Mapping Residual Stresses after Foreign Object Damage Using the Contour Method

A 51-mm thick plate of High-Strength Low-Alloy (HSLA-100) steel was impacted by a 6.4 mm diameter tungsten carbide sphere traveling at 2.2 km/sec. The projectile penetration left a 10 mm diameter and 12 mm deep crater. A residual stress map over a cross-section through the crater was measured by the contour method. The predominant feature of the stress map was a peak compressive stress of 900 MPa, or 1.3 times the yield strength, centered about 1 sub 1/2 crater radii below the crater floor. The results were compared with an explicit finite element simulation of the impact event. The model has good agreement with the measured residual stresses. As part of the study, residual stresses in the as-received HSLA-100 plate were also measured and found to be a typical quenching stress distribution with peak compressive stress of about 165 MPa a few mm below the surface and tensile stress of 200 MPa in the center of the plate thickness.