Influence of orientation of extrusion direction and strain rate on the mechanical behaviour of extruded thermoplastic sheets

Abstract

This paper investigates on the influence of rate of strain and orientation of extrusion direction on the mechanical behaviour of three commercial polymers, viz: High Density Polyethylene (HDPE), Acrylonitrile Butadiene Styrene (ABS), and isotactic PolyPropylene (i-PP). Uniaxial tension tests were carried out in specimens cut at three different orientations 00, 450 and 900 with ranges of strain rates varying between 0.01 s-1 and 0.3 s-1. It was found that for all three polymers, an increase in strain rate resulted in a rise of yield strength irrespective of their orientations. At lower strain rates, HDPE and PP undergo an initial yielding, work hardening and eventual failure, whereas ABS undergoes strain softening after initial yielding. As the strain rate increases, work hardening was not much evident, and resulted in early failure. All three polymers exhibited an evident necking at lower strain rate. At higher strain rates, HDPE and PP exhibited an evident neck formation, whereas it was not much evident for ABS. It was noted that the tensile behaviour of HDPE and PP changes from ductile to brittle due to an increase in strain rate.