SELF-REINFORCED COMPOSITE POLY(METHYL METHACRYLATE) - STATIC AND FATIGUE PROPERTIES

A novel material called 'self-reinforced composite poly(methyl methacrylate)' (SRC-PMMA) is described. This composite material consists of high strength, high ductility PMMA fibres embedded in a matrix of PMMA. Tensile tests, three-point flexural tests, fracture toughness tests and flexural fatigue tests were carried out on unidirectional continuous fibre SRC-PMMA materials. Commercial sheet PMMA and bone cement were also tested for comparison purposes. Two PMMA fibre sizes (40 and 120 mu m diameters) with different mechanical properties were used to make the SRC-PMMA materials. The results of this study show that the tensile strength, tensile modulus and tensile strain-to-failure were significantly greater for the SRC-PMMA compared with commercial PMMA (P < 0.05). The flexural strength was not increased in the SRC-PMMA compared with PMMA alone but was greater than that in bone cement (P < 0.05). There were no differences in flexural modulus between any group. The flexural strain-to-failure (30-35% for SRC-PMMA) was about three times greater in SRC-PMMA compared with bone cement and PMMA. Fracture toughness of these SRC-PMMA materials was also significantly greater than PMMA and bone cement (P < 0.001). Fracture toughness values of 3.2 MPa m(1/2) were found in the 40 pm SRC-PMMA compared with 2.3 MPa m(1/2) for the 120 mu m SRC-PMMA and 1.3 MPa m(1/2) for PMMA and bone cement. The fatigue strength of both SRC-PMMA samples was significantly greater (P < 0.001) at 80 MPa (10(6) cycles) compared with bone cement and PMMA, both of which had fatigue strengths of about 18 MPa. Fatigue damage in the form of fibre splitting and fibre-matrix interface failure was observed in the SRC-PMMA samples while the PMMA and bone cement showed only smooth fractures. During cyclic fatigue testing, the ongoing damage processes were periodically monitored using several novel computer-based and analysis algorithms. The measured cyclic loads and displacements are used to determine the creep-fatigue displacements, the sample stiffness (or modulus) and the hysteresis damage energy as functions of the number of applied cycles associated with the fatigue loading. The hysteresis damage energy to failure was about 25 times greater in the SRC-PMMA samples (2000 J at 10(6) cycles) compared with bone cement or PMMA at the same number of cycles to failure (80 J) indicating much greater fatigue damage tolerance in these materials. This material, SRC-PMMA, may be applicable for use in several medical and/or dental applications.