Polycarbonate and co-continuous polycarbonate/ABS blends: influence of notch radius

The influence of notch tip radius in the range of 1-0.002 mm was studied on polycarbonate (PC) and co-continuous PC/acrylonitrile-butadiene-styrene (ABS). Co-continuous PC/ABS blend was obtained by mixing PC and ABS containing 15% polybutadiene (PB) in a twin screw extruder. PC and PC/ABS specimens were injection moulded into test bars. A notch was milled-in, with notch tip radius of 1, 0.5, 0.25 and 0.1 mm. Very sharp notches with a radius of 0.015-0.002 mm were obtained with an Excimer LAZER. The specimens were tested by single edge notch tensile tests at 1 m/s (apparent strain rate 28.5 s⁻¹) and at different temperatures (−60 to 130 °C). Initiation and propagation phases of the fracture process were monitored and the brittle-ductile transition temperature (T_bd) determined. It appeared that the amount of deformation in the initiation phase of fracture was extremely sensitive to notch tip radius. Temperature measurements of the deformation zone showed that the size of the deformation zone decreased with decreasing notch radius. The T_bd of PC increased rapidly with decreasing notch radius, until the glass transition temperature was approached. Remarkably, for PC the notch sensitivity was strongest around the standard notch tip radius of 0.25 mm. This means that a small deviation of this standard notch leads to large deviations in the results. The PC/ABS blend was much less sensitive to notch tip radius and the T_bd was almost constant. Thus the sensitivity of PC to sharp defects can be neutralised by adding ABS.