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The aim of this paper is to demonstrate that a computer-controlled test machine can replace a test machine made compliant by a mechanical spring for tearing instability testing of simple compact and cracked pipe geometries. For both geometries tested herein, close agreement was demonstrated between the “computer compliant” and “spring compliant” test systems. The results show that though the computerized system utilized here is slower than the spring machine, this is not a serious drawback for structural materials with low to moderate rate dependence. The “inertia free” response of the computerized system is in fact a positive feature for studying tearing instability arrest and promises to be very useful to further studies in that area.
Experimental results obtained in this study on the circumferentially cracked pipe geometry show that J-R curves from the pipe geometry lie well above J-R curves obtained from subscale compact specimens removed from the pipe wall. Tearing instability occurs in the pipes at crack extension values well in excess of what was obtained from compact specimens of the scale utilized, and a prediction of pipe instability based on the compact J-R curve alone would give very conservative results.
elastic-plastic fracture, J-integral, J-R curves, slow crack growth, tearing modulus, tearing instability, compact specimens, circumferentially cracked pipe specimens, computer-controlled testing, tearing instability arrest
Associate professor, U.S. Naval Academy, Annapolis, Md.