Pointwise energy release rate in delaminated plates
A laminated plate theory suitable for analyzing delaminations has been derived. The theory is used to study the interaction between the top and bottom sublaminates in the intact region of a delaminated plate. Expressions are derived for the jump in force and moment resultants that occur across the delamination front. Using Irwin's crack closure integral, a simple expression for pointwise strain energy release rate G along the delamination front has been derived. The expression suggests that the G at any point on the delamination front is the difference between the plate strain energy densities behind and ahead of the delamination front. An estimate of error in computing G using plate theories is obtained by comparing the J integral obtained using exact stress fields and plate stresses. The procedure for computing G is first verified by applying it to double cantilever beam specimens (DCB) and elliptical delaminations in isotropic plates for which solutions are available or can be computed. Then the method is illustrated for a stitched graphite/epoxy DCB specimen and also for elliptical delaminations in 0-deg graphite/epoxy plates. The results demonstrate the usefulness of the present method in analyzing delaminated coupons and structures.