Assistant professor, Polytechnic Institute of Leiria, Lisbon,
Assistant professor, Polytechnic Institute of Setubal, Lisbon,
de Freitas, MJM
Associate Professor, Instituto Superior Tecnico, Technical University of Lisbon, Lisbon,
Pages: 16 Published: Jan 1999
The concept of fatigue crack closure, introduced in the 60's by Elber, has been used to explain a wide range of positive stress ratio crack propagation results (R ⩾ 0). Less attention has been given to fatigue loading for negative stress ratios (R < 0). In this work the results of crack propagation tests of middle-crack tension M(T) specimens of a normalized medium carbon steel DIN Ck 45 for a wide range of stress ratios from 0.7 ⩾ R ⩾ -3 are presented. Crack closure loads were measured with the compliance technique at test frequency, using a data acquisition system. Negative crack closure loads were found for negative stress ratios R ⩽ -1, which can explain higher crack propagation rates and accelerations in crack growth during variable-amplitude tests where compressive loads of different stress ratios are present.
fatigue, crack propagation, crack closure, stress ratio
Paper ID: STP15765S