Manufacture and testing of a functionally graded material

A novel technique is presented for the fabrication and fracture testing of large-scale polymeric based Functionally Graded Materials (FGMs). The technique generates a continuously inhomogeneous property variation by taking advantage of the susceptibility of a polyethylene carbon monoxide copolymer (ECO) to ultraviolet irradiation. The resulting FGMs exhibit a varying Young's modulus, usually in a linear fashion, from approximately 160 MPa to 250 MPa over 150 mm wide specimens. The fracture behavior of the FGM is experimentally investigated through the use of single edge notch fracture tests on both homogeneously irradiated and functionally graded ECO. Two approaches are used to evaluate fracture parameters: The first, a hybrid numerical-experimental method, is based on far field measurements only. The second uses digital image correlation to obtain near tip measurements. The energy release rates of uniformly irradiated ECO and of several FGMs are measured and compared. It was seen that the FGM showed a built-in fracture resistance behavior implying that it requires increased driving force to sustain crack growth.