Transient dynamic stresses around three coplanar cracks in an infinite elastic medium have been solved. Two equual rectangular cracks are placed on either side of a centrally situated rectangular crack so as to allow for geometrical symmetry. A self-equilibrated system of pressure is applied suddenly on the surfaces of the cracks. To solve the problem, two kinds of solutions are superimposed. One is a solution for a rectangular crack in an infinite elastic medium and the other is that for two rectangular cracks in an infinite elastic medium. Unknown coefficients in the combined solution are determined so as to satisfy boundary conditions at the surfaces of the cracks using the Schmidt method. Stress intensity factors are defined in the Laplace transform domain and these are inverted in the physical space with the aid of a numerical method.
