Limitations for elastic-plastic materials

The analysis of the thin film buckling phenomenon discussed in this section is based on the assumptions that the material deformation is everywhere within the elastic range, and that inelastic deformation associated with the delamination front at the edge of the buckled zone is sufficiently localized to fall within the range of applicability of linear elastic fracture mechanics. 

The restriction that the overall deformation should be elastic can be examined by considering the state of stress at the edge a = a of the buckled zone. The membrane force resultant has the value ta 0 throughout the zone —a x a. On the other hand, the bending moment mx x) varies throughout the zone, but it is readily confirmed that it does so between the limits of —ma and ma. The tensile stress (Txx that is largest in absolute value for this state of combined tension and bending is 

A rough estimate of the limits on the range of applicability of elastic 

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