SEDL / STP / STP743-EB / STP28807S

An R-Curve for a Surface Crack in Titanium

Lewis, JC
Member, technical staff, TRW, Defense and Space Systems Group, Redondo Beach, Calif.

Sines, G
Professor, School of Engineering and Applied Science, University of California at Los Angeles, Los Angeles, Calif.

Pages: 15    Published: Jan 1981

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Abstract

R-curves for surface cracks in Ti-6A1-4V titanium alloy were generated for the purpose of studying the resistance of the alloy to their subcritical growth under a monotonically increasing load typical of a proof test. Another purpose was to evaluate Ehret's compliance calibration for measuring the instantaneous size of a surface crack using the unloading slope of a load-versus-clip-gage-opening curve. Another purpose was to study “leak-before-burst” during sustained load and during subcritical crack growth under rising load.

Clips were mechanically attached to either side of the surface crack on the face of the specimen. A clip-gage extensometer was used to plot load-versus-clip-gage opening. Slopes were taken periodically by unloading about 10 percent so that subcritical crack growth could be distinguished from crack-tip plastic deformation. The tests were run in accordance with the ASTM Recommended Practice for R-Curve Determination (E 561-78T) as much as possible.