In this paper, the transient dynamic stress intensity factors are estimated for multiple cracks which are located at the interface between a nonhomogeneous elastic half-plane and an elastic half-plane. The material properties of the nonhomogeneous halfplane vary continuously in the y-direction. First, Laplace and Fourier transforms are applied to reduce the mixed boundary value problem to a system of singular integral equations with Cauchy kernels which are solved numerically. By numerical Laplace inversion technique, the dislocation density on the crack faces is obtained and then transient dynamic stress intensity factors at crack tips have been determined. For validity and accuracy of the method, the results are compared with other references and very good agreement is shown. The influences of nonhomogeneity parameters, crack length, the variation in time and the interaction between of cracks on the transient dynamic stress intensity factors are studied. It is observed that the mode I stress intensity factors decrease regularly with increasing the FG constant and the results are briefly discussed.

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