Distribution of stress near the hole-punched region before and after fatigue loading in advanced high-strength steels

Advanced high-strength steels (AHSS) are increasingly used in the automotive industry due to their superior strength-to-weight ratio, enabling thinner structural components and improved fuel efficiency. However, forming processes such as hole punching can induce surface roughness, shear-affected zones, and high residual stress concentrations that significantly reduce fatigue performance. This proposal aims to investigate the localized residual stress distribution near the hole-punched interface in AHSS components and how this evolves during fatigue loading.

In this work, we propose neutron diffraction mapping of residual strain in 350 × 100 × 8 mm³ steel plates with 15 mm diameter punched holes, focusing on two steels: AHSS (700MCPlus) and HSLA (500MC). Measurements will be conducted in the longitudinal, transverse, and normal directions over a 3 × 8 mm² area at the hole interface, using a 1 × 1 × 1 mm³ gauge volume for high spatial resolution. Samples in both the as-received and 1000-cycle fatigue-loaded states will be examined. These measurements will confirm simulation-predicted stress distributions, including high tensile and compressive regions, as well as help assess stress relaxation within this region after fatigue loading.

The results from this proposal will serve as essential ground truth for refining fatigue life models, as well as supporting the development of AHSS grades optimized for fatigue performance in automotive applications.