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Background: Damage index parameters that have been formulated to identify damage localization in plastically deformed materials typically require all six stress or strain components. Recently, simulations through Crystal Plasticity Finite Element Method (CPFEM) have been widely used to extract damage initiation parameters. However, these models are rarely verified due to the challenges in measuring the out of plane deformation/strains experimentally. Objective: A damage index combining the effective plastic strain and surface roughness change is investigated for identifying damage accumulation sites in a tensile sample. Method: A point-wise Digital Image Correlation (DIC) technique is developed to measure large deformations from surface topography images, based on which the effective plastic strains and the surface roughness changes are determined at different load levels. A simple technique that creates random, micro size reflective speckles for sub-grain strain calculation is demonstrated. Results: Damage accumulation sites detected by the effective strain, surface roughness change, and the combined damage index are assessed in terms of damage localization and localization consistency. The combined damage index identified the localized damage accumulation sites consistently after the yielding load. In contrast, the effective strain damage index showed a low degree of localization and consistency while the surface roughness damage index detected only half of the damage accumulation sites identified by the combined damage index. The detected damage accumulation sites were found to be associated with grain orientations that favor "sunken" out-of-plane deformations and large misorientations among neighboring grains. Conclusions: Considering both effective plastic strain and out of plane surface deformation, the combined damage index provides an enhanced damage localization and localization consistency. [ABSTRACT FROM AUTHOR]

In this paper, numerical study on crack location and crack number on the responses of representative unit cell of unidirectional composites under tension is conducted by extended finite element method (XFEM). The composites studied here are single-crack composites, two-crack composites, and three-crack composites. Each of the composites is under tension in the fiber (x) direction. From the simulation results, the averaged strength decreases as the embedded crack number increases when composites are under tension. One interesting finding is that a crack could be a dominant crack but becomes inactive when other different cracks are in presence under the same loads. The responses of representative unit cell of composites depend upon crack location and the applied loading direction. The results from these simulations can also explain why there is discrepancy of strength prediction from the composites manufactured under the same conditions. The simulation method presented here in this paper can be used to model degree of defects (by modelling the number of cracks) and stochastic characteristics of ultimate strength (by modelling distribution of crack strength). [ABSTRACT FROM AUTHOR]

Nanocrystalline soft magnetic materials are known to be prepared by primary crystallization of Fe-based amorphous precursors. Since the crystallization reaction is exothermic, the amorphous precursor may experience a temporary rise in its temperature relative to its surroundings during the process of nanocrystallization. Given the typical latent heat of primary crystallization (∼ 100 kJ/kg), this temperature rise may exceed hundreds of degrees if not adequately controlled and thus, lead to the formation of unwanted magnetically hard compounds. This effect is generally small for isolated ribbons annealed with a moderate heating rate. However, the recent adoption of high heating rates and short annealing times has caused the self-heating effect to become relevant even for small sample sizes. In this work, the effect of self-heating on the microstructure and magnetic properties of nanocrystalline Fe86B14 is investigated. It is found that magnetically hard Fe-B compounds cannot be avoided when annealing under vacuum in an infrared furnace with a heating rate ≥3 K/s due to the self-heating effect. However, the high thermal conductivity of the copper blocks used by the ultra-rapid annealing process can successfully prevent a self-heating induced temperature rise during annealing, avoiding unwanted compound formation. Finite Element Analysis is also used for predicting the extent of self-heating during infrared annealing. [ABSTRACT FROM AUTHOR]

The article presents a response by the authors to the comments of their study on cantilever deflections in undrained clay. Topics include the issues on soil stiffness estimation with hardening soil using finite element method, the introduction of modified system stiffness parameters for deep excavations and the uncertainty of finite element method in estimating soil stiffness.

The mechanism of brain contusion has been investigated using a series of three-dimensional (3D) finite element analyses. A head injury model was used to simulate forward and backward rotation around the upper cervical vertebra. Intracranial pressure and shear stress responses were calculated and compared. The results obtained with this model support the predictions of cavitation theory that a pressure gradient develops in the brain during indirect impact. Contrecoup pressure-time histories in the parasagittal plane demonstrated that an indirect impact induced a smaller intracranial pressure (-53.7 kPa for backward rotation, and -65.5 kPa for forward rotation) than that caused by a direct impact. In addition, negative pressures induced by indirect impact to the head were not high enough to form cavitation bubbles, which can damage the brain tissue. Simulations predicted that a decrease in skull deformation had a large effect in reducing the intracranial pressure. However, the areas of high shear stress concentration were consistent with those of clinical observations. The findings of this study suggest that shear strain theory appears to better account for the clinical findings in head injury when the head is subjected to an indirect impact. [ABSTRACT FROM AUTHOR]

In this research, the dynamic responses of a jacket-style offshore wind turbine under wind loads and coupled wind–ocean–wave loads are studied. The wind turbine is modelled by shell-based finite element model whereas the jacket-style foundation is modelled by beam-elements. Studies on natural vibration frequencies for both full model and lumped mass model show that using the lumped mass model may not capture natural vibration modes that can only be observed in the full model. The comparison of dynamic analysis between the full model and the lumped mass model shows that some responses in the full model are one order of magnitude larger than those in the lumped mass model. This study suggests that, a shell-element based full model is recommended in order to reliably predict the responses of offshore wind turbines under wind loads and coupled wind–ocean–wave loads. [ABSTRACT FROM AUTHOR]

This work presents a critical evaluation of the model factor for the mobilized strength design (MSD) method for cantilever deflection in undrained soft to medium-stiff clay. The model factor is characterized in two parts. A correction factor is first defined as the ratio between the wall-top deflection computed from the FEM and its corresponding value computed from the MSD. The hardening soil with a small-strain model is used in FEM. The statistics of are evaluated using 82 numerical simulations. Because is not random, and therefore cannot be modeled directly as a random variable, it is decomposed as a product of a systematic part () and a random part (). The random part is modeled as a lognormal random variable with a mean of 1.01 and a coefficient of variation (COV) of 0.18. The model factor for FEM () is next defined as the ratio between the measured wall-top deflection and the corresponding FEM result. The statistics of are evaluated using 45 field cases. The ratio is random and can be modeled directly as a lognormal random variable with a mean of 1.01 and a COV of 0.21. The model factor for MSD () is finally derived from the product of and . This proposed approach is validated by 14 centrifuge tests. The importance of including the proposed model factor in reliability analysis is illustrated using a field example. [ABSTRACT FROM AUTHOR]

In this paper, we utilized a bottom-up method to predict the transverse thermal conductivity of pitched-based carbon fibers. We used molecular dynamics simulations with Green-Kubo formalism to calculate the in-plane thermal conductivity and out-of-plane thermal conductivity of the graphite sheets. The effects of waviness on the thermal conductivity of the graphite sheets were studied by MD simulations. The calculated in-plane thermal conductivity and out-of-plane thermal conductivity of graphite sheets from MD simulations were then used for the prediction of transverse thermal conductivity of the pitch fibers by finite element method. In the finite element simulations, the waviness in the graphite sheets was found to decrease the transverse thermal conductivity of pitch fibers, though not significantly. The defects observed in the pitch fibers were simulated by the damage elements in the finite element analysis. The simulation results showed that the proposed model, in which 12.5% of damage was included, predicted the effective transverse thermal conductivity well compared to the value measured from experiments. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the integrated optimization of actuator placement and vibration control for piezoelectric adaptive truss is studied. Based on the dynamic finite element (FE) model and a linear-quadratic-Gaussian (LQG) model of vibration control for an adaptive truss, an integrated optimization model is built in which an improved quadratic performance index is adopted as the objective function and the mode closed-loop damping ratio, modal controllability and actuator number are selected as the constraints. A layered optimization strategy is implemented to address this optimization problem with discrete-continuous design variable. To prevent the optimization process from converging to the local optimal solution, the genetic algorithm (GA) for outside-layer optimization is extended with an improved penalty function. Numerical examples and the vibration control experiments for piezoelectric adaptive truss were used to validate the efficiency of the proposed method. The following conclusions were drawn from the results. (1) The improved penalty function can orient the optimization process to the global optimal solution. (2) Although the number of struts on the truss is large, the optimization computation time is short because of the high efficiency of the proposed method. (3) In the experiment, the quadratic performance index, modal response and sensor signals for the present paper''s optimal actuator placement scheme are better than those described in the literature, but the placement requires more energy, which is consistent with the numerical results. [Copyright &y& Elsevier]

A dual-resonator microstructure design is proposed for acoustic metamaterials to achieve broadband effective mass negativity. We demonstrate the advantage of acoustic wave attenuation over a wider frequency spectrum as compared to the narrow band gap of a single-resonator design. We explicitly confirm the effect of negative effective mass density by analysis of wave propagation using finite element simulations. Examples of practical application like vibration isolation and blast wave mitigation are presented and discussed. [ABSTRACT FROM AUTHOR]

In this paper, we studied the effect of microscopic surface roughness on heat transfer between aluminum and water by molecular dynamic (MD) simulations and macroscopic surface roughness on heat transfer between aluminum and water by finite element (FE) method. It was observed that as the microscopic scale surface roughness increases, the thermal boundary conductance increases. At the macroscopic scale, different degrees of surface roughness were studied by finite element method. The heat transfer was observed to enhance as the surface roughness increases. Based on the studies of thermal boundary conductance as a function of system size at the molecular level, a procedure was proposed to obtain the thermal boundary conductance at the mesoscopic scale. The thermal boundary resistance at the microscopic scale obtained by MD simulations and the thermal boundary resistance at the mesoscopic scale obtained by the extrapolation procedure can be included and implemented at the interfacial elements in the finite element method at the macroscopic scale. This provides us a useful model, in which different scales of surface roughness can be included, for heat transfer analysis. [ABSTRACT FROM AUTHOR]

Aim To evaluate the ex vivo effects of damping on stress concentration in root filled premolar teeth. Methodology Damping ratios of maxillary premolar teeth that had undergone root canal treatment were tested in a laboratory model. In addition, two-dimensional finite element (FE) models were established for dynamic analysis. Results The mean-damping ratio was significantly lower in premolar teeth that had undergone root canal preparation (8.50 ± 0.53%) than in unprepared teeth (14.42 ± 2.17%) ( P < 0.05). However, root filling had a significant positive effect on the damping ratio of the tooth (10.84 ± 1.70%) ( P < 0.05). When the damping ratio was taken into consideration, FE analysis revealed that peak stresses in the apical one-third of the root on the buccal side were reduced by 31.8% when mastication forces were applied on the palatal cusp and occlusal fossa. Conclusion Pulp tissue plays an important role in providing protective effects when teeth are subjected to a dynamic load. However, root filled teeth do not provide such protective effects. [ABSTRACT FROM AUTHOR]

Abstract: We study Adini’s elements for nonlinear Schrödinger equations (NLS) defined in a square box with periodic boundary conditions. First we transform the time-dependent NLS to a time-independent stationary state equation, which is a nonlinear eigenvalue problem (NEP). A predictor–corrector continuation method is exploited to trace solution curves of the NEP. We are concerned with energy levels and superfluid densities of the NLS. We analyze superconvergence of the Adini elements for the linear Schrödinger equation defined in the unit square. The optimal convergence rate is obtained for quasiuniform elements. For uniform rectangular elements, the superconvergence is obtained for the minimal eigenvalue, where or . The theoretical analysis is confirmed by the numerical experiments. Other kinds of high order finite element methods (FEMs) and the superconvergence property are also investigated for the linear Schrödinger equation. Finally, the Adini elements-continuation method is exploited to compute energy levels and superfluid densities of a 2D Bose–Einstein condensates (BEC) in a periodic potential. Numerical results on the ground state as well as the first few excited-state solutions are reported. [Copyright &y& Elsevier]

The aim of this study was to measure the structural damping constants of premolars after treatment with a cast Co-Cr post-core system or permanent root filling, and to evaluate the stress damping effects of these restored premolars. Both the damping ratio and the natural frequency (NF) of the cast Co-Cr post-core restored premolars and the permanent root-filled premolars were detected by in-vitro NF testing experiments. Unprepared premolars served as the control. The damping constants β of the samples were calculated from the measured damping ratios and natural frequencies. The measured damping constants β of the test premolars were then used for dynamic finite element (FE) analyses. Stress contours and damping effects of stresses in each treated type of premolar were computed and compared using ANSYS. The measured damping constants β were 0.75x10-5 for the unprepared premolars, 0.69x10-5 for the root-filled premolars with coronal restoration, and 0.72x10-5 for the cast Co-Cr post-core restored premolars. The unprepared intact premolars demonstrated the highest stress dissipation effects with a ratio of 29.3 per cent at the middle root opposite to the loading side. However, no stress dissipation effects were found in the premolars that had been restored with the cast Co-Cr post-core system. The FE analysis showed that metallic post treatment attenuated the damping properties of the premolar. The effects of damping on stress concentration were significantly lower in restored premolars than in untreated vital premolars. These findings suggest that future research on post material should take the damping property into consideration. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the potential for using the natural frequency (NF) as a parameter to detect vertical bone loss at the furcation of human molars as well as to assess the role that the surrounding bone plays in maintaining molar stability. A three-dimensional finite element model of the human maxillary molar was built. The NF values of the molar modal were calculated with one-sided, two-sided, and three-sided vertical bone loss. It was found that the change in the NF was less than 25 per cent in molars with a one-sided defect when the bone level varied by 10mm from the cementoenamel junction. However, when a three-sided bony defect was simulated, the change in the NF ranged from 40 to 60 per cent. In addition, it was found that bone loss that had reached the furcation entrance (4mm) resulted in a sharp change in the NF value. Furthermore, it was found that bone loss involving the mesial and distal surfaces resulted in a larger decrease in the NF value compared with bone loss involving the buccal and palatal surfaces. These results demonstrated that the bone surrounding the mesial and distal sides plays a more important role in maintaining molar stability than does the bone surrounding the buccal and palatal sides. [ABSTRACT FROM AUTHOR]

In this paper, numerical study on influence of parameters related to cracks and voids on the responses of the composites under tension, compression, and shear deformation is conducted by extended finite element method (XFEM). Under tension, the maximum stress of composites changes less than 5 % when crack orientation, fiber orientation, and void distance change. The maximum averaged stress could differ by 10 % when the crack location and crack length change. In the multi-crack composites, there is difference by 10 % in maximum stress due to relative crack location. Under shear deformation, crack orientation affects the maximum averaged shear stress significantly when compared to the same composites under tension. The difference of maximum averaged shear stress is more than 15 % when fiber orientation changes. The void distance results in 5 % difference on the maximum stress of composites. In the multi-crack composites, the relative crack location could result in 10 % difference in maximum averaged shear stress. Crack length also could result in significant difference in maximum stress of composites under shear deformation. Under tension and shear deformation, one crack is always the dominant crack and its propagation path determines the strength of the multi-crack composites. Unlike in tension and shear deformation, single crack in the composites under compression doesn't result in the failure of composites even when the strain is 0.03. That is, no geometric buckling occurs for the single crack composite under compression. Noticeable crack propagation starts in multi-crack composites under geometric buckling, which result from the existence of multi-cracks and their interaction in the composites. [ABSTRACT FROM AUTHOR]

The aim of this study was to test natural teeth stability under various simulated types and degrees of alveolar vertical bone loss, as well as to assess the role that the surrounding bone played for maintaining tooth stability. A three-dimensional finite element model of the human maxillary central incisor with surrounding tissue, including periodontal ligament, enamel, dentin, pulp, and alveolar bone, was established. One side and multiple vertical bone loss were simulated by means of decreasing the surrounding bone level apically from the cemento-enamel junction in 1&VeryThinSpace;mm steps incrementally downward for 10&VeryThinSpace;mm. Natural frequency values of the incisor model with various types and degrees of bone loss were then calculated. The results showed that, with one-sided bone resorption, the model with labial bone loss had the lowest natural frequency decreasing rates (8.2 per cent). On the other hand, in cases of multiple bone loss, vertical bone resorption at the mesial and distal sides had more negative effects on tooth stability compared to vertical bone losses on facial and lingual sides. These findings suggest that the natural frequency method may be a useful, auxiliary clinical tool for diagnosis of vertical periodontal diseases. [ABSTRACT FROM AUTHOR]

We study finite element approximations for positive solutions of semilinear elliptic eigenvalue problems with folds, and exploit the superconvergence of finite element methods (FEM). In order to apply the superconvergence of FEM for Poisson's equation in [Chen & Huang, 1995; Huang et al., 2004, 2006; Lin & Yan, 1996] to parameter-dependent problems with folds, this paper provides the framework of analysis, accompanied with the proof of the strong monotonicity of the nonlinear form. It is worthy to point out that the superconvergence of the nonlinear problem in this paper is different from that in [Chen & Huang, 1995]. A continuation algorithm is described to trace solution curves of semilinear elliptic eigenvalue problems, where the Adini elements are exploited to discretize the PDEs. Numerical results on some sample test problems with folds and bifurcations are reported. [ABSTRACT FROM AUTHOR]

This study investigated the effects of the stiffness of a maxillary sinus graft and the surface roughness of an immediately loaded implant using a non-linear three-dimensional finite element (FE) analysis (3D). Six FE models were created, including two stiffness values of grafted bone (345 and 3450 MPa of elastic modulus) and three conditions of implant–bone interfaces (Frictional coefficient of 0·3 for machined surface, 0·45 for rough implant surface and a bonded implant–bone interface for an osseointegrated implant). Computer tomographic images of a human skull were used to construct a posterior maxillary model. All implants were designed via the computer aided design software with a spiral threaded configuration. Three loading scenarios were investigated for each of the six models; axial loading and lateral loadings at 30° and 60°. The results showed that a 60° lateral loading has scored the highest level of bone stresses among the three loading conditions. Immediately loaded implants with 0·3 frictional coefficient have suffered the highest bone stresses which were higher than those with bonded interface by about 57%. Increasing the frictional coeffecient to 0·45, however, did not show any benefits in reducing the peak bone stress. Raising the stiffness of grafted bone diminished the bone stress by about 10% in both the immediately loaded and the osseointegrated implants. It was also noted that increasing graft stiffness and implant surface roughness reduced the sliding at the implant-bone interface which may improve the implant stability and long-term survival. [ABSTRACT FROM AUTHOR]

Self-piercing riveting (SPR) is now increasingly applied in the joining of aluminium vehicle body parts. However, the large distortion from assembly process is a prevalent quality problem. Thus the joint distortion of SPR has to be reduced to control the whole distortion of the aluminium vehicle body. The present paper studies the piercing process of 1·5 mm AA 5182-H11 sheets and analyses the joint distortion. At first, some experiments are performed to research the joint distortion of SPR. It is noticed that the clamping force has a great influence upon the joint distortion. Then a non-linear finite element model is built to study the joint distortion of SPR under different clamping forces, blankholder diameters and sheet sizes. The blankholder diameter is also found to be an important factor for the joint distortion, while the sheet size has minor effect. The relations of maximum joint distortion with clamping force, blankholder diameter and sheet size are obtained, based on which the appropriate process parameters could be found to reduce the joint distortion of SPR. [ABSTRACT FROM AUTHOR]

A robust finite element procedure for large deflection and inelastic analysis of imperfect steel frames with semirigid base is proposed and the nonlinear behavior of semirigid frames with various modes of initial imperfection is studied. Special consideration to the method of simulating the frame initial imperfections is given. The refined plastic hinge method is used for modeling of the section plastification and both the notional force and the initially imperfect geometry of the frames obtained by an eigenvalue buckling analysis are used for modeling the geometrical imperfections. The difference between the notional force and the eigenbuckling mode models and of semirigid base connections are studied. From the examples reported in this paper, the effective length is not required to be assumed and the advanced analysis is noted to be applicable to practical design of this type of steel frames. [ABSTRACT FROM AUTHOR]

Abstract: A discontinuous Galerkin (DG) finite element method (FEM) for the solution of linear elasto-dynamic problems is revisited and modified. The new DG FEM is based on a method originally proposed by [Comput. Methods Appl. Mech. Engrg. 84 (1990) 327] and recently adapted by [Comput. Methods Appl. Mech. Engrg. 191(46) (2002) 5315] for the solution of dynamic solid–solid phase transitions. As the FEM formulations in both the cited works have been found not to be unconditionally stable in cases where the underlying FEM grid is completely unstructured, this paper offers a modification of these formulations yielding a single-field DG FEM that is unconditionally stable without any restrictions on the grid structure. Furthermore, an energy conserving variant of the formulation is also suggested. [Copyright &y& Elsevier]

Elastoplasticity computation is the analysis foundation of many complex mechanical behaviours such as fatigue, damage, and fracture. It is impossible to realize real-time computation of elastoplasticity based on serial computer. The form of the element stiffness matrix is analyzed. A method that may realize the real-time computation of element stiffness matrix based on BP neural networks is proposed. The element stiffness matrix is computed using finite element analysis and BP neural networks, respectively. [ABSTRACT FROM AUTHOR]

A permanent magnetic yoke with a straight air gap was developed as the magnetic excitation unit, in order to improve the efficiency of magnetorheological (MR) polishing for ultra-smooth surface planarization. Finite element modelling was used to simulate the magnetic performance of the newly developed yoke, which was found to agree well with the experimental measurement. With the developed MR polishing apparatus, the effects of trough speed, work and excitation gap width, particle concentration within the MR fluid and workpiece size on the material removal rate were systematically investigated. Final tests were performed on glass specimens to examine the polishing performance. The polishing area in the developed process was much larger than that of the conventional MR finishing process with a carrier wheel and ultra-smooth surface of 1 nm in R a was achieved. [ABSTRACT FROM AUTHOR]