SEDL / STP / STP513-EB / STP34112S

Stress Intensity Factors for Surface Cracks in Bending

Grandt, AF
First Lieutenant, USAF, Air Force Materials Laboratory (AFML/LLP), Wright-Patterson AFB, Ohio

Sinclair, GM
Professor, University of Illinois, Urbana, Ill.

Pages: 22    Published: Jan 1972

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Abstract

Fracture mechanics solutions applicable to surface cracked plates in bending are studied. The flawed plate is modeled as a two-dimensional beam containing a spring to find the stress intensity factor at the point of intersection of a semielliptical surface crack with the free boundary. Results are given for cracks of various shapes and sizes. These findings, along with previous analytical solutions obtained from the literature, are then compared with experimental data. Since it is difficult to measure surface cracks in metals, polymethylmethacrylate, a transparent polymer, was selected for the test material. First, the relation between fatigue crack growth rate and range in stress intensity is calibrated for polymethylmethacrylate. Measured fatigue crack growth rates for surface flaws in bending are then used to calculate experimental values for the stress intensity factor which are compared with theory.