Search

Mixed-mode fracture is a common failure phenomenon of materials, while its experiment requires at least a material test machine, test materials and special machining procedures. In this paper, a simple but effective mixed-mode fracture experiment using office paper is proposed, so one can easily conduct the mixed-mode fracture experiment and understand its fracture criteria such as the maximum tensile stress (MTS) criterion. [ABSTRACT FROM AUTHOR]

Abstract: Macroscopic, freestanding graphene-based paper-like materials are of interest for use as mechanically strong, stiff, and flexible and electrically conductive materials. Chemically reduced graphene oxide paper shows promise for such applications. In this work, we studied the mechanical and electrical properties of a set of paper materials prepared by filtration of homogeneous colloidal suspensions of hydrazine-reduced graphene oxide with different concentrations. Young’s modulus, fracture strength, and fracture strain of each type of sample was determined by tensile tests. The paper sample prepared from the colloidal suspension with the lowest concentration of reduced graphene oxide platelets had the highest modulus and fracture strength and showed the smoothest surface morphology. The electrical conductivity measured by the four-probe measurement method increased as the concentration was increased. [Copyright &y& Elsevier]

This paper reviews the experimental and modeling work that has been carried out concerning the behavior of fiber-reinforced polymer (FRP) composites in fire since the 1980s. The first part focuses on the thermophysical properties and temperature responses, while the second considers thermomechanical properties and responses, which are significantly affected by the thermal exposure of the FRP material. Furthermore, the application of deformation-based or strength-based failure criteria enables the prediction of time-to-failure. If the fire exposure time is less than the time-to-failure, the post-fire behavior is of interest and the post-fire properties and their potential recovery after cooling are particularly addressed. This fundamental understanding obtained as a result of both modeling and experimental work makes a reliable endurance design for FRP structures in fire possible. [ABSTRACT FROM AUTHOR]

The dynamics of a “peeling front” or an elastic line is studied under creep (constant load) conditions. Our experiments show in most cases an exponential dependence of the creep velocity on the inverse force (mass) applied. In particular, the dynamical correlations of the avalanche activity are discussed here. We compare various avalanche statistics to those of a line with non-local elasticity, and study various measures of the experimental avalanche-avalanche and temporal correlations such as the autocorrelation function of the released energy and aftershock activity. From all these we conclude, that internal avalanche dynamics seems to follow “line depinning”-like behavior, in rough agreement with the depinning model. Meanwhile, the correlations reveal subtle complications not implied by depinning theory. Moreover, we also show how these results can be understood from a geophysical point of view. [ABSTRACT FROM AUTHOR]

Purpose: The paper's goal is to examine and illustrate the useful uses of submodeling in finite element modeling for topology optimization and stress analysis. The goal of the study is to demonstrate how submodeling – more especially, a 1D approach – can reliably and effectively produce ideal solutions for challenging structural issues. The paper aims to demonstrate the usefulness of submodeling in obtaining converged solutions for stress analysis and optimized geometry for improved fatigue life by studying a cantilever beam case and using beam formulations. In order to guarantee the precision and dependability of the optimization process, the developed approach will also be validated through experimental testing, such as 3-point bending tests and 3D printing. Using 3D finite element models, the 1D submodeling approach is further validated in the final step, showing a strong correlation with experimental data for deflection calculations. Design/methodology/approach: The authors conducted a literature review to understand the existing research on submodeling and its practical applications in finite element modeling. They selected a cantilever beam case as a test subject to demonstrate stress analysis and topology optimization through submodeling. They developed a 1D submodeling approach to streamline the optimization process and ensure result validity. The authors utilized beam formulations to optimize and validate the outcomes of the submodeling approach. They 3D-printed the optimized models and subjected them to a 3-point bending test to confirm the accuracy of the developed approach. They employed 3D finite element models for submodeling to validate the 1D approach, focusing on specific finite elements for deflection calculations and analyzed the results to demonstrate a strong correlation between the theoretical models and experimental data, showcasing the effectiveness of the submodeling methodology in achieving optimal solutions efficiently and accurately. Findings: The findings of the paper are as follows: 1. The use of submodeling, specifically a 1D submodeling approach, proved to be effective in achieving optimal solutions more efficiently and accurately in finite element modeling. 2. The study conducted on a cantilever beam case demonstrated successful stress analysis and topology optimization through submodeling, resulting in optimized geometry for enhanced fatigue life. 3. Beam formulations were utilized to optimize and validate the outcomes of the submodeling approach, leading to the successful 3D printing and testing of the optimized models through a 3-point bending test. 4. Experimental results confirmed the accuracy and validity of the developed submodeling approach in streamlining the optimization process. 5. The use of 3D finite element models for submodeling further validated the 1D approach, with specific finite elements showing a strong correlation with experimental data in deflection calculations. Overall, the findings highlight the effectiveness of submodeling techniques in achieving optimal solutions and validating results in finite element modeling, stress analysis and optimization processes. Originality/value: The originality and value of the paper lie in its innovative approach to utilizing submodeling techniques in finite element modeling for structural analysis and optimization. By focusing on the reduction of finite element models and the creation of smaller, more manageable models through submodeling, the paper offers designers a more efficient and accurate way to achieve optimal solutions for complex problems. The study's use of a cantilever beam case to demonstrate stress analysis and topology optimization showcases the practical applications of submodeling in real-world scenarios. The development of a 1D submodeling approach, along with the utilization of beam formulations and 3D printing for experimental validation, adds a novel dimension to the research. Furthermore, the paper's integration of 1D and 3D submodeling techniques for deflection calculations and validation highlights the thoroughness and rigor of the study. The strong correlation between the finite element models and experimental data underscores the reliability and accuracy of the developed approach. Overall, the originality and value of this paper lie in its comprehensive exploration of submodeling techniques, its practical applications in structural analysis and optimization and its successful validation through experimental testing. [ABSTRACT FROM AUTHOR]

Reasonable fracture criteria are crucial for the modeling of dynamic failure in computational spring lattice models. For experiments on the micro and on the meso scale exist successful criteria, which are based on the stress that a spring experiences. In this paper we test the applicability of these failure criteria to large scale models, where gravity plays an important role in addition to the externally applied deformation. The resulting brittle structures do not resemble the outcome predicted by fracture mechanics and geological observations. For this reason we derive an elliptical fracture criterion, which is based on the strain energy stored in a spring. Simulations using the new criterion result in realistic structures. It is another great advantage of this fracture model, that it can be combined with classic geological material parameters: the tensile strength σ0 and the shear cohesionτ0. While we tested the fracture model only for large scale structures, there is strong reason to believe that the model is equally applicable to lattice simulations on the micro and the meso scale. [ABSTRACT FROM AUTHOR]

The design of cover landfill requires an optimum thickness of the compacted fine soil layer with small permeability. In general, the objective is to reduce the thickness of the landfill cover. However, for a thin layer, and under natural evaporation, denser crack network growths occur during the desiccation by drying. Cracks change the geometrical properties during the drying and wetting cycles and significantly compromise the role of the cover layer, by inducing an infiltration water flow and gas migration. An important differential flexure deformation occurs. The landfill cover, where stiffness and tensile and shear strengths were reduced is being progressively damaged. Thus, this paper aims 1) to quantify the flexural deformation and 2) to provide a methodology and a guideline for studying the integrity of a cover landfill. So, a mechanical model is proposed and implemented in Code Bright software. The methodology starts from the calibration and the validation of the mechanical model based on 1) four-point flexural beam tests and 2) on existing published results. A physical prototype was employed to demonstrate the flexure deformation, and the crack development. Moreover, short natural fibers were mixed and embedded in the soil to make the soil reinforcement and delay crack propagation. In addition to the experimental investigation, mathematical constitutive equations were proposed, in which the contribution of short fibers in terms of increase of tensile strength was introduced. Finally, a simple case study was considered to demonstrate the role of the fiber-soil composite on flexural deformation and tensile stress distribution across the cover layer. An analysis of the numerical results was conducted to support the use of short fibers as reinforcement, which is an environmentally friendly and sustainable solution. [ABSTRACT FROM AUTHOR]

The fracture behavior of welding material at elevated temperatures can significantly affect the performance of steel welded connections in fires. Therefore, this paper investigates the fracture behavior and fracture model of welding material in steel welded connections exposed to elevated temperatures up to 700°C. Firstly, using the standard tension test data and numerical analysis method, the true stress–strain model of E7018 welding materials at elevated temperatures was derived for fracture prediction of steel welded connections. The fracture parameters of the welding materials at elevated temperatures in tension and shear were calibrated from the results of the standard tension test and longitudinal fillet-welded connection tension test, respectively. The 2D fracture models of welds at elevated temperatures were developed considering the relationship between stress triaxiality and equivalent plastic strain at fracture. The 3D fracture models of welds at elevated temperatures were then established from the 2D fracture model by considering the effect of Lode angle parameters in tension and shear. The 3D fracture models of welds were validated against the tension tests on the fillet welded connections at elevated temperatures under different load angles including 0°, 45°, and 90°. Finally, the fracture model as the function of temperature, stress triaxiality, Lode angle parameter, and plastic strain at fracture was proposed for E7018 welding material. According to the results, the welding material demonstrates ductile fracture behavior at elevated temperatures. The developed 3D fracture model can reasonably predict the fracture behavior of the welding material in steel welded connections at elevated temperatures. [ABSTRACT FROM AUTHOR]

In this paper, dynamically propagating cracks in anisotropic plates exposed to a generalised thermal shock are investigated. Here, the governing equations are considered according to the Lord-Shulman (LS) model as a fully coupled generalised thermoelasticity theory. The crack is modelled in the context of the eXtended Finite Element Method (XFEM). To evaluate Stress Intensity Factors (SIFs), a technique based on the J integral and crack tip opening and sliding displacements, previously applied for stationary cracks, is developed for a dynamically propagating crack in orthotropic solids. Besides, a variety of functions for enriching the displacement field are derived relying on the behaviour near the tip of a dynamically propagating crack in anisotropic materials. The maximum hoop stress criterion is also modified by using the asymptotic stress field for a dynamically propagating crack. In addition, the effect of the angular variation of fracture toughness in orthotropic materials is accounted in computing the crack propagation speed. In some examples, dynamic crack growth in complex cracked orthotropic structures subjected to LS thermal shock is studied in detail. The impacts of fibre orientations and LS relaxation time are also investigated in these examples. In conclusion, applying non-Fourier thermal shock for modelling dynamically propagating cracks in orthotropic structures is recommended to obtain more realistic results. In addition, by increasing the LS relaxation time, the crack grows less oscillatory and is more aligned along the material fibres. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new approach for numerically simulating the growth of cracks in unidirectional composite materials, termed extended isogeometric analysis, evaluating the maximum stress intensity factor and T-stress. To validate our approach, we used a small anisotropic plate with two edge cracks, beginning with formulating the governing equations based on the energy integral method, Stroh's Formula, and the Elastic Law describing the behaviour of anisotropic materials, while considering boundary conditions and initial states. A MATLAB code was developed to solve these equations numerically and to post-process the tensile stress and the stress intensity factor (SIF) in the first mode. The results for the SIF closely match those obtained using the extended finite element method (X-FEM), with a discrepancy of only 0.0021 Pa·m0.5. This finding underscores the credibility of our approach. The extended finite element method has demonstrated robustness in predicting crack propagation in composite materials in recent years, leading to its adoption by several widely used software packages in various industries. [ABSTRACT FROM AUTHOR]

Plasma stimulation is a form of waterless fracturing as it requires that only the wellbore be filled with an aqueous fluid. The technique creates multiple fractures propagating in different directions around the wellbore. The intent of this paper is to present an experimental and numerical investigation of the degree of competitiveness of plasma stimulation with hydraulic fracturing, especially in the case of stimulating tight formation. Several cases were run experimentally. The samples included limestone and sandstone to investigate plasma fracturing in different rock types. In addition, the main goal of the experiments was to study the creation of fracture(s) under confining stresses, the type of rock, the amount of electrical energy used in the experiment, and the length of the wire to generate the plasma reaction. A laboratory plasma equipment was designed and used to accomplish the experimental work. The experiments were then numerically matched using a finite element numerical simulator, HOSS developed by LANL (Los Alamos National Lab). HOSS was developed to simulate high-strain-rate fractures such as those created by plasma stimulation. It accounts for mixed-mode fracture mechanics which are tensile and shear fractures. The simulator governing equations obey the conservation of mass and momentum in a solid-mechanics sense and account for the nonlinear deformation of rock material. The matching of the experiment allowed us to validate the HOSS simulation of the process and showed that the numerical results are in good agreement with the experimental work. Using the HOSS simulator, we also investigated the effect of higher energy levels and/or short release time on a cement rock model. The pressure profile that is developed due to the energy release can vary in the peak pressure and the release time. The results showed that the plasma fracturing technique is an effective stimulation method in sandstone and limestone. Plasma fractures were developed in the rock samples and extended from the sample wellbore to the outer boundaries. The shape of the pressure pulse has an impact on the developed fractures. Moreover, the effect of plasma stimulation on natural fractures was studied numerically. It was found that natural fractures can arrest the plasma-generated fractures that propagate from the wellbore to the outer boundaries. However, new fractures may develop in the rock starting from the natural fracture tips. [ABSTRACT FROM AUTHOR]

The study on damage and fracture of superconducting Nb3Sn under cyclic loading is an indispensable part of understanding the origin of the irreversible strain limit in Nb3Sn. This paper uses molecular dynamics simulation to investigate the fracture and deformation damage behavior of polycrystalline and single crystal Nb3Sn/Nb composite materials under cyclic loading at extremely low temperatures. The effects of strain rate on crack initiation and growth were carefully analyzed in both polycrystalline and single crystal Nb3Sn/Nb composite materials. The results indicate that slip occurs in single crystal Nb3Sn/Nb composite materials after cyclic loading. When the local stress at the slip band intersection exceeds the material strength, microcracks initiate at the slip band intersection, leading to fracture failure of the composite material. In contrast, the failure of polycrystalline Nb3Sn/Nb composite materials is due to the inability of stress at grain boundaries to relax under cyclic loading, which leads to the initiation of microcracks at the grain boundaries and intergranular fracture of the composite material. The analysis of the different damage, fracture, and failure mechanisms of polycrystalline and single crystal Nb3Sn/Nb composite materials at different strain rates shows that the fracture is brittle at low strain rates. As the strain rate rises, the number of slip bands in the single crystal Nb3Sn layer increases, enhancing the toughness of the single crystal Nb3Sn/Nb composite material. Conversely, the influence of grain boundaries on material strength decreases in polycrystalline materials as the strain rate increases. Moreover, polycrystalline Nb3Sn/Nb composite materials exhibit significant residual strength after local fracture of Nb3Sn at high strain rates. The research results will contribute to a better understanding of the damage evolution process of Nb3Sn/Nb composite materials under cyclic loading and offer theoretical guidance for optimizing material performance. [ABSTRACT FROM AUTHOR]

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]

This paper presents assessments performed on a large database of virgin material and irradiated material thermal creep data from uniaxial and pressurised DIN 1.4970 Ti-stabilised austenitic stainless steel i.e. EN X10NiCrMoTiB15–15 or '15-15Ti' cladding tubes. The data base incorporates multi-heat data from uniaxial and bi-axial (internal pressure) creep tests conducted during the fast reactor R&D program of the DeBeNe (Deutschland-Belgium-Netherlands) consortium between the 1960s to the late 1980s together with more recent data, for example, from the European projects MATTER and PATRICIA and the EERA JPNM pilot project TASTE. The data comprises of a virgin material data base and a data base with irradiated creep data. The virgin material data comprises of time-to-rupture and time-to-0.2% creep strain in a temperature range of 600–800°C and covers a large range of stresses. The irradiated data base has less data and does not cover all material heats tested for the virgin material properties. The irradiation conditions are also different depending on the test reactor specifics and the irradiation campaign targets. The attained 'irradiation damage' in displacements per atom (DPA) for the irradiated materials range from 0.1 up to 38.1. Un-irradiated 'reference material' models for tensile strength and creep strength are constructed from the current-state of the art literature data and more recent results from the Sandvik 24% cold worked 1515–Ti cladding tube currently used as the main material batch studied at SCK CEN. The tensile strength model is used throughout the paper for normalizing creep strengths by the tensile properties, needed when applying the Wilshire (WE) creep model. Time factors (TF), stress factors (SF) and temperature ratio factors (TRF) are calculated for different material states for describing the impact of heat treatments, (virgin and irradiated) and irradiation conditions. This initial study targets to give estimates for the thermal creep properties of cladding tubes with a cold work range of 16–24% in a non-annealed state, as it is the preferred option for future designs according to the state-of-the art knowledge base. However, the main bulk of the available data on irradiated material is on claddings with a cold work range of 0-16% with and without annealing and at various levels of irradiation damage, thus leading to the need for estimation by interpolation and extrapolation assuming that irradiation damage levels and trends, e.g. time reduction factors found on a lower cold worked material can also be applied on materials with higher cold work levels. The results of the assessments clearly show relative strength differences between chosen material heats and heat treatments and has enabled constructing simple multilinear models for estimating the life of irradiated material. The models show that low creep test temperatures (and irradiation temperatures), low stress levels, low levels of cold work and high irradiation doses are increasing the detrimental difference between the specific material condition and the reference material. Also, it was found that the general level of life reduction (time factor TF and stress factor SF) for irradiation damaged material failure, in relation to the reference material failure, roughly coincides the corresponding values of time to 0.2% creep strain for virgin material. The estimated 'failure creep temperature limits' for 30 000 hours of service are studied and compared for both virgin and irradiated materials at a reference stress level of 1/3 of the tensile strength (at temperature). [ABSTRACT FROM AUTHOR]

Creep failure of hierarchical materials is investigated by simulation of beam network models. Such models are idealizations of hierarchical fibrous materials where bundles of load-carrying fibers are held together by multi-level (hierarchical) cross-links. Failure of individual beams is assumed to be governed by stress-assisted thermal activation over local barriers, and beam stresses are computed by solving the global balance equations of linear and angular momentum across the network. Disorder is mimicked by a statistical distribution of barrier heights. Both initially intact samples and samples containing side notches of various length are considered. Samples with hierarchical cross-link patterns are simulated alongside reference samples where cross-links are placed randomly without hierarchical organization. The results demonstrate that hierarchical patterning may strongly increase creep strain and creep lifetime while reducing the lifetime variation. This is due to the fact that hierarchical patterning induces a failure mode that differs significantly from the standard scenario of failure by nucleation and growth of a critical crack. Characterization of this failure mode demonstrates good agreement between the present simulations and experimental findings on hierarchically patterned paper sheets. [ABSTRACT FROM AUTHOR]

The article discusses a study which was carried out to investigate the local and effective fracture behaviour of polycrystalline silicon for microelectromechanical systems (MEMS). The apparent mode I critical stress intensity factor was determined from MEMS-scale tension specimens. The distribution of values was attributed to local cleavage anisotropy and to enhanced grain boundary toughening.

The method of backfill in underground mining is important for ground control as well as material recycling and energy efficiency. Even though extensive testing and field studies of backfill have been conducted, less is known about the detailed damage and fracturing that occurs directly at the rock/backfill interface. In this paper, cylindrical specimens containing an inner diameter of backfill and an outer diameter of rock (RB) were tested under triaxial compression. Acoustic emissions (AE) were used throughout testing, and X-ray computed tomography (CT) scanning was conducted before loading was applied and after the specimens had failed. The high-resolution CT images were then converted into point clouds to isolate the fractures and visualize them in three dimensions. The point clouds clearly show that fracturing occurred both in the rock and along with the contact between rock and backfill, while very little fracturing was found to occur in the backfill. Based on the point cloud and AE results, a unique evolution of fracturing is found to occur that includes two stages of shear fracturing in the rock, tensile fracturing along with the rock/backfill interface, and final tensile fracturing in the rock after delamination from the backfill, all of which contributed to the nonlinear stress–strain response. This paper presents a novel approach for investigating the initiation and propagation of 3D fractures in laboratory testing and can offer a useful reference for further studies on the mechanics of bi-material structures. [ABSTRACT FROM AUTHOR]

The leak-before-break design concept is based on J-R curves, which are obtained by J-R tests on various types of specimens and are known to be dependent on the cyclic load history. The J-R curves of standard specimens suggested by the American Society for Testing Materials are determined based on quasi-static tensile loading. However, seismic loading induces a reverse cyclic loading that alternately applies a tensile and a compressive load to nuclear plant piping. Therefore, it is very important to obtain the fracture toughness characteristics under reverse cyclic loading for the integrity estimation of nuclear plant piping. The objective of this paper is to study the effects of reverse cyclic loading on the fracture toughness characteristics of SA312 TP316L stainless steel, which is a nuclear plant piping material. J-R tests on a flat, equivalent stress gradient specimen with varying incremental displacement were carried out. The test results were reviewed by comparing the J-R test results under quasi-static loading. In addition, the safety margin of the nuclear plant piping was evaluated using a crack driving force diagram method. For the SA312 TP316L stainless steel, the results showed that the J-R curves were decreased with a decrease in the incremental displacement. When the incremental displacement was set to 0.25 mm, the unstable crack growth point value was about 73.0% of those for the quasi-static loading conditions. [ABSTRACT FROM AUTHOR]

This paper investigates the creep behavior, damage evolution, and failure probability of a solid oxide fuel cell (SOFC) with three different flow channel geometries—rectangular, round trapezoidal, and arched—under non-uniform temperature conditions over a 60,000 h operational period. A strain-based creep damage and failure probability model was developed to analyze the stress-strain distribution, creep damage evolution, and failure probability development inside the SOFC components. Results indicate a significant influence of SOFC channel geometry on stress relaxation. The three channel SOFC, rectangular, round trapezoidal, and arched, reach the damage threshold after 57,062 h, 43,577 h, and 49,560 h of operation, respectively, with crack initiation occurring near the inlet and outlet of the upper interconnector. The anode material exhibited the highest probability of failure, increasing by 116.3% and 36.4% for the transition from rectangular to round trapezoidal and arch-shaped gas channels, respectively. This study underscores the advantages of SOFC with rectangular channels in terms of mechanical stability and longevity, providing crucial insights for optimizing SOFC design and enhancing commercial viability. • Derivation of the non uniform temperature fields of different channel SOFCs. • Comparison of vulnerable locations in different channel SOFC components. • Evolution of creep damage in different channel SOFCs during 60 000 h of operation. • Study on the failure probability of different channel SOFCs. [ABSTRACT FROM AUTHOR]

This paper introduces a robust algorithm that efficiently generates high-quality unstructured triangular meshes to model complex two-dimensional crack growth problems within the framework of linear elastic fracture mechanics (LEFM). The proposed Visual Fortran code aims to address key challenges in mesh generation including geometric complexity, required simulation accuracy, and computational resource constraints. The algorithm incorporates adaptive refinement and updates to the mesh structure near the crack tip, resulting in the formation of rosette elements that provide accurate approximations of stress intensity factors (SIFs). By utilizing the maximum circumferential stress theory, the algorithm predicts the new crack path based on these SIFs. Throughout the simulation of crack propagation, a node splitting approach was employed to represent the progression of the crack, while the crack growth path is determined by successive linear extensions for each crack growth increment. To compute stress intensity factors (SIFs) for each increment of crack extension, a displacement extrapolation method was used. The experimental and numerical results demonstrated the algorithm's effectiveness in accurately predicting crack growth and facilitating reliable stress analysis for complex crack growth problems in two dimensions. The obtained results for the SIF were found to be consistent with other analytical solutions for standard geometries. [ABSTRACT FROM AUTHOR]

The traditional extended finite element method (XFEM) is suitable for simulating crack growth, but the crack‐tip stress field analysis still depends on the enriched function. In this paper, based on the numerical eigensolution of the singular displacement and stress field together with the Hellinger–Reissner (H–R) variational principle, a novel crack‐tip singular element is established to replace the enriched element in the crack‐tip region in the traditional XFEM. The stress field inside the element adopts a series expression instead of only including the leading‐order terms. The element only requires Gaussian integration at the element boundary and avoids mesh refinement in the crack‐tip region. The element can be used to analyze cracks in anisotropic materials, interface cracks, and cracks terminating at the bimaterial interface. The numerical solutions of the singular stress field in various crack forms are presented through numerical examples, which proves the effectiveness and versatility of the novel crack‐tip singular element. Highlights: An extended finite element method with a novel crack‐tip singular element is proposed.The convergence speed of the present extended finite element method is satisfactory.The compatibility between the singular element and other elements is good.The singular element has the feature of multifunction. [ABSTRACT FROM AUTHOR]

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 modelling. In this paper, we analyze the stress conditions in crevasse onset regions to better understand the failure criterion and strength relevant for large-scale modelling. 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 is 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 modelling are discussed. [ABSTRACT FROM AUTHOR]

The explosion products, such as shock waves, fragments and heat energy formed by explosion, act on the plate structure, which may cause structural damage, material failure and even phase transformation of material. In this paper, the damage mechanism and protective effect of near-field blast load on sandwich structure based on foam-nickel core material were studied. Firstly, the near-field explosion test was conducted to investigate the blast response of the foam-nickel sandwich structure subjected to blast shock from 8701 explosive at near-field position. The deformation characteristics and stress history of the sandwich structure on the acting location of blast load were carefully investigated via experimental methods. A finite element model of near-field explosion was established for effective numerical modelling of the dynamic behaviour of the sandwich structure using the explicit dynamics software ANSYS/LS-DYNA for more comprehensive investigations of the blast shock response of the sandwich structure. The finite element model is reasonable and validated by mesh independence verification and comparing the simulated response behaviour to that from the experimental results for the sandwich structure subjected to near-field blast load. On this basis, the damage mechanism and protection effect of the near-field explosion impact on foam-nickel cores with different density and porosity are simulated more systematically. The investigated results from the experiments and a series of numerical simulations show the large deformation effect due to the extensive energy absorption, which suggests that the sandwich structure based on foam-nickel core material may be expected to become a new choice of protective structure under near-field blast load. [ABSTRACT FROM AUTHOR]

As a typical hard and brittle material, gallium oxide crystal (β-Ga2O3) is easy to crack during processing. Diamond wire saw is the main way to produce β-Ga2O3 wafers. During the slicing process, a microcrack damage layer will be generated on the surface of the wafer. Under the stress, the microcracks will expand, leading to material breakage and fracture. In this paper, a finite element model of diamond wire sawing of β-Ga2O3 (010) crystal surface was established. The distribution of mechanical stress, thermal stress, and thermal-mechanical coupling stress during the sawing process were studied. The effects of sawing wire speed, feed speed and different parameter combinations under constant speed ratio on the thermal-mechanical coupling stress were analyzed. The research results show that: the thermal stress generated by sawing heat dominates the thermal-mechanical coupling stress during the sawing process; the mechanical stress caused by sawing force has a small numerical value and proportion, but it affects the distribution of thermal-mechanical coupling stress; increasing sawing wire speed and feed speed will increase the thermal-mechanical coupling stress. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to investigate the bearing capacity behaviour of cracked plates considering low-cycle fatigue (LCF) propagation under cyclic loads. The accumulative plastic damage after crack growth is treated as the residual stress and deformation of the plate. In this study, a cracked plate model is proposed to investigate the difference of its residual ultimate strength with preset crack and LCF crack. The present study has analysed the relationship between accumulated lateral deflection and residual stress of cracked plates in different cases. Its effect on the collapse behaviour of the cracked plate is also discussed. The influence factors such as crack length, tensile /compressive cyclic loads, maximum load, minimum load and crack location type are considered in the ultimate strength study of cracked plates. The numerical results clearly reveal the accumulative plastic damage and the bearing capacity behaviour of cracked plates under different cyclic loads. [ABSTRACT FROM AUTHOR]

This document is a summary of a special issue of the journal "Mechanics of Advanced Materials & Structures" titled "Recent Advances in Nonlinear Structural Mechanics and Failure Analysis." The special issue is a collection of selected papers presented at the first International Conference on Advanced Topics in Mechanics of Materials, Structures, and Construction (AToMech1) held in Saudi Arabia in March 2023. The conference aimed to foster sustainable development and facilitate international networking among researchers, practitioners, and educators in the fields of mechanics of materials, structures, and construction. The special issue covers various topics such as advanced structural models, damage and fracture mechanics, metamaterials and acoustics, large deformation analysis, peridynamic theory, multi-physics and coupled problems, and advanced materials and structures. The papers in the special issue explore innovative approaches and solutions in these areas. The special issue is internationally significant and was made possible through the collaboration of the journal, the conference organizing committee, and the guest editors from different countries. The summary expresses gratitude to all those involved in making the special issue possible. [Extracted from the article]

In solid mechanics, Maxwell stresses are known to be induced if a body is exposed to magnetic and, in the case of dielectrics, electric fields. Acting as tractions at outer or inner surfaces as well as volume forces, they are superimposed with tractions and stresses due to mechanical loads and provide a more or less significant contribution, depending on loading, material properties and geometric aspects. The Maxwell stress tensor, constituting the physical and mathematical basis, however, is controversially discussed to date. Several formulations are known, most of them having been suggested more than 100 years ago. Being equivalent in vacuum, they differ qualitatively just as quantitatively in solid or fluidic matter. In particular, the dissimilar effect of body forces, emanating from a choice of established Maxwell stress tensor approaches, on crack tip loading in dielectric solids is investigated theoretically in this paper. Due to the singularity of fields involved, their impact is basically non-negligible compared to external mechanical loading. The findings obtained indicate that fracture mechanics could be the basis of an experimental validation of Maxwell stress tensors. [ABSTRACT FROM AUTHOR]

When plates with edge cracks in the rolling process is straightened by cyclic tensile and compressive stress, the tip of edge crack always accompanied by stress concentration, which leads to crack propagation. In this paper, damage parameters are imported into the plate straightening model based on determining the GTN damage parameters of magnesium alloy materials by inverse finite element calibration method, the influence of different straightening process schemes and prefabricated V-shaped crack geometry on crack growth is analyzed through the way of the combination of simulation and straightening experiment. The results show that the peak values of equivalent stress and equivalent strain under each straightening roll appear at the crack tip. The value of longitudinal stress and equivalent stain decrease with the distance to crack tip becomes larger. The peak value of longitudinal stress appears when the crack circumferential angle is about 100°, and the crack tip is easy to form crack propagation; when the plate passes roll 2 and roll 4, the equivalent stress and strain concentration at the crack tip are most obvious; when the reduction reaches a certain degree, the void volume fraction (VVF) reaches the VVF of the material breaking; with the increase of the entrance reduction, the number of VVF at the crack tip which reaches the material fracture increases, and the length of crack propagation increases; the stress concentration at the tip of V-shaped crack with large length–width ratio is obvious, and the VVF is more likely to reach the VVF at the time of material fracture, crack initiates and propagates easily. [ABSTRACT FROM AUTHOR]

In this paper, a novel dual architecture phase lattice (DPL) structure consisting with hard and soft phases is proposed, and their mechanical properties as well as the deformation features under compression are investigated. Firstly, two different types of basic cubic cells are selected as the constitution phases, and the DPLs with different arrangements are then constructed by additive manufacturing. Quasi-static compression tests and numerical simulations are performed to explore the deformation patterns and stress-strain responses. The compressive strength, plateau stress and the specific energy absorption of the DPLs are characterized. The effects of base material fracture, rod diameter and the cell arrangements on the mechanical responses are explored. Results show that the deformation and failure initiate in the matrix phase and trigger the embedding of the reinforcing phase into the crushed regions. The fracture of the rods results in a lower stress level and more serious fluctuations in the stress-strain responses. Increasing the rod diameter is an effective approach for enhancing the compressive strength and specific energy absorption. Introducing appropriate agreements of reinforcement phases can result in 112% and 37% increments for the compression strength and specific energy absorption, respectively. The findings of this work can facilitate the designs of lattice structures with outstanding mechanical properties and energy absorption performances. [ABSTRACT FROM AUTHOR]

This article discusses several papers on civil engineering. A paper by Sami W. Tabsh presents an analytical approach for confined high-strength concrete columns. It describes some of the experimental stress-strain curves that do not match the experimental stress-strain curves reported by a previous study. Another paper by Yanhua Zhao, Shilang Xu and Zhimin Wu examines the variation of fracture energy in concrete along a fracture process zone based on the perturbed length method (PLM) and compares the results with experimental investigations based on Xu et al.

In the paper, new hybrid (numerical-analytical) methods to calculate the J-integral, the CTOD, and the load line displacement are presented. The proposed solutions are based on FEM calculations which were done for SEN(B) specimens dominated by plane strain condition. The paper includes the verification of the existing limit load solution for SEN(B) specimen with proposal of the new analytical formulae, which were used for building hybrid equations for determining three selected fracture mechanics parameters. [ABSTRACT FROM AUTHOR]

Bolted joints are often used in thin parts such as plates or shell-like components in lightweight structures, e.g. air- and spacecraft. This is also motivated by an inexpensive manufacturing and the ability to disassemble. To make these joints, holes need to be drilled and stress concentrations arise. Leading to the instantaneous destruction of the connection, attention should be drawn to fatal tension failure. The efficient and precise prediction of the corresponding failure stresses using analytical methods is the focus of this paper. Usually, rows of bolts are placed. Then, the load is partly introduced into one bolt while the rest stays in the plate. This setting is also referred to as bolted joint under combined bearing-bypass load, which shall be idealised as a linear 2D plate problem. The corresponding characteristic stresses are discussed for orthotropic laminates showing good agreement to Finite Element values. Then, failure analysis is conducted using Finite Fracture Mechanics. This part is dedicated to quasi-isotropic laminates. The size effect and in this context the failure stress reduction with increasing bolt diameter is analysed. Primary physical effects due to finite dimensions and the ratio of bearing and total load are identified. The higher this ratio and the larger the bolt diameter, the lower the sustained failure stress. Failure envelopes for the graphical determination of the critical bearing and bypass stresses are provided. All in all, a comprehensive and efficient framework for tension failure assessment of composite bolted joints under bearing-bypass load interaction is developed. [ABSTRACT FROM AUTHOR]

In multiscale analysis, homogenization methods are needed to up‐scale the micromechanical response obtained from investigating the underlying microstructure to the next higher scale. The standard homogenization schemes are based on volume averaging over the entire microstructure following Hill's approach, which requires that the virtual energies generated on the two involved scales equalize. However, these standard homogenization schemes are not applicable to softening phenomena due to localization, and representativeness of the considered microscale volume is lost. One way to overcome these drawbacks is to perform the volume averaging only within the localizing failure zone. Thereby, representative results can be achieved even in the softening region. In this paper, we apply the failure zone homogenization approach to both, mode I and mode II loading scenarios, as well as mixed‐mode loading of long fiber reinforced plastics. For an accurate description of material failure within the epoxy matrix, a scalar damage model at large strains with gradient enhancement is used, such that the obtained results are mesh‐independent. As a result, we show that for all considered cases representative volume element (RVE) sizes can be determined by using the failure zone homogenization scheme. Nevertheless, the energy distributions of all involved mechanisms have to be considered carefully in order to allow generalizations. [ABSTRACT FROM AUTHOR]

Frost crack evolution induced by cyclic freeze–thaw is responsible for rock deterioration in cold regions and poses major threats to public safety, engineering structures, and alpine slope stability. This paper presents experimental and numerical works aimed at investigating the frost crack evolution in fissured rock masses, as well as the interaction between frost cracks. A series of laboratory freezing experiments are conducted on rock-like specimens with various pre-existing fissures. Experimental results show that frost cracks initiate at the pre-existing fissure tips and propagate under the freeze–thaw treatment. Moreover, the frost crack evolution is significantly influenced by external stress conditions and frost crack interactions, forming several typical propagation patterns (e.g., deflection, coplanar and butterfly shape, etc.). Then, numerical simulations with a low-temperature thermal–mechanical coupled model, where the water/ice phase transition and hence volume expansion are explicitly simulated, are conducted to reproduce the experimental observation. The numerical results are consistent with the experimental observations and help to reveal the underlying mechanisms of the frost crack growth and frost crack interaction. This experimental and numerical investigation helps to improve the understanding of frost cracking mechanisms that can inform engineering design in cold regions with fissured rock masses. Highlights: Frost crack propagation and interaction under freeze-thaw cycles are investigated. Frost heaving pressure induced by ice expansion is large enough to drive crack propagation. Confining stresses alter the stress field around the crack tips, inducing crack orientation. Mutual interaction between adjacent frost cracks significantly affects the cracking pattern. Novel low-temperature thermal-mechanical coupling model is developed for frost cracking problems. [ABSTRACT FROM AUTHOR]

The clean utilization and green development of coal resources have become a research focus in recent years. Underground hydraulic fracturing technology in coal mines has been widely used in roof pressure relief, top coal pre-splitting, gas drainage, roadway pressure relief and goaf disaster prevention. Different in situ stress types cause great differences in the stress field around the boreholes, the critical pressure of the fracture initiation, and the direction of the fracture expansion trend; in addition, the stress shadow effect generated by the superposition of stress fields between boreholes relatively close together has a mutual coupling effect on the evolution of the stress field, the development of the plastic zone, and the crack propagation of the rock mass. Therefore, an effective method to solve the problem is to establish a mechanical model of hydraulic fracturing in boreholes for theoretical calculation, determine the influence mechanism of the crack shadow effect, and design a numerical simulation experiment of the equivalent stress fluid–solid coupling of hydraulic fracturing under different pore diameters and spacings. In addition, combining rock mechanics and fracture mechanics to analyze the influence of the shadow effect of the stress field between cracks on the evolution of the equivalent stress and the plastic zone is one of the important advances in this paper. Considering the engineering background of the site, the geological conditions and the requirements of general regulations, it is considered that the parameter selection of roof fracturing hydraulic fracturing technology in the Yushen mining area is more suitable when 0.12 m hole diameter and 3.5 m hole spacing are selected. [ABSTRACT FROM AUTHOR]

In this paper, a crack propagation assessment on a seamless stainless steel tube was carried out by comparing the crack growth driving force and the resistance. Crack growth driving force was given by finite-element analysis (FEA), the stress–strain relationship was given by digital image correlation (DIC) tensile testing, and the crack growth resistance was given by single-edge notched tensile (SENT) testing with the single-specimen flexibility method. Then, the proposed approach was compared with the failure assessment curve and validated by the full-size hydrotest of tube with an inner wall notch. The result of full-size test showed the assessment method of FEA was more accurate and the result of failure assessment curve was more conservative. [ABSTRACT FROM AUTHOR]

• The GDH-PD is proposed to address size-dependent effects and fracture problems. • The lower- and higher-order micro-modulus states of GDH-PD are firstly derived. • GDH-PD eliminates zero-energy modes of traditional higher-order peridynamics. • HOBCs are applied by constructing quadratic functional on the boundary points. • Nonlocal effects, size effects, strain gradient effects and damage are considered. In this paper, we propose the implicit stabilized dual-horizon peridynamics-based strain gradient damage model (GDH-PD) to describe the cross-scale fracture behavior of materials. To this end, firstly, the strain energy density function of GDH-PD is reformulated by considering the energy compensation to eliminate zero-energy modes of the traditional higher-order peridynamics. And then, the constitutive force state of GDH-PD is derived and explicitly expressed with the help of the proposed special dimension reduction of the nonlocal higher-order tensors. To solve the steady-state crack propagation problems, the implicit GDH-PD is developed by deriving the lower- and higher-order micro-modulus double state, such that the linearization of the equilibrium equation of GDH-PD is established. At last, the bond length-dependent energy-based failure criterion is used to characterize the cross-scale fracture in the form of bond breakage. The effectiveness of GDH-PD to characterize microstructure size effects and macrostructure strain gradient effects are investigated by numerical simulations. The numerical results are in good agreement with the analytical solutions or the available experimental results. We believe that the proposed GDH-PD may pave the way to an increased application of peridynamics to be used in the cross-scale fracture predictions for the advanced material. [ABSTRACT FROM AUTHOR]

Hydraulic fracture, whether a natural phenomenon or an engineered process, consists of a highly pressurized flow evolving within a rock and, when necessary, fracturing such a medium. Particularly, in the context of oil and gas exploitation, a mixture of water and proppant is injected through a well to improve the oil extraction conditions by artificially increasing the local permeability. From a modeling standpoint, it is fundamental to acknowledge that this complex flow involves, among other disciplines, fracture mechanics, fluid dynamics, non‐Newtonian flow, solid mechanics, and flow in porous media. Therefore, explicitly or not, a model bears multiple scales and multiple physics, leading to a non‐linear moving boundary mathematical problem that is hard to solve through analytical techniques. Amongst them, the Pseudo‐3D, which computes fracture evolution in reservoirs confined by symmetric stress barriers, is frequently employed in the oil and gas industry domain. The different assumptions made to obtain the P3D model lead to inaccurate predictions, like the overestimation of fracture height for important operating conditions. We propose a model discrepancy term in a multi‐fidelity approach to correct such drawbacks. The main difficulty associated is constructing a mapping between the inputs and outputs that faithfully represents the error between high and low fidelity models. In this paper, we investigated the performance of a nonlinear multi‐fidelity approach relying on Gaussian Processes. We present a careful analysis to assess the good performance of such a proposition and also present results involving Uncertainty Quantification, which is made feasible by using the bi‐fidelity surrogate. [ABSTRACT FROM AUTHOR]

In this paper, a numerical simulation method based on the camshaft casting process and crack expansion was proposed to study the propagation characteristics of casting hot cracks. The dynamic visualisation process of hot crack growth indicates that the formation of hot tear is dominated by opening mode cracks. And during the propagation process, the equivalent stress intensity factor at the crack front first decreases and then increases. Furthermore, the propagation characteristics of the crack under different hot tear initiation conditions were studied by this method. The results reveal that the expansion ability of a hot crack is affected by the equilibrium solidification scale, solidification sequence, and solidification path of the casting. Finally, using the microscopic morphology of the cracks, the semi-quantitative analysis of the elements illustrates that the carbon content decreases sharply at the crack formation site, while manganese and sulphur are relatively rich. [ABSTRACT FROM AUTHOR]

Purpose: Hydrofracturing technology has been widely used in tight oil and gas reservoir exploitation, and the fracture network formed by fracturing is crucial to determining the resources recovery rate. Due to the complexity of fracture network induced by the random morphology and type of fluid-driven fractures, controlling and optimising its mechanisms is challenging. This paper aims to study the types of multiscale mode I/II fractures, the fluid-driven propagation of multiscale tensile and shear fractures need to be studied. Design/methodology/approach: A dual bilinear cohesive zone model (CZM) based on energy evolution was introduced to detect the initiation and propagation of fluid-driven tensile and shear fractures. The model overcomes the limitations of classical linear fracture mechanics, such as the stress singularity at the fracture tip, and considers the important role of fracture surface behaviour in the shear activation. The bilinear cohesive criterion based on the energy evolution criterion can reflect the formation mechanism of complex fracture networks objectively and accurately. Considering the hydro-mechanical (HM) coupling and leak-off effects, the combined finite element-discrete element-finite volume approach was introduced and implemented successfully, and the results showed that the models considering HM coupling and leak-off effects could form a more complex fracture network. The multiscale (laboratory- and engineering-scale) Mode I/II fractures can be simulated in hydrofracturing process. Findings: Based on the proposed method, the accuracy and applicability of the algorithm were verified by comparing the analytical solution of KGD and PKN models. The effects of different in situ stresses and flow rates on the dynamic propagation of hydraulic fractures at laboratory and engineering scales were investigated. when the ratio of in situ stress is small, the fracture propagation direction is not affected, and the fracture morphology is a cross-type fracture. When the ratio of in situ stress is relatively large, the propagation direction of the fracture is affected by the maximum in situ stress, and it is more inclined to propagate along the direction of the maximum in situ stress, forming double wing-type fractures. Hydrofracturing tensile and shear fractures were identified, and the distribution and number of each type were obtained. There are fewer hydraulic shear fractures than tensile fractures, and shear fractures appear in the initial stage of fracture propagation and then propagate and distribute around the perforation. Originality/value: The proposed dual bilinear CZM is effective for simulating the types of Mode I/II fractures and seizing the fluid-driven propagation of multiscale tensile and shear fractures. Practical fracturing process involves the multi-type and multiscale fluid-driven fracture propagation. This study introduces general fluid-driven fracture propagation, which can be extended to the fracture propagation analysis of potential fluid fracturing, such as other liquids or supercritical gases. [ABSTRACT FROM AUTHOR]

This paper proposed an efficient two-dimensional fatigue crack growth simulation program for linear elastic materials using an incremental crack growth procedure. The Visual Fortran programming language was used to develop the finite element code. The adaptive finite element mesh was generated using the advancing front method. Stress analysis for each increment was carried out using the adaptive mesh finite element technique. The equivalent stress intensity factor is the most essential parameter that should be accurately estimated for the mixed-mode loading condition which was used as the onset criterion for the crack growth. The node splitting and relaxation method advances the crack once the failure mechanism and crack direction have been determined. The displacement extrapolation technique (DET) was used to calculate stress intensity factors (SIFs) at each crack extension increment. Then, these SIFs were analyzed using the maximum circumferential stress theory (MCST) to predict the crack propagation trajectory and the fatigue life cycles using the Paris' law model. Finally, the performance and capability of the developed program are shown in the application examples. [ABSTRACT FROM AUTHOR]

Aiming at the large deformation and the dynamic fracture of roadway during the underground excavation or mining, a physical simulation and strain testing system was established, and the deformation process of surrounding body and its inner strain characteristics of the simulated roadway under loading was carried out. Results showed that the inner strain change of the measurement points can be divided into three types: the strain firstly increases and then decreases, the strain slowly increases and then increases sharply, and strain firstly reduces and then increases. The strain starting time is closely related to the failure path and boundary of tested samples. This paper suggested two criteria for determining the instability of roadways, which are a huge and faster increase of strain at the location of the roof and floor with high absolute value, or a small increase with a peak value or irregular fluctuation. This paper provides a new idea for the simulation of roadway instability and is significant in deeper understanding the deformation and destabilization of underground roadway. [ABSTRACT FROM AUTHOR]

This paper describes the conditions leading to a sustained, low-rate, heave phenomenon affecting a building founded on hard Keuper anhydritic rock. The building was located in an abandoned gypsum quarry. Monitoring data as well as vertical profiles of gypsum and anhydrite content indicate that swelling was associated with the presence of a shallow level of anhydritic clay rock. This paper concludes that the initial quarry excavation as well as the additional building foundation work modified the original stress state and contributed to opening fractures at depth. It also resulted in a facilitated access of water to the upper rock levels, immediately under the foundation footings. Measured heave rates are substantially lower than other rates recorded in a few recent cases. An explanation is provided for the difference. This paper describes a comforting solution for the building. [ABSTRACT FROM AUTHOR]

Considering fracture constraint is an efficient way to describe stress-strain field and fracture toughness more accurately, so it is necessary to realise the relationship with in-plane and out-of-plane constraint for different standard specimens. In this paper, three-dimensional finite element method is applied to study the in-plane and out-of-plane constraint for both cruciform specimen and single edge notched bending specimen made from commercial pure titanium. Crack length and in-plane loading as the factors affecting in-plane constraint, and thickness as the factor affecting the out-of-plane constraint are used to study the effect on both in-plane and out-of-plane constraint in this paper. From the results, in-plane and out-of-plane constraint are both related to specimen geometries and loading styles. And there exist relationships with in-plane and out-of-plane constraint because of factors for different specimens. Depending on crack length, out-of-plane constraint increases with in-plane constraint. While depending on transverse loading, out-of-plane constraint decreases with in-plane constraint. In addition, when the in-plane constraint of a specimen is higher, in-plane constraint increases with out-of-plane constraint (thickness). When the in-plane constraint is lower, in-plane constraint almost remains unchanged with out-of-plane constraint. [ABSTRACT FROM AUTHOR]

Pipe bends, often referred to as 'elbows', are special pipeline components, widely used in onshore buried steel pipelines. They are sensitive to imposed deformations and their structural behavior is quite flexible and associated with the development of significant stress and strain, which may lead to failure. In the present paper, the mechanical performance of buried steel pipeline bends is investigated first, using rigorous finite element models that account for the pipe-soil interface. Three 36-inch-diameter pipe elbows are considered, subjected to pull-out force and embedded in cohesive soils. The elbows have bend angles equal to 90°, 60° and 30°, and bend radius-over-diameter ratio ( R/ D) equal to 5. The results show the increased flexibility of the pipeline bend with respect to the straight pipe, and are reported in the form of force-displacement diagrams. Furthermore the deformation limits of each elbow are identified in terms of appropriate performance criteria. The second part of the paper investigates the effect of pipe bends on the response of pipelines crossing active faults using a three-dimensional rigorous finite element model. The numerical results refer to a 36-inch-diameter pipeline crossing a strike-slip fault, and show that the unique mechanical response of pipe bends, in terms of their flexibility, may offer an efficient tool for reducing ground-induced deformations. The three-dimensional model employs the load-displacement curves of the first part of the paper as end conditions through nonlinear springs. Furthermore, the results show that there exist an optimum distance of the elbow from the fault plane, which corresponds to the maximum allowable ground displacement. Therefore, pipeline elbows, if appropriately placed, can be employed as 'mitigating devices', reducing ground-induced action on the pipeline at fault crossings. [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]

This research article investigated the stress-state and strain-rate-dependent mechanical properties and failure of alumina ceramic. Compression–shear testing was carried out using a split-Hopkinson pressure bar under equivalent strain rates ranging from 1 0 1 s−1 to 1 0 3 s−1. Ultra-high-speed images coupled with digital image correlation were used to investigate the in situ time-evolving strain field and the failure process (e.g., crack growth). Experimental results showed equivalent strength reduced from 4.27 ± 0.23 GPa for the uniaxial compression tests to 3.75 GPa and 2.00 GPa for compression–shear tests across the strain rates and shear angles (5 ° to 25 °), with the strength decreasing with an increasing shear angle. The crack speed ranged from 908 m/s to 3208 m/s across the range of strain rates and shear angles, with a positive correlation noted for crack speeds with strain rate and increasing sensitivity with an increasing shear angle. The extent of localization of shear strain in alumina under compression–shear deformation was observed to be strain-rate-dependent, and it increased with an increasing strain rate of deformation. Furthermore, axial and shear strain localization increased with the increasing shear angle, contributing to local shear failure before the complete failure of the specimen. Overall, this paper provides new insights and measurements of the strain-rate-dependent and shear-dependent strength and crack speeds of alumina under compression–shear loading, and these serve as vital inputs for future computational model development and validation. [ABSTRACT FROM AUTHOR]

Surface cracks are commonly observed in coatings and films. When structures with coatings are subject to stretching, opening mode cracks are likely to form on the surface, which may further lead to other forms of damage, such as interfacial delamination and substrate damage. Possible crack forms include cracks extending towards the interface and channeling across the film. In this paper, a two-dimensional numerical model is proposed to obtain the structural strain energy at arbitrary crack lengths for bilayer structures under uniaxial tension. The energy release rate and structural stress intensity factors can be obtained accordingly, and the effects of geometry and material features on fracture characteristics are investigated, with most crack patterns being confirmed as unstable. The proposed model can also facilitate the analysis of the stress distribution in periodic crack patterns of films. The results from the numerical model are compared with those obtained by the finite element method (FEM), and the accuracy of the theoretical results is demonstrated. [ABSTRACT FROM AUTHOR]

Large-size lump (e.g., coal reject or waste rocks) is one of the most popular backfill materials for underground mines attributed to its cost-effective and easy-to-obtain. The massive void between lumps, however, does generally affect the overall performance in eliminating the ground subsidence. This paper presents a conceptual backfill material, termed as lump-grout (LG) material, the attractive feature of which is that the voids between lumps are totally filled up with high-water content cementitious grout (CG) material. To explore the mechanical behaviour of LG material, a total of 36 LG specimens were prepared and tested under the uniaxial compression and the tensile loading. Other 20 CG specimens were tested in parallel for comparison. Key configurations investigated in the present research covered the particle size of lumps and the water-to-powder ratio of CG material. Test results indicated that the stress–strain behaviour of LG specimen is predominately affected by the strength of CG material. The failure of LG material generally occurred along the interface between lumps and the cementitious grout material rather than the lumps themselves. Compared to CG material, the axial deformation ability of LG material is slightly superior, when the utilization of CG material is significantly reduced. In addition to the backfill material, the proposed LG material can be also used as the infill material for the artificial standing supports for underground spaces. [ABSTRACT FROM AUTHOR]