Mechanical testing of polystyrene/polystyrene laser welds

Properties of polystyrene/polystyrene (PS/PS) diode laser (808 nm) welded lap-joints were evaluated. First, the reptation time of the selected PS was determined using plate/plate oscillatory rheometry. The reptation time was critically dependent on temperature, but as long the temperature was above 200 degrees C, the reptation time was less than 8 ms. The reptation time is, therefore, smaller than the process time, permitting development of full weld strength. Two methods were selected for mechanical testing; a lap-joint shear test to evaluate the weld strength [kJ/m(2)] and a double cantilever beam (DCB) method to evaluate the critical strain release energy (G(Ic)) [J/m(2)]. The shear test suggested constant weld strength of 21 kJ/m(2) independent of laser heat input, while the DCB method resulted in varying G(Ic) with an optimum at a laser power of 50 W and a laser speed of 153.8 mm/s. This difference was ascribed two different fracture mechanisms; chain rupture and chain pull-out. (C) 2013 Elsevier Ltd. All rights reserved.