Soon Wan Chung

Virtual Material Characterization of 3D Orthogonal Woven Composite Materials by Large-scale Computing

In this paper, the virtual material characterization of three dimensional (3D) orthogonal woven composite materials is investigated by large-scale finite element analyses to predict the elastic properties. To numerically model the complex geometry of 3D orthogonal woven composites, a unit structure including the stuffer yarns, filler yarns, weaver yarns, and the resin region is generated based on direct numerical simulation (DNS) and the unit structures with the same pattern are assembled into an orthogonal woven composite structure composed of several millions of degrees of freedom. The influence of the geometrical irregularities, such as the inconsistent tow spacing and the waviness of the filler yarn, on the mechanical properties are also discussed by separately generating the yarns and the resin. From the numerical examples, it is shown that the pattern of tow distribution affects the shear modulus, and the direct modeling of the wavy yarns can produce more accurate stiffness knockdown. It is also emphasized that large-scale numerical analyses can be one of the methodologies sufficient for the material characterization of the orthogonal woven composites and can be more applicable in the realistic structure subject to complex loading compared to the unit cell approach.

A remeshing algorithm based on bubble packing method and its application to large deformation problems

The remeshing algorithm based on the bubble packing method (BPM) is developed for finite element analysis (FEA) because the optimal position of nodes can be obtained systematically when only the bubble size function is given. The triangular meshes are generated by Delaunay triangulation with the advancing front concept. To use the automatically generated mesh information in FEA, a new bandwidth minimization scheme with high efficiency in CPU time is also developed. A refining circle is proposed to specify the refinement area using the bubble size in the remeshing step. The remeshing algorithm is applied to the metal forming problem to replace the distorted mesh at the largely deformed area with regular and fine meshes. The numerical results show that the remeshing algorithm based on the BPM works well at the region with large error and is able to control the refinement area and the new mesh size easily through two parameters (ηmax*,q).

Finite element simulation of metal forming and in-plane crack propagation using ductile continuum damage model

The continuum damage model for ductile damage and ductile fracture is applied to metal forming and crack propagation by finite element method. The highly nonlinear equilibrium equation is formulated in order to include geometric, material nonlinearities and frictional contact condition. The effect of friction on the damage concentration is shown in the upsetting process. Then it is verified that the ductile fracture using this damage model is reasonable by the comparison with the experimental result in CCT specimen. The influence of the hole at the crack tip is shown through the numerical simulations of edge-cracked plates with different hole size. Finally, the strain energy release rate in this damage model is compared with J-integral using ABAQUS to relate the result of damage analysis to the concept of fracture mechanics.

Large-scale actuating performance analysis of a composite curved piezoelectric actuator

In this paper, the electromechanical displacements of curved piezoelectric actuators composed of PZT ceramic and laminated composite materials are calculated on the basis of high performance computing technology and the optimal configuration of the composite curved actuator is examined. To accurately predict the local pre-stress in the device due to the mismatch in the coefficients of thermal expansion, carbon/epoxy and glass/epoxy as well as PZT ceramic are numerically modelled by using hexahedral solid elements. Because the modeling of these thin layers increases the number of degrees of freedom, large-scale structural analyses are performed using the PEGASUS supercomputer, which is installed in our laboratory. In the first stage, the curved shape of the actuator and the internal stress in each layer are obtained by cured curvature analysis. Subsequently, the displacement due to the piezoelectric force (which results from the applied voltage) is also calculated. The performance of the composite curved actuator is investigated by comparing the displacements obtained by variation of the thickness and the elastic modulus of laminated composite layers. In order to consider the finite deformation in the first stage of the analysis and include the pre-stress due to the curing process in the second stage, nonlinear finite element analyses are carried out.

Investigation of actuating displacement performance of curved actuator by large-scale computation

In this paper, the electromechanical displacements of curved actuators such as THUNDER are calculated by the finite-element method to design the optimal configuration of curved actuators. To predict the internal stress in the device due to the mismatch in coefficients of thermal expansion, the adhesive as well as metal and PZT ceramic is also numerically modeled by using hexahedral solid elements. Also, the nonlinear finite-element formulation is implemented to include the variation of material constants during the curing process and acquire more accurate actuating displacements. Because the modeling of these thin layers causes the numbers of degree of freedom to increase, large-scale structural analyses are performed in a cluster system in this study. The curved shape and internal stress in the actuator are obtained by the cured curvature analysis, and the displacement subject to the piezoelectric force by an applied voltage is also calculated to investigate the performance of curved actuators. The thickness of metals and adhesive, and the number of metal layers, are chosen as design variables.

Investigation of Instability in Crash Analysis on Various Computing Environments

To reduce computing time in crash simulations, parallel version of commercial crash code is widely used. However, the reliability of parallel computing results on the various computing environment has been issued. In this study, the differences in the maximum acceleration, the average and maximum differences in nodal positions are investigated on the various parallel computing environments. First, the effects of aliasing errors in acceleration and the repeatability issues are reviewed in detail. The tables of differences in acceleration s or nodal positions are constructed. Based on the tables, it can be shown that the amount and the tendency of differences depend on the computing environments. The crash models considered are car crash model and helicopter crash model. The hardware platforms considered are IBM SP2, Regatta and self-made Linux clusters. LS-DYNA was used for crash simulation.

Optimal design of curved actuator through high-performance computing

In this paper, the electromechanical displacements of curved actuators such as THUNDER are calculated by finite element method to design the optimal configuration of curved actuators. To predict the pre-stress in the device due to the mismatch in coefficients of thermal expansion, the adhesive as well as metal and PZT ceramic is also numerically modeled by using hexahedral solid elements. Because the modeling of these thin layers causes the numbers of degree of freedom to increase, large-scale structural analyses are performed in a cluster system in this study. The curved shape and pre-stress in the actuator are obtained by the cured curvature analysis. The displacement under the piezoelectric force by an applied voltage is also calculated to compare the performance of curved actuator. The thickness of metal and adhesive, the number of metal layer are chosen as design factors.

Large-scale computational simulation for optimal design of curved piezoelectric actuator using composite material

In this paper, the electromechanical displacements of curved piezoelectric actuators with laminated composite material are calculated using high performance computing technology, and the optimal configuration of composite curved actuator is proposed. To predict the pre-stress in the device due to the mismatch in coefficients of thermal expansion, carbon-epoxy and glass-epoxy as well as PZT ceramic are numerically modeled by using hexahedral solid elements. Because the modeling of these thin layers causes the numbers of degree of freedom to increase, large-scale structural analyses are performed through the PEGASUS supercomputer which is composed of 400 Intel Xeon CPUs. In the first stage, the curved shape of the actuator and the internal stress in each layer are obtained by the cured curvature analysis. Subsequently, the displacement due to the piezoelectric force by an applied voltage is also calculated and the performance of composite curved actuator is investigated by comparing the displacements according to the configuration of the actuator. To consider the finite deformation in the first stage and include the pre-stress in each layer in the second analysis stage, nonlinear finite element analyses will be carried out. The thickness and the elastic constants of laminated composite are chosen as design factors.