A comparison of the failure modes of PMMA and polypropylene test pieces cut using different manufacturing methods

The purpose of this study is to compare the failure modes and effects of stress-concentrations created in specimens produced by conventional machining and also laser cut equivalent specimens by means of simple tensile testing. Two polymeric materials have been studied: polypropylene, a widely-used engineering polymer and polymethyl methacrylate (PMMA) a relatively strong but brittle commercial polymer. The failed specimen pieces and their load-extension graphs are analyzed for trends in behaviour and in particular, the variance in results are considered. Finite Element analysis is used in addition to validate the significance of the results. The paper illustrates the differences in strength of the specimens for both machining methods, the stress-concentration factors (based on the failure of specimens); The results indicate significant differences in terms of nominal strengths for stress concentration areas between two machining methods.