Residual Stress Measurements in Front of a Propagating Fatigue Crack

X-ray residual stress measurements were made near the fatigue crack tip in round-robin specimens by the X-Ray Fatigue Division of the SAE Fatigue Design and Evaluation Committee. Steel specimens, furnished by the Cumulative Fatigue Damage Division from their fatigue program, were of two strength levels and either constant-amplitude or program loaded. Results showed the need for more work in establishing the small beam x-ray technique. Residual stress patterns ahead of the crack correlated qualitatively with the Rice model, and higher compressive stresses in the higher strength material correlated with increased resistance to crack propagation in the fatigue program. Stresses measured across the crack also reinforced the Elber crack closure concept.