| Tensile testing is important in the classification of plastics, but failure properties (tensile strength, elongation at break) are sensitive to flaws, aging, humidity, etc., leading to variability. Likewise, while plastics engineers frequently make attempts to alter the deformation mechanisms of plastics for practical purposes, much less work has been done on quantifying such changes. In this study, polypropylene homopolymer and copolymer tensile bars were tested at rates of 50, 100, 200, and 400 mm/min while monitoring their heat output using an infrared video camera. Stress-strain-temperature curves and plots correlating mechanical work with heat output were then generated. Significant differences in deformation mechanism were observed via this approach, reflecting the more subtle variations measured in the course of conventional tensile testing as a function of material and draw rate but not otherwise predicted by static analyses of microstructure (scanning electron microscopy, differential scanning calorimetry). The results demonstrate that changes in deformation behavior may be quantified via this approach, providing a new means of relating loading conditions, microstructure and failure properties. |
