Application of Residual Stress Measurements In Failure Analysis and Field Inspection 670154

Investigation of cracked rotor “D” spar revealed an area of tensile residual stress in the area of the failure origin. Normal rotor spar processing results in the formation of compressive residual. The service history of the cracked spar indicated that it had been buckled, and that compressive yielding had occurred. This resulted in a “wiping out” of the compressive residual stress, and the subsequent formation of a tensile residual stress.
Laboratory tests aimed at reproducing the buckle proved successful and full scale fatigue tests of the buckled spars resulted in failures significantly below the normal test scatter.
Inspection criteria, based on X-ray diffraction residual stress analysis, have been instituted.


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