Effect of crystal orientation on fatigue-crack initiation in polycrystalline aluminum alloys

J. G. Weinberg, J. A. Bennett
naca-tn-3990
Aug 1957


It was determined that fatigue cracks initiate in preexisting slipbands on planes that are parallel to (111) planes from tests on large-grained specimens of 1100 and 5052 aluminum alloys. The resolved shear stress on these planes in crystals where fatigue cracks had developed was compared with that in uncracked crystals. In bending fatigue tests the cracks always started in crystals at the corner of the cross section; this made comparison difficult, but it appeared that grain size and shape as well as resolved shear stress had an influence on the initiation of cracks. Under torsional loading the resolved shear stress appeared to be the only important factor that governed which crystal developed cracks.

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