Annealing effect on microhardness and elastic constants of PMMA

The ultrasonic velocities of both longitudinal and shear waves were measured in thermoplastic discs of poly methyl methacrylate (PMMA) as a function of annealing temperatures ranging from 23degreesC to 95degreesC (23degreesC, 45degreesC, 60degreesC, 75degreesC, 80degreesC, and 95degreesC). Ultrasonic velocity measurements were taken at 2 MHz ultrasonic frequency using the pulse echo method. From the experimental data, the longitudinal modulus, rigidity, and Young's modulus are derived. Effect of annealing on microhardness of PMMA was studied using ultrasonic pulse echo method as well as mechanical measurements. The critical stress intensity factor was also determined at the same annealing conditions. In all events, the microhardness and the elastic constant are found to be changed at annealed temperature named 80degreesC.