X-Ray Diffraction Measurements of Crack Tip Stresses as a Crack Advances through a Single Overload Affected Zone
Final rept. Nov 1977-Jul 1978
AIR FORCE FLIGHT DYNAMICS LAB WRIGHT-PATTERSON AFB OH
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Stress levels were measured in the vicinity of a crack tip using an x-ray diffraction technique to determine the correlation of these measurements with crack closure and residual stress theories. A single tensile overload was applied to a modified compact specimen of 1020 steel. The material had been heat-treated to obtain an ASTM grain size of 10 to 11 and a yield strength of 70 ksi. Crack tip residual stresses were measured in the unloaded condition and crack tip applied stresses were measured under load. These measurements were made as the crack was extended into and past the overload affected zone. Results suggested that overload retardation was primarily due to residual compressive stresses generated at the point of overload. It was observed that the effect of the overload had dissipated by the time the crack was propagated through a distance approximately equal to the plastic zone caused by the overload.
- Metallurgy and Metallography