The precise determination of the forming limit strains of a sheet metal is necessary in order to accurately predict the onset of failure in sheet metal forming processes. The method used to detect the onset of necking (i.e. the necking criterion) is a most important factor in formability analysis as it significantly affects the forming limit strains. Many different necking criteria have been developed, which take advantage of the flexibility and high resolution of digital image correlation (DIC) strain measurements. Several time-dependent and time/geometry-dependent necking criteria were carefully investigated in order to evaluate their ability to reliably and consistently detect the onset of necking of TRIP780 sheet specimens that were stretch-formed over a hemispherical punch. It was found that the geometry-dependent, surface slope criterion was the most robust and consistent criterion of those evaluated.

为了精确地预测钣金成形过程中失效的开始，必须精确确定钣金成形极限应变。用于检测颈缩开始的方法（即颈缩标准）是可成形性分析中最重要的因素，因为它会显着影响成形极限应变。已经开发出许多不同的颈缩标准，这些标准利用了数字图像相关（DIC）应变测量的灵活性和高分辨率。仔细研究了几种与时间有关和与时间/几何有关的颈缩标准，以评估其可靠和一致地检测在半球形冲头上拉伸形成的TRIP780薄板试样颈缩的能力。发现与几何有关，