No abstract

SiCp/Al composite is widely used in the aerospace, electronics and automobile industries due to its ultrahigh strength and wear resistance. Surface integrity in the machining process can be influenced by tool corner radius. A finite element model is developed by DEFORM-2D to study on the effect of tool corner radius on residual stresses, cutting force and temperature in machining SiCp/Al composite process. The results show the large corner radius can improve cutting force, but hardly influence cutting temperature. Meanwhile, value of residual stresses is influenced by tool corner radius, but distribution of residual stress is not. The larger corner radius is, the greater the curve fluctuation of residual stresses is. And the large tool corner radius can effectively improve surface residual compressive stress.

The mechanical analysis of weld zone is a significant problem during the nuclear power plant design due to the fact that the material property of weld zone is complex. In most of the standards and codes, the weld zone is assumed as an effective homogeneous material. However, the weld zone is non-homogeneous at micro-scale, and the microstructure has great effect on the mechanical property, especially the fracture behaviors. Therefore, how to propose an accurate and convenient model to analyze fracture behavior of the weld zone of nuclear pipe or components becomes a major issue. The objective of present work is to develop an accurate method to investigate the fracture behavior of weld zone from the microstructure of weld zone. To achieve the objective, a double smoothed image based reconstruction method is developed to generate the finite element mesh from digital image of weld zone directly. Then a cohesive finite element framework is utilized to simulate the initiation and propagation of micro-cracks in weld zone. Moreover, a damping boundary condition is used to apply the complex loading case on the micro-scale model.

In order to study the dynamic characteristics and fluid structure interactions of tubular structures under the action of fluid in reactor, such as fuel rod bundles and heat transfer tube bundle of steam generator, the dynamic equations and the acoustic wave equations of structures are discretized by finite element method. The acoustic wave equations are simplified from continuity equation and momentum equation of fluid field. Based on the fluid structure coupling method, the dynamic characteristics of the tube under the internal flow, external flow and combined action of internal and external flow are calculated respectively. The influence of flow field domain, element type and grid number on the dynamic characteristics of the tube is also analyzed. Secondly, based on the computational fluid dynamics and computational structural dynamics, the interaction between the two physical fields of fluid and structure is considered simultaneously. The finite volume method is used to discretize the fluid control equations and the turbulent flow is investigated using the large eddy simulation method (LES). The Newmark algorithm is used to solve the structural dynamic equations. Combined with the dynamic mesh control technique, a numerical model for flow induced vibration of three-dimensional flexible tube is established. Finally, the flow induced vibration of a three dimensional flexible single tube and a square arrangement tube bundle is calculated using the numerical model. By comparing with the existing research results, it is found that the numerical simulation results are in good agreement with the experimental results. Thus, the correctness of the model is verified. It is also shown that the numerical model established in this paper can be used to simulate the dynamic characteristics and flow induced vibration of tubular structures.

Residual stresses induced during the process of high speed cutting are very critical due to safety and corrosion resistance. Based on the nonlinear finite element code DEFORM, thermodynamic couple model of residual stress was built. Effect distribution of residual stresses on three different materials physical properties of hardness are analyzed by using the finite element model during the process of high speed cutting. The results show that metal material hardness is the key factors to residual stress. When materials’ hardness is higher, residual tensile stress is easy to form on the machined surface due to high cutting temperature, such as hardened steel SKD11(HRC=62). To lower hardness material, residual compressive stress is generated on the machined surface for plastic deformation, such as softer materials 7075Al (HRC=23).