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**Published:** Jan 1980

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**Source: **STP711-EB

Time-varying shear force measuring techniques have been used to investigate the dynamic critical stress-intensity factor versus crack propagation velocity curve. The product of the shear force at the loading end times the square root of the loading time on a rapidly wedged double cantilever beam specimen is uniquely related to the critical bending moment at the crack tip. Static compliance measurements on side-grooved specimens were incorporated into a Bernoulli-Euler beam model for calibration purposes and to eliminate the inappropriate built-in beam assumption. The compliance calibration shows a crack length shift from a measured crack length to a beam model length at a fixed compliance value. This shift does not affect the magnitude of the calculated critical bending moment at the crack tip when the load and the load-point displacement are measured quantities. The effective crack length is calculated from the beam model length with the length shift correction. The *K*^{Id}-values (calculated from the critical bending moment) versus crack velocity have been investigated at several test temperatures for a low-carbon steel. *K*^{Id}-values show a generally decreasing trend when crack velocity increases. *K*^{Ic} at fast fracture initiation is larger than the corresponding *K*^{Id}-value for all tests recorded.

**Keywords:**

cantilever beams, crack propagation, fracture properties, critical stress intensity, crack velocity

**Author Information:**

Chow, C-L *Research assistant and professor, University of RochesterDe Havilland Aucraft of Canada, Ltd., RochesterDownsview, N.Y.Ont.*

Burns, SJ *Research assistant and professor, University of RochesterDe Havilland Aucraft of Canada, Ltd., RochesterDownsview, N.Y.Ont.*

**Committee/Subcommittee:** E08.03

**DOI:** 10.1520/STP27450S