Fracturing by ductile damage occurs quite naturally in metal forming processes, and ductile fracture of strain-softening alloy, here 42CrMo steel, cannot be evaluated through simple procedures such as tension testing. Under these circumstances, it is very significant and economical to find a way to evaluate the ductile fracture criteria (DFC) and identify the relationships between damage evolution and deformation conditions. Under the guidance of the Cockcroft-Latham fracture criteria, an innovative approach involving hot compression tests, numerical simulations, and mathematic computations provides mutual support to evaluate ductile damage cumulating process and DFC diagram along with deformation conditions, which has not been expounded by Cockcroft and Latham. The results show that the maximum damage value appears in the region of upsetting drum, while the minimal value appears in the middle region. Furthermore, DFC of 42CrMo steel at temperature range of 1123~1348 K and strain rate of 0.01~10 s−1 are not constant but change in a range of 0.160~0.226; thus, they have been defined as varying ductile fracture criteria (VDFC) and characterized by a function of temperature and strain rate. In bulk forming operations, VDFC help technicians to choose suitable process parameters and avoid the occurrence of fracture.
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机译：延性破坏引起的断裂在金属成型过程中很自然地发生，应变软化合金（此处为42CrMo钢）的延性断裂无法通过简单的程序（例如拉伸测试）进行评估。在这种情况下，找到一种方法来评估延性断裂标准（DFC）并确定损伤演化与变形条件之间的关系非常重要且经济。在Cockcroft-Latham断裂准则的指导下，涉及热压缩试验，数值模拟和数学计算的创新方法为评估延性破坏累积过程和DFC图以及变形条件提供了相互支持，但Cockcroft和拉瑟姆。结果表明，最大损伤值出现在up粗鼓区域，而最小值出现在中间区域。此外，42CrMo钢的DFC在1123〜1348 K的温度范围和0.01〜10 s -1 的应变速率下不是恒定的，而是在0.160〜0.226的范围内变化。因此，它们被定义为变化的韧性断裂标准（VDFC），并具有温度和应变率的函数特征。在批量成型操作中，VDFC帮助技术人员选择合适的工艺参数并避免断裂的发生。
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