A calculation method to obtain an approximate estimate of interfacial debonding during cooling caused by the difference in thermal expansion between the fibre and matrix was presented using a single fibre-composite model. With this method, the energy release rate for the initiation and growth of debonding with matrix cracking were calculated for some examples. It was shown that the larger the difference in thermal expansion between fibre and matrix, the lower the fibre volume fraction and the higher the Young's modulus of the matrix, the higher the energy release rate for debonding becomes, resulting in a higher temperature for the initiation and growth of debonding. It was also shown that the debonding grows unstably upon initiation when the Young's modulus of the matrix is lower than that of the fibre, while it grows stably with decreasing temperature in the early stage and then unstably in the late stage when the former is higher than the latter.
