Use of photostress to analyze behavior of an aft skirt test specimen
Strains at twenty-one selected points in the critical lower weld region of a aft skirt of a solid rocket booster of the shuttle were measured using photoelastic coatings and stress separator gages. Data were taken at loads of 5, 14, 20, 28, 42, 56, and 70 percent of the design limit load. Results indicate that general yielding occurred in the weld metal and for a short distance outside the fusion boundaries on either side of the weld metal. The fusion boundaries did not yield at the 70 percent load. Slight non-linearity in the load strain curves were observed at several points above the 20 percent load level. Maximum measured strains occurred at points in the forged metal of the holddown post along a line 0.50 inches from the centerline of the weld. Maximum shearing strains within the area covered by the photoelastic coating occurred at points approximately 0.33 inches to the right of the weld centerline near points 6 and 7 and lying along a yellow vertical line extending from just below point 6 to point 11. Photoelastic coatings were shown to be an excellent method to provide the whole field strain distribution in the region of the critical weld and to enhance the overall understanding of the behavior of the welded joint.