The stress triaxiality and the Lode angle parameter are two well established stress invariants for the characterization of damage evolution. This work assesses the limits of this tuple by using it for damage predictions via ductile damage models from continuum damage mechanics. Isotropic and anisotropic formulations of two well-established models are used to avoid model-specific restrictions. The damage evolution is analyzed for different load paths, while the stress triaxiality and the Lode angle parameter are controlled. The equivalent plastic strain is moreover added as a third parameter. These analyses reveal that this triple does still not suffice to uniquely define the damage state. As a consequence, well-established concepts such as fracture surfaces depending on this triple have to be taken with care, if complex paths are to be investgated. These include, e.g., load paths observed during metal forming applications with varying load directions or multiple stages.

翻译：应力三轴度与Lode角参数是表征损伤演化的两个经典应力不变量。本研究通过连续损伤力学中的延性损伤模型进行损伤预测，评估了该参数对的局限性。为避免模型特异性限制，采用两种经典模型的各向同性与各向异性表述。在控制应力三轴度与Lode角参数的同时，分析不同加载路径下的损伤演化，并引入等效塑性应变作为第三参数。分析表明，该三重参数仍不足以唯一确定损伤状态。因此，在涉及复杂加载路径（如金属成形应用中载荷方向变化或多阶段加载）的研究中，需审慎对待依赖该三重参数的经典概念（如断裂面）。