Development of Exact Prediction Method of Flow Stresses of Metallic Materials at Room and Elevated Temperatures, amnd Application of the Method to Forming Simulation

为获得成功的、优化的金属成形工艺，进行了详细的分析和成形模拟。这些分析和模拟都需要考虑变形过程中应变、应变速率和温度的变化，得到反映变形过程中材料流变应力的本构方程。实验结果表明，许多金属材料在温变形和热变形温度下的流变应力具有显著的应变率依赖性。本课题组组长提出了预测铜在变应变速率和变温度下变形的流变曲线的加工硬化速率方程。将该方法应用于铝合金（1100-0）、铝合金（6063 AA）、不锈钢（SUS 304）和0.39C低碳钢的流变曲线预测。在此基础上，建立了包含材料常数的加工硬化速率方程，并编制了流动曲线预测程序。该程序可用于预测铝、铝合金和不锈钢在室温-0.9Tm（Tm：熔点K）温度范围内的流动曲线，以及0.39C钢（球化碳化物结构）在室温附近和0.39C钢（奥氏体结构）在800 ℃以上的流动曲线。应用该程序计算了铝合金平面应变热挤压变形区的有效应力分布。在此基础上，考虑了应变速率分布、应变分布和温度分布（包括塑性功温升）对挤压过程中有效应力分布的影响，预测了挤压过程中有效应力分布。结果表明，在热成形过程中，有效应变率对有效应力的影响是非常显著的。

Detailed analysis and forming simulation are proceeded to achieve successful and optimized metalforming processes. Those analysis and simulation require the constitutive equation representing flow stresses of a forming material with regard to deformation pass involving strain variation, strain-rate variaion and temperature variation in a deformation process. Experimental results reveal that many metallic materials show remarkable strain-rate dependence of flow stress at warm and hot deformation temperature. Head investigator proposed previously the work-hardening rate equations for predicting the flow curves of Copper deformed at varying strain-rate and at varying temperature. The method was adopted to the flow curve prediction of Aluminum (1100-0), Aluminum alloy (6063AA), Stainless steel (SUS304) and 0.39C low carbon steel in the present investigation. Then, the work-hardening rate equations involving some material constants could be determined for the above materials and the computer program of flow curve prediction was constructed. The program is available to predict the flow curves at temperatures in temperature range, room temperature-0.9Tm (Tm : Melting point K), for Alumninum, Aluminum alloy and Stainless steel, and at around room temperature for 0.39C Steel (Spheroidized carbides structure) and at above 800 ﾟC for 0.39C steel (Austenite structure). The above computer program was employed to evaluate the effective stress distribution in the deformation zone of Aluminum alloy billet in plane strain hot extrusion using some non-symmetric dies. Then, the effective stress distribytions in extrusion were predicted with taking into account effects of strain-rate distribution, strain distribution and temperature distribution (involving temperature rise due to plastic working energy). The results show variation of effective strain-rate on effective stress is quite remarkable and significant in the hot forming processes.