Residual Stress Measurements of Cast Aluminum Engine Blocks Using Diffraction

Residual stresses and strains in as-cast and annealed aluminum engine blocks were mapped in the main web area above the bearing split using diffraction. Automated coordinate-mapping of the surface and bulk strains was accomplished with X-ray and neutron diffraction, respectively. LabVIEW-based software was developed for improved efficiency, flexibility and quality of data analysis. In the hoop direction, an overall reduction in compressive surface stress level was found with increasing heat-treatment temperature. The radial surface stresses shifted similarly except that the final strains were slightly tensile. Residual strain mapping in the bulk was performed in two orthogonal directions with neutron diffraction. In the Y and Z (axial) directions, the bulk tensile strains were reduced from tensile to slightly tensile/compressive with increasing heat-treatment temperature. The opposite trend was observed in the surface.