Li Xiaoqiang

Modeling and Simulation for the Stress Relaxation Behavior of Ti-6Al-4V at Medium Temperature

Abstract Stress relaxation is a significant characteristic of titanium alloys at elevated temperature and load, which is the theoretical foundation of hot sizing and heat treatment. The tensile stress relaxation behaviors of a Ti-6Al-4V sheet over the medium temperature range from 923 K to 1023 K and at several strain levels were investigated. Comprehensive analysis results indicate that the stress relaxation rate increases with the increase of temperature. The residual stress in Ti-6Al-4V alloy reaches the relaxation limit gradually after a period of relaxation. In addition, the stress relaxation limits reach the same value for the different initial stresses at the same temperature. Furthermore, an explicit constitutive equation with a cubic delay function was established and its prediction precision is as high as 97% and this has laid the foundation of process design and theoretical analysis. Finally, the implicit creep-type constitutive equation was developed to describe the stress relaxation behavior of Ti-6Al-4V alloy, and identified material parameters were input into ABAQUS to simulate a stress relaxation process of Ti-6Al-4V alloy due to the creep forming. Comparison results show that the stress change simulated is in agreement with the stress relaxation curve. It is proved that the creep-type constitutive equation is valid for the simulation of stress relaxation.

Solution to Boundary-value Problems in Fabrication of High-precision Reflector Panels

Abstract The fabrication of high-precision panels for the compact antenna test range (CATR) with a sandwich construction of two aluminum skin-plates and one aluminum middle plate, which are bonded to two aluminum honeycomb core-layers poses a lot of tricky problems. Of them, the force analysis of individual skin-layers and the springback calculation of sandwich are of utmost importance. Under reasonable assumptions, by using Fourier expansion of stress function and power series expansion of deflection function, two boundary-value problems of skin-layer and sandwich, i.e. force analysis and springback calculation, are solved. An analytical solution of stress function in series form and an approximate solution of deflection function are obtained. Compared with finite element method (FEM), the generalized double Fourier series method used in individual skin force analysis is superior in accuracy. Compared with experimental results, the weighted residual method used in springback calculation of sandwich-structured panel is acceptable from view of precision. Based on calculation results, processing parameters to panel fabrication are determined more efficient and accurate.