钛合金绝热剪切的敏感性分析及环境温度的影响

Analysis of Adiabatic Shear Sensitivity and Effect of Ambient Temperature for Titanium Alloy

摘要:

通过引入与Batra及Kim类似的观点，将绝热剪切带宽度定义为绝热剪切带的中心区域的宽度(w5%)，在该区域上温度比其峰值小5%，利用Johnson-Cook模型及梯度塑性理论分析Ti-6Al-4V绝热剪切带的厚度随环境温度的演变规律。计算表明，随着环境温度的升高，绝热剪切带宽度增加，这与许多实验观测结果一致。当绝热剪切带的总厚度在上限时，绝热剪切带宽度-环境温度曲线是稍微上凹的；但是，当绝热剪切带的总厚度在下限时，绝热剪切带宽度-环境温度曲线基本上是直线，著名的Dodd及Bai模型无法预测这些新现象。关于绝热剪切带宽度的计算结果非常接近于Liao及Duffy的实测结果。在忽略应变硬化的条件下，采用线性软化模型及梯度塑性理论推导w5%的简化解析式，发现环境温度、密度、热容、软化模量、剪切应力的增加使绝热剪切的敏感性降低，而功热转化因子及抗剪强度的降低使绝热剪切的敏感性降低。

Abstract:

The Johnson-Cook model and gradient-dependent plasticity were used to investigate the adiabatic shear band (ASB) width and the ambient temperature effect for Ti-6Al-4V. The ASB width was defined as the width (w5%) of the region surrounding the band center over which the temperature differed from its peak value by less than 5%, which was similar to the viewpoint proposed by Batra and Kim. Theoretical results show that at higher ambient temperatures, the ASB is wider, as is in agreement with many experimental observations. At higher total ASB widths, the ASB width-ambient temperature curve is slightly concave-upward. However, at lower total ASB widths, the ASB width-ambient temperature curve is approximately linear. These new phenomena cannot be predicted by the famous Dodd and Bai’s model. The calculated ASB widths are closer to the measured results by Liao and Duffy. A simple expression for the ASB width was derived under the condition of neglecting the strain-hardening effect and adopting the linear softening model and gradient-dependent plasticity. It is found that higher ambient temperature, density, heat capacity, softening modulus and shear stress, or lower work to heat conversion factor and shear strength lead to lower adiabatic shear sensitivity and wider adiabatic shear band