Aspect ratio compression effects on metals and polymers

Abstract

Abstract. Previous research has studied the effects of altering the shape and size of samples over a range of compression rates. Several discrepancies exist in the published data, probably due to the wide range of techniques used. The research here was carried out to bridge this gap. Cylindrical polycarbonate and aluminium (6082) samples, with varying aspect ratios, were subject to a range of strain rates between 10 −4 -10 2 s −1 , with further data gained for polycarbonate at higher strain rates between 10 2 -10 3 s −1 , and the stress-strain relationships obtained, compared and discussed. IntroductionThe range of strain rates examined here were achieved using quasi-static, drop-weight tower, and Split Hopkinson Pressure bar (SHPB) techniques. All the experiments were carried out at ambient temperature and humidity.To ensure the validity of results for a given experimental technique, sample dimensions and ratios must complement the load and loading rate. For example, in Split Hopkinson Pressure Bar experiments, it is important that stress equilibrium is reached inside the specimen: the sample should be sufficiently thin to obtain >3 internal reflections of the stress wave. The sample diameter should be both less than the diameter of the bars, and sufficiently small to ensure that any stresses due to radial inertia are negligible [1].Here we present results over a wide range of strain rates. The effects of sample geometry on the mechanical behaviour of aluminium 6082 and polycarbonate are investigated.Polycarbonate is an amorphous thermoplastic polymer with high transparency and toughness, and has a large variety of applications. It has an average density of 1.20 g cm 3 and a glass transition temperature of +148 • C. The aluminium 6082-T6 (BS EN755) has a density of 2.70 g cm 3 and a melting point of +650 • C. The chemical composition in this aluminium alloy is 0.97% silicon, 0.71% magnesium and 0.51% manganese, with trace amounts of iron, titanium, copper, zinc and chromium. The alloy has been solution heat treated and artificially aged (precipitation hardened).Cylindrical samples have been machined to a constant diameter of 4 mm and thicknesses of 1 -12 mm. The samples will henceforth be designated by their aspect ratios (ratio of length to diameter), and will range between 0.25 -3.

Temperature and strain rate effects on the piezoelectric charge production of PZT 95/5

“…A 250 kN universal testing machine Instron (model 5584) was used for quasi-static loading [15]. A compression rate of 0.001 mm s −1 was adopted.…”