Experiment of Dynamic Crack Propagation in Brittle PMMA Strip
脆性PMMA带板中的动态裂纹传播实验

In order to study the dynamic crack propagation in brittle materials, an experimental technique was developed to measure the velocity of crack propagation in a preloaded brittle strip. A rectangular PMMA specimen without any precrack is clamped on upper and bottom sides by two heavy steel fixtures attached to a MTS test machine. When the tensile load attains a prescribed level, a sharp-pointed crack is initiated artificially at the middle of one side of specimen. The crack propagates fast across the specimen due to the tensile preload. Its propagation velocity is measured by equally spaced conductive lines that are printed on the specimen surface before experiment. Preloads with different amplitudes are applied to specimens with different shape in experiment, thus steady propagation speed of crack is determined. Experimental results show that for each preloaded strip, cracks arrive at a steady velocity v0 after a short acceleration stage. The steady velocity of crack propagation is found to be an increasing function of energy Gc stored in the preloaded strip. This represents velocity-toughening effect of PMMA material. Obvious crack speed oscillation occurs when the average steady velocity exceeds certain critical level.