Evaluation of methods of determining fracture parameters for a glassy polymer: Poly(methyl methacrylate)

Abstract

Fracture criteria for the brittle fracture of a glassy thermoplastic, poly(methyl methacrylate), have been evaluated using three test piece geometries; the double cantilever beam (DCB), three-point bend (TPB), and compact tension (CT). For the DCB good agreement is obtained with published estimates of the fracture parameters using either a compliance calibration calculation for the critical energy release rate, G1c, or a polynomial function for the critical stress intensity factor, K1c. Anamolously high values of G1c or K1c were obtained using the TPB test piece. These high values of K1c may be partially due to the difficulty of “sharpening” the crack, but there is a test piece size effect which also contributes to the over estimation of K1c. For the CT test piece use of either a new compliance calibration for the determination of G1c or a standard polynomial function for K1c, good agreement was obtained with our own DCB and other published data. The range of applicability of the CT test geometry is discussed critically, and with some reservations it is considered suitable for the evaluation of either G1c or K1c.