Dependence of Crack Velocity on Stress Intensity Factor in PMMA Using Single-Edge-Notched Clamped Beams

Abstract

The Single-Edge-Notched Clamped Beam (SENCB) geometry, which has been used for studying fracture in graded coatings, is adapted to the study of fracture in macroscopic specimens of PMMA , a brittle, transparent polymer. Test materials were fabricated by compression molding, pre-cracked using a safety razor, and loaded at constant displacement rate at room temperature, while crack propagation was monitored with a video camera. Crack growth with time was tracked and velocity computed. The load measured from the experiment was used in FEM in conjunction with the crack length to determine the applied stress intensity factor at the different instance of crack propagation and was correlated with crack velocity. Crack grew from the interior, and a jump in crack velocity was observed as the crack spanned the width of the sample. Pre-cracking is done by physically restraining the legs and unloading as the crack propagates across the width. The average velocity of crack front was correlated with stress intensity factor (K) and was found to broadly agree with what is reported for PMMA at velocities more than 0.1 mm s⁻¹. At low velocity, the curve appears to become insensitive to K at a plateau of ~0.7–0.9 MPa m^1/2.