中文摘要：

针对新型低应力弯曲下料中棒料V型槽尖端形状的特殊性,提出对V型槽尖端起裂和裂纹扩展分别处理,采用应力集中系数计算V型槽尖端起裂所需的初始外力,采用裂纹扩展门槛值计算V型槽尖端裂纹扩展所需的外力。利用曲线拟合方法,耦合出外力与裂纹起裂扩展长度间呈近似1/4凹圆弧递减关系。基于低应力下料特点,设计4种形式的外力控制曲线。下料实验结果表明,所提出的凹圆弧递减外力控制曲线能使下料时间最短、断面质量最好。

英文摘要：

According to particularity of shape of V-shaped notch tip in a new-type of low stress precise cropping,it is proposed that the initial external load is obtained by means of stress concentration coefficient method when the tip of V-shaped notch is checking,and the variable external load is obtained by using the fracture mechanics when the macroscopic crack of V-shaped notch tip appears.Based on it,the relationship of the external force and crack propagation length is coupled out.Based on the characteristics of the low stress precise cropping,four types of external load control curves are designed in detail.The experimental results show that the cropping time is the shortest,and the section quality is best for LY8 bar by the approximate concave arc decreasing external control curve,which is also proposed.