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A Conductor on Round Core (CORC) cable wound with a high-temperature superconductor is an important cable concept for high-current density applications. It is widely used in large power systems because of its advantages of good flexibility and high engineering current density. However, the complex design structure of CORC cable makes it very difficult to understand its electromagnetic properties (such as AC loss). In particular, the different winding directions of each layer in multi-layer cable have a great influence on its electromagnetic characteristics. In this paper, the H-method is used to solve the electromagnetism and mechanics equations. The influence of the winding direction of CORC cable on its electromagnetic field distribution characteristics, AC loss, and mechanical variation under the action of external magnetic field is investigated. The AC loss study of single-layer cable reveals that when the applied magnetic field is increased from 0.01 to 0.02 and 0.03 T, the AC loss peak of the cable increases by 107 and 103 orders of magnitude, respectively, indicating that the effect of low applied magnetic field on the AC loss of the cable is more significant. For multi-layer cables, cables with opposite winding directions have a greater depth of current density penetration than cables with the same winding direction. In addition, the mechanical variations of multi-layer cables with different winding orientations are explored. The results show that the Mises stress in the cable with the same winding direction is about 32% higher than that of the cable with the opposite winding direction, which indicates that the method of winding the cable in the opposite direction between adjacent layers of tape can avoid excessive mechanical stress. [ABSTRACT FROM AUTHOR]

The Journal of Materials Science awards the annual Robert W. Cahn Prize to recognize the best paper published in the journal each year. The winner of the 2023 Cahn Prize is a research paper titled "Molecular modelling of graphene nanoribbons on the effect of porosity and oxidation on the mechanical and thermal properties." The paper presents molecular simulation models of graphene nanoribbons and examines the impact of porosity and oxidation on their mechanical and thermal conductivity properties. The paper is well-written and provides valuable insights for researchers in this field. Two other papers were selected as runners-up for the prize. All the monthly finalists for the Cahn Prize can be downloaded for free on the journal's website. [Extracted from the article]

[Display omitted] • Imidazole based AIE active molecular probe is synthesised. • The probe, weakly emissive in solution, exhibits excellent solid state emission. • In solid state, the probe exhibits reversible mechanochromism and acidochromism. • The mechanochromic property is employed to fabricate the rewritable papers. • Acidochromism is demonstrated on paper strips for use in real sample analysis. Stimuli modulated fluorescence properties of imidazole-based molecular probe (E)-2-(5,5-dimethyl-3-(4-(1,4,5-triphenyl-1H-imidazole-2-yl)styryl)cyclohex-2-en-1- ylidene)malononitrile (Ph-ISO) in the solid state is presented. Not only did the probe display aggregation induced emission (AIE) activity with intense solid-state fluorescence emission, but also exhibited several repetitive cycles of reversible mechanochromism as well as acidochromism. The solid-state emission is ascribed to the intermolecular interactions in the highly twisted conformation of Ph-ISO via multiple C–H---N and C–H---π interactions as confirmed by the single crystal X-ray analysis. The applied mechanical stress in the form of grinding results in the transformation of crystalline state to the amorphous state with a red shifted emission band attributed to attaining more planar conformation vs twisted conformation, with extended molecular conjugation. While reversible mechanochromism makes the probe suitable for rewritable papers, the switchable acidochromism is useful for the on-site monitoring of pH differences in biological and environmental media. [ABSTRACT FROM AUTHOR]

In this paper, a new Stroh formalism for gradient electro-mechanics is derived for the first time, which is both mathematically concise and numerically powerful, applicable to generally coupled anisotropic material systems. Based on this new formalism, the complicated Lamb wave in flexoelectric and piezoelectric plates is investigated. The dispersion equation is obtained by solving the eigenvalue problem along with the unconditionally stable dual-variable and position method. From the obtained dispersion equation, the dispersion curves and mode shapes of the Lamb wave are calculated by the 1D form of the multidimensional moduli ratio convergence method. Two important and interesting features are observed from our analysis: One is the difference in the mode shape symmetry between the piezoelectric and flexoelectric cases, and the other is the size-dependent property of the flexoelectric effect as observed by nondimensionalization. These features are further illustrated by comparing the dispersion curves and wave-mode shapes among the three different material models (purely piezoelectric, purely flexoelectric, and flexoelectric and piezoelectric coupled). The newly derived Stroh formalism offers a robust, concise, and unified approach for dealing with strain gradient electro-mechanic materials with crystal systems of general anisotropy. The present work also explains the physical mechanism of symmetry breaking observed, as induced by flexoelectric coupling in piezoelectric materials. [ABSTRACT FROM AUTHOR]

The Fenshui River Bridge is a steel–concrete composite girder bridge with a main span of 90 m. Due to the topographical constraints, the steel box girder was constructed without the use of auxiliary piers, employing incremental launching techniques. This article focuses on the construction technology used for the steel box girder of the Fenshui River Bridge. Firstly, using the influence matrix method, the cable force is determined based on the maximum cantilever state of the structure, with the vertical deformation of the front end of the guide beam and the horizontal deformation of the top of the tower as the control objectives. The unstressed cable length is then calculated based on the mechanical relationship between cable deformation and cable force. A calculation method for adaptive cable force is proposed, which is based on the variation of the stress-free cable length within the adaptive structural system. Next, the finite element analysis method was employed to determine the optimal layout position for the tower. The results indicate that during the incremental launching construction of the steel box girder, the calculated cable forces using the method proposed in this paper are in close agreement with the measured cable forces. At the maximum cantilever state of the structure, the calculated and measured values of the cable force resulted in a percentage difference of 3.96%. The calculated values of deformation and stress in key sections showed a percentage difference of 6.4% for deformation and 6.6% for stress. To maximize the effectiveness of the tower and cable, the tower should be positioned above the bridge pier when the guide beam crosses the maximum span. The findings of this paper can serve as a reference for the construction of similar types of bridges. [ABSTRACT FROM AUTHOR]

This paper introduces a metamodelling technique that employs gradient-enhanced Gaussian process regression (GPR) to emulate diverse internal energy densities based on the deformation gradient tensor F and electric displacement field D 0 . The approach integrates principal invariants as inputs for the surrogate internal energy density, enforcing physical constraints like material frame indifference and symmetry. This technique enables accurate interpolation of energy and its derivatives, including the first Piola-Kirchhoff stress tensor and material electric field. The method ensures stress and electric field-free conditions at the origin, which is challenging with regression-based methods like neural networks. The paper highlights that using invariants of the dual potential of internal energy density, i.e., the free energy density dependent on the material electric field E 0 , is inappropriate. The saddle point nature of the latter contrasts with the convexity of the internal energy density, creating challenges for GPR or Gradient Enhanced GPR models using invariants of F and E 0 (free energy-based GPR), compared to those involving F and D 0 (internal energy-based GPR). Numerical examples within a 3D Finite Element framework assess surrogate model accuracy across challenging scenarios, comparing displacement and stress fields with ground-truth analytical models. Cases include extreme twisting and electrically induced wrinkles, demonstrating practical applicability and robustness of the proposed approach. [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]

This paper aims to derive the motion equations for a small-scale flexoelectric-multilayer plate and move deep through its vibrational response to several determining variable variations. Flexoelectricity indicates the electrical polarization induction in response to the non-uniform strain gradient. As moving toward small scales, the importance and the role of this property comes more to the picture. The under-examination structure is fabricated of three layers; a mid-layer which is assumed to be composed of the porous exponential and power law-functionally graded materials, two flexoelectric face sheets, and the Vlasov foundation. The motion equations are derived mathematically based on the new EP of porous material, Hamilton's principle, and modified couple stress theory. Utilizing the new EP power law besides evaluating the influence of the variables, length scale parameter, materials composition, geometrical characteristics, porosity, foundation parameter, and boundary conditions (B.C.s) on the dimensionless natural frequency (DNF) of such a sandwich model is the novelty of this paper. It is revealed that the lateral ratio enhancement causes DNF and stiffness reduction in the model. Furthermore, among all considered B.C.s, simply support and clamped support refer to the lowest and the highest DNF, respectively. The content of the recent paper serves as a good source to provide a better understanding of the vibrational response of high stiffness-to-weight ratio structures to different variable variations. [ABSTRACT FROM AUTHOR]

Under various stress paths, the deformation characteristics represented great differences. In this paper, a series of cyclic triaxial tests have been conducted with Fujian standard sand. By comparing the constant deviatoric (CDS) and constant axial stress paths (CAS), the influence mechanism of the cyclic amplitude of the deviatoric stress was discussed. The test results showed that the stress path significantly influenced the volumetric and shear strains. The increasing and decreasing trend in the volumetric strain (ɛv) was consistent with the spherical stress (lnp). Compared with the two stress paths, the slope of the ɛv−lnp curve during the loading and unloading stages was larger under the CAS path. In the CDS path, qc almost did not affect the cumulative volumetric strain, and in the CAS path, the effect was obvious. The shear strain curve was in accordance with the direction of the stress path. As the cyclic number increased, the shear strain gradually accumulated. The shear strain accumulation under the CAS path was larger. The shear strain largely depended on the relative position between the critical state line (CSL) and the stress state of the soil during cyclic loading and unloading. Practical Applications: In practical engineering, the soil will experience various stress paths. For example, in slope or earth–rock dam engineering, where the water level rises and falls repeatedly, the soil often goes through the stress path of constant deviational stress with the cyclic increase and decrease in the spherical stress. In foundation pit engineering, the soil often experiences the stress path of the constant axial stress (CAS) with cyclic loading and unloading of the lateral stress. The stress path greatly influences the deformation and strength of soil. Therefore, the previous two stress paths are compared in this paper to discuss the influence of the cyclic amplitude of deviatoric stress. Under three different consolidation states, the cyclic amplitude of the deviatoric stress significantly influenced the volumetric and shear strains. The shear strain largely depended on the relative position between the critical state line (CSL) and the stress state of the soil during cyclic loading and unloading. Therefore, in practical engineering, if the stress path in the experiment differs from the actual value, the influence of the stress path should be properly considered. The results should be modified according to the degree of influence of each stress condition. [ABSTRACT FROM AUTHOR]

In this paper, the thickness debit and stress concentration effects of a nickel‐based directionally solidified superalloy were investigated through strain‐controlled low cycle fatigue (LCF) and creep–fatigue interaction (CFI) experiments. Compared to the fatigue lives of solid specimens provided in the existing literature, the results of this paper indicate that when the wall thickness of the specimen is reduced from 5 to 1.125 mm, the fatigue life with different strain amplitudes decreases by about 45%. When film‐cooling holes (FCHs) are introduced into the hollow specimens, the fatigue life is further reduced by about 25%. Based on the observation of the scanning electron microscope (SEM), the formation mechanisms of the thickness debit and stress concentration effects under LCF and CFI loads were revealed. Subsequently, two parameters, the “wall‐thickness coefficient” and “hole coefficient,” were proposed to establish a new fatigue life prediction method. [ABSTRACT FROM AUTHOR]

Capacitive and optical-based pressure sensors are considered for wide application in industries and R&D labs due to their superior performance. In general, these sensors use a diaphragm as a sensing element that needs to be designed accurately to achieve the desired level of accuracy for a higher operating range of the sensor. To design such a diaphragm, the conventional strain-based model cannot be used efficiently as the strain gradient starts dominating to introduce non-linear deformation with respect to the applied load when the diaphragm thickness reduces or the operating range increases beyond a certain value. Thus, there is a need to establish a comprehensive understanding and accurate modeling method to establish the underlying mechanism of the strain gradient. In view of this, a finite element analysis is carried out with moving-mesh to investigate the effect of the strain gradient phenomenon extensively in this paper. For the investigation, a few parameters are studied such as strain, strain gradient, bending rigidity, and deflection. It shows that the strain gradient spreads radially on the diaphragm and its zone of influence depends on the thickness as well as the applied pressure. This increases the bending rigidity significantly and the diaphragm deflection becomes non-linear as compared to the classical theory of bending. For validation of the present model, the bending rigidity and the deflection behavior are also compared with an earlier developed mathematical model as well as experimental results, and the same is discussed in this paper. The present work is useful for an accurate design and optimization of a diaphragm or a flexure for small size or/and higher operating range of pressure sensors and actuators. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to compare and evaluate the influence of package designs and characteristics on the mechanical reliability of electronic assemblies when subjected to harmonic vibrations. Design/methodology/approach: Using finite element analysis (FEA), the effect of package design-related parameters, including the interconnect array configuration, i.e. full vs perimeter, and package size, on solder mechanical stresses are fully addressed. Findings: The results of FEA simulations revealed that the number of solder rows or columns available in the array, could significantly affect solder stresses. In addition, smaller packages result in lower solder stresses and differing distributions. Originality/value: In literature, there are no papers that discuss the effect of solder array layout on electronic packages vibration reliability. In addition, general rules for designing electronic assemblies subjected to harmonic vibration loadings are proposed in this paper. [ABSTRACT FROM AUTHOR]

Deep rock are often in a true triaxial stress state. Studying the impacts of varying unloading speeds on their strain energy (SE) density is highly significant for predicting rock stability. Through true triaxial unloading principal stress experiments and true triaxial stress equilibrium unloading experiments on sandstone, this paper proposes a method to compute the SE density in a true triaxial compressive unloading principal stress test. This method aims to analyze the SE variation in rocks under the action of true triaxial unloading principal stresses. Acoustic emission is used to verify the correctness of the SE density calculation method in this paper. This study found that: (1) Unloading in one principal stress direction causes the SE density to rise in the other principal stress directions. This rise in SE, depending on its reversibility, can be categorized into elastic and dissipated SE. (2)When unloading principal stresses, the released elastic SE density in the unloading direction is influence by the stress path and rate. (3) The higher the unloading speed will leads to greater increases in the input SE density, elastic SE density, and dissipative SE density in the other principal stress directions. (4) The dissipated SE generated under true triaxial compression by unloading the principal stress is positively correlated with the damage to the rock; with an increase in unloading rate, there is a corresponding increase in the formation of cracks after unloading. (5) Utilizing the stress balance unloading test, we propose a calculation method for SE density in true triaxial unloading principal stress tests. [ABSTRACT FROM AUTHOR]

Tunnel excavation induces the stress redistribution of the surrounding rock. Structural cracks may develop in the secondary lining due to this stress redistribution and bias pressure, consequently affecting the overall construction safety of the tunnel. This paper aims to achieve real-time monitoring of the excavation stability of the lining structure by integrating two monitoring technologies: structural deformation monitoring and fiber grating strain monitoring. Additionally, it proposes a method to simultaneously measure the thermal strain and applied stress–strain of the structure. By analyzing the displacement and deformation of the lining structure, its stability can be preliminarily evaluated in the short term. To achieve long-term real-time monitoring and a more accurate assessment of the tunnel structure's stability, the paper introduces fiber Bragg grating (FBG) strain sensor monitoring technology. First, based on the geological stratigraphy information obtained from the exploration, a simulation model of the tunnel under different section bias angles is established. The displacement and stress concentration areas of the lining structure are then analyzed to optimize the sensor deployment array and provide a theoretical basis for the sensor arrangement. FBG strain sensors are installed on the surface of the structure to measure thermal strain and loading stress–strain, whereas FBG temperature sensors measure local temperature. The findings indicate that following tunnel excavation, the maximum daily strain differences at K107+043 and K107+240 were 126.87 µ ε and 209.38 µ ε , respectively. After a period of rock disturbance, the average daily strain differences due to applied stress–strain were 16.8 µ ε and 12.65 µ ε , respectively. The thermal strain was close to the daily strain difference. Therefore, after the rock disturbance subsided, the strain fluctuations in the lining structure were mainly caused by local temperature changes, and the surrounding rock tended to stabilize. This offers a viable method for evaluating structural stability post-tunnel excavation. [ABSTRACT FROM AUTHOR]

Twinning is an important deformation mechanism for magnesium alloys, which has a significant impact on the texture evolution and mechanical properties. Pre-twinning deformation has been considered as an effective method for texture regulation. For each twinning mode, there are six crystallographically equivalent variants. Properly identifying the activated twin and understanding its variant selection criteria are essential for the development of high-performance magnesium alloys. As summarized in this paper, the observed twin variant by the commonly employed electron backscatter diffraction technique can be identified by several approaches, including misorientation analysis, trace analysis and matrix method. Schmid factor analysis was commonly performed to explain the selection of twin variants. To broaden the application scope under complex stress state, a generalized Schmid factor was derived by introducing a stress tensor. The efficiency of Schmid criteria to assess twin variant selection was confirmed to be influenced by the type of the applied stress. To consider the local effect on twin activation, in particular twin-twin transfer and slip-induced twinning, displacement gradient tensor calculation and geometrical compatibility factor analysis have been employed. It was demonstrated that local strain accommodation played a critical role in selecting the variants of cross-boundary twins in magnesium alloys. Assisted with crystal plasticity finite element modeling, the resolved shear stress on twinning and a composite Schmid factor combining the global Schmid factor and geometrical compatibility factor were obtained to better explain the activated twin variants in magnesium alloys. All the above-mentioned Schmid law based criteria and some energy based criteria as well are summarized in this paper. Their applications in evaluating twin variant selection in magnesium alloys are critically reviewed and discussed. [ABSTRACT FROM AUTHOR]

The carbon/glass hybrid rod exhibits high tensile strength, light weight, and strong corrosion resistance. However, the bottleneck of interlayer splitting exists in the interlayer hybrid rod, severely impeding safe operation. To solve the problem of rod splitting, this paper proposed a new scheme of an intralayer carbon/glass hybrid rod. Based on the material constitutive model, a full‐scale simulation model was developed. The stress distribution and deformation of the hybrid rod were analyzed and the progressive damage mechanism of the hybrid rod was explained. The results indicated that, for the intralayer carbon/glass hybrid rod, (a) the ultimate experimental tensile load witnessed a significant increase, rising by 14.0% from 452.4 to 515.7 kN compared to the interlayer hybrid rod; (b) the numerical model predicted the tensile load of 525.9 kN, with an error of 1.9% compared to the test result, meeting engineering accuracy requirements; (c) the elastic deformation stage saw a 146.7% increase from 280.2 to 691.3 MPa in the maximum axial stress of the carbon‐fiber layer, and a 120% increase from 89.8 to 198.0 MPa in the maximum radial stress of the glass fiber layer as the tensile displacement increased from 0.16 to 0.32 mm. In conclusion, the intralayer carbon/glass hybrid rod proposed in this paper can significantly improve the tensile strength compared to the interlayer hybrid rod, which can accelerate the application of carbon/glass hybrid rods in oil and gas fields. Highlights: According to the problem of interlayer splitting in the interlayer carbon/glass hybrid rods, a novel scheme of an intralayer carbon/glass hybrid rod was proposed.Based on the material constitutive model, a full‐scale simulation model of an intralayer carbon/glass hybrid rod was developed to analyze the stress distribution and deformation response under tensile load.The dynamic progressive damage analysis method for intralayer carbon/glass hybrid rods was proposed to reveal the damage evolution mechanism. [ABSTRACT FROM AUTHOR]

In this paper, we have studied the behaviour of two symmetric mode-III collinear cracks in a functionally graded material (FGM). The fundamental goal of this paper is to provide insight on the interaction of two cracks in FGMs with the strain gradient effect. To assess the influence of gradient elasticity, we have considered two key parameters ℓ and ℓ ′ , which describe the size scale effect caused by the underlying microstructure and are related to volumetric and surface strain energy, respectively. The crack boundary value problem have been solved by the approach involving Fourier transforms and the innovative hyper-singular integro-differential equation method, where the integral equation contains the two terms in integrals for the both cracks. A system of equations has been constructed by employing the Chebyshev polynomial expansion and then by choosing the suitable collocation points the system of equation have been solved. Our investigation involves the determination of stress intensity factors at both crack tips. These factors are vital for understanding the material's fracture behavior and structural integrity. Furthermore, we explore the variations in the displacement profile when the distance between the cracks is reduced to close proximity. This particular scenario is of significant interest as it provides insights into how the interaction between the cracks impacts the overall structural response. [ABSTRACT FROM AUTHOR]

Seismic faults are known to exhibit a high level of spatial and temporal complexity, and the causes and consequences of this complexity have been the topic of numerous research works in the past decade. In this paper, we investigate the origins and the structure of this complexity by considering a numerical model of laboratory earthquake experiment, where we introduce a fault with homogeneous mechanical properties but allow it to evolve spontaneously to its natural level of complexity. This is achieved by coupling the elastic deformability of the off‐fault medium (and therefore allowing for heterogeneous stress fields to develop) and the discrete degradation and gouge formation at the fault plane (and therefore allowing for structural heterogeneity to develop). Numerical results show the development of persistent stress, damage, and gouge thickness heterogeneities, with a much larger variability in space than in time. Strong positive correlations are found between these quantities, which suggest a positive feedback between local normal stress and damage rate, only mildly mitigated by the mobility of the granular gouge in the interface. For a wide range of confining stresses, after a sufficient number of seismic cycles, the fault reaches a state of established disorder with a constant roughness, a certain amount of periodicity at the millimetric scale, and a power law decay of the Power Spectral Density at smaller spatial scales. The typical height‐to‐wavelength ratio of geometrical asperities and the correlations between stress and damage profiles are in good agreement with previous field or lab estimates. Plain Language Summary: Earthquakes occur on faults in the Earth curst, and these faults are known to be highly complex, both from a geometrical and structural point of view. This complexity is now introduced artificially in many numerical and theoretical models of faults in order to derive meaningful knowledge related to earthquake mechanics. There is little knowledge, however, about the way this complexity develops. In this paper, we employ a numerical model to observe the spontaneous development of this complexity, in order to understand its origin, its structure, and its evolution. Key Points: A coupled discrete‐continuum model of laboratory earthquakes allows the spontaneous development of fault complexity along seismic cyclesFault heterogeneity is persistent in space and time, with a strong positive correlation between normal stress, damage, and gouge thicknessStress fields exhibit a millimetric periodicity and a self‐affinity at smaller scales, in quantitative agreement with previous estimates [ABSTRACT FROM AUTHOR]

In order to explore the flexural behavior of a concrete sandwich panel under concentrated boundary conditions, based on Kirachhoff's elastic thin plate theory in this paper, the geometric deformation, physical conditions, and equilibrium relationship of a sandwich panel are deduced by constructing the layered analysis model of the sandwich panel, the basic differential equation of the flexural deformation of the concrete sandwich thin plate is obtained, and the mathematical expression of the internal force and displacement under the boundary condition of concentrated support is given. Combined with an engineering example, the proposed calculation method is verified. The results show that, in the arrangement of reliable connectors for concrete sandwich panels, the concrete wythes bear the load while the contribution of the core layer to the bending capacity of the structure can be ignored. When subjected to a laterally distributed load, the sandwich panel mainly experiences out-of-plane bending deformation, and the bending normal stress in the concrete panel layer shows a linear non-uniform distribution along the thickness direction of the panel. The bending deformation performance and bearing efficiency of a concrete sandwich slab with the change in concentrated support position have significant effects, and the load transfer efficiency can be improved by optimizing the arrangement of supports. Except for small local areas near the supports, the bending stress distribution and deformation behavior of the concrete sandwich panel can be accurately analyzed by the calculation method established in this paper. [ABSTRACT FROM AUTHOR]

The aim of this paper is to propose an experimental procedure for determining the characteristic length of a strain gradient model. The identification problem is studied through a virtual pull-out test of a rigid bar along the symmetry axis of a cylindrical strain gradient elastic domain. To allow an accurate parameter identification based on measured data, we investigate the effect of the characteristic length on the mechanical fields for this problem. We see a significant sensitivity of the inflection point of the displacement profile evaluated on the cross section of the cylinder, with respect to the characteristic length. By adjusting the characteristic length of the strain gradient such that the theoretical models match best with experimental measurements of the surface displacement fields, the characteristic length of the strain gradient can be estimated. In order to allow for more efficient analysis and an almost real-time parameter identification, the initial three-dimensional (3D) problem is reduced to a one-dimensional (1D) problem by exploiting the cylindrical symmetry of the problem. As will be shown, an accurate 1D finite element method (FEM) strain gradient solution can be obtained for this simplified problem. Since the cylindrical symmetry is only true in an infinitely long cylinder, specific boundary conditions are constructed on a cylinder of finite length, which is then used for the comparison of the 1D and 3D problems. Results show, however, that the structural response at the inflection point is insensitive to whether the specific boundary conditions are considered or not, which is why the 1D model can be used for parameter identification. Since the proposed approach is methodological, it can be applied to any material. As a prototype problem in this paper, we consider the case of a bar embedded in Portland cement concrete. [ABSTRACT FROM AUTHOR]

This study focuses on the area of large deformation of soft rocks across the fault in Dongmachang China to investigate support methods for fractured surrounding rocks Negative Poisson's Ratio (NPR) anchor cable support. The research employs field monitoring, 3D physical model experiments, and numerical simulations. The results show that: (1) the maximum settlement displacement of the Dongmachang Tunnel section with original support can reach about 476 mm and has an upward trend, the limit of initial branch intrusion is 41.2 cm, and the width of invert joint is 5–50 mm; (2) the dynamic impact experiment of NPR anchor cable shows that the NPR anchor can withstand several impacts, the maximum cumulative impact deformation within the range of constant resistance is 500–1,000 mm, and the impact resistance is strong; and (3) NPR anchor cable can effectively control the large deformation disaster of surrounding rock in the fault fracture zone of Dongmachang Tunnel, basically ensuring that the deformation of the surrounding rock is below 300 mm, and the control effect is good. These findings suggest that NPR anchor cables are effective for controlling large deformations in tunnels constructed through soft rock across faults and provide a scientific basis for implementing new support systems for other similar tunnels. At present, the international support of deep-buried underground engineering still takes the new Austrian method as the mainstream, but the core idea of the new Austrian method is passive support, which often cannot effectively support the deep-buried soft rock with high stress and large deformation. This paper takes the anchor cable with high preload (350 kN) as the core and the excavation compensation method proposed by Academician He Manchao as the starting point, and innovatively supports the deep-buried soft rock large deformation tunnel, which provides a new idea for the support of other deep-buried underground projects. Although this paper studies the support effect of negative Poisson's ratio (NPR) cable compensation mechanics from the perspectives of laboratory test, physical model experiment, and numerical simulation, because the tunnel has not yet been started, it has not been studied from the perspective of field application. The support effect of NPR anchor cables on surrounding rock in the fracture zone needs further study. [ABSTRACT FROM AUTHOR]

This paper presents the results of the study of stress relaxation fields, deformation, and temperature of the system of nanostructured multilayer coatings. In the work, a nonlinear relationship between strain and stress was used to take into account nonlinear effects in the mechanism of nanostructure formation. The paper assumes that a friction surface is provided by the self-organization of shear components: both stress and strain on the one hand, and temperature on the other. The studied objects are described in the adiabatic approximation, taking into account the fact of the evolution of stresses and strains. With the help of phase portraits of the system, the dependence of the deformation processes on the stresses arising in the system without coating and with coating is shown. It is shown that the rate of change of deformation depends on the characteristics of the mechanical impact on the coating and on the amount of stress and deformation. A conclusion is drawn regarding the transition process in the presence of two regions (Hooke and plastic deformation) in the corresponding phase portrait of the strain–stress field of the system. The results of the work can be used to determine the effective parameters of a coating in the analysis of experimental time dependences of stresses. [ABSTRACT FROM AUTHOR]

The paper presents an analysis of the low-cycle fatigue (LCF) properties of C45, X20Cr13, and 34CrNiMo6 steels subjected to various heat treatment processes. Strain-controlled LCF tests were carried out with a total cyclic strain amplitude equal to 0.5, 1 and 1.5%. Fatigue life, cyclic stress-strain behavior and hardness were analyzed. Qualitative and quantitative relationships between material LCF properties resulting from the heat treatment processes, were related to the indentation force P*, which was derived experimentally by applying an instrumented indentation procedure with the use of the Vickers indenter. The proposed parameter P* and its changes ΔP* seem to be promising for the identification of the structural stress parameter σ* that is necessary for deriving values of the fatigue strength coefficients σf' corresponding to different tempering temperatures. The common feature of all steels analyzed in this paper is that the elastic parts of the strain-life characteristics remain parallel after being subjected to different tempering temperatures. [ABSTRACT FROM AUTHOR]

Underground reservoirs in coal mines, consisting of goafs (By goaf, we mean the space that remains underground after the extraction of valuable minerals), are commonly utilized for mine water storage and drainage, with their primary load-bearing structures being the "roof–coal pillar" systems. Consequently, this structure must endure the repeated immersion behavior resulting from fluctuations in the mine water level, resulting in the risk of geological disasters. This paper analyzes the variation in mechanical properties of sandstone–coal composite samples after repeated immersion cycles through axial loading tests. The results indicate that the water content of the sample exhibits a notable and rapid increase with each successive immersion cycle. This corresponds to a decrease in the stress threshold and modulus parameters of the samples. Moreover, the acoustic emission signals serve as indicators of the softening characteristics of the samples. With the increase in immersion cycles, there is an augmentation in both the frequency and extent of shear cracks. The non-linear failure characteristics of the samples become more pronounced. Consequently, water significantly weakens the cementing material between rock grains. Both sandstone and coal display a decrease in deformation resistance capabilities at a macroscopic level. The constitutive model of the composite sample was improved based on the degradation characteristics of mechanical strength and strain energy parameters, which offers enhanced accuracy in analyzing the degradation process caused by water immersion. This paper offers a crucial theoretical foundation for comprehending the deterioration evolution characteristics of the "roof–coal pillar" bearing structure affected by repeated immersion. [ABSTRACT FROM AUTHOR]

Shallow-buried cavities and underground structures are inevitably subjected to transient perturbation from earthquakes or engineering activities during their life circle, leading to the occurrence of dynamic failure. The investigation presented by this paper concentrates on the dynamic responses triggered by an aperiodic transient P wave around a circular lined tunnel with an imperfect interface in a half-space and the spring model is employed to describe the interface between rock mass and liner. Resorting to the wave function expansion scheme, the large arc assumption, the Graf's addition theorem and the numerical inversion algorithm of Laplace transformation, the dynamic responses around a circular shallow lined tunnel with an imperfect interface are evaluated theoretically. The good agreement of time–history curves and contour snapshots for stress between the theoretical solutions and the numerical counterparts validates the analytical scheme. The effect of disturbance direction, embedment depth, thickness of liner and interface coefficients on the dynamic responses around the shallow-buried lined tunnel is analyzed. The results indicate that the positions of peak hoop dynamic stress concentration factor (DSCF) are approximately perpendicular to the perturbation direction. The DSCF distributions converge to be stable when the ratio of embedment depth to excavation radius exceeds 10.0. The thickness of the liner mainly affects the dynamic responses around the interface. Increase of elastic coefficient induces a decreasing DSCF in rock mass and an increasing counterpart in the liner. The results may provide the theoretical basis for the transient responses and aseismic design of underground tunnels. [ABSTRACT FROM AUTHOR]

The Accelerated Pseudo-Transient (APT) method is a matrix-free approach used to solve partial differential equations (PDEs), characterized by its reliance on local operations, which makes it highly suitable for parallelization. With the advent of the memory-wall phenomenon around 2005, where memory access speed overtook floating-point operations as the bottleneck in high-performance computing, the APT method has gained prominence as a powerful tool for tackling various PDEs in geosciences. Recent advancements have demonstrated the APT method's computational efficiency, particularly when applied to quasi-static nonlinear problems using Graphical Processing Units (GPUs). This manuscript presents a comprehensive analysis of the APT method, focusing on its application to quasi-static elastic, viscoelastic, and coupled hydro-mechanical problems, specifically those governed by quasi-static Biot's poroelastic equations, across 1D, 2D, and 3D domains. We systematically investigate the optimal numerical parameters required to achieve rapid convergence, offering valuable insights into the method's applicability and efficiency for a range of physical models. Our findings are validated against analytical solutions, underscoring the robustness and accuracy of the APT method in both homogeneous and heterogeneous media. We explore the influence of boundary conditions, non-linearities, and coupling on the optimal convergence parameters, highlighting the method's adaptability in addressing complex and realistic scenarios. To demonstrate the flexibility of the APT method, we apply it to the nonlinear mechanical problem of strain localization using a poro-elasto-viscoplastic rheological model, achieving extremely high resolutions – 10,0002 voxels in 2D and 5123 voxels in 3D – that, to our knowledge, have not been previously explored for such models. Our study contributes significantly to the field by providing a robust framework for the effective implementation of the APT method in solving challenging geophysical problems. Importantly, the results presented in this paper are fully reproducible, with Matlab, symbolic Maple scripts, and CUDA C codes made available in a permanent repository. [ABSTRACT FROM AUTHOR]

The flexoelectric effect describes phenomena where strain gradients induce electrical polarization and electric field gradients cause strain in materials. This specific type of electromechanical coupling effect is remarkable for being independent of material symmetry, Curie temperature, and it exhibits notable effects in small‐sized materials. The study of flexoelectric effects has provided fresh insights into materials science, particularly highlighting how thin‐film structures, with their unique geometrical and dimensional attributes, are highly responsive to flexoelectric influences, thereby offering significant opportunities for modulating electrical properties. Herein, this paper presents the fundamental concepts and theories underlying the flexoelectric effect are presented. Various methods for inducing this effect in thin films are explored, including the optimization of growth and deposition conditions, and the application of external mechanical stresses to create strain gradients. Additionally, recent advances in utilizing the flexoelectric effect to modulate ferroelectric domains, modify properties of thin films, and enhance functionalities in photovoltaic systems, nanogenerators, sensors, and actuators are reviewed. Finally, the challenges and future prospects for flexoelectric effects in advanced electronics are briefly presented. [ABSTRACT FROM AUTHOR]

Using salt caverns for the Underground Hydrogen Storage (UHS) is a promising means to address climate change and the energy crisis. However, the complex Thermal-Hydro-Mechanical (THM) coupling problems existing in the UHS salt caverns pose a challenge to the safe and efficient storage of hydrogen. In this paper, a coupled THM model which considers the thermodynamic properties of hydrogen, the thermal expansion and creep of the surrounding rock, and the hydrogen seepage was proposed. The model was validated by the results of a field test and a numerical simulation. A numerical model was established to analyze the stability and tightness of the UHS cavern in bedded salt rock under different Frequencies of Hydrogen Injection and Withdrawal (FHIW). The results show that with the increase of the FHIW, there is an increase in the variation ranges of pressure and temperature. The distributions of the von Mises stress, the first principal stress and the effective creep strain suggest that the risk of failure induced by creep and tensile is more significant at the interface of the salt rock and interlayer on the cavern wall. Additionally, the displacements, Volume Loss Rate (VLR), and hydrogen loss ratio of the cavern all increase with the increase of FHIW, and the maximum displacement of the cavern is found at the roof. The interlayer is the main channel for hydrogen leakage, and the existence of the "seepage step" and "seepage peak" indicates that frequent injections and withdrawals primarily impacts the region close to the cavern. [Display omitted] • A novel coupled thermal-hydro-mechanical model for hydrogen storage in salt cavern was proposed. • The stability and tightness of the cavern under different frequencies of hydrogen injection and withdrawal were analyzed. • The risk of failure induced by creep and tensile is more significant at the interface of the salt rock and interlayer. • The injection and withdrawal of hydrogen will produce the "seepage step" and "seepage peak", respectively. [ABSTRACT FROM AUTHOR]

The viability of hydrogen storage in bedded salt caverns hinges on understanding the geomechanical challenges posed by the anisotropic stress states and complex geology of such environments. This study presents a comprehensive geomechanical analysis focusing on a proposed cavern within the Carribuddy Formation in Western Australia, characterized by its interbedded salt layers. This paper introduces a new geomechanical workflow, encompassing 1D and 3D modeling techniques to provide detailed changes of mechanical properties and stress state in interbedded salt formation allowing to identify the initial optimal operational pressures for underground hydrogen storage. Initial 1D models evaluated mechanical properties and in-situ stresses, while subsequent 3D simulations, enriched by data from neighboring wells, detailed the stress, strain, and displacement responses of the cavern walls to internal pressure changes. The analysis pinpointed an initial safe gas pressure range between 3000 and 4000 psi, attributing this margin to the robust characterization of the mechanical and in-situ stress of the formation. Our findings underscore the significance of high-resolution geomechanical modeling in identifying initial optimal operational pressures for hydrogen storage in salt caverns, ensuring both safety and structural integrity. • Integrated 1D and 3D models assess hydrogen storage in salt caverns. • Cavern within Carribuddy Formation exhibits initial safe pressure of 3000–4000 psi. • High-resolution models are crucial for understanding geomechanical behavior. • Study emphasizes the formation's robustness and stress resilience. • Findings guide optimal operational pressures for safety and integrity. [ABSTRACT FROM AUTHOR]

The majority of atomic force microcode (AFM) probes work based on piezoelectric actuation. However, some undesirable phenomena such as creep and hysteresis may appear in the piezoelectric actuators that limit their applications. This paper proposes a novel AFM probe based on dielectric elastomer actuators (DEAs). The DE is modeled via the use of a hyperelastic Cosserat model. Size effects and geometric nonlinearity are included utilizing the modified couple stress theory and the von-Kármán strains. A non-contact interaction condition is adopted for AFM, which is taken into account via the van der Waals force. Governing equations are derived employing Hamilton's principle, and a reduced model is obtained using an extended Galerkin scheme. The free vibration of the system is formulated when a static voltage is applied to the elastomer. The forced vibration is then formulated when the system is under a combination of static and dynamic voltages. The ordinary differential equations of the free and forced vibrations are numerically and analytically solved by the backward differentiation method and multiple time scales method, respectively. Results are presented in time histories, phase portraits, Poincaré maps, fast Fourier transforms, and frequency amplitude curves. Overall, the obtained information displays that the system undergoes quasiperiodic and periodic motions. Moreover, the resonant response of the DE-based AFM is softening-type. [ABSTRACT FROM AUTHOR]

This paper presents a modified relationship between small and large strain convergence by applying a small (residual) dilation angle, which behaves accurately for rock mass with the strain-softening behavior and complex dilatancy model. The modified relationship extends its applicability to a more general two- and three-dimensional excavation problems than previous study, irrespective of the constitutive behavior and rock dilatancy. On this basis, the longitudinal displacement profile (LDP) considering finite-strain is proposed, which can be corrected simply from the small strain analysis or obtained according to the actual parameters related to large deformation. The capability of the finite-strain LDP for estimating large convergences during tunnel advancement is verified by several comparisons with the existing numerical simulation and theoretical analysis results. The developed finite-strain LDP is promising to improve the convergence − confinement method when it applied to the rock-support interaction analysis in problems involving large deformation. The applicability of the displacement-release coefficient obtained from the small strain analysis for quantifying the stress relief to squeezing ground conditions is also investigated. Highlights: A relationship between small and large strain convergence is modified to accurately calculate large convergences from small strain analysis. Two equivalent formulas for the longitudinal displacement profile in squeezing ground considering finite strain are proposed. The applicability of displacement-release coefficient by small strain analysis for quantifying the stress relief to squeezing ground is obtained. [ABSTRACT FROM AUTHOR]

The permeability evolution of fractures in geologic media plays a pivotal role in various geo-mechanical activities, ranging from energy resources recovery to the deep geologic disposal of hazardous materials. This paper presents both laboratory and computational investigations into the evolution of fracture permeability under the influence of varying confining stress levels in a crystalline granitic rock from the Canadian Shield. Steady state permeability experiments were conducted to assess variations in fracture permeability in areas where stress conditions may significantly change due to large-scale underground excavations. A high accuracy laser scanner was used to capture the geometric features of the fracture surface, enabling the numerical simulation analysis of stress-induced hydromechanical behavior. The fracture permeability evolution was systematically investigated under both isotropic stress and deviatoric stress conditions, including four loading–unloading sequences and a series of sequentially increased deviatoric stresses. Simulations of fracture closure under increasing confining pressure and corresponding fluid flow process were performed incorporating a model constructed from fracture elevation data obtained through scanning. The results demonstrate a reduction in permeability exceeding 50% as the triaxial confining stress increases from 5 to 40 MPa. Additionally, permeability hysteresis during stress relief was observed. These findings are relevant to deep geological construction activities where excavation leads to the development of an excavation damage zone and stress alterations, affecting overall fluid flow process. Highlights: The fracture permeability evolution in Lac du Bonnet granite under four loading–unloading sequences has been systematically investigated. Stress-induced fracture closure process and its corresponding fluid flow process were simulated based on a model constructed from fracture elevation data obtained through scanning techniques. Fracture permeability showed a clear dependence on stress level and permeability hysteresis was observed during the stress relief. [ABSTRACT FROM AUTHOR]

This paper presents a recent investigation into the electromechanical behavior of thermally reduced graphene oxide (rGO) as a strain sensor undergoing repeated large mechanical strains up to 20.72%, with electrical signal output measurement in multiple directions relative to the applied strain. Strain is one the most basic and most common stimuli sensed. rGO can be synthesized from abundant materials, can survive exposure to large strains (up to 20.72%), can be synthesized directly on structures with relative ease, and provides high sensitivity, with gauge factors up to 200 regularly reported. In this investigation, a suspension of graphene oxide flakes was deposited onto Polydimethylsiloxane (PDMS) substrates and thermally reduced to create macroscopic rGO-strain sensors. Electrical resistance parallel to the direction of applied tension ( x ^ ) demonstrated linear behavior (similar to the piezoresistive behavior of solid materials under strain) up to strains around 7.5%, beyond which nonlinear resistive behavior (similar to percolative electrical behavior) was observed. Cyclic tensile testing results suggested that some residual micro-cracks remained in place after relaxation from the first cycle of tensile loading. A linear fit across the range of strains investigated produced a gauge factor of 91.50(Ω/Ω)/(m/m), though it was observed that the behavior at high strains was clearly nonlinear. Hysteresis testing showed high consistency in the electromechanical response of the sensor between loading and unloading within cycles as well as increased consistency in the pattern of the response between different cycles starting from cycle 2. [ABSTRACT FROM AUTHOR]

Due to its exceptional mechanical and chemical properties at high temperatures, Inconel 718 is extensively utilized in industries such as aerospace, aviation, and marine. Investigating the flow behavior of Inconel 718 under high strain rates and high temperatures is vital for comprehending the dynamic characteristics of the material in manufacturing processes. This paper introduces a physics-based constitutive model that accounts for dislocation motion and its density evolution, capable of simulating the plastic behavior of Inconel 718 during large strain deformations caused by machining processes. Utilizing a microstructure-based flow stress model, the machinability of Inconel 718 in terms of cutting forces and temperatures is quantitatively predicted and compared with results from orthogonal cutting experiments. The model's predictive precision, with a margin of error between 5 and 8%, ensures reliable consistency and enhances our comprehension of the high-speed machining dynamics of Inconel 718 components. [ABSTRACT FROM AUTHOR]

Laser shock peening (LSP) is a formidable cold working surface treatment that provides high-energy precision to enhance the mechanical properties of materials. This paper delves into the intricacies of the LSP process, offering insights into its methodology and the simulation thereof through the finite element method. This review critically examines various points, such as laser energy, overlapping of shots, effect of LSP on residual stress, effect of LSP on grain refinement, and algorithms for simulation extrapolated from finite element analyses conducted by researchers, shedding light on the nuanced considerations integral to this technique. As the significance of LSP continues to grow, the collective findings underscore its potential as a transformative technology for fortifying materials against mechanical stress and improving their overall performance and longevity. The discourse encapsulates the evolving landscape of the LSP, emphasizing the pivotal role played by finite element analysis in advancing our understanding and application of this innovative surface treatment. [ABSTRACT FROM AUTHOR]

Elastic yarns are the key component of high-performance compression garments. However, it remains a challenge to fabricate anti-fatigue yarns with high mechanical force and long elongation for generating compression garments with prolonged wear. In this paper, we report the development of anti-fatigue double-wrapped yarns with excellent mechanical properties by wrapping high-denier Spandex with nylon filaments in opposite twists. In particular, high-denier (560 D) Spandex as the core was untwisted, which can maximally reduce the interaction between the core and wrapping filaments, enabling high elongation of double-wrapped yarns. In addition, we chose 70 D nylon filaments with a tensile force of 3.87 ± 0.09 N as the wrapping materials to provide sufficient force for double-wrapped yarns. Notably, opposite twists were induced for the inner and outer wrapping filaments to achieve a balanced stable yarn structure. By systematically optimizing manufacturing parameters, including inner wrapping density, outer wrapping density, take-up ratio, and drafting ratio, we obtained double-wrapped yarn with excellent tensile stress (32.59 ± 0.82 MPa) and tensile strain (357.28% ± 9.10%). Notably, the stress decay rate of optimized yarns was only 12.0% ± 2.2%. In addition, the optimized yarn was used as the weft-lining yarn for generating weft-lined fabrics. The elastic recovery rate of the obtained fabric was decreased by only 2.6% after five cyclic stretches, much lower than the control fabric. Our design of anti-fatigue double-wrapped yarns could be widely used for fabricating high-performance compression garments. [ABSTRACT FROM AUTHOR]

This paper is concerned with a rate-type theory of thermoviscoelasticity in which the second gradient of the displacement and the second temperature gradient are added to the classical set of independent constitutive variables. Viscoelasticity and related phenomena are of great importance in the study of biological materials. An adequate modeling of rubber-like materials and of biological soft tissues requires the use of the theory of viscoelasticity. Introduction of the concept of thermal displacement and the theory of multipolar continua allows us to show that Green-Naghdi thermomechanics can be used to derive a second gradient theory. The basic equations of the theory are established and the boundary conditions associated to nonsimple materials are investigated. The stress tensor and hyperstress tensor are shown to depend on the first and second temperature gradients. For rigid heat conductors we find that the temperature satisfies a fourth order equation. The boundary-initial-value problems are formulated. A uniqueness result in the dynamic theory of thermoviscoelastic materials is presented. We establish an existence result and prove the analyticity of the solutions. As a consequence, the exponential decay of the solutions and their impossibility of localization are obtained. [ABSTRACT FROM AUTHOR]

Compared to homogeneous beams, metamaterial-based sandwich beams are known to be lighter and provide better mechanical characteristics. However, their application has mainly been limited to large-scale structures, and their potential for granting small-scale structures enhanced characteristics has not been fully explored yet. The present manuscript aims to investigate nonlinear vibration in size-dependent metamaterial-based sandwich microbeams with hexagonal and triangular lattice cores. To do so, well-known homogenization techniques based on modeling the representative volume element (RVE) of the lattice have been utilized to find the equivalent properties of the nonlinear cores. Moreover, the modified strain gradient theory is used to obtain the governing equation of motion for a small-scale microbeam and the multiple scales method is adopted to investigate the free vibration and primary resonance of the discretized system. Further, size effects and the effect of geometry on the free and forced nonlinear vibration of lattice sandwich beams are examined. In addition to highlighting the size effects, the results indicate that properly implementing nonlinear metamaterials in microbeams can enhance and tune vibrational performance across various length scales. The results of the present paper can provide a more detailed perception of the concept of nonlinear metamaterial-based microbeams and their application in MEMS/NEMS devices. [ABSTRACT FROM AUTHOR]

Dynamic and vibrational behavior of nonlinear resonant pressure micro sensors is studied in this paper using a proposed dynamic model. The basic part of the device is a microplate deflects due to external pressure in presence of electrostatic actuation. The frequency changes because of the microplate deformation is used to estimate the external pressure. For modeling of the micro sensor, the nonlinear governing equation of size dependent microplate in polar coordinate system and based on the modified couple stress theory is presented. Assuming specified number of Taylor expansion terms for electrostatic force, the linear and nonlinear ODE is obtained and nonlinear equation is solved both with multiple time scales method (MTS) and finite difference numerical method. Results indicate that considering finite terms of Taylor expansion (1 term for linear and three terms for MTS method) is the source of error in estimation of pressure or system stability. Using sufficient terms of Taylor Expansion, the error in linear and MTS solutions is vanished. Therefore, the limited values of microplate vibrational amplitude is extracted to increase the accuracy of the sensor in linear action. The effect of size dependency, applied voltage on nonlinear behavior and linearization error is also studied. [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 large deformation of the skew microplate made of laminated composite enhanced with graphene nanosheets is investigated using first shear deformation theory (FSDT) when the plate undergoes combination of mechanical and thermal loads. Halpin-Tsai model is utilised to model mechanical properties while for thermal properties Schapery model is considered. First, shear deformation of the plate was obtained while using Green-Lagrange tensor the non-linear strain of the microplate is extracted using the von-Karman assumptions. Then, by Modified Coupled Stress Theory (MCSD), the components of Cauchy and Couple stress tensors are specified. Finally, using Hamilton Principle the governing equation of the microplate and boundary conditions are computed. After deriving analytical governmental equation results are presented for the simple support boundary condition and the proposed model is validated by previously reported data and it proves to be promising. Primary results showed that with raising skew angle deflection and bending moment decreases which means microplate becomes more rigid in higher skew angles. Higher mechanical loads lead to higher deflections and bending moments. Four different configurations of the layers were analysed from which angle-ply configuration possessed highest deflection and bending while UD configuration revealed the lowest values of deflection and bending moment. [ABSTRACT FROM AUTHOR]

Accurate prediction of excess pore water pressure (EPWP) generation in saturated sandy soils remains one of the most challenging issues in sandy site responses to strong earthquakes and extreme marine environments. This paper presents experimental results of undrained and drained multidirectional cyclic hollow cylinder (MCHC) tests on saturated coral sandy soils under various cyclic loadings. The results show that threshold generalized shear strain γga,th , below which EPWP and volumetric strain can be neglected, is an inherent property depending only on the soil type and initial state. Furthermore, there exists a virtually unique form of relationships between the generalized shear strain amplitude (γga) and the cumulative dissipated energy per unit volume of soil (Wc) at different relative density (Dr), irrespective of drainage conditions and cyclic loading conditions. These findings highlight the fundamental mechanism for cyclic deformation behavior and the uniqueness of correlations among rup (peak EPWP ratio), εvp (peak volumetric strain), and γga of saturated sandy soil at the similar Dr , regardless of cyclic loading conditions. Based on these findings, a novel unified model of γga -based cyclic shear–volume coupling and EPWP generation is established, which is independent of cyclic loading conditions over a wide loading frequency range. Then the applicability of the proposed model is validated by the experimental data of the same tested coral sandy soil and siliceous Ottawa sand, as well as the data of siliceous fine sands in previous work. It is found that the proposed model surpasses the existing strain- and stress-based models in accurately predicting EPWP generation under complex cyclic loadings, which can offer new insights into the mechanisms of the EPWP generation in saturated sandy soils. [ABSTRACT FROM AUTHOR]