Compact Tension Test Specimens Research Articles

A microcomputer control system for the measurement of fatigue crack growth data

A microcomputer-based system for the measurement of fatigue crack growth da/dn versus cyclic stress intensity factor ΔK data using compact-tension test specimens is described. The procedure has been developed to allow automatic measurement of crack growth rate under any specified combination and sequence of load conditions, i.e. ΔK and R (stress ratio) and includes the capability of establishing the threshold cyclic stress intensity factor ΔK 0 . Crack extension measurement is effected from the elastic compliance evaluated from the AC component of the load and displacement signals to an accuracy of ∼-3 μm every 1000 load cycles. Results from a typical low-alloy-steel rotor forging are presented to illustrate the use of the system.

Stress intensity calibrations and compliance functions for fracture toughness and crack propagation test specimens

Experimental determination of compliance over the approximate range of a/W from 0.3 to 0.7 has been undertaken for compact tension and cantilever beam test specimens. The test data have been processed using a recently proposed analytical procedure, and the results for compliance functions have been compared with some standard results available in the literature. The agreement between the experimental results and the proposed compliance functions equation for compact tension geometry of ASTM E399 is excellent. However, for the cantilever beam specimen, it is demonstrated that the usual Srawley and Brown equation for pure bending may underestimate the compliance function by as much as 14%.