Comments on the analysis of substrate cracking and spalling experiments

Data on crack spalling and on residual stress induced substrate cracking are reanalysed using a global energy release rate partitioning scheme. The stability of the crack path is analysed in terms of the maxima in the mode I component. This is compared with the previous analysis based on local stress field partitioning. It is suggested that some microcracking may have occurred and an attempt at including friction effects is given. It is concluded that crucial experiments would require very large substrate depths.