SEDL / STP / STP677-EB / STP34916S

Crack Closure During Fatigue Crack Propagation

Shaw, WJD
President, Shaw Engineering and Research Corp., Saskatoon,

Le May, I
Professor, University of Saskatchewan, Saskatoon,

Pages: 14    Published: Jan 1979

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Abstract

Crack closure in single edge notched fatigue specimens of AISI 4140 steel was studied and it was determined that crack closure occurs at the edges of the specimen in the area of slant mode fracture while the center portion remains open. It was demonstrated that errors arise in the determination of crack opening and crack closure loads if the displacement measurements are not taken an adequate distance from the crack tip. Following careful evaluation of the loads for complete crack opening and complete crack closure, it has been demonstrated that in the equation for correlation or prediction of fatigue crack propagation, improved correlation results when an effective value of ΔK is taken based on the range of stress intensity factor to maximum load from complete crack closure rather than from complete crack opening or minimum load.