Temperature variation relevant to fatigue crack initiation and propagation in a single crystal material

抄録

The Evaluation of fatigue limit by measuring temperature change using infrared thermography has attracted significant interest owing to its potential for rapid assessment. However, physical background and validity of this technique are not yet fully understood. The utilization of infrared thermography is not limited to the study of the fatigue limit; research on the relationship between crack propagation and temperature dissipation has also been carried out as part of the study of fatigue damage in metallic materials. In this study, temperature change during cyclic loading is measured by infrared camera using four types of single crystal notched specimens with different crystallographic orientations. Local slip deformation is quantified using crystal plasticity finite element analyses. First, the effect of crystallographic orientation on fatigue crack initiation and the temperature field was investigated. It is found from the experimental and numerical results that the distribution and magnitude of second harmonic temperature and the local slip deformation (a plastic shear strain on the most active slip system) are affected by the crystallographic orientation. However, the correlation between plastic shear strain and second harmonic amplitude when crack initiates, as well as threshold values of these parameters for crack initiation, is independent of the crystallographic orientation. Second, the effect of crystallographic orientation on fatigue crack propagation and temperature field was investigated. It is found that the magnitude of second harmonic amplitude differ corresponding to the fatigue crack propagation rate and the fatigue crack growth threshold in each orientation. However, the correlation between the plastic shear strain and the second harmonic amplitude when crack propagates, as well as the threshold values of these parameters for crack growth threshold, is independent of the crystallographic orientation.