Practical Application of the Hole Expansion Test

Until now the hole expansion ratio has been generally regarded as a relative “local formability” parameter with limited application to edge-cracking analysis and prediction. In this study a constrained statistical test data analysis methodology is introduced, where the lower-bound hole expansion ratio is the basis for three practical edge-cracking failure criteria. The Maximum Edge Stretch Criterion is directly compatible with CAE simulation. The Edge Thinning Limit Criterion and the Critical Thickness Criterion are more useful in field work and post mortem laboratory failure analysis. Two case studies are described, where hole expansion test data are used to analyze edge cracking of Advanced High Strength Steel (AHSS) in real-world automotive seating applications. Finally the intrinsic local and global formability parameters of the subject AHSS materials were explored, and a linear relationship between the hole expansion ratio and reduction of area at fracture in tension was demonstrated.