The fracture of acrylic polymers in water

This paper describes the application of linear elastic fracture mechanics analysis to the fracture of acrylic polymers in water. Three denture base acrylics were studied in addition to Perspex. The effects of strain rate and temperature were investigated using double torsion specimens and three-point bend specimens. It was found for most materials that the fracture toughness was dramatically increased on testing in water compared with testing in air. Crack propagation at fast strain rates was unstable in water and the fracture toughness and flaw size were strain-rate dependent, increasing with decreasing test rate, whilst the un-notched fracture strength decreased with decreasing strain rate. At low strain rates, stable crack propagation was achieved and fracture toughness then decreased with decreasing strain rate. The results are discussed in terms of Williams' model for environmental fracture and the effect water has on the crazing process taking place at the crack tip.