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The influence of dynamic testing on the J - R resistance curve behavior of medium density polyethylene

The dynamic fracture behaviour of medium density polyethylene has been investigated using an instrumented drop weight machine. Quasi-static and dynamic J R resistance curves were obtained on both the parent and weld material. Three point bend specimens were used with a width of 30mm and a thickness of 15mm. All specimens were sidegrooved to a depth of 10% on each side. In the case of the welded specimens the notches were located in the weld centre line. All tests were carried out in accordance with the ESIS protocol on R curve testing of plastics. Dynamic tests were carried out over a range of impact velocities between 0.5 and 1m/sec. Load time data were obtained using a piezoelectric force transducer and displacement was derived from the double integration of the acceleration. Energy to maximum displacement was used to calculate J. Little difference was observed between the parent and the weld materials under both quasi-static and dynamic test conditions. Impact loading significantly reduced the level of the J R curves for both the parent and weld materials particularly at higher values of ∆a. J0.2 values were reduced by up to 50%. The results were rationalised in terms of increased constraint resulting from the elevation of tensile properties under dynamic test conditions.