Abstract A new experiment for determining the equivalent plastic strain at fracture of a ductile material subjected to loading under a state of stress of in-plane biaxial tension and out-of-plane compression is introduced. In this experiment a small diameter spherical punch is pushed into a thin specimen plate that is backed up by another plate made of a different material. Upon loading, the material element at the back surface of the specimen along the center line of the punch that is in contact with the backing plate deforms under a state of stress of in-plane biaxial tension and out-of-plane compression and eventually fractures. A combined experimental–numerical approach is used to determine the state of stress throughout the test and the final strain at the fracture point. The experiment is simulated using an assumed plasticity model, and the results are validated by comparing the simulated and measured quantities (force and displacement of the punch and strain at the back surface of the specimen). The results from the experiment provide data needed for the construction of a surface of plastic strain to fracture as a function of triaxiality and Lode parameter. In testing specimens made of 2024 aluminum and a backing plate made of annealed copper, the equivalent plastic strain to fracture is determined for Lode parameter of about −1 and several values of triaxiality.

中文翻译：

---

面内双轴拉伸和面外压缩下的韧性断裂

摘要 介绍了一种新的确定塑性材料在面内双轴拉伸和面外压缩应力状态下承受载荷时断裂等效塑性应变的实验。在这个实验中，一个小直径的球形冲头被推入一个由不同材料制成的另一个板支撑的薄样品板中。加载时，试样背面沿冲头中心线与背板接触的材料单元在面内双轴拉伸和面外压缩的应力状态下变形，最终断裂. 结合实验-数值方法用于确定整个测试过程中的应力状态和断裂点处的最终应变。使用假定的塑性模型模拟实验，并且通过比较模拟量和测量量（冲头的力和位移以及试样背面的应变）来验证结果。实验结果提供了构建作为三轴度和 Lode 参数函数的塑性应变表面所需的数据。在由 2024 铝制成的测试样品和由退火铜制成的背板中，断裂的等效塑性应变由约 -1 的 Lode 参数和几个三轴度值确定。实验结果提供了构建作为三轴度和 Lode 参数函数的塑性应变表面所需的数据。在由 2024 铝制成的测试样品和由退火铜制成的背板中，断裂的等效塑性应变由约 -1 的 Lode 参数和几个三轴度值确定。实验结果提供了构建作为三轴度和 Lode 参数函数的塑性应变表面所需的数据。在由 2024 铝制成的测试样品和由退火铜制成的背板中，断裂的等效塑性应变由约 -1 的 Lode 参数和几个三轴度值确定。