 41%, 80% and 92% compared with the reference mix with a mean compressive strength of 1.15 MPa. The AEA was found to be the most effective additive for increasing the compressive strength, with obtained strengths of up to 2.93 MPa (an increase of 155% compared with the reference mix). The efficiency of each mix was evaluated through a strength/cost ratio. In addition, an overall comparison of compressive strength, shrinkage, deformation, cost and workability was performed using an analytic hierarchy process. Finally, the experimental results were compared with the mechanical requirements of various codes. [ABSTRACT FROM AUTHOR]

With the development of pre-fabricated composite structures, concrete filled steel tubular (CFST) columns have been widely used, and researches on T-shaped CFST slender columns have attracted much attention. Since ordinary T-shaped CFST columns have weak constraint on concrete at the sectional concave angle region and local buckling easily occurs in this region, a multi-cellular T-shaped concrete filled steel tubular (MCT-CFST) column was developed for improving the axial resistant performance. In this study, the global stability performance of MCT-CFST slender columns under uniaxial eccentric compression was investigated. Firstly, three pin-ended MCT-CFST slender columns were tested under eccentric compression with different eccentricities. Secondly, a refined finite-element (FE) model of MCT-CFST column was established, and the load–displacement curves, Mises stress and deformation diagrams from the FE analysis were compared with the experimental results to verify the validity of the FE model. Moreover, based on the validated FE model, a parametric analysis was carried out to study the effects of normalized slenderness ratio, thickness of steel plate and material strength on the global stability performance of MCT-CFST slender columns under combined axial and bending loads. Finally, N - M interaction curves were obtained from the numerical simulations, and these results were considered to provide valuable references for designing MCT-CFST slender columns in engineering practice. [ABSTRACT FROM AUTHOR]

Cryogenic tanks are still considered the most efficient method of storing fluids. This is due to its resistance to much damage caused by corrosion induced by low temperature and internal pressure. In this study, the finite element method is used to analyze the repair performance by a composite wrap in a corroded tank. A parametric analysis was carried out in order to highlight the effects of low temperature and pressure on the thermo-mechanical behavior of the corroded structure and to predict the evolution of stresses in the vicinity of corrosion. An approach to this problem based on the notion of material strength was necessary since it was essential to take both the size of the pre-existing defect and the amount of mechanical stresses. The results obtained show the effect of thermal and mechanical loading to examine their impact on the strength of the structure on the one hand, and on the other hand, the influence of the composite wrap repair in the different corrosion lengths (Path 1, 2, 3) on the reinforcement of the tank. Finally, repairing damage (corrosion) using FRP composites increases the durability of cryogenic tanks, which increases their efficiency their performance and increases their life, although the rate of improvement depends largely on operating conditions, such as pressure and temperature. [ABSTRACT FROM AUTHOR]

Subcritical crack growth is often observed in oxide ceramics. This effect is ascribed to the interaction between the strained chemical bonds at the crack tip and water molecules present in the working environment of the material. Owing to this reaction, combined with stresses at the crack tip, slow cracking of the material and relevant strength reduction may occur. In non-oxide ceramics (i.e., without significant oxide sintering additives), no subcritical crack growth was observed. The present work demonstrates slow crack propagation in an aluminum oxynitride (AlON) material. AlON samples were prepared via sintering in nitrogen at 1800 °C. This resulted in dense translucent samples. Constant stress rate tests were carried out in both air and water to assess the influence of water on material strength. The strength results were used to further evaluate the effects of subcritical cracking. A clear decrease in strength was observed at low stress rates. Measurement points below 10 MPa/s were used to determine the lowest stress rate for inert strength. The slope of the fitting line indicated the value of subcritical cracking parameter n. [ABSTRACT FROM AUTHOR]

The study aimed to evaluate the effects of fibers insertion and restorative material type on the stress distribution in endocrowns with finite element analysis. Five 3D models of first mandibular molars were created and restored as follows: (1) IN: intact tooth, (2) IPS-E: tooth restored with lithium disilicat ceramic endocrowns, (3) C-E: tooth restored with composite endocrowns, (4) IPS-E + F: lithium disilicate ceramic endocrowns + fiber, (5) C-E + F: composite endocrowns + fiber. Vertical masticatory load was imitated with finite element analysis. The equivalent stress of von Mises failure criterion (mvM) was calculated. The maximum mvM stress, enamel/crown, dentin and cement were compared among models and strength of the materials. Endocrowns presented a lower mvM stress level than intact tooth. In IPS-E, the mvM stress values in the crown and dentin were higher than C-E, while the mvM stress values in cement were higher in C-E group. Fibers insertion did not affect the stress level of IPS-E and C-E groups. In IPS model, fiber showed more stress absorption than C-E. The restorative material type changed the stress distribution of endocrown restorations. The fiber application did not affect the stress distribution in either endocrown group. But, more stress absorption was observed in fiber under IPS-E than C-E. [ABSTRACT FROM AUTHOR]

The relevance of problems related to the fracturing of engineering materials and structures will not decrease over time. Fracture mechanics methods continue to be developed, which, combined with numerical methods of computer modeling, are implemented in software packages. However, this is only one facet of the complex of actual problems related to modeling and analyzing the behavior of brittle materials. No less important are the problems of developing not only numerical, but also new analytical models. In this paper, analytical models of only one class are considered, the distinguishing feature of which is that they describe the full load–strain curve using only one equation. However, the determination of model parameters requires tests for which the destruction of the test object is necessary, which may be unacceptable if controlled destruction is technically impossible or economically unreasonable. At the same time, in practice, it is possible to obtain values of stresses and strains caused by loads smaller than the peak load. Pre-peak loads can be used to predict strength using numerical methods, but it is desirable to have a suitable analytical model to extend the capabilities and to reduce the cost of applied research. Such a model was not found in the known literature, which motivated this work, which aims to modify the analytical model to predict strength and the full load–displacement (or stress–strain) curve using only pre-peak loading. This study is based on the analysis of known data and synthesis using mathematical modeling and fracture mechanics. The input data for the model do not include the particle size distribution and other physical and mechanical properties of the components of the material under study. These properties may remain unknown, but their influence is taken into account indirectly according to the "black box" methodology. Restrictions of the scope of the model are defined. The simulation results are consistent with experiments known from the literature. [ABSTRACT FROM AUTHOR]

By appending a constant to the Weierstrass form of the conventional Tresca yield condition, a new yield condition is generated that allows a continuous transition of yield criteria spanning the Tresca to the von Mises and beyond. The Weierstrass form of the Tresca yield condition is defined by a cubic algebraic relationship between the second and third invariants of the deviatoric stress tensor. In general, the Weierstrass form is commonly associated with a family of plane curves called elliptic, which have special group properties. The additional parameter of the generalized Tresca yield condition is determined from an analytical expression that relates the yield strength of a material in tension to the yield strength of a material in pure shear. Solutions of plane stress, perfectly plastic, mode I crack problems are then obtained for the generalized Tresca yield condition for variations in this parameter. Through insight gained by varying this parameter, an analytical mode I perfectly plastic solution is proposed for the traditional Tresca yield condition under plane stress loading conditions. Unlike the corresponding mode I perfectly plastic solution for the von Mises yield condition, which has three distinct sectors in the upper half plane of symmetry, the solution for the Tresca yield condition requires a fourth distinct sector. [ABSTRACT FROM AUTHOR]

Background: Distortion arises during machining of metallic parts from two main mechanisms: 1) release of bulk residual stress (BRS) in the pre-form, and 2) permanent deformation induced by cut tools. Interaction between these mechanisms is unexplored. Objective: Assess this interaction using aluminum samples that have a flat surface with variations of BRS, where that surface is subsequently milled, and we observe milling-induced residual stress (MIRS) and distortion. Methods: Plate samples are cut from two kinds of large blocks, one kind stress-relieved by stretching and a second kind solution heat treated, quenched and aged. The BRS field in the plates is known from a recent series of measurements, being small in the stress relieved plates (within ±20 MPa) and large (±100 MPa) in the quenched plates, varying from tension to compression over the surface that is milled. MIRS is measured following milling using hole-drilling. Distortions of thin wafers cut at the milled surfaces are used to elucidate BRS/MIRS interactions. A finite element (FE) model and a strength of materials model are each used to assess consistency between wafer distortion and measured MIRS. Results: Milling in samples with high BRS magnitude changes the directions of MIRS and distortion relative to the milling direction, with the direction of maximum curvature rotating toward or away from the milling direction depending on the sign and direction of BRS. High magnitude BRS was also found to increase the wafer peak arc height, nearly doubling the amount found in low BRS samples. Conclusion: Measured residual stress and observed wafer distortion both show interactions between MIRS and BRS. Stress analysis models show that the differences in measured MIRS are consistent with the differences in observed distortion. [ABSTRACT FROM AUTHOR]

Materials subjected to dynamic environments experience a complex and wide range of stress, strain, and strain-rate conditions. To have confidence in material models, an accurate, predictive capability is required. In this study, we present a series of flyer-plate impact tests on well characterized, high purity tantalum. The shock-waves generated at impact release from the free-surfaces, reflect, and interact to produce incipient spall fracture. By varying the flyer-plate material and impact velocity, both the peak stress and the strain-rate in the samples were controlled independently. Velocimetry was used on the rear free-surface of the samples to measure the shock-response and the spall strength. While this measurement provided the same spall strength for all cases, at approximately 5.1 GPa, when the samples were sectioned during post-mortem, the quantity and distribution of internal damage was markedly different. For the high-strain rate cases, voids remained small and isolated, whereas in the lower strain-rate experiments, the spall damage was far more localized, with a well-defined continuous spall plane. With the use of hydrocode simulations, this was discovered to result from how the different release rates affect the interaction volume inside the sample. These results highlight the importance of careful sample recovery, and the risks of relying solely on free-surface velocity measurements. [ABSTRACT FROM AUTHOR]

Large, thin-walled, and curved surface shells are challenging to deform using traditional forming technologies owing to wrinkling and rupture defects that coexist during the deformation process. In this study, the process of double-sided pressure sheet hydroforming (DSHF) was developed to overcome these issues and fabricate large curved components integrally. A theoretical analysis model was established by considering the stress and strain distributions at varying double-sided pressure ratios during DSHF. Simulations and experiments were conducted using the DSHF process on a hemispherical shell to analyse the effects of the pressure ratio on deformation behaviour, stress and strain, thickness distribution, and deformation defects. Furthermore, a phenomenon called “planar deformation state” was observed, and the stress state was optimised by setting a proper pressure ratio. Under this condition, the thickness distribution was improved and the formed curved shells were free from wrinkling and rupture defects. A CNC sheet hydroforming machine developed by Harbin Institute of Technology was employed to perform a case study of the DSHF process. Lastly, to demonstrate the application of the proposed process, an aluminium-alloy dome with a diameter of 3 m and a uniform thickness distribution was fabricated. [ABSTRACT FROM AUTHOR]

The parameters of a small-scale failure zone in the bonding material of a piecewise-homogeneous body under plane strain condition are determined using the Wiener–Hopf method. The failure zone is located at the end of an interface crack with tip at the corner point of the polygonal interface of the materials. The crack faces contact according to the law of dry friction. The failure zone is modeled by discontinuity line of the normal displacement on which the normal stress is equal to the tensile strength of the bonding material. Expressions for the length of the failure zone, the opening displacement of the crack faces, and local stress field near the crack tip are derived. The starting mechanism of the initial crack is described. It is assumed that a microcrack nucleates in some part of the failure zone and coalesces with the initial crack with increasing load. The dependence of the parameters of the failure zone, the microcracks, and the limiting load on the load and the parameters of the composite are analyzed numerically. [ABSTRACT FROM AUTHOR]

On the basis of modeling of stresses, we analyzed the technological conditions guaranteeing the required cutting properties of grinding wheels in the operations of rough and finishing grinding performed in the course of their dressing by turning with diamond tools. We performed the theoretical analysis of force interactions between diamond crystals and abrasive grains and established stresses formed in the "abrasive grain–diamond crystal" contact system. The models of equivalent stresses were created according to the theory of maximum normal stresses. We also considered the theoretical aspects of simulation of the stresses in the "abrasive grain–diamond crystal" impact system with regard for the contact strength of the material of grains. [ABSTRACT FROM AUTHOR]

A model is presented to analyze the evolution of mechanical stresses in the vicinity of the coating–substrate interface under processing conditions. The model takes into account different mechanisms of stress formation, including the temperature and phase composition changes. It is shown that the coating stresses significantly exceed the strength limit of the material, with the main contribution coming from the changes in the composition. [ABSTRACT FROM AUTHOR]

Modeling the postpeak behavior of brittle materials like concrete remains a challenge from the point of view of computational mechanics due to the strong nonlinearities arising in the material behavior during softening and the complexity of the yield criterion that may describe their deformation capacity under generic triaxial stress states. A numerical model for plain concrete in compression is formulated within the framework of the coupled elastoplastic damage theory. The aim is to simulate, via the finite-element (FE) method, the stress-strain behavior of concrete at the mesoscale, where local confinement effects generally characterize the cement paste under the action of the surrounding aggregates. The mechanical characterization of the components are accomplished through a specific experimental campaign. With the subsequent validation study, it is shown that a few calibration parameters give a good prediction of the material strength and deformation capacity encountered in real uniaxial compression tests. [ABSTRACT FROM AUTHOR]

Due to sedimentation, irregular particles of sand arrange anisotropically in nature. Anisotropy diversifies the internal friction angles between relative research planes at different directions in soil material. Thus, to analyze the mechanical mechanism of strength anisotropy, except for conventional inherent anisotropy of the material, stress distribution caused by external loads should also be considered in addition. The level and direction of the inherent strength anisotropy of geomaterials can be measured by a modified anisotropic variable, which is derived from the stress tensor and the fabric tensor. It is assumed that the overall shear strength of the material depends on the shear strength of the most mobilized plane, which is the spatially mobilized plane (SMP) and has a closely relationship with the stress state according to the SMP criterion. Therefore, the orientation of the most mobilized plane builds a bridge that connects the anisotropy of geomaterials and the magnitude and direction of stress. On this basis, a general description of anisotropic strength, considering both the magnitude and directions of the principal stresses, is given, of which the parameters can be easily obtained by triaxial tests. Besides, the variation of the sliding plane along with the direction of the major principal stress is approached. Furthermore, three types of tests, including the direct shear test, the true triaxial test and torsion shear test, were performed to prove the reliability of the new criterion. It shows that both the anisotropic shear strength and the orientation of the sliding plane can be predicted accurately by the newly built anisotropic strength criterion. [ABSTRACT FROM AUTHOR]

A series of polyimine-epoxy vitrimers has been synthesized using commercially available monomers using a two-step synthetic route to maximize the content of imine groups in the resulting structures. The first step consists of the synthesis of amine terminated polyimine oligomers, which were synthesized by a condensation reaction of terephthalaldehyde (TA) with different proportions of diethylenetriamine (DETA) and a polyetheramine (Jeffamine D-230 or D-400). After that, the obtained viscous oligomers were cross-linked with bisphenol A diglycidyl ether (DGEBA). The design of network architectures using this approach is a powerful tool that allows controlling the concentration of imine groups, the dimensions of the intermediate polyimine oligomer and the polarity and mobility of its chains, confirming that it is an effective way to tune the thermal, mechanical and thermomechanical properties of the final materials. Furthermore, this work confirmed that an accurate design of the network architecture allows simultaneously improving the two main requirements of vitrimers by increasing the content of imine groups: fast stress relaxation processes and high creep resistance. Stress relaxation curves proved that these polyimine vitrimers could relax the 63 % of the initial stress in less than 9.6 min at 160 °C without any added catalyst. Besides, replacing Jeffamine D-400 with Jeffamine D-230 in the imine oligomer increases the material's resistance to creep at service temperatures. All the materials prepared present high thermal stability and showed T g s between 31 and 93 °C. • A series of polyimine-epoxy vitrimers were synthesized by a two-step procedure. • Well-defined oligomers with known imine groups were synthetized. • Vitrimeric behavior and creep resistance were correlated with imine concentration. • Materials prepared with Jeffamine D-230 showed good creep resistance at 20 °C. • Chemical degradation of these vitrimers depends on the materials' composition. [ABSTRACT FROM AUTHOR]

Nowadays, the high levels of copper production generates significant amounts of waste called tailings. In response to the latter, there is an increased need to understand the tailings behaviour in order to ensure the mechanical stability of dams. In this context, it is of great importance to study the resistance of tailings against the liquefaction phenomenon. Several studies have shown that the level of confining pressure affects the cyclic resistance of sands, proposing the correction factor Κσ. Similarly, it has been observed that the initial static shear stress also affects the cyclic strength, so the correction factor Κα has been introduced. However, the coupled effect of both variables, which corresponds to the real ground condition, has not been properly investigated for tailings sands. By means of undrained cyclic triaxial tests consolidated both isotropically and anisotropically, in this work the joint effect of both variables on the cyclic resistance of this material has been studied, for different levels of initial relative density. The results obtained from the coupled effect have been condensed through the parameter Κσα. [ABSTRACT FROM AUTHOR]

The effect of the creep of materials of a structure on the nature of the contact interaction between its elements during long-term operation is investigated. The problem of the stress-strain state of the rotor blade interlock for the medium-pressure cylinder of a steam turbine for ultrasupercritical steam parameters (over 240 at and 565°C) is solved using a finite element software package. As a model of creep, a modified model of creep with hardening is considered. The methodology for solving the thermal contact problem of interaction between the interlock elements under creep conditions is based on the application of a contact layer model. The calculation is made for the case of the total loads of the centrifugal forces of blades and the temperature field in which the structural element is operated. The results on the distribution of total strains, equivalent stresse,s and contact stresses during long-term operation are analyzed. The points of time, upon reaching which the permissible strength characteristics of the materials used were exceeded, were determined. A change in the nature and level of contact stresses on the bearing surfaces of interlock elements due to the redistribution of the stress-strain state of the structure as a whole is shown. The moments of the appearance of detachment and absence of contact stresses on individual contact surfaces were determined. The results obtained are compared with the data from the operation, during which the structure was damaged. [ABSTRACT FROM AUTHOR]

Granular materials often present correlations between particle size and shape due to their geological formation and mechanisms of weathering and fragmentation. It is known that particle shape strongly affects shear strength. However, the effects of shape can be modified by the role the particle plays in a sample given its size. We explore the steady shear strength of samples composed of particles presenting size‐shape correlations and we focus on the case of particle elongation in two opposite scenarios: (A) large elongated grains with finer circular grains and (B) large circular grains with elongated finer grains. By means of numerical simulations, we probe the shear strength of samples of varying particle size span from mono to highly polydisperse and particle aspect ratios varying between 1 and 5. We find that the two correlations tested strongly impact the shear strength as particle size span evolves. Microstructural analyzes allow us to identify how each correlation affects connectivity and anisotropies linked to the orientation of the particles and load transmission. Decompositions of the stress tensor let us identify the sources of the different mechanical behavior in each correlation and determine the contributions of each particle shape to macroscopic shear strength. This study proves that common small‐scaling methods based on truncated or parallel particle size distributions can incur in under/over‐estimations of shear strength if particle shapes are not considered in the scaling process. [ABSTRACT FROM AUTHOR]

Most measurements of compressive strength of ductile materials have involved Hopkinson–Kolsky bars or Taylor anvils placing samples in uniaxial compression. In these geometries, strain is limited by the tendency of the sample to petal, in analogy to necking in uniaxial tension. Estimation of strength for any other form of the stress tensor requires assuming a shape of the yield surface; because data exist only for uniaxial compression, these assumptions are untested. In an imploding spherical shell, compression is biaxial, the plastic strain may not be small, and the material behavior may be nonlinear as a result of work hardening and heating by plastic work. We outline a method of measuring the strengths of materials in biaxial compression, both quasistatically and dynamically, using the compression of thin spherical shells. We suggest surrounding the shell with an annulus filled with a mixture of H2 and Cl2 gases whose homogeneous ignition is initiated by a flash of blue and near-ultraviolet light. Less promising approaches are described in Appendixes A–C. [ABSTRACT FROM AUTHOR]

The conventional flow rule and plasticity constitutive models implicitly assume that the principal stress and plastic strain rate are coaxial, which often result in various setbacks in modeling, for example, the bifurcation and the evolution of shear band cannot be accurately and adequately captured. In this work, we investigate the non-coaxial effects of an elastoplastic constitutive model on strain localization in the framework of micropolar plasticity theory. The vertex-like yield surface is introduced in the flow rule, and a non-coaxial Drucker–Prager model is implemented in a user-defined finite element subroutine (UEL) in ABAQUS. The simple shear test and the plane strain compression test have been conducted to study the non-coaxial stress–strain response and the strain localization behavior. Effects of boundary condition on bifurcation, shear band orientation and thickness are investigated. Results indicate that the proposed model shows a good performance in the simulation of the non-coaxial behavior of geomaterials. On the premise of overcoming mesh dependency, the shear band orientation and width predicted by the non-coaxial model possess higher values than those predicted by the coaxial model, and a better agreement with the experimental results are achieved by the non-coaxial model. Moreover, by analyzing stress–strain responses, we have found that material strength may be systematically overestimated by the coaxial model. [ABSTRACT FROM AUTHOR]

The constraint effect with material parameters mismatch between every parts of planar solid oxide fuel cell (SOFC) plays an important role in the operation life. In this study, the mismatch effect of material creep strength coefficient on creep damage and failure probability of planar SOFC was investigated by finite element method. The results show that the maximum equivalent creep strain and failure probability of SOFC are located in the outer corner of sealant layer. With the increase of the creep strength coefficient of the sealant layer, the maximum creep damage, damage area and failure probability of the sealant layer all increase gradually. The creep strength coefficient of the sealant layer is suggested to be smaller than that of the frame material, which will improve service life of SOFC. • Effect of material constraint on creep and failure probability of SOFC was studied. • The maximum creep damage and failure probability are located in sealant layer. • The higher mismatch with softer sealant makes the SOFC more prone to creep damage failure. • The sealant layer is suggested to has smaller creep coefficient than the frame. [ABSTRACT FROM AUTHOR]

Objective: Design the landing gear for a CESTOL type aircraft according to FAR 23 using: (i) the conceptual designs of the nose and main gear and (ii) evaluate the structural strength of the design by means of finite element analysis at a stage of landing. Materials and methods: The initial requirements for the theoretical development of a preliminary landing gear design are used as a case study. The aircraft's structure is taken as a base for the different design stages. This analysis is according to a static and level landing condition selected on each gear with a side and supplementary load. Additionally, calculations of geometric parameters and mechanical resistance with preselecting materials for the component analysis to determine and compare theoretical results with finite elements to evaluate the reliability of the design approach. Results and discussion: It is determined to move the main landing gear backward near the cargo area. That allows for better aircraft performance, placing the GC in front of the main gear and avoiding an overturn. However, this load percentage changes in proportion to the longitudinal stability criterion, where it generates an increase in the contribution to the mechanical stress in the structure of the gear. Conclusions: Results obtained about stability, controllability, and structural analysis are acceptable for the regulations of FAA Part 23 with standards associated with airworthiness, being corroborated with theoretical analysis and combined loads. [ABSTRACT FROM AUTHOR]

Flow channel inserts (FCI) are functional components designed to minimize the magnetohydrodynamic pressure drop and also serve as a thermal and tritium permeation barrier. In the simplified design of the FCI component, the ceramic is directly exposed to contact with Pb-16Li at elevated temperature. As the FCI must withstand mechanical stresses resulting from the thermal gradient during the demanding operation, the assessment of mechanical response of ceramic in contact with Pb-16Li is essential. Pristine Al 2 O 3 and SiSiC were subjected to three-point bending at room temperature and at 650 °C in argon. While SiSiC showed no change in flexural strength at both temperatures, flexural strength of Al 2 O 3 decrease when the test temperature was increased. Inspection of the fracture surfaces revealed mixture of intergranular and transgranular brittle fracture for both materials in investigated temperature range. Pre-exposed samples were tested at 650 °C in liquid Pb-16Li to assess the effect of mechanical strength degradation caused by Pb-16Li. Testing of the pre-exposed Al 2 O 3 samples showed the similar flexural strengths to the unexposed ones. In the case of SiSiC, the sample exposure resulted in decrease of the flexural strength. The analysis of the pre-exposed tested samples revealed deteriorated surface by Pb-16Li only in the case of SiSiC. [ABSTRACT FROM AUTHOR]

The ideal strength is crucial for predicting material behavior under extreme conditions, which can provide insights into material limits, guide design and engineer for enhanced performance and durability. In this work, we present a method within an allows for the estimation of tensile, shear, and indentation strengths in any crystallographic direction or plane. We have examined the strain-stress relationships of several well-known structures and compared our findings with previous work, demonstrating the effectiveness of our approach. Moreover, we performed extensive investigations into the indentation strength of hexagonal WC, β -SiC, and MgAl 2 O 4. The current study uncovers the modes of structural deformation and the underlying atomistic mechanisms. The insights gained from this study have significant implications for the further exploration and design of superhard materials. [Display omitted] [ABSTRACT FROM AUTHOR]