Effect of Pre-Strain on Edge Cracking Limit for Advanced High-Strength Steel Using Digital Image Correlation

Advanced high-strength steel (AHSS) is gaining popularity in the automotive industry due to its higher final part strength with the better formability compares to the conventional steel. However, the edge fracture occurs during the forming procedure for the pre-strained part. To avoid the edge fracture that happens during the manufacturing, the effect of pre-strain on edge cracking limit needs to be studied. In this paper, digital image correlation (DIC), as an accurate optical method, is adopted for the strain measurement to determining the edge cracking limit. Sets of the wide coupons are pre-strained to obtain the samples at different pre-strain level. The pre-strain of each sample is precisely measured during this procedure using DIC. After pre-straining, the half dog bone samples are cut from these wide coupons. The edge of the notch in the half dog bone samples is created by the punch with 10% clearance for the distinct edge condition. The pre-strained half dog-bone samples are tested under a uniaxial tension to acquire the edge cracking limit. The thinning strain is measured to calculate the edge cracking limit using the DIC system. The detailed experimental setup, procedure, and results are described in this article. The effect of pre-strain on edge cracking limit for different material direction at different pre-strain level is discussed and concluded.