Procedures for Precision Measurement of Fatigue-Crack-Growth-Rate Using Crack-Opening-Displacement Techniques

摘要

This paper describes experimental and analytical procedures whereby the conventional commercial fracture mechanics clip-gage can be used for precision measurement of fatigue-crack-growth-rate in compact tension specimens. Potential sources of error in measuring crack length via COD techniques are delineated. Comparisons are made among crack length data obtained via specimen surface observations and crack-opening-displacement (COD) techniques. Comparisons are also made among data analyzed by the secant and 7-point incremental polynomial methods. It is emphasized that COD techniques can enhance the accuracy of the secant method of data reduction. Step-loading procedures using COD techniques are described. Proposed amendments to ASTM E647-78T regarding incrementing of crack-length measurements via COD techniques are discussed. (Author)