A three-dimensional dynamic steady state analysis for extension of a semi-infinite
plane crack is considered. Fracture is brittle and driven by loads applied
to the crack surfaces. An analytical solution is obtained, and examined in light of two
criteria: energy release (rate) and strain energy density. Introduction of a quasipolar
coordinate system allows, for each criterion, generation of a nonlinear first-order
differential equation for the distance from the origin to any point on the crack
edge. These in turn give insight into the crack contour generated by the crack edge.
In particular, for loading by compressive point forces, the equation generated by the
energy release (rate) criterion is solved exactly. Calculations depict a crack edge contour
that tends to the rectilinear, but deviates markedly from that near the point forces.
