Stress Intensity Distributions and Width Correction Factors for Natural Cracks Approaching “Benchmark” Crack Depths

A series of frozen stress photoelastic experiments were conducted on natural surface flaws in both wide and finite width flat plates under uniform uniaxial tension. The flaws grown under monotonic load were semielliptic and retained that shape (but with varying aspect ratio) up to 75% of the plate depth. The stress intensity distributions compared favorably with the predictions of the Newman-Raju analysis, but were slightly higher at the points of maximum flaw penetration for the deeper flaws. The crack growth path of the photoelastic models differed from that resulting from fatigue tests on aluminum up to a/T ≈ 0.3. The difference is conjectured to be caused by crack closure in the fatigue tests.