The use of laser extensometer to study the behavior of short fatigue cracks

✍ Scribed by M.L. Bartlett; A. Saxena

• Publisher: Elsevier Science
• Year: 1988
• Tongue: English
• Weight: 921 KB
• Volume: 30
• Category: Article
• ISSN: 0013-7944
• DOI: 10.1016/0013-7944(88)90157-9

✦ Synopsis

For short fatigue cracks, the measured compliance based on additional crack mouth opening displacement (CMOD) due to the presence of the crack load under linear-elastic conditions is a good measure of the crack tip stress field. This relationship is due to the proximity of the measurement point and the crack tip. In this study, an accurate telemetric laser extensometer (TLE) with a resolution of 1.27 x lop4 mm was used to measure CMOD for edge cracks in the range of 0.2mm to 2mm deep in uniformly stressed specimens. This paper describes the test set-up and the preliminary test results.

The measured CMOD for short cracks (< 1 mm deep) were higher than the analytically calculated values based on the contribution to the deflection from the K-term alone. It is argued that for short cracks, the strain energy reIease rate, G, is not equal to 1(*/E where, E = elastic modulus. G is proposed as a candidate parameter for characterizing the growth rate of short cracks. It is noted that the rate of growth of short fatigue cracks in mild steel correlate with AJ under fully plastic conditions which is consistent with the above proposal.