A procedure of total potential energy release rate is developed for a general FGM beam, which is considered as a double cantilever beam (DCB). The mechanical properties vary as a general function of thickness. The procedure is based on a technical engineering theory for calculation of strain energy release rate. By choosing a suitable displacement field based on second-order shear-thickness deformation theory and using the principle of minimum total potential energy, the equilibrium equations are obtained. The energy release rate is obtained by using the J integral for the DCB model. The distribution of displacements and stresses are determined for a special case and the results are compared with the results of finite element method. This comparison shows good agreement between the results. The separation of J integral into modes I and II is carried out by decomposition of stress and strain fields from point symmetric to the crack plane. The separation technique is applicable for both symmetric and asymmetric geometry with respect to the crack plane. The results of J integral are compared with those of the other methods and present good agreement between the results.

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