Papers by Author: Guo Qun Zhao

Abstract: The frameworks for finite element (FE) model of bone tissue available in pervious literatures, to some extent, are expert-oriented and give rise to a considerable deviation in geometric model and assignment of material property. The objective of this study is to develop a new framework to reconstruct accurate individual bone FE model based on CT images rapidly and conveniently. In image-processing, automatic segmentation of the region of interest (ROIs) improves the efficiency. The idea of enclosed volume of interest (VOI) overcomes the drawback of geometric ambiguity in Marching Cube (MC) method. Geometric model is easily obtained by a STL translator and smooth operator in home-made program. In the material property assignment, two templates for hexahedron and tetrahedron FE models, respectively, are put forth to smoothing an abrupt change of material property in the region from cortical to cancellous. K-mean algorithm is introduced to cluster material properties to improve partition performance. Finally, the new framework is demonstrated by the implementation of a femoral FE model.

Abstract: The shape of welding chamber is a key parameter in flat porthole die extrusion process, which influences product quality and die life-span directly. In this paper, by means of numerical simulation of the extrusion process for an aluminum hollow profile, the effects of multi-step welding chamber on metal flow and die strength have been investigate. The numerical results revealed that the multi-step welding chamber was effective to balance metal flow in the die cavity. In addition, with an increasing step of welding chamber, the maximum stress and deflection of the lower die decreased, while the deflection of the mandrel kept almost unchanged and the maximum stress of upper die increased.

Abstract: In hot stamping process, the die suffers complex thermal mechanical loads. In this paper, the process model and the materials model were set up. And with the example of U-channel forming, a coupled thermal-mechanical analysis is performed with ABAQUS. According to the simulation result, the stress and strain fields of the die show a great uneven distribution in place and time. And the explanation for the non-uniform was given out in this paper. Finally, the fatigue life of the die was evaluated, and the suggestions were proved for optimizing the fatigue lifetime of hot stamping die.

Abstract: Hot stamping of quenchable boron steels is a new and complex forming technology integrating metal hot forming and quenching process. In order to gain the Time – Temperature - Transformation (TTT) curves of 22MnB5, the phase-transformation temperatures of boron steel 22MnB5 are measured by DIL 805A/D quenching and deformation dilatometer. According to the expansion curves of phase-transformation at some constant temperatures, the start and finish temperatures of phase-transformation are calculated by using the expansion method and the tangential method. The types of metallographic phases after phase-transformation are judged by the optical microscope and micro hardness. The TTT curves of 22MnB5 are drawn in terms of the results of testing and calculating.

Abstract: A fully transient method for the simulation of the coupled plastic part and mold temperature in the filling stage of Rapid Heat Cycle Molding process was presented. Unlike the constant temperature boundary conditions in conventional injection molding simulation methods, the mold temperature was assumed to be variable in the filling process. The mold temperature in the heating process was first simulated. In the filling process, the flow equations were solved only on the cavity domain, while the energy equations were solved in a coupled manner for the cavity and mold domain at the matrix level. The temperature evolution in a two-dimensional filling process with heated mold was simulated. Numerical results showed that the proposed coupled simulation method provides reliable temperature estimations in mold filling process.

Abstract: The viscoelastic flow and swell behaviors of polymer melts in the profile extrusion process can significantly influence the performance and dimension of the final products. In the study, the viscoelastic flow pattern of a commercial low density polyethylene (LDPE) extruded through out of the hollow profiled extrusion die is investigated by means of finite element simulation. The mathematical model of three-dimensional viscoelastic flow and swell of polymer melts is established with a differential Phan-Thien and Tanner (PTT) constitutive model. A penalty method is employed to solve the non-linear problem with a decoupled algorithm. The computation stability is improved by using the discrete elastic-viscous split stress (DEVSS) algorithm with the inconsistent streamline-upwind (SU) scheme. A streamface-streamline method is introduced to adjust the swelling free surface of the extrudate. The essential viscoelastic flow characteristics of LDPE flowing through out of the hollow profile extrusion die is investigated based on the proposed numerical scheme. Both the redistribution of flow velocity and the release of stress are found to be the reasons for the swell phenomenon.

Abstract: Rapid electrical heating cycle injection molding technology can be used to produce polymer parts with no weld mark, flow mark and other surface defects on the parts surface. Recently, it has been gradually found wide use in plastic injection industry. In this paper, a structure of the rapid electrical heating cycle injection mold and its working processes were presented. As the production efficiency and the part’s quality are seriously affected by the temperature of the mold cavity surface and its distribution uniformity, the heat transfer process of the mold was analyzed by using 3D finite element simulation. The transient temperature values on different places of the cavity surface were obtained. The results provided theoretical guidelines for the engineers to evaluate the layout of the heating rods in the mold.

Abstract: Combining element free Galerkin method with rigid/visco-plastic flow theory, the paper establishes the three-dimensional rigid/visco-plastic element free Galerkin method, and introduces it to analyze three-dimensional bulk metal forming processes. The velocity field is approximated by MLS method. Employing the incomplete generalized variation principle, stiffness matrix equation and solution formulas are derived. And STL format discrete triangular patches are used to describe the mould cavity. An analysis program for simulating three-dimensional bulk metal forming processes is developed. The program is capable of simulating three-dimensional unsteady bulk metal forming processes with severe deformation and arbitrarily shaped dies. A numerical example is analyzed. Numerical results such as material flow patterns and distributions of the effective stress are obtained. The effectiveness and validity of the proposed method and techniques are demonstrated by comparing with results obtained by using commercial finite element software.

Abstract: The abrasive waterjet machining is a powerful tool in processing various materials, especially, for brittle materials, such as ceramic, glass and so on. However, the material removal of a brittle material when impacted by abrasive waterjet is not understood in detail. In this paper, the material removal model in fracture erosion of brittle materials by abrasive waterjet has been developed.