  We consider dynamic motion of a linearized elastic body with a crack subject
to a modified contact law, which we call the Signorini contact condition of
dynamic type, and to the Tresca friction condition. Whereas the modified
contact law involves both displacement and velocity, it formally includes the
usual non-penetration condition as a special case. We prove that there exists a
unique strong solution to this model. It is remarkable that not only existence
but also uniqueness is obtained and that no viscosity term that serves as a
parabolic regularization is added in our model.
