Misinterpreting the results: How similitude can improve our understanding of fatigue delamination growth

Use of the strain energy release rate for characterizing delamination growth in composite and bonded structures is now commonplace. Analogous to the use of the stress intensity factor range for fatigue crack growth in metals, the strain energy release rate range, defined as the arithmetic difference between maximum and minimum values, is often used to characterize fatigue delamination growth behaviour. The basis for similitude for these two parameters, however, is different and can lead to misinterpretations of delamination growth behaviour if this difference is not understood. This paper examines the basis of similitude for the strain energy release rate range and how it can be redefined in order to avoid potential misinterpretations of fatigue delamination growth.