Impact breakage of poly-methylmethacrylate (PMMA) extrudates .1. Chipping mechanism

Poly-methylmethacrylate (PMMA) extrudates in the size range 2.36-2.80 mm were subjected to repeated impacts at velocities in the range 10-60 m s(-1). The impact event was observed by means of high-speed photography. Two damage mechanisms were identified depending primarily on impact velocity: the chipping mechanism up to about 30 m s(-1) and the fragmentation mechanism above this velocity, for the particle size rested. Only the description of the chipping mechanism is presented here and it is demonstrated that the fractional loss per impact follows a power law relationship with impact velocity, whose power index is 2.18 for the first five impacts and 2.41 for 20 consecutive impacts. It is also shown that satisfactory predictions of the impact breakage of PMMA at low impact velocities can be obtained, if the experimental results for the chipping mode are interpreted with reference to the mechanistic model of Ghadiri and Zhang.