Three-Dimensional Nature of Strain Field Near Coldworked Holes.

摘要

As part of a comprehensive program to develop understanding of fatigue-rated fasteners, the three-dimensional aspects of the radial, hoop, and transverse strains which are created by drawing a tapered mandrel through a cylindrical hole were measured. A unique 3-dimensional moire procedure was used. Specimens were fabricated with multiple embedded grids. These grids were photographed for eachspecimen state. Moire fringe photographs were extracted from the replicas by coherent optical processing. Digital analysis of the fringes gave the desired strain maps. The residual radial strain after coldwork inside the specimen was found to be smaller than on the surface. The transverse strain changes from tension near the top surface where the mandrel enters to maximum compression at the midplane, where it begins to decrease. The hoop strain is maximum on the entry surface and decreases to a minimum at the midplane. The change in this component is only about four percent of the maximum value. Potential problems in the use of such coldworking processes might arise from the low value of the interior radial strain in comparison with the surface value and the existence of tensile transverse normal strain near the surface. (Author)