Standardization of strength evaluation methods using critical distance stress

The stress and displacement fields near the bonding edge, sharp notch, and contact edge show singularity behaviors, so methods of evaluating the strength of these points using maximum stresses calculated by a numerical stress analysis, such as the finite element method, are generally not valid. We have previously presented a new method of evaluating the strength of these singular points using two stress singularity parameters H and lambda. The difficulty with this method was in obtaining the critical value of the intensity of the stress singularity parameter H-c for each order of stress singularity lambda. Then we have developed a method of formularizing critical value of stress singularity parameter H-c for each order of stress singularity by utilizing critical distance stress theory. Firstly we apply this method to the delamination strength evaluation. The estimated delamination criteria H-c(lambda) agrees well with the experimental results. Then we apply this method to general sharp notch corner and contact edge fatigue problems. In these cases the fatigue-crack initiation criteria can be derived from two typical strength parameters, namely, fatigue limit sigma(w0) and threshold stress intensity factor range Delta K-th. These estimated critical H-th(lambda) value agrees well with the experimentally measured value. Using this simple critical distance stress approach we estimated the fretting fatigue-crack initiation criteria for any contact edge angle and optimized the contact edge geometry. Moreover, we can apply this new strength criterion to stress singularity fields for general stress-concentration structures. (c) 2007 Elsevier Ltd. All rights reserved.