Cutting resistance of polyethylene

A thin polyethylene strip was cut along the centerline, the legs being pulled apart to minimize friction. Fracture energy Gc was obtained from the total work expended in cutting and tearing, yielding values of 4 kJ/m2 for HDPE, 2 kJ/m2 for HDPE crosslinked with 2.5% dicumyl peroxide, and 1 kJ/m2 for LDPE. For an oriented sample of HDPE the value was 1.5 kJ/m2. These values are considerably smaller than for simple tearing, about 10 kJ/m2, suggesting that plastic yielding has been reduced. However, they are much higher than expected in the absence of yielding, about 50 J/m2. Values of Gc were found to be proportional to yield stress and decreased in a similar way with temperature. On comparing results for Gc with work-to-break in tension, the diameter of the plastic zone at the cut tip was inferred to be about 15–20 μm, or one to three spherulite diameters, many times larger than the blade tip radius.