热成形韧性断裂判据的建立及应用

针对大锻件设备或配件在热成形过程中产生的裂纹缺陷，采用热力学实验方法，研究了以50＃钢为代表的热裂行为.结果显示：临界断裂应变与变形温度和应变速率呈函数关系.基于热裂行为分析和损伤力学理论，提出了预测裂纹发生的韧性断裂判据.将判据应用于不同变形条件下的镦粗试验，能够较好地预测裂纹发生时所对应的压下量及裂纹产生的位置，并通过嵌入不同判据预测镦粗过程中的开裂.结果表明：所建立判据对于大锻件高温热成形过程的开裂现象具有更高的预测精度.

A Novel Ductile Criterion for Hot Forming and Its Applicability

In order to predict occurrence of cracks of heavy forging equipment or accessories during hot forming, the high-temperature fracture behaviors of No. 50 steel were investigated by using the experimental thermodynamic method. The results show that the critical fracture strain is a function of the temperature and strain rate. Based on these results and the theory of damage mechanics, a ductile criterion was proposed, which could predict the occurrence of cracks. Besides, the accuracy of the proposed criterion was verified by conducting upsetting tests with different deformations and the corresponding simulation. Additionally, the applicability of the proposed criterion was investigated by implanting the criterion and various uncoupled criteria into simulation. The result shows that the proposed criterion can best predict the occurrence and location of cracks.