Papers by Author: Bao Xiang Qiu

Abstract: The fatigue crack growth behavior of one compact tension specimen of 16MnR steel under high-low sequence loading was investigated. The symmetric half finite element model under plane-stress state was used to calculate the elastic-plastic stress-strain responses, in which the Armstrong-Frederick type cyclic plasticity model was implemented as a user material subroutine UMAT of ABAQUS. A recently developed dynamic crack growth model was used to simulate the effects of high loading step on the successive low loading step. The detailed evolution process of the crack closure and cyclic plastic zone within the retardation region of fatigue crack growth was obtained. The extend of the crack closure, the size of cyclic plastic zone and the stress gradient have significant influence on the fatigue crack growth rate. The predicted fatigue crack growth rate is in good agreement with the experimental data.

Abstract: Fatigue crack growth was simulated by using a newly developed unified model on the fatigue initiation and crack growth based on an incremental multiaxial fatigue criterion. The cyclic elastic-plastic stress-strain field was analyzed using the general-purpose finite element software (ABAQUS) with the implementation of a robust cyclic plasticity theory. The fatigue crack growth rates with respect to three different stress ratios were selected as the benchmark to check the unified model. The predicted results agreed with the experimental data very well. The insensitivity of the crack growth rate to the stress ratio is due to the fast mean stress relaxation.

Abstract: In this investigation two fatigue crack growth models based on the different physical assumptions were systematically analyzed. One model makes use of the size of the stable damage distribution zone near crack as the major contributor to the fatigue crack growth. This model is based on the concept that a material point failures and a new crack will form when the fatigue damage value of the material point reach the critical damage. The other model supposes that fatigue growth can be described as a process with sequentially breaking small volume elements behind the crack tip. The fatigue crack growth can be regarded as successive crack re-initiation over a critical distance. The fatigue crack growth rate can be determined as the ratio of the critical distance to the average life within critical distance. Both models use macro parameter to describe the microscopic mechanism. An elastic-plastic finite element analysis (FEA) was used to obtain the detailed stress-strain history of the notched component with a detailed consideration of the cyclic plasticity of the material using a robust cyclic plasticity model. The fatigue damage distribution and the average damage within the critical distance near the crack tip can be obtained by combining the fatigue damage parameter with the stress strain distribution from the finite element analysis. These two models were evaluated using the experimental results obtained from the crack grow experiments on compact specimens made from 16MnR. The predicting results using these two models correlate well with the experimental data. The results show that two models can well describe the notch effect on the fatigue crack growth.

Abstract: A reasonable finite element (FE) model of grinding temperature field has been developed on the basis of analysis of the transient temperature field， and three kinds of boundary conditions are loaded on the element of a moving heat source. The study, which is based on the finite element principle, has been carried out using the numerical simulation software ANSYS. Many results have been obtained including three dimensional temperature distribution map. The simulated results under different conditions show good agreement with the experimental results. With the comparison of the dry-grinding and wet-grinding, the result shows that the wet-grinding temperature with a proper grinding fluid is rather lower than the dry-grinding temperature. Finally, the variable coefficient of convective heat transfer and the different form heat source have been discussed in detail.