Accurate characterization of the fracture limit in plane strain tension of automotive sheet metals is critical for the design and crash performance of structural components. Plane strain bending using the VDA 238–100 V-bend test has potential for proportional fracture characterization by avoiding a tensile instability. The VDA 238–100 V-bend test was evaluated using DIC strain measurement to characterize the plane strain fracture limit under proportional plane stress loading and to evaluate the effect of the VDA pre-straining methodology for ductile alloys upon the material response. The load-based failure criterion of the V-bend test was evaluated with DIC to monitor the development of surface cracking. The influence of the non-linear strain path imposed by the pre-straining procedure for ductile materials was then evaluated for three automotive alloys: an advanced high strength dual phase steel, DP1180, a rare-earth magnesium, ZEK100, and an AA5182 aluminum. A fracture criterion based on the load threshold was reasonable for the three alloys considered. Pre-straining in uniaxial tension prior to plane strain bending affected each alloy differently. The DP1180 was not affected by the non-linear strain path whereas the cumulative equivalent strain for the AA5182 and ZEK100 increased by strains of 0.07 and 0.05 strain, respectively. The non-linear strain path within the VDA pre-straining methodology creates ambiguity in comparing the fracture limits of different materials. The plane strain fracture limit for proportional loading can be readily obtained in the V-bend test with DIC strain measurement.

中文翻译：

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对 VDA 238–100 汽车钣金平面应变断裂特性的紧密半径弯曲试验的评估

汽车钣金平面应变张力断裂极限的准确表征对于结构部件的设计和碰撞性能至关重要。使用 VDA 238-100 V 弯曲测试的平面应变弯曲具有通过避免拉伸不稳定来表征断裂的潜力。使用 DIC 应变测量来评估 VDA 238-100 V 弯曲试验，以表征比例平面应力加载下的平面应变断裂极限，并评估 VDA 预应变方法对延性合金的材料响应的影响。使用 DIC 评估 V 型弯曲试验的基于载荷的失效准则，以监测表面裂纹的发展。然后对三种汽车合金对延性材料的预应变程序施加的非线性应变路径的影响进行了评估：高级高强度双相钢 DP1180、稀土镁 ZEK100 和 AA5182 铝。对于所考虑的三种合金，基于载荷阈值的断裂标准是合理的。在平面应变弯曲之前在单轴拉伸中预应变对每种合金的影响不同。DP1180 不受非线性应变路径的影响，而 AA5182 和 ZEK100 的累积等效应变分别增加了 0.07 和 0.05 应变。VDA 预应变方法中的非线性应变路径在比较不同材料的断裂极限时会产生歧义。