ISSN: 1945-7553
CODEN: JTEVAB
Page Count: 6

Computer-Controlled Stress Intensity Gradient Technique for High Rate Fatigue Crack Growth Testing

Donald, JK
Vice-president and staff engineerMembers of ASTM, Del Research Division, PSC Professional Services Group, Inc., Hellertown, Pa.

Schmidt, DW
Vice-president and staff engineerMembers of ASTM, Del Research Division, PSC Professional Services Group, Inc., Hellertown, Pa.

Abstract

An automated test system utilizing a computer for data acquisition and machine control was used to obtain crack growth rate data from 2.5 × 10⁻⁸ to 2.5 × 10⁻⁶ m/cycle (1 × 10⁻⁶ to 1 × 10⁻⁴ in./cycle) on a compact type specimen. The crack length was monitored continuously by using the elastic compliance technique, enabling the stress intensity K to be increased according to the equation ΔK = ΔK exp [C(a − a₀)] (where a₀ and a are the initial and instantaneous crack lengths and C is a test variable). Crack growth data were obtained on a Ni-Cr-Mo-V rotor steel by using both different, programmed K gradients and the more conventional constant-load-amplitude method where the stress intensity increases as a function of increasing crack length. Excellent agreement was observed between the two test procedures.

Keywords:
fatigue (materials), crack propagation, stresses, K gradient, computers, compliance

Paper ID: JTE10588J
DOI: 10.1520/JTE10588J
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