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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]

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]

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 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]

• 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]

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]

This document is an editorial from the journal Frontiers in Materials titled "Innovators in mechanics of materials." It highlights the contributions of researchers in the field of mechanics of materials and aims to provide a snapshot of the current state of the field and potential future developments. The editorial showcases six key contributions, including topics such as metal foams, acoustic insulation panels, functionally graded beams, solid-state batteries, rock deformation, and non-Newtonian nanofluid flow. The Research Topic aims to stimulate collaboration and knowledge exchange among researchers in the field. [Extracted from the article]

Griffith's 1920 fracture criteria is well known in the engineering community. Griffith produces a simple formula for the fracture stress of a material using the first law of thermodynamics by relating the decreased elastic energy of an applied load to the increased surface energy of a crack. However, evidence in fatigue research, most notably the concept of fracture fatigue entropy (FFE), suggests that the fracture mechanism is more intimately related to irreversibility and can be treated via the second law of thermodynamics. In this paper, Griffith's model is approached from the perspective of the second law of thermodynamics, producing a new equation for fracture stress centered on entropy. Fracture tests are performed on 304 stainless steel (SS) and 110 copper specimens. Experimental crack lengths at fracture determined via digital image correlation (DIC) are compared to predicted crack lengths at fracture determined via the entropic fracture stress relation to assess accuracy. Predicted crack lengths at fracture are determined to be accurate to within 2.88% for 304 SS specimens and 7.62% for copper specimens, both of which are comparable to the corresponding accuracy of Griffith criteria predictions. Further, it is shown that the developed entropy model is capable of predicting the entropy-based debonding strength of a material, matching experimental debonding strength values evaluated via DIC to within 25%. [ABSTRACT FROM AUTHOR]

Sapphire is widely used in aerospace, microelectronics and defense applications. Due to its high hardness and low fracture toughness, it is difficult to achieve high efficiency and low damage machining. Laser-assisted machining is an effective method for machining hard and brittle materials and has been explored in many experimental and theoretical studies. In this paper, the mechanical property of sapphire and the variation of the coefficient of friction assisted by different laser powers are investigated in detail. Meanwhile, Raman spectroscopy was employed to reveal the residual stress characteristics in the deformation zone of the scratch grooves, and to analyse the changes in the depth of plastic-brittle transition of sapphire after heat treatment with different laser powers. Comparing the material removal behavior of sapphire in indentation and scratching experiments with and without laser-assisted heat treatment (LAHT), and exploring their material removal mechanisms. Experimental results show that LAHT can improve the ductility and workability of sapphire by reducing the hardness and improving the fracture behavior of the material. Hardness and elasticity modulus decrease with increasing power, and the distribution of residual stress changes from compressive to tensile with increasing power. Laser treated surface was found to possess shorter crack length, no significant localized chipping and spalling in indentation, and its scratch grooves were deeper with no radial cracks observed, the scratching force ratio was higher, the critical load for brittle-plastic transition became larger, and plastic flow lines and lumpy spalling debris appeared in the scratch areas. Nearly zero cracks were observed in material subsurface under the LAHT. With LAHT, the material is removed at a higher rate and in a more plastic way, fracture behavior of the material is improved, surface and subsurface damage is reduced, and the machining efficiency is enhanced. This study has important implications and benefits for the machining of sapphire in ensuring surface quality and achieving high efficiency. [Display omitted] [ABSTRACT FROM AUTHOR]

• Matrix, strain rate and temperature affect the mechanical property of the alloy. • High strain rate and temperature led to the fracture in the model, and the crack path is located in the matrix- γ Phase. • Lomer-Cottrell lock and stacking fault tetrahedron affect the strength of alloy. Nickel (Ni)-based single-crystal superalloys are of great importance in the aircraft industry due to their excellent mechanical properties, and cracks as unavoidable defects may affect the mechanical performances of materials dramatically. In this paper, large scale molecular dynamics (MD) simulations are carried out to understand the deformation mechanisms of Ni-based single crystal with a central crack under tension. Here, the effects of matrixes (γ, γ′ and γ/γ′), strain rates (1 × 109 s−1 ∼ 3 × 109 s−1) and temperatures (300 K∼900 K) on the role of crack propagation are considered. It is observed that dislocations and slip systems in the γ′ model are concentrated near the crack, resulting in the rapid expansion of dislocation, which leads to the fastest crack growth speed and early fracture. While the crack propagation rate of γ and γ/γ′ models are relatively slow, due to the combined action of the Lomer-Cottrell lock and stacking fault tetrahedron structure and Stair-rod dislocation, which hinders crack propagation. In addition, deformation at increased strain rates and/or reduced temperatures, lead to superior yield stress and Young′s modulus for models with a central crack at γ/γ′ interface. On the other hand, high temperature and high strain rate will promote crack propagation in the γ phase, and the higher the strain rate and/or temperature, the faster the crack propagation speed will be. These results will enrich our understanding on the crack propagation and evolution mechanisms in Ni-based single crystal superalloy. [ABSTRACT FROM AUTHOR]

Understanding the long-term behavior of brittle rocks requires fundamental consideration of time-dependent strain evolution and brittle creep processes. Previous studies have evaluated sub-critical crack growth during time-dependent deformation and damage evolution in brittle rocks; however, there is an incomplete knowledge of how damage evolves spatially and temporally within the body of intact rocks, where distributed regions of damage interact and coalesce during creep. This paper presents laboratory research focusing on evaluating brittle creep damage processes in Stanstead granite (SG) using 2-dimensional digital image correlation (2D-DIC). In the laboratory, the prismatic SG specimens were loaded beyond an estimated Crack Damage stress threshold (CD) level and then maintained a constant stress to initiate the creep process. DIC was used to characterize full-field spatiotemporal strain evolution, which was then interpreted in the context of local regions of “damage”, determined according to a strain-based criterion. A method was proposed for identifying “existing” and “new” damage regions over specified intervals during the test, followed by spatial clustering of these regions to assess their spatiotemporal evolution. The clustering analysis results demonstrated the extension of existing damage regions was the main damage process during brittle creep, which is consistent with existing models of sub-critical crack growth. In addition, temporal analysis of tensile and shear strains on a point-by-point basis revealed both new damage formation and the strain concentration within existing damaged regions significantly contribute to overall specimen strain during primary creep. In contrast, during secondary creep, increases in specimen deformation are influenced by the accumulation of strains within already damaged regions. [ABSTRACT FROM AUTHOR]

• Considering wear improved the accuracy of fretting fatigue life prediction. • Wear delays the crack initiation and propagation, leading to an increase in fatigue life. • Wear causes the crack initiation position to move away from the symmetry center. • Wear has little effect on crack propagation path. • The effect of wear is more important under low stress amplitude. Fretting fatigue is a common type of problem in the engineering fields. Due to its multiaxial characteristics, it leads to a shorter overall fatigue life compared to plain fatigue. Fretting fatigue is caused by the micro slip at the contact surface, which is always accompanied by interface wear. This paper presents a refined elastic numerical simulation method combining interfacial wear with continuum damage mechanics (CDM) and fracture mechanics to predict fatigue life. The crack initiation life is determined by damage evolution law and the initiation position is determined by the total dissipated energy. Crack propagation life and path can be predicted using stress intensity factor. The stress redistribution and geometric change of contact surface caused by wear are considered in the whole fatigue process. Results indicate that the fretting fatigue simulation method incorporating wear has higher accuracy compared with the experimental results in the literature. It is noteworthy that wear retards nucleation damage process and crack propagation. As stress amplitude decreases, fatigue life increases, and delay effect of wear becomes more obvious. Additionally, wear causes the crack initiation position to move out, but crack initiation region is still near the slipping zone and propagation path does not change. [ABSTRACT FROM AUTHOR]

• The paper focuses on the use of Raman spectroscopy to determine local mechanical stresses in metal–oxide–semiconductor (MOS) structures and its correlation with electrical parameters such as flat band voltage and contact potential difference. • The document discusses the importance of studying stress distribution in gate oxides for optimizing performance and reliability of electronic devices. It highlights the influence of stress on electrical parameters in MOS structures, emphasizing the need to consider stress in design and optimization processes. • The study demonstrates the correlation between stress and electrical parameters and the effectiveness of Raman spectroscopy in measuring stresses in MOS structures. • The results show accurate stress determinations under and beside the AlSiCu gate, impacting flat band voltage and contact potential difference values. • Experimental techniques like micro-Raman spectroscopy are essential for evaluating stress levels for material failure prevention. • The study also explores the significance of stress in affecting electrical properties of MOS structures and the relation between stresses and key electrical parameters. The development research of metal oxide semiconductors (MOS) nanomaterials provides to produce electronic modules of fast response, low manufacture cost, long work life, and energy consumption. The MOS principles nanostructures utilizing hold great potential in manufacturing and other branches of the economy. The article includes the determination of local mechanical stresses in MOS structures by optical methods and the study of the effect of these stresses on electrical parameters. The main goal of this work was to determine local mechanical stresses in MOS structures and find a correlation of these stresses with basic electrical parameters of MOS structures such as the contact potential difference and flat band voltage in a semiconductor. In the first stage of the work, an attempt at the average value of these stresses using, among others, interferometry and ellipsometry was made. These attempts failed, although they brought other interesting results not related to the main purpose of the research field. However, Raman spectroscopy proved to be an effective tool for measuring stresses in the investigated structures. The authors also determined the stresses using refractive indices based on ellipsometry measurements. The study of MOS structures can be enhanced by using interferometry and ellipsometry, which provide valuable information on changes in thickness and internal stresses. The obtained results have differed from the values presented in the literature. These studies combined with the weighting method contributed to developing, among others an analytical relationship between the refractive index n and the density of SiO 2 layers. According to the conducted studies, can be concluded that the only adequate method is Raman spectroscopy. It was possible to determine the stresses in the SiO 2 layer under the gate and nearby with an accuracy of 20 MPa and 100 MPa, respectively. Similarly, the distributions of the structure's electrical parameters were similar in shape. Based on these results, it was possible to establish a relationship between the stress and the parameters V FB and ϕ MS. In conclusion, stress in the SiO 2 layer influences the parameters of V FB and ϕ MS in the MOS structure. This method provides no limitations related to the size of the spot, oppositely to the measurements of spectroscopic ellipsometry. [ABSTRACT FROM AUTHOR]

To explore the influence of the working face excavation rate on the rock deformation mechanism and seepage characteristics, deformation and seepage tests of sandstone under different loading and unloading stress paths, such as constant axial pressure unloading confining pressure and loading axial pressure unloading confining pressure, were carried out. Particle Flow Code in 3 Dimensions (PFC3D) and Python were used to realize fluid-solid coupling, and numerical simulation calculations were performed along the test path to analyze the influence of the unloading rate on the fine-scale deformation mechanism and permeability characteristics of sandstone, and the relationship between crack type and permeability was obtained. A sandstone fracture mechanics model is established to analyze the stress concentration degree at the end of the branch crack of the test path. The results show that the rate of confining pressure unloading is inversely proportional to the strain. Additionally, permeability correlates with the principal stress difference in an exponential manner. Interestingly, the sensitivity of permeability to stress shows an inverse trend with the unloading rate of confining pressure. Furthermore, there exists a linear relationship between permeability and the number of cracks. During the unloading process, tensile cracks predominate, and the propagation of shear cracks lags behind that of tensile cracks. The proportion of tensile cracks decreases with the increase of the unloading rate when the axial pressure is unchanged but increases when axial pressure is added, resulting in axial compression deformation and expansion deformation along the unloading direction. These research outcomes offer theoretical insights for the prudent selection of mining rates, and they hold significant implications for mitigating water inrush disasters in deep mining operations. [ABSTRACT FROM AUTHOR]

Fracture in ductile materials often occurs in conjunction with plastic deformation. However, in the bond-based peridynamic (BB-PD) theory, the classic mechanical stress is not defined inherently. This makes it difficult to describe plasticity directly using the classical plastic theory. To address the above issue, a unified bond-based peridynamics model was proposed as an effective tool to solve elastoplastic fracture problems. Compared to the existing models, the proposed model directly describes the elastoplastic theory at the bond level without the need for additional calculation means. The results obtained in the context of this model are shown to be consistent with FEM results in regard to force-displacement curves, displacement fields, stress fields, and plastic deformation regions. The model exhibits good capability of capturing crack propagation in ductile material failure problems. [ABSTRACT FROM AUTHOR]

A large number of experimental studies have demonstrated that the permeability and damage of rock are not constant but rather functionally dependent on stresses or stress-induced deformation. Neglecting the influence of damage and permeability evolution on rock mechanics and sealing properties can result in an overestimation of the safety and stability of underground engineering, leading to an incomplete assessment of the risks associated with surrounding rock failure. To address this, the damage and permeability evolution functions of rock under compression were derived through a combination of experimental results and theoretical analysis, unifying the relationship between porosity and permeability in both porous media flow and fractured flow. Based on this, a fluid–solid coupled seepage model considering rock damage and permeability evolution was proposed. More importantly, this model was utilized to investigate the behavior of deformation, damage, and permeability, as well as their coupled effects. The model's validity was verified by comparing its numerical results with experimental data. The analysis results show that the evolution of permeability and porosity resulted from a competitive interaction between effective mean stress and stress-induced damage. When the effective mean stress was dominant, the permeability tended to decrease; otherwise, it followed an increasing trend. The damage evolution was primarily related to stress- and pressure-induced crack growth and irreversible deformation. Additionally, the influence of the seepage pressure on the strength, damage, and permeability of the investigated rock was evaluated. The model results reveal the damage and permeability evolution of the rock under compression, which has a certain guiding significance for the stability and safety analysis of rock in underground engineering. [ABSTRACT FROM AUTHOR]

In the present paper, we extend results recently given by Ciavarella et al. (J Mech Phys Solids 169:105096, 2022) to show some actual calculations of the viscoelastic dissipation in a crack propagation at constant speed in a finite size specimen. It is usually believed that the cohesive models introduced by Knauss and Schapery and the dissipation-based theories introduced by de Gennes and Persson-Brener give very similar results for steady state crack propagation in viscoelastic materials, where usually only the asymptotic singular field is used for the stress. We show however that dissipation and the energy balance never reach a steady state, despite the constant propagation crack rate and stress intensity factor. Our loading protocol permits a rigorous solution, and implies a short phase with constant specimen elongation rate, but then possibly a very long phase of constant or decreasing elongation, which differs from typical experiments. For the external work we are therefore unable to use the de Gennes and Persson-Brener theories which suggested that the increase of effective fracture energy would go up to the ratio of instantaneous to relaxed modulus, at very fast rates. We show viscoelastic dissipation is in general a transient quantity, which can vary by orders of magnitude while the stress intensity factor is kept constant, and is largely affected by dissipation in the bulk rather than at the crack tip. The total work to break a specimen apart is found also to be possibly arbitrarily large for quite a large range of intermediate crack growth rates. [ABSTRACT FROM AUTHOR]

Distortion-induced fatigue cracks at web gaps often occur in multi-girder steel bridges under vehicle loads. This paper presents full size digital simulations of steel girder bridges with different geometrical configurations, to explore the distortion-induced fatigue cracking performance. In the digital simulations, four geometrics are considered, in addition to two web gap details, namely the vertical stiffener web gap and the horizontal gusset plate web gap. Introducing multi-layer and multi-pass welds residual welding stress fields, digital fatigue simulation results show that the distortion-induced fatigue cracks at both web gaps are Mode I-II-III combined cracks dominated by Mode I. The coupling of the three modes is more prominent at the vertical stiffener web gap compared to the horizontal gusset plate web gap. In the skewed bridge, curved bridge, and skewed-curved bridge, the significant bending-torsional coupling effect, the structural asymmetry, and the stress deformation asymmetry cause an increment in distortion ranges, fatigue crack growth rates, and the proportions of Mode II and III cracks. The fatigue strength categories for vertical stiffener web gap and horizontal gusset plate web gap in straight, skewed, curved and skewed-curved bridges are category 125, 112, 110 and 110, and category 160, 140, 100 and 100 of the Chinese specification and Eurocode, respectively. Therefore, the geometrical configuration is an important factor affecting the distortion-induced fatigue behavior, which should be considered in the fatigue design and maintenance of steel girder bridges. [Display omitted] • Vertical stiffener web gaps show more prominent Mode I/II/III crack coupling. • Significant bending-torsional coupling effect increases fatigue crack growth rate. • Skew angle or/and horizontal curve radius reduce fatigue strength in two web gaps. [ABSTRACT FROM AUTHOR]

The ability of wood–plastic composites (WPCs) to withstand various loads and resist plastic failure is attracting more and more interest due to the global increase in demand for WPCs by over 6 million tons per year. Among the most important and innovative research methods are those based on fracture mechanics—their results enable material designers to optimize the structures of these hybrid polymer composites at the nano, micro and macro levels, and they allow engineers to more accurately evaluate and select functional, sustainable, long-lasting and safe product designs. In this study, standard single-edge notched bending (SENB) tests were used to analyze the fracture toughness of two different extruded WPCs along the longitudinal (L) and transverse (T) directions of extrusion. In addition to their resistance to crack propagation, critical fracture criteria, initial contact stiffness, fracture parameters and fracture surfaces, the mechanical properties of these composites were also investigated. The results showed that WPC-A coded composites withstood higher loads until failure in both directions compared to WPC-B. Despite the larger data spread, both types of composites were more resistant to crack propagation in the T direction. Mode II of crack propagation was clearly visible, while mode III was not as pronounced. The experimental results and the numerical finite element (FE) model developed up to 58% of the maximum load correlated well, and the obtained deformation curves were best approximated using cubic equations (R2 > 0.99). The shear stress zone and its location, as well as the distribution of the equivalent stresses, had a major influence on crack propagation in the fracture process zone (FZP). [ABSTRACT FROM AUTHOR]

• The failure behavior of prefabricated jointed granite is studied using triaxial cyclic loading. • The failure mode of non-persistent jointed rock masses depends more on the joint angle than the amplitude and frequency of the slight disturbance. • A formula is established to calculate a threshold above which a slight disturbance may induce fault-slip bursting. A slight disturbance can induce fault-slip burst failure in deep rock masses. In this paper, a series of triaxial tests were conducted to investigate the strength, deformation characteristics, and failure behavior of non-persistent jointed granite specimens subjected to slight cyclic loading. A representative stress–strain curve for non-persistent jointed rock was generated and used to study the crack evolution process (initiation → propagation → coalescence). The effects of varying the joint angle and frequency and amplitude of the disturbance were then analyzed. A theoretical (fracture mechanics) model for a non-persistent joint subject to triaxial cyclic loading was also established and used to investigate the combined effects of static confining stress and slight disturbances. Finally, the mechanical mechanism by which a slight dynamic disturbance induces fault-slip burst was discussed. Our results show that the failure mode of a non-persistent jointed rock mass depends more on the joint angle than the amplitude and frequency of the slight disturbance. The disturbance induces the initiation and extension of cracks. It can also induce fracture-slip bursting once the disturbance exceeds a certain threshold. The value of this threshold depends on the initial stress state, joint angle, length, dynamic and static friction coefficients, and fracture toughness of the rock. The study thus enriches our mechanistic understanding of the crucial ingredients involved in the triggering of fault-slip rock bursts in deep rock masses by slight disturbances. [ABSTRACT FROM AUTHOR]

The main cause of failure in bonded ceramic restorations is material fracture due to excessive stress concentration at the base of the prosthesis. The design of restorative functionally graded materials (FGM) could represent a major advance in dissipating mechanical stresses during occlusal contacts. The aim of this paper is to carry out a complete factorial design of finite element analyses to optimize a multilayer FGM introduced at the bottom of an overlay prosthesis. The number and thickness of layers vary within a spectrum compatible with ceramic shaping processes whereas Young's moduli variations are set in the range of dental tissues. For a 1.5-mm thick prosthesis, the optimal FGM configuration appears to be a 5 layers of 0.2 mm thickness with a linear distribution of Young's modulus from 30 to 70 GPa. This configuration was implemented in a 3D model of a restored tooth with realistic geometry to validate the proof-of-concept. [ABSTRACT FROM AUTHOR]

The plasticity and fracture properties of high-strength bolts are crucial to the mechanical behaviours of bolted connections subjected to extreme loadings. However, the material properties of high-strength bolts have not been comprehensively studied. This paper presents a collaborative experimental and numerical investigation to characterise the material plasticity and fracture properties of normal high-strength bolts (NBs) and weathering high-strength bolts (WBs) under monotonic tension. Eighteen cylindrical tensile coupons, cut from M20, M24 and M30 grade 10.9 NBs and WBs, are tested to capture the full-range engineering stress-strain relationships. The combined Swift-Voce weighting model is modified to describe and calibrate the material true stress-strain relationship of NBs and WBs. Then, a void-growth model (VGM) incorporated with the calibrated true stress-strain relationship is used to simulate the ductile fracture of tensile coupons. The calibration process collaborating experimental results and finite element (FE) simulations to obtain material parameters of high-strength bolts is demonstrated in detail. This collaborating method is further employed to simulate the plasticity and fracture properties of normal bolts with various grades under tension, as well as grade 10.9 high-strength bolts subjected to monotonic tension at elevated temperatures in literature. FE simulation results show a high accuracy with experimental results across all specimens, proving the rationality of the proposed method for material plasticity and fracture properties of high-strength bolts. • Tensile coupon tests are conducted on normal and weathering high-strength bolts. • The combined Swift-Voce model is used to calibrate the true stress-strain relationships of bolt materials. • The void growth model is calibrated to predict the tensile fracture of bolt materials. • The calibration process is suitable to common grade bolts and bolts at elevated temperatures. [ABSTRACT FROM AUTHOR]

Deep underground surrounding rock is often in the true triaxial stress state. Therefore, it is of great practical importance to recognize the short-term stress-strain relationship of progressive failure and the long-term characteristics of creep failure for the design, construction and maintenance of underground engineering in the true triaxial stress state. This paper aims to propose a feasible theoretical model to solve the problem of the constitutive relation and creep characteristics of rocks under true triaxial compression. Starting from the stress intensity factor, an angular parameter on the crack surface is introduced to characterize the true triaxial stress state. Then, the relationship between microcrack length and macroscopic strain is derived by various representations of rock damage, and then the constitutive relation during rock fracture is derived by combining it with the rock strength factor formula. Finally, the creep failure law of rocks is derived by introducing the relationship between the length of subcritical crack growth and time. The rationality of the theoretical model is verified by comparing theories and experiments. The effects of minimum principal stress, intermediate principal stress, and the crack inclination angle on the stress-strain relationship are analyzed, providing an important basis for selecting the stress state for long-term creep behavior. The analysis examines the relationship between creep failure time and principal stress, and discusses the effect of the crack angle on creep failure time and steady-state creep strain rate. [ABSTRACT FROM AUTHOR]

• Multi-physics calculations include electromagnetic eddy currents, heat flux, fluid dynamics, heat transfer, nonlinear mechanics. • Coupled analyses of the radial and angular stress distributions revealed that crack tip fields have no a separable solution. • CGR is interpreted in terms of elastic and plastic SIFs, affected by phase relation between mechanical loading and temperature. • An order of arrangement of isothermal and thermo-mechanical fatigue fracture diagrams of XH73M nickel-based alloy is found. In service-power engineering and aviation, gas-turbine engine structures are operated at elevated temperatures and under extensive variable mechanical loading, which is classified as thermomechanical fatigue (TMF). This coupling effect leads to flaw initiation and growth in components fabricated from thermally resistant nickel-based alloys. This paper presents experimental crack-growth data for isothermal pure fatigue, in-phase and out-of-phase TMF conditions. A crack-growth testing method is developed using inductive heating/forced convective cooling and direct crack-tip opening displacement techniques. The crack-growth experimental results are interpreted based on finite element analyses of the stress–strain rate fields at the crack tip under TMF conditions. Therefore, multi-physics numerical calculations are employed for the interaction of the heat loss from magnetic-field eddy currents with forced convective air cooling through a computer fluid dynamics model, which presents a nonuniform mechanical elastic–plastic stress distribution. Consequently, the dependence of the new nonlinear stress intensity factors on the crack length are obtained for each of the isothermal and thermomechanical cyclic deformation conditions. The polycrystalline XH73M nickel-based alloy tests performed show that, from the crack-growth acceleration viewpoint, the following order of arrangement of fatigue fracture diagrams is formed: isothermal pure fatigue, in-phase TMF, out-of-phase TMF, and isothermal pure fatigue at T = 400 °C and T = 23 °C. The differences and corresponding conclusions based on the interpretation of the experimental results of the crack growth rate characteristics at elevated temperatures in terms of elastic and nonlinear fracture resistance parameters are discussed. [ABSTRACT FROM AUTHOR]

The structural stability of engineering rock mass under dynamic disturbance is directly associated with the fracture mechanics properties in engineering practice. Fully understanding the rock's fracture mechanical behavior and crack evolution caused by stress concentration at the crack tip in engineering rock mass under dynamic load can offer useful insight into the rock's dynamic fracture mechanism. A dynamic test using split-Hopkinson pressure bar (SHPB) test system was performed on a single prefabricated fissure sandstone centrally cracked Brazilian disk (CCBD) specimens. Based on the theory of fracture mechanics and one-dimensional stress wave theory, the dynamic crack initiation criterion of CCBD specimen is proposed, and the regression model of sandstone's dynamic fracture toughness under the coupling effect of fissure angle and strain rate is established by using response surface methodology (RSM). The influence of strain rate and fissure angle on stress wave characteristics, dynamic tensile mechanical behavior, and fracture mechanics characteristic was investigated in this study. The findings demonstrate that: (1) The fissure angle plays a pivotal role in determining the failure mode of sandstone. As the fissure angle increases, three distinct failure modes emerge in the sandstone specimens, while variations in strain rate have minimal impact on the fracture mode of these specimens. (2) Alterations in the fissure angle result in changes to the waveform of transmitted waves. When the fissure angle is below 30°, the transmitted wave exhibits "double peak" characteristics; when it exceeds 30°, a "single peak" waveform is observed. This phenomenon can be attributed to diffraction principles governing incident waves. (3) When the impact pressure is 0.2 MPa, the peak load initially exhibits an increase followed by a decrease, with the peak load reaching its maximum at a fracture angle of 60°; when the impact pressures are 0.3 and 0.5 MPa, there exists a negative correlation between the peak load and the fissure angle. (4) The influence of strain rate on sandstone's fracture resistance is predominant, with alterations in fissure angle exerting an auxiliary effect on this property. The research results can provide a theoretical and experimental basis for dynamic disaster prevention in urban underground space. [ABSTRACT FROM AUTHOR]

This study determines the equivalent stress intensity factor (SIF) model that best fits the experimental behavior of low-carbon steel under mixed modes ( I and I I ). The study assessed Tanaka, Richard, and Pook's equivalent SIF models. The theoretical values used for comparison correspond to the experimental results in a modified C(T) geometry by machining a hole ahead of the crack tip subjected to fatigue loads with a load ratio of R = 0.1. The comparison involved the SIF for six experimental points and the values computed through the numerical simulation. The Paris, Klesnil, and Modified Forman–Newman crack growth models were used with each equivalent SIF to analyze the prediction in the estimated number of cycles. The Klesnil model showed the closest prediction since the error between the calculated and experimentally recorded number of cycles is the lowest. However, the material behavior reflects a reduced crack propagation rate attributed to plasticity in the crack tip. The results suggest that Asaro equivalent SIF conservatively estimates the element lifespan with increasing errors from 2.3% at the start of growth to 27% at the end of the calculation. This study sheds light on the accuracy and limitations of different equivalent SIF models, providing valuable insights for structural integrity assessments in engineering applications. [ABSTRACT FROM AUTHOR]

Residual stresses are usually not considered in engineering calculations of components and structures, however, they are present more or less in most of components, such as castings, welded components, components produced by rolling, bending, etc. The main objective of presented research is to determine the residual stresses in seamless thin-walled pipes, i.e. in ring specimens cut out from hot-rolled pipes. Pipe Ring Notched Bend specimens cut out from a pipe are considered as an alternative to the standardized Single Edge Notched Bend specimen used for determination of pipe material fracture toughness. In this research, residual stresses in ten ring specimens are measured by two methods: Incremental Hole Drilling Method (IHDM) and X-Ray Diffraction (XRD). Hoop residual stress is considered as the most important one in pipes. Principal stresses, as well as orientation of principal coordinate system, are determined by IHDM, and subsequently, hoop residual stress is calculated. Direct residual stress in hoop direction is measured by XRD. All results are shown on diagrams up to the depth of 1 mm from outer surface of each ring. Direct comparison of results referring to residual stresses obtained by both methods of measurement is presented to conclude that measurement with XRD shows uncertainty at some depths of measurement, since that method of measurement gives results with some large local oscillations. [ABSTRACT FROM AUTHOR]

• Shear behavior of reinforced concrete beams with inclined pre-cracks was studied. • Digital image correlation was used to analyze the crack growth and kinematics. • An explanation for the effect of inclined pre-cracks on shear capacity was given. • The effect of inclined pre-crack to failure mode was studied. Extended growth of existing cracks in reinforced concrete (RC) structures may negatively impact structural performance and cause great risks to structural safety. However, the influence of inclined pre-cracks on shear behavior of RC structures as well as the mechanism behind it are still unclear. In this paper, an experimental investigation is conducted in order to study the correlation between inclined pre-cracks and the shear behavior of RC beams without transverse reinforcement. Eight beams with identical geometric designs and different pre-cracking conditions were categorized into four series and successfully tested: (i) reference beams without pre-cracks, (ii) beams with pre-cracks in the bending span induced via loading, (iii) beams with pre-cracks in the shear span induced via loading, and (iv) beams with artificial pre-cracks in the shear span. The deformation and strain fields were measured by digital image correlation (DIC) technique with a strong focus on the shear-transfer mechanism and cracking propagation. The obtained results reveal that inclined pre-cracks in the bending span may not develop into the critical shear crack (CSC) and exert minor effects on the shear capacity. In contrast, pre-cracks near supports within the shear span tend to develop into the CSC and influence its path and kinematics. This further affects the activation of arch action and aggregate interlock, ultimately resulting in a 3–24% reduction in the load-bearing capacity of this series compared to the reference beams. To summarize, this study reveals the relationship between inclined pre-cracks and shear behavior of RC structures, providing new insight for assessment. [ABSTRACT FROM AUTHOR]

Several components of aeronautical motors and power plant stations are subjected to high temperatures, leading to creep deformation. It’s common practice to predict crack development in such components by using Continuum Damage Mechanics (CDM). Nevertheless, mesh dependency is a well-known issue in the classical CDM approach. The mesh sensitivity problem can be solved by using a nonlocal continuum approach. In the present study, in order to improve the numerical efficiency, a stress regime dependent creep model has been extended to a nonlocal model using a nonlocal theory from the literature. The nonlocal creep model was applied to a commercial finite element code, such as ABAQUS, with the help of user-defined routines (CREEP+USDFLD) to predict the load point displacement (LPD) and creep crack growth (CCG) for a compact tension (CT) specimen made of high creep strength 1CrMoV steel. A comparison between the results of the new nonlocal model and experimental data was made for verification. The mesh dependency of the new nonlocal model was investigated. The results indicate that the proposed nonlocal creep model demonstrates good mesh objectivity that was not feasible when considering the traditional local creep model. [ABSTRACT FROM AUTHOR]