A common problem during pre-cracking of compact tension (CT) specimens is skewed crack fronts. It is also one of the most common reasons for which tests according to, for instance, ASTM E1820-11: Standard Test Method for Measurement of Fracture Toughness, Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA, 2012, do not give valid results. This problem is normally a result of the fact that specimens and fixtures are not perfectly aligned, even when the testing setup meets the requirements of ASTM standards. In the present investigation, aluminum bushings have been used to rearrange the loads transferred from the testing machine to the specimens. Geometrical errors were deliberately introduced to the testing setup so that the specimens were asymmetrically loaded. The introduced errors were, however, within the tolerances of ASTM standards. Steel specimens with two different notch types, Chevron and straight notches, were tested, both with and without aluminum bushings. The specimens were pre-fatigued and thereafter broken under monotonic loading. The specimen crack lengths were measured and validated according to ASTM E1820-11. The results related to pre-fatigued specimens with aluminum bushings were shown to be valid, whereas the results for specimens without bushings did not meet the ASTM standards requirements.
KTH, Royal Institute of Technology Dept. of Solid Mechanics, Stockholm,
Stock #: JTE20120299