Stress and Strain at Onset of Crazing of Polymethyl Methacrylate at Various Temperatures.

摘要

The stress and strain at the onset of crazing of polymethyl methacrylate were determined at 23 deg, 50 deg, and 70 deg C. The materials tested were commercial cast polymethyl-methacrylate sheets of both general-purpose and heat-resistant grades. Most of the tests were made on samples 0.15 inch thick. Load-elongation graphs were made during the tests and the onset of crazing was observed visually and noted on the graph. The results indicate that a 'critical-strain theory' for the threshold of crazing, as has been suggested for polystyrene by Maxwell and Rahm, is not applicable to polymethyl methacrylate. The strain at the threshold of crazing tended to decrease with increase in temperature from 23 deg to 50 deg C. Between 50 deg and 70 deg C no consistent trend for the strain at crazing was detected. The stress at the threshold of crazing was about 80 to 95 percent of the tensile strength at all temperatures.