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Drilling glass fiber reinforced polymer matrix (GFRP) composites typically causes burrs, splintering, and microcracks within the GFRP structure, as well as delamination, fiber pull‐out, and thermal degradation of the polymer matrix. Designing and manufacturing molded‐hole GFRP components, as opposed to drilling, has recently been proposed as a promising method for overcoming the issues associated with drilling, for which there is limited research. Specifically, the mechanical response of molded‐hole GFRP has not been fully addressed in the literature. In the present study, molded and drilled GFRP composites with epoxy matrix were fabricated by hand lay‐up, and then the samples were analyzed utilizing experimental and numerical analysis techniques. Stress and strain analyses of GFRP samples were performed in Ansys Transient Structural Analysis. Although the fiber orientations of the layer geometries [0°/90°] and 3D models were the same, an additional layer was defined in the direction of the fiber orientation [45°/−45°] of molded‐hole composites to simulate the fiber accumulation effect. Experimental findings revealed that the flexural strength of molded composites was 12% greater than that of drilled composites. According to the numerical analysis, 98.7% proximity was achieved between the experimental and numerical results. Thus, the present study has provided numerical modeling to understand the flexural strength of molded composites for the first time, which will contribute to the increased use of molded composites in numerous applications in the fields of aerospace, automotive, and marine. Highlights: Drilled‐ and molded‐hole GFRP composites were produced by hand lay‐up.Flexural properties of the composites were examined via 4P bending tests.Flexural strength of molded composites was higher than that of drilled ones.98.7% proximity was achieved between the experimental and FEM results.A unified FEM method is proposed for the molded‐hole composites. [ABSTRACT FROM AUTHOR]

Excavation‐induced rock failure and deformation near an underground opening boundary is closely associated with the intermediate principal stress, strain softening and rock mass dilation. By combining theoretical analysis and numerical simulation to explore the mechanical evolution of the roadway surrounding rock during excavation. The elastic–plastic criterion solutions for surrounding rock stress, displacement, and the plastic zone of a circular roadway were deduced by including the intermediate principal stress, strain softening and rock mass dilation, based on the Drucker–Prager criterion and the nonassociated flow rule. Furthermore, ABAQUS finite element software was utilized for numerical simulations to scrutinize the influence of mechanical parameters on stress redistribution, surface displacement, and plastic range. The results of the numerical simulations verify the reliability of the theoretical analysis and affirm the high consistency of the results with the theoretical solution. The research findings indicate that the strength of surrounding rock is significantly influenced by the intermediate principal stress, and the deformation and failure of rock mass are primarily impacted by rock mass dilation, while strain softening mainly affects the thickness of the fractured zone. Moreover, the study reveals that enhancing the residual strength of the surrounding rock can improve its resistance to deformation and failure. Furthermore, the excavation of the roadway is observed to increase the original rock stress in the surrounding rock, but increasing the ground support strength effectively controls the deformation and failure of surrounding rock. Ultimately, the research outcomes offer valuable references for engineering calculations and ground support design of surrounding rock in deep roadways. [ABSTRACT FROM AUTHOR]

This study focuses on assessing the effectiveness of an empirically recommended support design through numerical modelling. Numerical techniques are utilized to accurately evaluate tunnel stability under various geological conditions. Numerical analysis is conducted on two different rock types along the tunnel route, employing the recommended support design based on the existing rock mass rating (RMR) and Q-system. Furthermore, support recommendations are made using the modified RMR and Q-system, considering the impact of stress. The numerical analysis indicates that the support recommended by the existing RMR may not substantially impact the total displacement and vertical stresses around the tunnel crown in the “Fair” to “Poor” rock mass of the study area. However, extending the bolt length by modifying the RMR to incorporate stress effects results in a reduction of total displacement and vertical stresses, ultimately achieving a stable level. These results underline the importance of considering stress effects and utilizing modified support designs to enhance tunnel stability. [ABSTRACT FROM AUTHOR]

With the increasing depth of engineering in rock masses, the issue of significant rheological deformation becomes notably prominent. To accurately characterize the deformation and failure behavior of the surrounding rock near the goaf in deep small coal pillars, we have developed a viscoelastic–plastic constitutive model that takes into account the initial stress associated with creep. This model builds upon an existing viscoelastic–plastic constitutive framework and is implemented numerically using C++ in the FLAC3D. The Oedometer test method is used to check the creep components and the calculated parameter (η/G) ensure convergence of numerical operations. We conducted both pre‐improvement and post‐improvement tests of the constitutive model in a simple numerical analysis of roadways. The enhanced model demonstrates improved accuracy in deviational stress calculations and proves suitable for modeling deep, soft roadways. Furthermore, we applied the improved model to simulate actual working conditions at Zhaozhuang Mine, where mining operations near the working face induce a fracture zone of approximately 3 m in the small coal pillar located at the goaf's edge. The new model closely aligns with the observed results, further validating its suitability for tunneling along the goaf. Tunneling and mining activities result in significant deformation at various locations, including the shoulder socket of the working face, the top angle of the coal pillar, and the bottom angle of the floor. The crushing zone at the working face extends up to 4 m. Rheological effects transform the triangular elastic core, from its original high‐pressure elastic state to a fracture and plastic zone in the deep coal. Stress in deep coal is transmitted along the triangular elastic core. Numerical simulation results closely match the excavation profile of the tunneling, providing valuable insights into the impact of mining activities. This study can provide reference for deformation of similar geological conditions and engineering situation. [ABSTRACT FROM AUTHOR]

We develop automated methods for fault detection utilizing static stress and deformation fields at the onset of failure derived from numerical analysis. We calculate combinations and normalization of the distance from the Mohr circle to the Coulomb envelope, and of the second deviatoric strain invariant. A variation of the Cauchy distribution of these fields allows us to focus on the low values indicating rupture, with the help of the scale parameter δ. A threshold is then applied to decide at each spatial node of the mesh whether the material has reached failure or not. We then determine fault lines and planes from these isolated failure zones using image processing techniques, such as the Hough and the Radon transforms, or through a combined approach involving automated sorting of the nodes reaching failure through the k‐means clustering technique followed by polynomial fitting to retrieve analytic expressions of the fault curves (in 2D) or fault surfaces (in 3D). The methods are efficient except when the stress field results in diffuse rupture zones that do not localize onto fault surfaces despite tuning δ. We also highlight the advantages of using the combined clustering/poly‐fitting approach for 3D models compared to the image processing techniques. These automated fault detection methods should be useful in the interpretation of diverse failure mechanisms obtained through parametric sensitivity analyses requiring hundreds of simulations. The stress and strain fields used were derived from a numerical implementation of limit analysis, but classical finite‐difference or finite‐element techniques could have been used. [ABSTRACT FROM AUTHOR]

Current research focuses on the induction of residual stresses in a component during its manufacturing process, which shows a significant impact on the final component's properties. During the manufacturing of a hot bulk forming component, the temperature evolution allows to influence the resulting residual stress state efficiently and purposefully. Following the characterization of residual stresses on different scales, single‐scale finite element simulations are carried out on macro‐ and microscale. In contrast to previous findings for two‐dimensional boundary value problems, the effects of the third dimension are demonstrated. Furthermore, it is shown that the residual stress distribution is effectively influenced by choosing different cooling routes in targeted manner. Eventually, the importance of microscopic residual stress investigations is discussed. [ABSTRACT FROM AUTHOR]

The welding and flame‐cutting process in the steel construction are commonly used, especially for the bridge structure. Some experiments about welding and cutting have been done separately by some researchers. The results from the experiments were also compared with the results from the numerical simulation under 3D or 2D models. The agreements between those results are as good as they predicted. Therefore, the numerical simulation is a better way to analyze the quality of the steel construction after welding and cutting without time‐consuming and a large amount of cost. But there are only a few research about the numerical simulation and the some of them are aimed to verify the experiments. In this study, the calculation about the residual stresses after welding and thermo‐cutting are considered from 3D‐model into 2D‐Model. The heat source model is simply regarded as curves of time and welding energy with the algorithm methods. And no matter the change of the parameters of the model and the heat source, the heat transfer and the residual stresses can be calculated with the 2D models as fast as possible. By the means of the finite element software Abaqus, the I‐profiles are easy to receive the job results with the input parameters. The influence of the welding and cutting process are visual and direct. [ABSTRACT FROM AUTHOR]

To further the accuracy of a virtual process, links between sequenced numerical methods are established to create a process chain, which considers all influences on a manufactured part in its early design stages. In order to transform numerical results into initial conditions of a preceding simulation method, the data is "mapped" from a source to a target finite element mesh. The data transfer depends heavily on the difference in mesh discretization as well as the utilized interpolation method. Errors occur using different inter‐ and extrapolation methods. This contribution aims to establish a hybrid interpolation method to transfer tensorial stress data between FEM meshes without using an external solver. The applied method consists partly of a radial basis and of a weighted areas interpolation. [ABSTRACT FROM AUTHOR]

This paper numerically investigates three typologies of Gerber saddle in existing ordinary and post‐tensioned girder concrete bridges. The main goals of this work concern the evaluation of the effective load‐bearing capacity of Gerber saddles, and the identification of weak points (i.e., lack of enough diagonal reinforcement, loss of pretension in tendons) of existing dapped‐end connections, which lead to the re‐entrant corner diagonal crack, typical of these kinds of structural elements. At this aim, two analytical approaches, with different level of approximations, are used. First, different strut‐and‐tie models are arranged for each typology of Gerber saddle considered, and the global safety factor is estimated for several cases. Second, using nonlinear finite‐element method, the results obtained by strut‐and‐tie models are compared. In addition, several information about the condition of Gerber saddle at collapse are obtained (deformation and stress of concrete and steel rebar, crack patterns) also taking into account the corrosion‐damage effects. Moreover, the results of analyses allow identifying the potential modes of crisis of the dapped‐end connections and their critical aspects. [ABSTRACT FROM AUTHOR]

Effective stress analysis using liquefaction parameters is often employed for the numerical analysis of soil liquefaction. However, to the best of our knowledge, liquefaction parameters that simultaneously reproduce the liquefaction strength curve and effective stress path have not been reported to date. Herein, we propose a new method to estimate the model parameters used in effective stress analysis: the liquefaction strength and pore pressure curves obtained from laboratory tests are used as targets for inverse analysis. The results confirmed that the parameters obtained by our method could reproduce the liquefaction strength, pore pressure curves, and the effective stress path with high accuracy, which was difficult to achieve using conventional methods. [ABSTRACT FROM AUTHOR]

In situ synchrotron X‐ray diffraction experiments were carried out during laser surface line hardening of the common tempering steel AISI 4140 at beamline P05@PETRA III operated by Helmholtz‐Zentrum Geesthacht at the Deutsches Elektronen Synchrotron, Hamburg, Germany. A unique process chamber was used to investigate the phase and transverse surface stress evolution during a laser line hardening processes. Synchrotron radiation, in combination with microstrip line detectors, allows for a time resolution of 50 Hz. Specimen geometries were hardened using a high‐power diode laser under control of the surface temperature and constant laser beam feed. Herein, it is focused on web‐structured specimens in contrast to a flat geometry. The experimental results are discussed with regard to the workpiece geometry effect of the web structure dimensions on the temporal and spatial stress evolution. In addition, numerical process simulations based on the finite element method were carried out to support the drawn conclusions. The presented model is able to predict the surface transverse stresses inside the process zone center, while providing further 3D information. A heat build‐up in the web leads to a wider and deeper process zone, however, the absolute hardness increase and the transverse residual stresses at the surface center are not affected. [ABSTRACT FROM AUTHOR]

Coalbed methane (CBM), which is extremely rich in deep coal reserves in China, is not only the material cause of gas explosion and coal‐gas outburst disasters but also a clean and environmentally friendly energy source. Gas drainage must be carried out during deep coal mining to avoid gas accidents while obtaining clean energy. The low‐level roadway is an effective gas drainage measure for coal seams with high coal‐gas outburst risk and low‐permeability, and it can simultaneously realize the functions of gas drainage before and during mining. Roadway tunneling has a strong influence on the stress and permeability properties of the adjusted coal seams, and further determines the gas drainage efficiency and the layout of the air‐return roadway. Taking the Pingshu Coal Mine as an example, this paper analyzes the influence of the vertical distance between the low‐level roadway and the underlying coal seam, and the influence of the width and height of the low‐level roadway on the stress relief and deformation characteristics. The results indicate that the low‐level roadway tunneling results in a nonuniform stress disturbance of coal seam #15. And a reasonable layout and size parameters of the air‐return roadway in coal seam #15 were proposed based on which gas drainage practices were carried out with good effects in panel #15211. The research can effectively guide the elimination of coal and gas outburst in return air roadway, and achieve the purpose of safe and rapid tunneling coal roadway under the environment of highly‐gassy coal seam. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this work the chaotic dynamics of flexible curvilinear Euler–Bernoulli micro‐beams embedded into a stationary temperature field is investigated. The temperature field is modelled based on a the Duhamel–Neumann theory and is free from the restrictions on the temperature field distribution along beam thickness. The von Kármán geometric strain–stress relations are employed. The governing nonlinear PDEs are yielded by the Hamilton principle with an account of the modified couple stress theory. The finite dimension problem is truncated to a finite system of nonlinear ODEs using the finite difference method (FDM) and then the Cauchy problem is solved with a help of the Runge–Kutta method. Action of the 2D thermal field is defined by solution to the heat transfer PDE which is also solved by FDM of the second order of accuracy. The so‐called charts of vibration regimes (amplitude‐frequency planes) are constructed. In particular, novel features of nonlinear (chaotic) dynamics versus the change of the magnitude of the size (length) dependent parameter are reported. The carried out numerical analysis is supported by the monitoring of frequency power spectra based on the fast Fourier transform (FFT), phase space projections, Poincaré maps and LLEs (largest Lyapunov exponents). We have also analyzed system chaotic dynamics of the classical and size‐dependent beam models versus series of values of the two control parameters, i.e. beam curvature and its size‐dependent length. Moreover, we have detected and illustrated the novel scenarios of transition form regular to chaotic vibrations of the studied beams, governed by non‐linear PDEs. [ABSTRACT FROM AUTHOR]

Experimental data show that inelastic straining occurs even at very low pressure before and during brittle fracturing. This process is therefore investigated within the framework of elastoplasticity using 2‐D, three‐layer finite difference modeling. The constitutive model includes both tensile and shear failure mechanisms coupled at the level of the strain softening law. The modeling results show that sets of parallel joints initiate as pure dilation bands, the narrow σ3‐normal bands of localized dilatant damage (inelastic deformation). The band thickness, length, and the initial strain softening degree within it are proportional to the ductility of the material, which increases with the effective stress level (σ1) or pressure. The strength reduction within the bands is accelerated at a certain stage, and the strength locally reaches zero resulting in fracture initiation. The initial fracture then propagates in Mode I following the propagating band. The fracture (joint) appears thus as a band of damaged material with the increased porosity, which is maximum along the axial zone of the band where the material is completely broken. The damage is due to both tensile and shear mechanisms. The role of shear failure increases with the ductility (pressure) increase, which also leads to the band thickness increase. These processes can result in small (band thickness)‐scale oblique shear fractures within the band, causing the increase in the roughness of fracture walls organized in plumose patterns typical of both natural and experimentally generated joints. Key Points: Parallel joint sets were generated in three‐layer FD elastoplastic models that include tensile and shear failure with different brittlenessJoints are initiated as dilation deformation bands and propagate to different distances across the layer following the band propagationBand thickness in the models is proportional to the material ductility (pressure) as is also suggested by the experimental data [ABSTRACT FROM AUTHOR]

This work was aimed at examining the overall contributions to displacement of panels of compressed boxes, such as panel compression strain and flap and crease displacements. 3D digital image correlation (DIC) was used to analyse motion of side panels of corrugated fiberboard regular slotted containers. The vertical displacement and the vertical component of strain of the panel face during box compression test were examined. Measuring displacements of the whole compressed box with DIC enables measurement of the in‐plane compression of a panel in isolation from the horizontal fold or crease zone displacement, without having to test tube sections of the box to infer or extract the in‐plane panel compression behaviour. Detailed study of two box designs in three representative test cases was presented, which in future could be extended to other box designs. At peak load, the in‐plane compression of the panels, calculated from the average vertical component of the strain along the right edge of the long panel of the box, was 3% to 6% of total crosshead displacement for the test cases. At peak load, the portion of the box compression associated with bottom box flaps or crease zone crushing was 48% to 59% of total crosshead displacement for the different cases. The analysis showed that the majority of the vertical displacement of the box occurred in the top and bottom creased folds and that these folds are responsible for the low apparent in‐plane stiffness of a box. 3D digital image correlation (DIC) was used to analyse the separate contributions of the in‐plane compression of panels and the horizontal fold displacements to the overall vertical displacement of whole compressed boxes, without having to test tube sections of the box. At peak load, the in‐plane compression of the panels and the bottom box flaps crushing was, respectively, 3% to 6% and 48% to 59% of the total crosshead displacement for three representative test cases. [ABSTRACT FROM AUTHOR]

Summary: Within the framework of the second‐order work theory, the onset of instabilities is explored numerically in loose granular materials through three‐dimensional DEM simulations. Stress controlled directional analysis are performed in Rendulic's plane, and a particular attention is paid to transient evolutions at the microscale. Thanks to a micromechanical analysis, the onset and development of transient mechanical instabilities is explored. It is shown that these instabilities result from the unjamming and bending of a few force chains associated with a local burst of kinetic energy. This burst of kinetic energy propagates to the whole sample and provokes a generalized unjamming of force chains. As force chains buckle, a phase transition from a quasi‐static to an inertial regime is observed. At the macroscopic scale, this results in a transient softening and a loss of controllability. After the collapse of existing force chains, the development of plastic strain is eventually stopped as new stable force chains are built. [ABSTRACT FROM AUTHOR]

Summary: We investigate spatial stability with various numerical discretizations in displacement and pressure fields for poroelasticity. We study 2 sources of the early time instability: discontinuity of pressure and violation of the inf‐sup condition. We consider both compressible and incompressible fluids by employing the monolithic, stabilized monolithic, and fixed‐stress sequential methods. Four different spatial discretization schemes are used: Q1Q1, Q2Q1, Q1P0, and Q2P0. From mathematic analysis and numerical tests, the piecewise constant finite volume method for flow provides stability at the early time for the case of the pressure discontinuity. On the other hand, a piecewise continuous (or higher‐order) interpolation of pressure shows spatial oscillation, having lower limits of time step size, although lower approximations of pressure than displacement can alleviate the oscillation. For an incompressible fluid, Q2Q1 can be better than Q1P0, because Q1P0 might not satisfy the inf‐sup condition. However, regardless of fluid compressibility and the pressure discontinuity, the fixed‐stress method can effectively stabilize the oscillation without an artificial stabilizer. Even when Q1P0 and Q1Q1 with the monolithic method cannot satisfy the inf‐sup condition, the fixed‐stress method can yield the full‐rank linear system, providing stability. Thus, the fixed‐stress method with Q1P0 can effectively circumvent the aforementioned 2 types of instability. [ABSTRACT FROM AUTHOR]

In this article we consider a problem of the plane theory of elasticity for a finite doubly-connected domain whose external boundary is a square whose vertices vicinities are cut with the equal smooth unknown full-strength arches and whose internal boundary is the unknown full-strength hole. Absolutely smooth rigid punches with rectilinear bases, which are under the action of the force that applies to their middle points are attached to each component of the broken line of the outer boundary of the plate. Unknown part of the boundary is free from external forces. Using the methods of complex analysis, the unknown part of the boundary is found under the condition that the tangential normal stress on that takes a constant value. Numerical analysis is performed and the corresponding graphs are constructed. [ABSTRACT FROM AUTHOR]

The paper proposes a stress-driven integration strategy for Perzyna-type viscoplastic constitutive models, which leads also to a convenient algorithm for viscoplastic relaxation schemes. A generalized trapezoidal rule for the strain increment, combined with a linearized form of the yield function and flow rules, leads to a plasticity-like compliance operator that can be explicitly inverted to give an algorithmic tangent stiffness tensor also denoted as the m-AGC tangent operator. This operator is combined with the stress-prescribed integration scheme, to obtain a natural error indicator that can be used as a convergence criterion of the intra-step iterations (in physical viscoplasticity), or to a variable time-step size in viscoplastic relaxation schemes based on a single linear calculation per time step. The proposed schemes have been implemented for an existing zero-thickness interface constitutive model. Some numerical application examples are presented to illustrate the advantages of the new schemes proposed. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Fibrous soft biological tissues such as skin, ligaments, tendons, and arteries are non-homogeneous composite materials composed of fibers embedded in a ground substance. Cyclic tensile tests on these type of materials usually show a hysteretic stress-strain behavior in which strain rate dependence (viscoelasticity) and softening (Mullins' effect) play a coupled role. The main contribution of the present paper is to present unified variational approach to model both coupled phenomena: nonlinear viscoelasticity and Mullins-like softening behavior. The approach is labeled as variational because viscous-strain and damage internal variables are updated based on the minimization of a hyperelastic-like potential that takes a renewed value at each time step. Numerical examples explores (a) the versatility of the proposed model to account for the two described phenomena according to the chosen functions for the free-energy and dissipative potentials, (b) the ability of the time-integration scheme embedded in the incremental potential definition to allow for large time increments, and (c) the capability of the model to mimic experimentally obtained stress-strain cyclic curves of soft tissues. The model implementation on standard finite elements is also tested in which symmetric analytic tangent matrices are used as a natural consequence of the variational nature of the proposed approach. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This contribution gives a short introduction into the topic of fluid-structure-control interaction (FSCI). This is a multi-field problem, where three fields are coupled, namely a fluid-flow, structural dynamics and closed-loop control of structures. The interactions are identified as surface-coupling of fluid flow and structural dynamics as well as signal-coupling of structural dynamics and closed-loop control. At first a simple model problem is introduced, which allows an efficient investigation of the convergence behavior and stability of such kind of problem. In this context an iterative partitioned approach, using a serial Gauß-Seidel scheme, is presented. Finally, the insights gained by the model problem are used to set up a multi-dimensional numerical experiment. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

In the present study, a local stress based concept for the fatigue assessment of weld ends in thin sheet structures under combined normal and shear loading is introduced. The notch stresses were calculated using the finite element method and submodel technique. An idealised weld end model was used in order to determine the stress state for such loading situations. Moreover, a numerical method was used to consider size effects, which combines both the geometrical and statistical size effects, to an integrated approach. Therewith and in connection with the cycles-to-failure from fatigue test results, a standardised S-N curve was derived. [ABSTRACT FROM AUTHOR]

Present work focuses on evaluating the suitability of newly proposed compact pipe (CP) fracture specimen geometry for determining critical SZW. The effect of varying the parameter of CP specimen (outer diameter, thickness, a/W ratio and straight and radial crack front) on critical SZW have been studied. It is found that SZWc values decreases slightly with the increase in outer diameter of CP specimen. In CP specimen, thickness greater than a specified value is to be used for geometry independent evaluation of SZWc. Critical SZW shows significant variation with a/W ratio, straight and radial crack front. The CP specimen and Three Point Bend (TPB) specimen also compared in terms of stress tri-axiality. [ABSTRACT FROM AUTHOR]

A stabilized scheme is developed for mixed finite element methods for strongly coupled diffusion problems in solids capable of large deformations. Enhanced assumed strain techniques are employed to cure spurious oscillation patterns of low-order displacement/pressure mixed formulations in the incompressible limit for quadrilateral elements and brick elements. A study is presented that shows how hourglass instabilities resulting from geometrically nonlinear enhanced assumed strain methods have to be distinguished from pressure oscillation patterns due to the violation of the inf-sup condition. Moreover, an element formulation is proposed that provides stable results with respect to both types of instabilities. Comparisons are drawn between material models for incompressible solids of Mooney-Rivlin type and models for standard diffusion in solids with incompressible matrices such as polymeric gels. Representative numerical examples underline the ability of the proposed element formulation to cure instabilities of low-order mixed formulations. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Traditional self-centering coupling beams display a beam elongation effect under large shear deformation. The beam elongation effect conflicts with the rigid slab assumption and may induce harmful compressive stress between the coupling beam and the walls. This paper proposes a novel self-centering coupling beam, aimed at eliminating the beam elongation effect. The proposed self-centering coupling beam consists of two connecting parts and one central rocking part. The main feature of the self-centering coupling beam is the gap between the central rocking part and the one connecting part. This gap provides sufficient space for the beam elongation effect. Friction dampers are installed at the corners of the coupling beam to provide energy dissipation capacity. An experimental study, including three specimens, was carried out. The test results demonstrate the satisfactory self-centering and energy dissipation capacities of the novel coupling beam. Based on these test results, we quantitatively discuss the pretension force in the pretensioning strands, the friction force of the damper and the gap width in the coupling beam. A finite element analysis is performed, showing that the coupling beam gap protects the coupling beam and adjacent shear wall from damage caused by the beam elongation effect. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Pressure drops associated with reservoir production generate excess stress and strain that cause travel-time shifts of reflected waves. Here, we invert time shifts of P-, S-, and PS-waves measured between baseline and monitor surveys for pressure reduction and reservoir length. The inversion results can be used to estimate compaction-induced stress and strain changes around the reservoir. We implement a hybrid inversion algorithm that incorporates elements of gradient, global/genetic, and nearest neighbour methods and permits exploration of the parameter space while simultaneously following local misfit gradients. Our synthetic examples indicate that optimal estimates of reservoir pressure from P-wave data can be obtained using the reflections from the reservoir top. For S-waves, time shifts from the top of the reservoir can be accurately inverted for pressure if the noise level is low. However, if noise contamination is significant, it is preferable to use S-wave data (or combined shifts of all three modes) from reflectors beneath the reservoir. Joint wave type inversions demonstrate improvements over any single pure mode. Reservoir length can be estimated using the time shifts of any mode from the reservoir top or deeper reflectors. We also evaluate the differences between the actual strain field and those corresponding to the best-case inversion results obtained using P- and S-wave data. Another series of tests addresses the inversion of the time shifts for the pressure drops in two-compartment reservoirs, as well as for the associated strain field. Numerical testing shows that a potentially serious source of error in the inversion is a distortion in the strain-sensitivity coefficients, which govern the magnitude of stiffness changes. This feasibility study suggests which wave types and reflector locations may provide the most accurate estimates of reservoir parameters from compaction-induced time shifts. [ABSTRACT FROM AUTHOR]

In engineering practice, the prevention of early-age cracking in massive concrete structures is of great importance to their serviceability during the whole life cycle. From the scientific viewpoint, this engineering concern requires the control of the early-age performance of concrete structures. Following earlier research projects against the background of the Hong Kong- Zhuhai-Macao Link, the focus of this work is to obtain insights into the evolution of the early-age behaviour of precast concrete in an immersed tunnel. To this end, a full-scale test was performed, from which the behaviour of early-age concrete could be observed directly. After validating the constitutive model developed with the test results, the early-age performance during the entire fabrication process of the precast concrete immersed tunnel is evaluated numerically. It was also found that stress relaxation plays a major role in stress development in the immersed tunnel, although the thermal strain is the main source of early-age stresses. This in-depth investigation resulted in a comprehensive understanding of the early-age behaviour of an actual precast concrete immersed tunnel. What is more important, the early-age performance of concrete structures can be accurately evaluated and further adjusted or controlled with the help of the validated numerical modelling, which is no doubt beneficial for the control of early-age cracking in massive concrete structures in engineering. [ABSTRACT FROM AUTHOR]

Nonlinear fracture analysis of rubber-like materials is computationally challenging due to a number of complicated numerical problems. The aim of this paper is to study finite strain fracture problems based on appropriate enrichment functions within the extended finite element method. Two-dimensional static and quasi-static crack propagation problems are solved to demonstrate the efficiency of the proposed method. Complex mixed-mode problems under extreme large deformation regimes are solved to evaluate the performance of the proposed extended finite element analysis based on different tip enrichment functions. Finally, it is demonstrated that the logarithmic set of enrichment functions provides the most accurate and efficient solution for finite strain fracture analysis. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Dynamic crack-branching instabilities in a brittle material are studied numerically by using a non-local damage model. PMMA is taken as our model brittle material. The simulated crack patterns, crack velocities, and dissipated energies compare favorably with experimental data gathered from the literature, as long as the critical strain for damage initiation as well as the parameters for a rate-dependent damage law are carefully selected. Nonetheless, the transition from a straight crack propagation to the emergence of crack branches is very sensitive to the damage initiation threshold. The transition regime is thus a particularly interesting challenge for numerical approaches. We advocate using the present numerical study as a benchmark to test the robustness of alternative non-local numerical approaches. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY An analytical solution of cavity expansion in two different concentric regions of soil is developed and investigated in this paper. The cavity is embedded within a soil with finite radial dimension and surrounded by a second soil, which extends to infinity. Large-strain quasi-static expansion of both spherical and cylindrical cavities in elastic-plastic soils is considered. A non-associated Mohr-Coulomb yield criterion is used for both soils. Closed-form solutions are derived, which provide the stress and strain fields during the expansion of the cavity from an initial to a final radius. The analytical solution is validated against finite element simulations, and the effect of varying geometric and material parameters is studied. The influence of the two different soils during cavity expansion is discussed by using pressure-expansion curves and by studying the development of plastic regions within the soils. The analytical method may be applied to various geotechnical problems, which involve aspects of soil layering, such as cone penetration test interpretation, ground-freezing around shafts, tunnelling, and mining. © 2014 The Authors. International Journal for Numerical and Analytical Methods in Geomechanics published by John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY The concentration factor introduced by O. K. Fröhlich is visualized as a procedure for examining the pattern of load transfer from surface loads to the interior of a geomaterial. The historical details that led to the introduction of the concentration factor are scant although it is widely used in the area of soil mechanics problems associated with tillage-induced soil compaction. The purpose of this note is to examine the concentration factor in terms of the geomechanics of an elastic continuum and to identify the precise conditions that are satisfied by the distribution of stresses and strains that accommodate the concentration factor. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY In the numerical analysis of 2-D bimodular materials, strain discontinuity is problematic, and the traditional iterative algorithm is frequently unstable. This paper develops a stable algorithm for the large-displacement and small-strain analyses of 2-D bimodular materials and structures. Geometrically nonlinear formulations are based on the co-rotational approach. Using the parametric variational principle (PVP), a unified constitutive equation is created to resolve the problem induced by strain discontinuity in the local coordinate system. Because the traditional stress iteration is not required, the local linear stiffness matrix does not need to be updated when computing the global stiffness matrix and the nodal internal force vector. The nonlinear problem is ultimately transformed into a complementarity problem that is simply solved by combing the Newton-Raphson scheme and the mature quadratic programming algorithm. Numerical examples demonstrate that the PVP algorithm presents better convergence behavior than the traditional iterative algorithm. By incorporating the concept of material modification, the new algorithm is also be successfully extended to the wrinkling analysis of thin membranes. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Für die Ermittlung des Kräftegleichgewichts bei Membranstrukturen können nur innere elastische Zugnormalspannungen und Schubspannungen herangezogen werden, die tangential zur Membranfläche gerichtet sind. Für Belastungen, die aus der Membranebene heraus auftreten, weisen Membrane mit geringer Krümmung eine entsprechend geringe Steifigkeit auf. Unter Verwendung des Prinzips der virtuellen Verschiebungen wird eine konsistente Finite-Elemente-Diskretisierung vorgestellt, welche eine näherungsweise Ermittlung des Membranverformungs- und des Membranspannungszustandes ermöglicht. Das Berechnungsverfahren wird für den verwendeten Elementtyp analysiert und auf eine Hyparmembran unter Verkehrslast sowie auf eine Spinnakermembran unter horizontaler Belastung angewendet. 3D Membrane Theory. For the force equilibrium of membrane structures only inner tensile normal stresses and shear stresses tangential to the membrane surface can be considered. For load that acts in out-of-membrane-plane direction membranes with small curvature appropriately show only small stiffness. By application of the principle of virtual displacement a consistent finite element discretization is presented that allows an approximate determination of membrane displacement and membrane stress state. The presented computational approach is analyzed for the applied element type and is applied to a hypar membrane exposed to work load as well as to a spinnaker membrane exposed to horizontal load. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper presents further assessments of the previously reported round-robin fatigue data obtained from high-frequency mechanical impact (HFMI)-improved longitudinal welds. A detailed statistical analyses of geometry measurements of HFMI-treated weld toe profiles are presented. The fatigue analyses based on notch stress as defined by the International Institute of Welding are performed using the finite element method. Notch stresses are assessed based on both the fictitious weld toe radius and the addition of measured actual notch radius to the fictitious radius. While no large differences are observed between the results of methods, the former one is found to be more practical and faster to implement from the end-user point of view. [ABSTRACT FROM AUTHOR]

ABSTRACT A transient behaviour is observed in the numerical analysis of plasticity induced crack closure at the beginning of crack propagation, as the residual plastic field is being formed. The extent of crack propagation prior to plasticity induced crack closure measurement has a major influence on the accuracy of numerical prediction and on computation time. The objective here is to quantify and understand the minimum propagation, Δ astb, required to obtain stabilized crack opening values. For plane stress state, Δ astb was found to increase with Δ K. Under plane strain conditions, a peak of closure exists at the beginning of crack propagation for relatively low Δ K values, which promotes relatively large transient periods. Two driving forces explain the stabilization behaviour, the formation of residual plastic wake and the stabilization of plastic strain, but the second seemed to control the phenomenon. Finally, two strategies are proposed to accelerate convergence. The first, consisting of a progressive increase of maximum load, is relevant in plane strain and 3D studies, in order to eliminate the initial peak. The second strategy consists of an extrapolation model and is very effective for plane stress conditions. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper investigates the temperature dependence of the material length scale in the conventional mechanism-based strain gradient (CMSG) plasticity theory. The work reported here also examines the plastic strain gradient effect on the opening displacement near a sharp crack tip. The study examines the mechanical properties of two typical structural steels (S355 and S690) in onshore and offshore structures at two different temperatures (20 and 300 °C) through both the uniaxial tension test and the indentation test. The CMSG-based finite element analysis then confirms a constant material length scale for these two steels at the two tested temperatures, despite the apparent temperature dependence of the macroscopic material parameters measured from the tension test. Using the calibrated material length scale, the subsequent numerical study demonstrates that the magnitude of the near-tip crack opening displacement computed by the CMSG theory remains significantly lower than that computed from the classical plasticity. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper introduces a numerical model to estimate fatigue life under step-stress conditions, using the Weibull and lognormal distributions. The maximum likelihood method was used to estimate the free parameters of the distributions. The model was fitted to an experimental data on fatigue life in the specimens of steel SAE 8620, by using evolutionary computation to optimize the likelihood function. Results are reported on the values of the parameters and their confidence interval. Also, a validation of the model is discussed using analysis of residuals. [ABSTRACT FROM AUTHOR]

SUMMARY Wheeler, Sharma and Buisson proposed an elasto-plastic constitutive model for unsaturated soils that couples the mechanical and water retention behaviours. The model was formulated for isotropic stress states and adopts the mean Bishop's stress and modified suction as stress state variables. This paper deals with the extension of this constitutive model to general three-dimensional stress conditions, proposing the generalized stress-strain relationships required for the numerical integration of the constitutive model. A characteristic of the original model is the consideration of a number of elasto-plastic mechanisms to describe the complex behaviour of unsaturated soils. This work presents the three-dimensional formulation of these coupled irreversible mechanisms in a generalized way including anisotropic loading. The paper also compares the results from the model with published experiments performed under different loading conditions. The response of the model is very satisfactory in terms of both mechanical and water retention behaviours. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY This paper presents a numerical analysis of the influence of initial stress state on the response of deep excavation supported by retaining wall. Indeed, the influence of diaphragm wall installation prior to excavation works may affect the soil response and lateral wall deflection induced by excavation process. The first part of this paper gives a short review of the numerical methods aimed to reproduce the retaining wall installation. Numerical analysis of a deep excavation in two-dimensional and three-dimensional conditions is then performed according to the methods previously presented. In three-dimensional conditions, diaphragm wall installation is performed considering a sequence of panels, described by their number and length. Results of three-dimensional calculations confirm that stress state is disturbed by wall installation, which has a sensitive effect on the ground response induced by soil excavation. It is also noted that these results are not easily reproduced in two-dimensional conditions. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper deals with the problems of blunt V-notch with various notch shapes. The purpose is to develop a new method capable of obtaining more accurate solutions for the stress fields around a blunt V-notch tip under opening and sliding modes. The key method is to use the principle of superposition for linear elastic materials. On the basis of the superposition method and the conventional stress fields for a sharp V-notch, the stress fields useful for any shapes of blunt V-notch is proposed. The notch stress intensity factors are estimated by the numerical analysis with finite element analysis, and then the effectiveness and validation of the proposed superposition approach are discussed by comparison with the results from the literature. [ABSTRACT FROM AUTHOR]

Numerical investigations of a full three-dimensional (3D) packing process and flow-induced stresses are presented. The model was constructed on the basis of a 3D nonisothermal weakly compressible viscoelastic flow model combined with extended pom-pom (XPP) constitutive and Tait state equations. A hybrid finite element method (FEM)-finite volume method (FVM) is proposed for solving this model. The momentum equations were solved by the FEM, in which a discrete elastic viscous stress split scheme was used to overcome the elastic stress instability, and an implicit scheme of iterative weakly compressible Crank-Nicolson-based split scheme was used to avoid the Ladyshenskaya-Babuška-Brezzi condition. The energy and XPP equations were solved by the FVM, in which an upwind scheme was used for the strongly convection-dominated problem of the energy equation. Subsequently, the validity of the proposed method was verified by the benchmark problem, and a full 3D packing process and flow-induced stresses were simulated. The pressure and stresses distributions were studied in the packing process and were in agreement with the results of the literature and experiments in tendency. We particularly focused on the effects of the elasticity and pressure on the flow-induced stresses. The numerical results show that normal stress differences decreased with incremental Weissenberg number and increased with incremental holding pressure. The research results had a certain reference value for improving the properties of products in actual production processes. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

ABSTRACT This study applies a new scaled boundary element-free Galerkin (EFG) method to determine the coefficients of the Williams' series expansion for the elastic crack tip asymptotic stress field. Scaled boundary methods can calculate the coefficients of Williams' series without any special crack tip treatment. Unlike the conventional scaled boundary finite element method, in this paper an EFG approach is used in the circumferential direction of the scaled boundary model. The EFG method offers high accuracy, rapid convergence and smooth stress solutions without post-processing, and no mesh generation is required. The proposed method is verified through numerical examples comparing the new approach with analytical, reference and conventional scaled boundary FEM solutions, and results are obtained which indicate that the new approach converges even more rapidly than the conventional scaled boundary finite element method. [ABSTRACT FROM AUTHOR]

This paper presents a novel control methodology for robust high-precision positioning systems. This methodology is based on strain feedback using a piezoelectric element. The mechanical vibration modes at around the control bandwidth cause deterioration of system stability. This prevents the positioning performance from being robust, particularly against variations in the vibration frequency. In this research, therefore, a robust positioning system was designed by applying an additional compensation loop by strain feedback; here, a piezoelectric element that acts as a strain sensor detects the vibration signal. This makes the performance of the system robust. The proposed compensation approach has been verified by numerical analyses and by experiments using a positioning device for industrial galvano scanners. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(4): 41-50, 2012; Published online in Wiley Online Library (). DOI 10.1002/eej.21267 [ABSTRACT FROM AUTHOR]

ABSTRACT The main purpose of the paper is to propose a numerical method for evaluation of J-integral in plates made of functionally graded materials (FGM) with sharp and blunt V-notches under Mode I loading. The material properties have been assumed to be varied exponentially along the specimen width (notch direction). Using the proposed method, the effect of material gradient on the J-integral for two cases of sharp and blunt V-notches has been studied. The results have shown that in FGMs with sharp V-notches, the J-integral is not proportional to . So, the parameter JL is path dependent. It has been observed that the material gradient has larger effect on the J-integral in sharp V-notch compared with that in blunt V-notch. [ABSTRACT FROM AUTHOR]

ABSTRACT The fretting fatigue behaviours in 35CrMoA steel were investigated under conditions of the various contact pressure and the same maximum equivalent stress of cyclic multi-axial loading. The specimens were characterized by optical microscopy and scanning electron microscopy. Results showed that the fretting fatigue life has complex variation with the increase of contact pressure. The different contact pressure also played very important role in fretting wear model and various wear scars were formed. The influence of them at the fretting surface on the fretting fatigue life was finally discussed by the comparison of the experimental and numerical analysis results. [ABSTRACT FROM AUTHOR]

The safety of the 610 m Guangzhou New Television Tower, due to become China's tallest structure on completion, is an issue that concerns many parties because of the lack of sufficient experience, official design codes, and construction guidelines for such a skyscraper. This article investigates the strain/stress development of this supertall structure through the integration of finite element analysis and field monitoring during the construction stage with a particular focus on the following issues: (1) the shrinkage and creep properties of high-strength low-shrinkage concrete; (2) the strain response of the structure to extreme events including typhoons, a major earthquake, and unfavorable construction loads; and (3) the stress evolution of the supertall structure as construction activity progresses. Field monitoring results demonstrate that the strain responses of the structure to natural hazards are within safe ranges. Finite element model predictions made at different stages of construction are in good agreement with measurement data. The monitoring exercise described in this article provides the designer, the contractor, and the client valuable data regarding the safety of the tower. It verifies the effectiveness and importance of monitoring during the construction phase for such a complex supertall structure. [ABSTRACT FROM AUTHOR]

Finite element method is a commonly used method in the simulation of plate and shell deformation. Usually, researchers in this field establish elements based on displacements of nodes and gradients of displacements with respect to a reference configuration as nodal variables. Recently, a new formulation, absolute nodal coordinate formulation (ANCF), has been developed. In this formulation, the gradients of the global position vector are used as nodal coordinates and no rotations are interpolated over the finite element. In this paper, the application, efficiency and domain of the application of these two formulations have been studied by considering some numerical examples. These examples show that high nonlinearity and very large computation time and extra wrinkling in the predicted deformed shape of plate are some disadvantages of the ANCF models in comparison with the classical finite element method models. The major discussion is about the performance of ANCF shape functions for rectangular elements. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The subject of the study are open circular cylindrical thin shells with two edges supported and two edges free. The elastic buckling and limit load of these shells in pure bending state are investigated. The study includes simple analytical description, numerical analysis with the use of the Finite Element Method (FEM), and laboratory tests for shells. The results of these three investigation methods are compared and presented in figures. The critical load and limit load for these shells are described in detail. Moreover, an analytical formula of critical stresses for open circular cylindrical thin shells in pure bending state is proposed. The main goal of the paper is comparison of the results of critical load values obtained by analytical, numerical (FEM), and experimental methods. [ABSTRACT FROM AUTHOR]

This work is related to the so-called non-conventional finite element formulations. Essentially, a methodology for the enrichment of the initial approximation which is typical of the meshless methods and based on the clouds concept is introduced in the hybrid-Trefftz formulation for plane elasticity. The formulation presented allows for the approximation and direct enrichment of two independent fields: stresses in the domains and displacements on the boundaries of the elements. Defined by a set of elements and interior boundaries sharing a common node, the cloud notion is employed to select the enrichment support for the approximation fields. The numerical analysis performed reveals an excellent performance of the resulting formulation, characterized by the good approximation ability and a reduced computational effort. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to calculate and develop equations for crack-surface displacements for two-symmetric cracks emanating from a circular hole in an infinite plate for use in strip-yield crack-closure models. In particular, the displacements were determined under two loading conditions: (1) remote applied stress and (2) uniform stress applied to a segment of the crack surface (partially loaded crack). The displacements were calculated by an integral-equation method based on accurate stress-intensity factor equations for concentrated forces applied to the crack surfaces and those for remote applied stress or for a partially loaded crack surface. A boundary-element code was also used to calculate crack-surface displacements for some selected cases. Comparisons made with crack-surface displacement equations previously developed for the same crack configuration and loading showed significant differences near the location where the crack intersected the hole surface. However, the previous equations were fairly accurate near the crack-tip location. Herein an improved crack-surface displacement equation was developed for the case of remote applied stress. For the partially loaded crack case, only numerical comparisons were made between the previous equations and numerical integration. A rapid algorithm, based on the integral-equation method, was developed to calculate these displacements. Because cracks emanating from a hole are quite common in the aerospace industry, accurate displacement solutions are crucial for improving life-prediction methods based on the strip-yield crack-closure models. [ABSTRACT FROM AUTHOR]