Prediction of fracture strain in incremental sheet forming (ISF) process is quite essential to evaluate the formability under optimized process design. In the present work, new analytical formulas of stress triaxiality are derived after considering the effects of bending, shearing and cyclic loading based on membrane analysis. These deformation mechanisms, considered as key factors of improved formability, are thoroughly analyzed through the derivation of stress triaxiality. A novel analytical prediction model of fracture strain is further proposed by combining the analytical model of stress triaxiality with a generalized ductile fracture criterion. For the validation of analytical models, a set of experiments for conical part and pyramid part with different sheet materials and process parameters have been carried out. Finite element analysis is also conducted to further validate the prediction accuracy of stress triaxiality and equivalent strain. The effects of deformation mechanisms on fracture strain are evaluated in details by range analyses.

预测渐进片材成形（ISF）过程中的断裂应变对于评估优化过程设计下的可成形性非常重要。在目前的工作中，在基于膜分析的基础上考虑了弯曲，剪切和循环载荷的影响，推导了新的应力三轴分析公式。这些变形机制被认为是改善可成型性的关键因素，通过推导应力三轴性对其进行了全面分析。通过将应力三轴性分析模型与广义延性断裂判据相结合，提出了一种新的断裂应变解析预测模型。为了验证分析模型，已对具有不同板材和工艺参数的圆锥形零件和金字塔形零件进行了一组实验。还进行了有限元分析，以进一步验证应力三轴性和等效应变的预测精度。通过范围分析详细评估了变形机制对断裂应变的影响。