The Stress Intensity Factor for an Elliptic Crack Under a Piecewise-Constant Load

A closed approximate solution is given for the stress intensity factor (SIF) at the front of an elliptic crack under uniform loading on the elliptic ring. The solution is constructed by modifying Rice's variational formula that integrally relates the SIFs for two different states on the crack faces. The first state is a combination of the second and principal states such that the total SIF is zero. In this case, Rice's formula reduces to the virtual-displacement principle for a combined loading on the crack faces.