SEDL / STP / STP1058-EB / STP24090S

Fatigue Crack Initiation and Growth in Tensile-Shear Spot Weldments

McMahon, JC
Engineer, Advanced Cardiovascular Systems, Temecula, CA

Smith, GA
Engineer, General Electric Corp., Cincinnati, OH

Lawrence, FV
Professor of civil engineering and metallurgy, University of Illinois at Urbana, Urbana, IL

Pages: 31    Published: Jan 1990

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Abstract

Fatigue crack initiation and growth in SAE 960X steel tensile-shear spot welds were studied by sectioning companion specimens and by replicating the exposed site of crack initiation in a presectioned weldment. Constant-amplitude R = 0 and R = -1 tests, as well as variable-load history tests were performed on as-welded weldments and weldments peened (“coined”) after welding.

Approximately 50% of the total fatigue life was devoted to developing a 0.25-mm-depth crack under constant-amplitude loading in the life range 10⁴ to 10⁶ cycles. At lives greater than 10⁶ cycles, this percentage appeared to increase. Similar results were found under a variable load history, although, in this case, only 40% of the life was devoted to developing a 0.25-mm-depth crack. Postweld coining increased the fatigue life by over an order of magnitude. Several analytical models for predicting the fatigue life of the tensile-shear spot weldments studied were compared.