Abstract
The erosion mechanism of polymethyl methacrylate (PMMA) which is predominant at high angle of attack (>60deg.) has been studied by use of falling glass beads with an impact velocity of 12 to 36m/sec.
In this mechanism, a characteristic ring-like damage pattern and transverse cracks were observed at or under the surface. Corresponding to each ring pattern, the cross section of damaged surface showed a step-like structure. Therefore, the damaged partis supposed to consist of many removed layers which have an equal step height of each ring. Based on these observations, new damage model was proposed. That is, the longitudinal cracks initiate from the surface, and then the transverse cracks initiate and propagate from the tip of longitudinal cracks. As the result of the intersection of these cracks, the material surrounded with cracks is removed. This makes the first ring. The damage process goes on similarly to deep direction.
From the analysis of ring patterns and damage curves, the erosion rate was found to be proportional to the height of each layer and inversely proportional to the amount of impact particle during the incubation period. Accordingly, the design equation to estimate the erosion rate was proposed. The estimated results based on this new model agreed well with the experimental results.
