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The present study proposes a finite element method (FEM)-based framework to assess the synergistic effect of hydrogen-induced damage (HID), internal pressure, and corrosion effects on the failure behavior of elbows. The mechanical properties degradation of pipeline steel subjected to HID is incorporated into the FE modeling to model corroded pipe elbows serviced in a hydrogen-rich environment. Two dimensionless metrics (σ max / σ y and σ max / σ u) are proposed to quantify the parameter effects and sensitivity. The results demonstrate that 1) the combination of corrosion effects, internal pressure, and HID significantly reduces the load-bearing capacity at the pipe elbow; 2) σ max / σ u exceed 1 in all cases under a hydrogen-rich environment for more than 12 h, indicating that prolonged exposure to an environment abundant in hydrogen may promote elbow failure; 3) the critical defect length (ϕ / π = 9 %) and neutral-line bend radius (R / D = 4.5) are determined, exceeding which the elbow failure behavior is significantly affected; 4) σ max / σ y and σ max / σ u are lower than 1 when the defect occurs at the extrados, implying that the synergistic effects of HID and corrosion are unlikely to cause the elbow failure if corrosion occurs at the extrados, but it is not applicable to defects occurring at other locations, especially at the intrados; 5) The maximum von Mises stress exhibits the highest sensitivity to internal pressure, followed by defect location, defect depth, neutral-line bend radius, defect length, and hydrogen damage. • Assessed pipe elbow condition under hydrogen-induced damage, corrosion effects, and internal pressure. • Modeled stress distribution at corrosion defect on pipe elbow with various parameter effects. • Proposed two dimensionless metrics to quantify the parameter effects and sensitivity. [ABSTRACT FROM AUTHOR]

This study aims to establish an effective method for predicting the fatigue life of an automotive wheel in the accelerated dynamic cornering fatigue test. The test was simulated by linear transient dynamic finite element analysis, in which a rotating force of constant magnitude was applied to the moment arm tip to simulate the rotational bending effect on the wheel, with the wheel being fixed. Furthermore, transient strain histories of the elements were obtained and the critical elements with the largest amplitudes in their respective steady radial strain histories were found. The steady radial strain histories of all the critical elements were processed based on the local stress-strain approach, and the shortest simulated fatigue lives were taken as the predicted wheel fatigue lives. The predicted fatigue life was in good agreement with the average real-world test life of the investigated wheel. [ABSTRACT FROM AUTHOR]

Systematic procedures are developed to investigate sealing characteristics of a 2-in-1 electronic connector applied to audio equipments in the present study. A silicon elastomer gasket located between a plastic housing of the connector and a back-cover of the audio equipment will be squeezed to provide the sealing function when the back-cover is displaced at a designated position. Gas is subsequently pumped into the confined chamber up to the specific pressure while the internal pressure is continuously monitored. Leakage indicated by the pressure loss percentage, however, could occur through the gasket after a certain period. A finite element analysis is performed to explore the time-dependent response of the silicon elastomer gasket. The Mooney–Rivlin and the Prony series constitutive models are employed in the numerical simulations to account for the hyperelasticity and the stress-relaxation behaviors of the gasket material, respectively. Required parameters of these mathematical models are evaluated based on experimental measurements of the specified silicon elastomer specimen subjected to the uniaxial compression–relaxation and tensile–relaxation loading conditions as well. Sealing performances can be then assessed by the introduction variations of the contact stress at the critical location of the gasket over the relatively long period to a proposed leakage rate prediction model. Pressure loss percentages in the chamber based on the numerical calculations agree well with those based on the corresponding experiments. In order to validate the appropriateness of the current developed procedures, the leakage of an enclosed cavity of an audio jack connector is further examined here. [ABSTRACT FROM AUTHOR]

The bridge crossing water way is in the risk of impact by vessel, and thus it is very important to estimate the collision force for the safety of bridge. The impact force between bridge pier and vessel is investigated by numerical simulation and various empirical formulae. The collision response between a 5000t DWT bulk carrier with bulb bow and rigid bridge pier is simulated in the explicit finite element code of ANSYS LS-DYNA. The difference of the impact force between the empirical formulae and FE analysis are discussed. Based on the comparison of the results, the coefficient in the formulae is suggested for obtaining more accurate assessment of impact force. [ABSTRACT FROM AUTHOR]

The maximum crack opening displacement is introduced to investigate the effect of compressive loads on crack opening stress in tension-compression loading cycles. Based on elastic-plastic finite element analysis of centre cracked finite plate and accounting for the effects of crack geometry size, Young's modulus, yield stress and strain hardening, the explicit expression of crack opening stress versus maximum crack opening displacement is presented. This model considers the effect of compressive loads on crack opening stress and avoids adopting fracture parameters around crack tip. Besides, it could be applied in a wide range of materials and load conditions. Further studies show that experimental results of d a/d N − Δ K curves with negative stress ratios could be condensed to a single curve using this crack opening stress model. [ABSTRACT FROM AUTHOR]

Load distribution factor (LDF) is an important index for evaluating the performance of existing bridges. However, few researchers have studied the change of transverse load distribution coefficients of beams before and after the widening and reinforcement of existing bridges. To work out such problem, a reinforcement method for widening longitudinal and cross beam was proposed. A Finite element (FE) model was built to simulate the widening reinforcement of existing bridge, Load distribution factor for all girders were analyzed in the cases of different position, quantity and stiffness of cross beam, different added width of girder, different existing bridge stiffness and different connection system. Results show that the LDF of side beams decreases by 63.92% to the highest extent after bridge reinforcement, which significantly improves load-carrying condition of girder. However, the LDF at fulcrum increases by 30% after reinforcement. Therefore, some strengthening measures are necessary in these positions. The quantity, position and dimension of cross beam have not much influence on the LDF of each girder. The LDF of beams are smaller when the widened girders are connected rigidly to the old girders than that hinge connected to. The LDF of each girder shows not much difference when the main beams are connected to widened girders with rigid or hinged connection, respectively. This study is meaningful for the development of widening and reinforcement design of existing bridges. [ABSTRACT FROM AUTHOR]

A new differential transformation method is developed in this paper and is applied for free vibration problem of pipes conveying fluid. The natural frequencies, critical flow velocities, and vibration mode functions of such pipes with several typical boundary conditions are obtained and compared with the results predicted by Galerkin method and finite element method (FEM) and with other results archived. The results show that the present method is of high precision and can serve as an analytical method for the vibration of pipes conveying fluid. [ABSTRACT FROM AUTHOR]

Dent-corrosion defects are a typical combination of defects and pose a significant threat to the safety and integrity of energy pipelines. In general, the corrosion features rather than dents are considered the primary factor of fitness-for-service of pipelines containing a dent-corrosion defect. In this work, a finite element (FE) based model was developed to predict the failure pressure of pipelines containing a dent-corrosion defect and investigate its dominant factor. Parametric analysis results demonstrated that the presence of dents reduced the failure pressure of corresponding pipelines containing a single corrosion defect. The dominant factor of the failure pressure changed from corrosion feature to dent feature if (1) an increase in dent depth and a decrease in the pipe diameter-to-thickness ratio, (2) exceeding the critical dent depth by 8% of diameter (D), and (3) below the critical indentation radius by 10% D. Longitudinal dent gave a significant reduction of the failure pressure, making dent feature a dominant factor; Oppositely, the effect of the circumferential dent was marginal. • The presence of dents reduces the failure pressure of corroded pipelines. • Parameter effects on failure pressure of combined defected pipelines are investigated. • The dominant factors of failure pressure under different conditions are determined. [ABSTRACT FROM AUTHOR]

The thermal behavior during the selective laser melting of metal powders is a key issue to the product quality in 3D printing, so it is of benefit to the development of 3D printing industries to explore the heat transfer characteristics during the selective laser melting process. Based on the TiAl 6 V 4 powder system, the energy conservation equation with a moving Gaussian energy source is developed, in which the temperature-dependent thermal physical properties of materials are taken into account. By means of the finite element methods, the temperature distribution and molten pool dimensions are presented, and the related modeling and numerical methods are validated by previous experimental and numerical works. The effects of the linear energy density, volume shrinkage, scanning track length, hatch spacing and time interval between two neighboring tracks on the temperature distribution and molten pool dimensions are obtained and analyzed. The results show that the increased laser power is superior to the reduced scan speed in thermal performance, which can improve the temperature distribution and molten pool dimensions. Shorter track, shorter hatch spacing and less time interval can lower the temperature gradient and increase the temperature of each track. The average temperature and dimensions of the molten pool are influenced by the volume shrinkage, which should be considered during the numerical simulation. [ABSTRACT FROM AUTHOR]

Three-dimensional finite element analysis of clamped single-edge tension specimen is performed to examine the accuracy of the crack-mouth opening displacement compliance equations reported in the literature. The analysis covered both plane-sided and side-grooved specimens with a wide range of specimen configurations including nine relative crack lengths (a/W) ranging from 0.1 to 0.9 and seven relative thicknesses (B/W) ranging from 0.25 to 4. Based on the finite element analysis results, the crack length/compliance modification factors ((a/W) and (BCE)) are developed to improve the accuracy of the compliance equations. The results of this study can improve the accuracy of the experimentally determined J-R and CTOD–R curves using the single-specimen technique and single-edge tension specimens. [ABSTRACT FROM AUTHOR]

Based on the two-dimensional elasticity theory, this study established a mechanical model under chordally opposing distributed compressive loads, in order to perfect the theoretical foundation of the flattened Brazilian splitting test used for measuring the indirect tensile strength of rocks. The stress superposition method was used to obtain the approximate analytic solutions of stress components inside the flattened Brazilian disk. These analytic solutions were then verified through a comparison with the numerical results of the finite element method (FEM). Based on the theoretical derivation, this research carried out a contrastive study on the effect of the flattened loading angles on the stress value and stress concentration degree inside the disk. The results showed that the stress concentration degree near the loading point and the ratio of compressive/tensile stress inside the disk dramatically decreased as the flattened loading angle increased, avoiding the crushing failure near-loading point of Brazilian disk specimens. However, only the tensile stress value and the tensile region were slightly reduced with the increase of the flattened loading angle. Furthermore, this study found that the optimal flattened loading angle was 20°-30°; flattened load angles that were too large or too small made it difficult to guarantee the central tensile splitting failure principle of the Brazilian splitting test. According to the Griffith strength failure criterion, the calculative formula of the indirect tensile strength of rocks was derived theoretically. This study obtained a theoretical indirect tensile strength that closely coincided with existing and experimental results. Finally, this paper simulated the fracture evolution process of rocks under different loading angles through the use of the finite element numerical software ANSYS. The modeling results showed that the Flattened Brazilian Splitting Test using the optimal loading angle could guarantee the tensile splitting failure initiated by a central crack. [ABSTRACT FROM AUTHOR]

The material prescription, potential distribution, contamination trend and surface insulating properties under contamination and lightning conditions for the ceramic long rod insulator are investigated. The surface contamination trend of the ceramic long rod insulator can be fitted to an exponential function in a low rainfall area. Potential distribution calculation by three-dimensional finite element method shows that over 50% operating voltage concentrates on the single unit of high-voltage polarity for the long rod insulator string, which is more uneven in comparison with the disc ceramic insulator string. Five-hundred kilovolt full-scale artificial pollution test demonstrates that the contamination flashover voltage of the ceramic long rod insulator has a negative exponential relationship with equivalent salt deposit density and a linear relation with string length. A lightning impulse discharge test confirmed that the relation between 50% lightning impulse discharge voltage and dry arcing distance was also linear for a ceramic long rod insulator string. [ABSTRACT FROM AUTHOR]

ABSTRACT Three-dimensional (3D) finite element analyses are carried out on single-edge bend [SE(B)] specimens for which the J-integral resistance curves ( J-R curves) have been experimentally determined to develop the constraint-corrected J-R curves for the X80 grade pipe steel. The constraint parameters considered in this study include QHRR, QSSY, Q SSY_ m, QLM, Q BM1, Q BM2, A2, h and Tz. The constraint-corrected J-R curves were developed on the basis of the constraint parameters obtained from finite element analysis and experimentally determined J-R curves associated with deeply cracked and medium-cracked SE(B) specimens and validated against shallow-cracked SE(B) specimens. The analysis results indicate that all the constraint parameters considered in this study except QHRR, QSSY, Q SSY_ m and QLM lead to reasonably accurate constraint-corrected J-R curves if the crack extensions are relatively small (≤0.7 mm). For larger crack extensions (≤1.5 mm), the Q BM1-based constraint-corrected J-R curve leads to the most accurate predictions of J among all the constraint parameters considered. [ABSTRACT FROM AUTHOR]

Huang Y., Keilig L., Rahimi A., Reimann S., Bourauel C: Torque capabilities of self-ligating and conventional brackets under the effect of bracket width and free wire length Orthod Craniofac Res 2012; 15:255-262. © John Wiley & Sons A/S Structured Abstract Objectives - To numerically investigate the torque capacity of conventional and self-ligating brackets under the effect of varying bracket width and free wire length. Material and Methods - Finite element models of three kinds of orthodontic brackets in the 0.022-inch slot size were investigated: Discovery, Damon 3MX, Speed. Additionally, finite element (FE) models of Speed and Damon brackets were generated with the same width as the Discovery. From the left upper incisor to the right upper canine, four brackets each were modelled. The total wire length at the upper right incisor was kept constant at 12 mm for all brackets types. For the Discovery brackets, the wire length was increased from 12 to 16 mm in 2-mm steps. A torque of 20° was applied to the upper right incisor with 0.46 × 0.64 mm2 (0.018″ × 0.025″) and 0.48 × 0.64 mm2 (0.019″ × 0.025″) wires. Wires made of stainless steel, titanium molybdenum and nickel titanium were studied. Torque angle/moment characteristics were recorded. Results - Wider brackets showed more torque control capability (e.g. Discovery: 10.6 Nmm, Damon: 9.2 Nmm, Speed: 4.0 Nmm for the NiTi wire). Even with the same width as the Discovery bracket, Damon and Speed brackets showed lower torque capability than the Discovery bracket. Increasing the free wire length decreased the torsional stiffness of the wire and thus decreased the torque capability. Conclusion - The results showed that the bracket design has less influence on the torquing moment than other parameters, such as bracket width, free wire length, wire/slot play or misalignment. [ABSTRACT FROM AUTHOR]

This study seeks a practical method for simulating the vertical bending fatigue test of the BANJO housing of a five-link rear axle. Linear static and transient dynamic finite element models are constructed for the rear axle in which the rubber bushings and the bearings of the axle shafts are reasonably modeled with solid and shell elements, respectively, for simplicity. The calculated results are compared with the measured strain histories, and the results indicate that the finite element models constructed are reasonable. The hypothesis of equal fatigue damage is applied to determine the Hainan proving ground driving life prediction that is equivalent to the constant amplitude fatigue life in the vertical bending fatigue test. [ABSTRACT FROM AUTHOR]

Abstract: A crystal plasticity based finite element model is developed to simulate grain fragmentation during equal-channel angular extrusion (ECAE). Route C multiple passes are approximated by repetitive planar simple shears. Results are presented in terms of plastic strain distribution, texture and grain size evolution. Numerical results are found to be in qualitative agreement with experimental observations associated with the grain refinement in ECAE. [Copyright &y& Elsevier]

We consider the Stokes problem on a plane polygonal domain Ω ⊂ R2. We propose a finite element method for overlapping or nonmatching grids for the Stokes problem based on the partition of unity method. We prove that the discrete inf-sup condition holds with a constant independent of the overlapping size of the subdomains. The results are valid for multiple subdomains and any spatial dimension. [ABSTRACT FROM AUTHOR]

The extended rmin technique is incorporated into an incrementally updated Lagrangian formulation (ULF) of an elasto-plastic finite element computer code in order to handle contact boundary conditions to analyse the axisymmetric tube flaring process with a conical tool. A modified Coulomb friction law was adopted to calculate the influence of the friction coefficient on the tube flaring process. The effects of size and mechanical properties of tubes, as well as lubricants and tool semi-angle on flaring load were studied. It was found that good lubrication is effective in reducing flaring load. An optimum tool semi-angle (tool load is lower) in flaring is determined by frictional and bending activity at the tool inlet. In addition, the forming behaviour of the tube end is investigated to understand whether outward curling takes place and how much influence the tool semi-angle and tube size (initial thickness/initial mean diameter of tube) have on outward curling mode. [ABSTRACT FROM AUTHOR]

The multiscale simulation is important to the development of nanotechnology and to the study of materials and systems across multiple length scales. In order to develop an efficient and accurate multiscale computation method within a unified theoretical framework, we propose an order-N atomic-scale finite element method (AFEM). It is as accurate as molecular mechanics simulations, but is much faster than the widely used order-N2 conjugate gradient method. The combination of AFEM and continuum finite element method provides a seamless multiscale computation method suitable for large scale static problems. [Copyright &y& Elsevier]

In many investigations, a liquid crystal display (LCD) has been used as the photo mask in a stereolithography system. The LCD mask has the potential to increase the speed of rapid prototyping (RP) fabrication as well as to reduce the system cost. Compared to the conventional laser-scanning technique used in 3D systems stereolithography apparatus (SLA), the reaction heat of layer curing is released as the area is exposed, and it is higher than that of the laser scanning in which the reaction heat only releases point-by-point. On the other hand, mask type stereolithography has a more serious shrinkage effect than the other methods and requires further analysis. This paper analyses the shrinkage deformation of the mask type stereolithography process. A simulation code based on the dynamic finite-element method has been developed to predict the 3D shrinkage and to monitor the RP fabrication, which consists of three stages of simulation which include the pre-processor, the analytic processor and the post-processor. In order to fabricate experimental parts, a mask type stereolithography system has been assembled. The principle of the experimental apparatus is also briefly described. For evaluation of the experimental and simulation results, a thin shell wall rectangular part was fabricated and measured. The simulation program developed has been proved to be in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Stereolithography is one of the rapid prototyping processes which uses a photopolymer as the raw material to build prototypes. The photopolymer absorbs energy by selective laser exposure. The curing effect starts when the absorbing energy exceeds a critical value, and the process is called photopolymerisation. The photopolymerisation changes the phase from liquid to solid. The cured volume can expand and then shrink on cooling. The process parameters such as the scanning speed, scanning path, scanning pitch, and the slicing thickness, lead to different shrinkage and curl distortion, so, the photopolymerisation process is a dynamic material behaviour. In this study, a dynamic finite element simulation code has been developed to simulate the photopolymerisation process. The simulated result for a suspended beam which corresponds to the process parameters shows that a short raster causes less curl distortion than a long raster. The experimental result agrees very well with the simulated result. [ABSTRACT FROM AUTHOR]

The performance variation caused by the stress field near a through-silicon via (TSV) is measured using 28-nm node devices across 12-in wafers. The TSV is fabricated by a via-last process. The back-end-of-line dielectrics on TSV cause the asymmetric stress field, i.e., the absolute value of radial stress ( \vert \sigma r\vert ) does not equal to that of tangential stress ( \vert \sigma \theta \vert ) on silicon and leads to the asymmetric keep-out zone (KOZ), different from previously reported. A modified KOZ model with the asymmetric radial and tangential stress field is proposed and verified by 3-D finite-element analysis simulation and experiment data. The physics behind the asymmetry is also described. Comparable KOZ size for nFETs and pFETs is observed. [ABSTRACT FROM AUTHOR]

This letter presents experimental, numerical, and analytical studies of Au thin films on elastomeric substrates of poly(dimethylsiloxane) that are designed with sinusoidal, “wavy” features of surface relief. Such systems can be useful as stretchable conductors in electronic or sensory devices. The maximum film strain is obtained in terms of film and substrate elastic moduli, film thickness, amplitude and wavelength of the wavy profile, and the applied strain. These analytical solutions agree well with both finite element analysis and experimentally measured changes in the sinusoidal profile under small, uniaxial strains. A simple expression for the system stretchability and compressibility is established. [ABSTRACT FROM AUTHOR]

Buckled thin films on elastomeric substrates have many applications. Films of this type exhibit periodic, sinusoidal “wavy” relief profiles, except near edges that lie perpendicular to the wavevector associated with waves. In these locations, the amplitudes of the waves steadily decrease until the films become completely flat, in a manner that can be used to advantage in applications. This paper quantitatively describes the mechanics of this phenomenon. The finite element analysis shows that the edge effect results from the traction-free boundary condition. The edge-effect length is proportional to the thin-film thickness, and decreases with the increasing prestrain and substrate modulus. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an efficient method to optimize the intermedial tool surfaces in the multi-step sheet metal stamping process to obtain improved quality of a product at the end of forming. The proposed method is based on a combination of finite element modeling (FEM) and the response surface method (RSM). The objective of the optimization is to minimize the thickness variation of the part at the final stage. The constraint function of local fracture is introduced by the use of the forming limit curve (FLC). With acceptable accuracy and high efficiency, the multi-step inverse method is used together with RSM to check various intermediate surfaces to search for the optimal shape parameters. After the convergence of the optimization, the result is validated using commercial software DYNAFORM®. [Copyright &y& Elsevier]

Nix and Gao [J. Mech. Phys. Solids46, 411 (1998)] established an important relation between the microindentation hardness and indentation depth for axisymmetric indenters. We use the conventional theory of mechanism-based strain gradient plasticity [Y. Huang et al., Int. J. Plast.20, 753 (2004)] established from the Taylor dislocation model [G.I. Taylor, Proc. R. Soc. London A145, 362 (1934); G.I. Taylor, J. Inst. Met.62, 307 (1938)] to study the Berkovich and other triangular pyramid indenters. The three-dimensional finite element analysis shows that the widely used equivalence of equal base area leads to significant errors, particularly in microindentation. A new equivalence of equal angle is proposed for triangular pyramid indenters, and it has been validated for a large range of indenter angles and indentation depths. [ABSTRACT FROM AUTHOR]

Abstract: Nix and Gio [Nix, W.D., Gao, H.J., 1998. Indentation size effects in crystalline materials: a law for strain gradient plasticity. Journal of the Mechanics and Physics of Solids 46, 411–425] established an important relation between the micro-indentation hardness and indentation depth for axisymmetric indenters. For the Berkovich indenter, however, this relation requires an equivalent cone angle. Qin et al. [Qin, J., Huang, Y., Xiao, J., Hwang, K.C., 2009. The equivalence of axisymmetric indentation model for three-dimensional indentation hardness. Journal of Materials Research 24, 776–783] showed that the widely used equivalent cone angle from the criterion of equal base area leads to significant errors in micro-indentation, and proposed a new equivalence of equal cone angle for iridium. It is shown in this paper that this new equivalence holds for a wide range of plastic work hardening materials. In addition, the prior equal-base-area criterion does not hold because the Berkovich indenter gives much higher density of geometrically necessary dislocations than axisymmetric indenter. The equivalence of equal cone angle, however, does not hold for Vickers indenter. [Copyright &y& Elsevier]

Abstract: The effect of superimposed hydrostatic pressure on fracture in round bars under tension is studied numerically using the finite element method based on the Gurson damage model. It is demonstrated that while the superimposed hydrostatic pressure has no noticeable effect on necking, it increases the fracture strain due to the fact that a superimposed pressure delays or completely eliminates the nucleation, growth and coalescence of microvoids or microcracks. The experimentally observed transition of the fracture surface, from the cup-cone mode under atmospheric pressure to a slant structure under high pressure, is numerically reproduced. It is numerically proved that the superimposed hydrostatic pressure has no effect on necking for a damage-free round bar under tension. [Copyright &y& Elsevier]

Abstract: The stress distribution outside the contact-induced plastic zone can be estimated by the superposition of a Hertzian field and the field for an embedded center of dilatation (ECD) in a half-space, while the residual stress distribution can be estimated by the ECD field alone. This model has a simple closed-form analytical expression, matching with finite element results nearly perfectly. [Copyright &y& Elsevier]

Abstract: The effective elastic properties of a fiber-reinforced composite material with multiple transversely isotropic inclusions are estimated by the use of a generalized self-consistent method, which considers strong interactions between the inclusion and matrix as well as among inclusions. The accuracy of this method is established by comparing to the closed-form analytic solutions by Christensen when the matrix and inclusion are isotropic. Furthermore, current predictions from the generalized self-consistent method for a composite with multiple inclusions correspond well with the numerical results from finite element analysis. The generalized self-consistent method can be particularly useful in establishing micromechanics models of natural biological composite materials such as cortical bone to examine the dependence of the elastic properties of cortical bone on its porosity. [Copyright &y& Elsevier]

Transfer printing is a volatile tool to retract micro devices from a donor substrate via elastomeric stamps, from which the devices are grown or fabricated, followed by printing to a receiver substrate where the device is assembled to an array for integration in various applications. Among the five approaches of transfer printing summarized in the paper, the viscoelastic property of stamps is widely adopted to modulate the interfacial adhesion between the stamp and devices by applying different pulling speeds. A viscoelastic model for transfer printing is analytically established. It shows that the interfacial adhesion increases with pulling speed, which is verified by the experiments and numerical simulations. [ABSTRACT FROM AUTHOR]

Abstract: The combined analysis of the fracture toughness enhancement of carbon nanotube (CNT)-reinforced composites is herein carried out on the basis of atomistic simulation, shear-lag theory and facture mechanics. It is found that neither longer reinforced CNTs nor stronger CNT/matrix interfaces can definitely lead to the better fracture toughness of these composites. In contrast, the optimal interfacial chemical bond density and the optimal CNT length are those making the failure mode just in the transition from CNT pull-out to CNT break. To verify our theory, an atomic/continuum finite element method (FEM) is applied to investigate the fracture behavior of CNT-reinforced composites with different interfacial chemical bond densities. Our analysis shows that the optimal interfacial chemical bond density for (6,6) CNTs is about 5–10% and that increasing the CNT length beyond 100nm does not further improve fracture toughness, but can easily lead to the self-folding and clustering of the CNTs. The proposed theoretical model is also applicable to short fiber-reinforced composites. [Copyright &y& Elsevier]

The effect of cladding a ductile layer on necking and fracture in sheet metals under plane strain tension is studied numerically using the finite element method based on the Gurson damage model. It is demonstrated that the cladding increases both the necking and fracture strains. The increase in necking strain is due to the fact that cladding a ductile layer enhances the overall work hardening for the layered metal sheets according to the rule of mixtures. Furthermore, the increase in necking strain slows down the development of the the axial tensile stress inside the neck, which delays the void nucleation and growth, and which, in turn, contributes to enhancement in ductility. [ABSTRACT FROM AUTHOR]

Abstract: A batch of constitutive models for steel reinforcing bar, prestressing tendon, concrete and fiber-reinforced plastic are proposed for the nonlinear finite element analysis of reinforced concrete structures, prestressed concrete structures, reinforced concrete structures strengthened by fiber-reinforced plastics and prestressed concrete structures strengthened by fiber-reinforced plastics. These material models have been tested against series of experimental data and good agreements have been obtained, which justifies the validity and the usefulness of the proposed nonlinear constitutive models. [Copyright &y& Elsevier]

Abstract: Atomic-scale finite element analyses show that 2:1 internal resonance mechanism exists in a range of single-walled carbon nanorings (10–60). When an initial radial breathing mode (RBM) vibration with sufficiently high velocity is imposed to a nanoring, circumferential flexural modes (CFMs) can be excited after a period of RBM-dominated vibration. Then, mode transformations between RBM and the excited CFMs can be observed in the subsequent vibration process. When single-walled carbon nanorings are assembled to make double- or triple-walled carbon nanorings, the 2:1 internal resonance may change to 1:1 internal resonance in a specific ring due to the strong interactions between these nanorings. Furthermore, mode transformations between RBM and the excited CFMs can become unstable in a specific ring if the excited CFMs in neighbouring layer rings are not symmetrically matching between each other. 2:1 internal resonance is also shown in selected armchair single-walled carbon nanotubes except in a special case (armchair (9,9)), in which 1:1 internal resonance occurs. [Copyright &y& Elsevier]

Abstract: A shell theory established from the interatomic potential for carbon nanotubes is compared with the atomistic simulations. This shell theory is implemented in the finite element program ABAQUS via its user-material subroutine UGENS for shells. The numerical results for the representative loadings of tension, torsion and bending agree well with the atomistic simulations, which provide direct validation of this atomistic-based shell theory for carbon nanotubes. [Copyright &y& Elsevier]

Abstract: The effect of superimposed hydrostatic pressure on sheet metal formability is studied analytically and numerically. A tensile sample of power-law hardening material under superimposed hydrostatic pressure is first analyzed using the classical isotropic plasticity theory. It is demonstrated that the superimposed hydrostatic pressure p lowers the true tensile stress level at yielding by the amount of p, while material work-hardening is independent of p. It is showed, based on the Considère criterion, that the superimposed hydrostatic pressure increases the uniform strain. The effect of superimposed hydrostatic pressure on sheet metal formability is further assessed by constructing the Forming Limit Diagram (FLD) based on the M-K approach. It is found that the superimposed pressure delays the initiation of necking for any strain path. The difference in predicted FLDs between the superimposed hydrostatic pressure and the stress component normal to the sheet plane is demonstrated. Finally, the effect of superimposed hydrostatic pressure on fracture in round bars under tension is studied numerically using the finite element method, based on the Gurson damage model. The experimentally observed transition of the fracture surface, from the cup-cone mode under atmospheric pressure to a slant structure under high pressure, is numerically reproduced. [Copyright &y& Elsevier]

Abstract: A finite-deformation theory is developed to study the mechanics of thin buckled films on compliant substrates. Perturbation analysis is performed for this highly nonlinear system to obtain the analytical solution. The results agree well with experiments and finite element analysis in wavelength and amplitude. In particular, it is found that the wavelength depends on the strain. Based on the accurate wavelength and amplitude, the membrane and peak strains in thin films, and stretchability and compressibility of the system are also obtained analytically. [Copyright &y& Elsevier]

Abstract: The finite element method is used to numerically simulate localized necking in AA6111-T4 under stretching. The measured EBSD data (grain orientations and their spatial distributions) are directly incorporated into the finite element model and the constitutive response at an integration point is described by the single crystal plasticity theory. We assume that localized necking is associated with surface instability, the onset of unstable growth in surface roughening. It is demonstrated that such a surface instability/necking is the natural outcome of the present approach, and the artificial initial imperfection necessitated by the macroscopic M–K approach [Marciniak and Kuczynski (1967). Int. J. Mech. Sci. 9, 609–620] is not relevant in the present analysis. The effects of spatial orientation distribution, material strain rate sensitivity, texture evolution, and initial surface topography on necking are discussed. It is found that localized necking depends strongly on both the initial texture and its spatial orientation distribution. It is also demonstrated that the initial surface topography has only a small influence on necking. [Copyright &y& Elsevier]

Abstract: The effect of damage due to particle debonding on the constitutive response of highly filled composites is investigated using two multiscale homogenization schemes: one based on a closed-form micromechanics solution, and the other on the finite element implementation of the mathematical theory of homogenization. In both cases, the particle debonding process is modeled using a bilinear cohesive law which relates cohesive tractions to displacement jumps along the particle–matrix interface. The analysis is performed in plane strain with linear kinematics. A detailed comparative assessment between the two homogenization schemes is presented, with emphasis on the effect of volume fraction, particle size and particle-to-particle interaction. [Copyright &y& Elsevier]

This paper employs the atomic-scale finite element method (AFEM) to study critical strain of axial buckling for carbon nanotubes (CNTs). Brenner et al. "second-generation" empirical potential is used to model covalent bonds among atoms. The computed energy curve and critical strain for (8,0) single-walled CNT (SWNT) agree well with molecular dynamics simulations. Both local and global buckling are achieved, two corresponding buckling zones are obtained, and the global buckling behavior of SWNT with a larger aspect ratio approaches gradually to that of a column described by Euler's formula. For double-walled CNTs with smaller ratio of length to outer diameter, the local buckling behavior can be explained by conventional shell theory very well. AFEM is an efficient way to study buckling of CNTs. [ABSTRACT FROM AUTHOR]