Effect of Residual Stress on Stress Corrosion Cracking in Maraging Steel Blades

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Abstract:: Maraging Steel blades are employed for the attenuation of Earth’s vibrational motion in the VIRGO and LIGO interferometers. In LIGO and KAGRA many units failed catastrophically after exposure to environmental air. Stress corrosion cracking is determined upon inspection. Notably, the failed units were ground to final thickness, which removed a layer likely under compression stress, and/or were resolubilized which has a similar effect. Blades that were made of untreated, cold rolled sheets are largely immune from this failure, despite coming from the same source. This thesis will attempt to confirm using X-Ray Diffraction and theory that the residual stress from cold rolling retards the progress of crack formation and propagation and that Stress Corrosion Cracking was inhibited in some blades by the layer of residual stress left by the cold rolling process. This knowledge will allow production of safer blades in the future. Diffraction measurements yielded confirmation that a compressive layer exists on the surface of the cold rolled blades, with a stress value of approximately -300MPa. This result was confirmed by comparing samples to maraging steel blades first ground to eliminate the surface layer, then manually cold rolled and finally precipitation hardened.

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LIGO Document P1800124-v1