综合考虑应变、应变率和温度对绝热剪切的影响,通过理论推导建立了基于J-C本构方程的绝热剪切失稳判据。以45号钢、TC4钛合金和7050航空铝合金3种不同的金属晶格材料为例,计算得出了出现锯齿形切屑的临界切削速度,并以临界切削速度为参量,以敏感度作为衡量敏感性的统一标准,进行了本构参数对绝热剪切的敏感性分析,旨在说明J-C本构参数对绝热剪切的影响大小,为材料的本构研究和工程中绝热剪切的预测提供一定的理论参考。研究结果表明:3种材料中,TC4钛合金对绝热剪切的敏感性最大;J-C本构参数对锯齿形切屑的出现皆有影响,对绝热剪切的敏感性最大的是本构参数A,次大的是硬化系数n。
A theoretical model is proposed based on the Johnson-Cook law to predict the critical cutting speed for the onset of serrated chips in a high speed cutting process which takes into consideration the effect of the strain, strain rate and temperature on adiabatic shear. Critical cutting speeds are calculated for three workpiece materials of titanium alloy TC4, steel 45, and aluminum alloy 7050 with different space lattices. An analysis of the influence of material behavior parameters on the sensitivity of adiabatic shear is made by taking the critical cutting speed as the parameter and the sensitivity as the uniform criterion. Sensitivity of constitutive equation parameters is calculated and compared. Analytical results show that titanium alloy TC4 is the most sensitive of the three materials to adiabatic sheer. The hardening module and strain rate sensitivity coefficients have less effect on the adiabatic shear of steel 45 than on the other two materials. All J-C parameters have influence on adiabatic shear. Yield strength and hardening coefficient both play a significant part in the generation of serrated chips for all three materials studied in this paper. Except for TC4, the hardening module coefficient is the one factor which has less influence on the serrated chip, while the strain rate sensitivity and the thermal softening coefficients are located in a middle position.
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