Papers by Author: Guo Qun Zhao

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Authors: Xiao Hui Huang, Wen Guang Liu, Guo Qun Zhao, Xin Hai Zhao
Abstract: In this investigation, we propose a new concept to embed cohesive zone into the continuum structure of bone cement, an example of brittle material, in investigating the mechanical behavior and fracture mechanism and to predict the fracture which elastic fracture mechanics (EFM) is unable to. Four finite element (FE) models with embedded cohesive zones for the simulations of tensile, compression, double shear and 3-point bending tests have been implemented. Cohesive zones (CZ) are embedded at high risks of fracture with orientations determined by fracture mode. A bilinear cohesive traction-separation law (TSL) is applied. The fracture parameters in traction-separation curve are validated and justified in the simulations to agree well with the force-displacement curves in the four practical tests. Apart from the maximum load, the perpetual safe working load (SWL) in theory also can be predicted by tracing the history of the stiffness degradation of fractured cohesive zone by means of simulation. A distinct advantage of our numerical model is that it is able to extend to investigate the mechanical behavior and fracture mechanism of other brittle materials. The proposed method with embedded cohesive zones in FE models can be introduced to predict the fracture and to forecast the maximum load and safe working load (SWL) of the continuum structure in more complicated loading conditions.
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Authors: Lei Zhang, Guo Qun Zhao, Hui Ping Li
Abstract: With finite element software Abaqus, a coupled thermal mechanical simulation of hot stamping process of U-Channel part using high strength steel was performed. Through the analysis of the temperature field distribution on the die surface, the influence of contact state between die and blank on the temperature field distribution was discussed. With temperature history curve of a selected node on die corner, the heat flow on two contact boundaries (die surface and cooling water channel surface) was discussed and its effects rules on the die temperature were given.
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Authors: Wen Juan Li, Guo Qun Zhao, Xin Wu Ma, Jun Gao
Abstract: The true stress-strain curves of AZ31B magnesium alloy sheet were obtained by using the uniaxial tensile tests at the temperature ranging from 50°Cto 300°C and the initial strain rate ranging from 0.001/s to 0.1/s. The influence of temperature and strain rate on the flow stress was analyzed. The results show that the flow stress decreases and the elongation in fracture increases with increasing temperature and decreasing strain rate,and the plastic performance is improved obviously. Through the analysis of the true stress-strain curves,a mathematical model of the flow stress was established based on an exponential form whose power is a quadratic function. All the coefficients in the model were fitted as functions of temperature and strain rate. The comparison of the calculated results with experimental data shows that the model established in this study can accurately reflect work hardening and strain softening effect of AZ31B magnesium alloys during the hot deformation. It can be used for the prediction of flow stress for AZ31B magnesium alloys under hot work conditions and numerical simulation of forming processes.
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Authors: Lu Sun, Guo Qun Zhao
Abstract: Surface matching technique is a key technique in automatic generation of 3D finite element mesh. In this paper, a surface matching technique including surface-gap filling, boundary match and C-node match, is introduced. Eight types of free facet configurations and their corresponding matching rules are established. Then a combined method of priority nodes and relative position relationships for boundary match is presented, and an effective method for C-node match is given, too. The methods can achieve precise match between mesh boundaries and model boundaries, and establish reasonable geometry and topology connections of matched nodes. Several examples are provided to demonstrate the accuracy and efficiency of the algorithms presented in this paper.
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Authors: Xin Wu Ma, Guo Qun Zhao, Wen Juan Li
Abstract: This paper deals with problems in the coining process for manufacturing surgical slit knife using two-dimensional (2D) and three-dimensional (3D) finite element (FE) simulations. The FE simulations are performed to investigate the material flow, and especially stress distribution on the coining dies. The main objective of this paper is to study the feasibility of a coining process for manufacturing a given geometry of surgical slit knife without forming defects and die failure. Very high stress distribution on the coining dies is found by 2D simulations of the coining process that exceeds the strength limit of the die material. The optimum preform and preforming die geometry are determined by FE simulations in order to reduce the die stress. 3D simulations of the preforming and coining processes are conducted with the optimal design to show that the geometry of the product can be achieved without defects by the coining process.
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