Functional grading of IPN parts: plates with single and multiple cracks

Functional grading (FG) around the crack tip is studied to improve the load capacity in parts made of graded interpenetrating polymer networks (IPN). To calculate the capacity, the stress intensity factor at the crack tip is calculated by blending the displacement correlation technique and finite element solutions. This process is integrated into an optimization process that uses linear scaling to obtain optimal material grading in a fixed domain around the crack tip. The process is demonstrated using a known poly(methyl methacrylate)/polyurethane IPN system for the case of internal and edge cracks. The FG-IPN parts obtained by this optimization show substantially improved load capacity compared to both optimal uniform plates, and plates with simple toughening of the region around the crack.