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

A novel material called 'self-reinforced composite poly(methyl methacr ylate)' (SRC-PMMA) is described. This composite material consists of h igh strength, high ductility PMMA fibres embedded in a matrix of PMMA. Tensile tests, three-point flexural tests, fracture toughness tests a nd flexural fatigue tests were carried out on unidirectional continuou s 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 mak e the SRC-PMMA materials. The results of this study show that the tens ile strength, tensile modulus and tensile strain-to-failure were signi ficantly 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 f lexural strain-to-failure (30-35% for SRC-PMMA) was about three times greater in SRC-PMMA compared with bone cement and PMMA. Fracture tough ness of these SRC-PMMA materials was also significantly greater than P MMA 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) f or 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 greate r (P < 0.001) at 80 MPa (10(6) cycles) compared with bone cement and P MMA, both of which had fatigue strengths of about 18 MPa. Fatigue dama ge in the form of fibre splitting and fibre-matrix interface failure w as observed in the SRC-PMMA samples while the PMMA and bone cement sho wed only smooth fractures. During cyclic fatigue testing, the ongoing damage processes were periodically monitored using several novel compu ter-based and analysis algorithms. The measured cyclic loads and displ acements are used to determine the creep-fatigue displacements, the sa mple stiffness (or modulus) and the hysteresis damage energy as functi ons of the number of applied cycles associated with the fatigue loadin g. 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 ce ment or PMMA at the same number of cycles to failure (80 J) indicating much greater fatigue damage tolerance in these materials. This materi al, SRC-PMMA, may be applicable for use in several medical and/or dent al applications.