Static and fatigue strength of laser-textured adhesive-bonded polyamide 66 (PA 66) joints

Abstract

Nanosecond pulsed laser texturing has been performed as surface preparation for adhesive-bonded polyamide 66 (PA 66) joints. A Design-of-Experiments approach was firstly applied for optimization of laser parameters in terms of static joint strength, after which the fatigue strength of the best performing joints was determined. Quasi static and fatigue lap shear tests were performed on joints bonded with Teroson PU 9225. Laser texturing of PA 66 was found to be far less sensitive to heat accumulation in the hatch direction than in the laser scanning direction. Static average shear strength was generally found to increase with laser energy dose up to approximately 8–20 J/cm 2 , while no correlation was observed between the microscale surface roughness and static strength for low values of the former (S a < 2 μm). A shear strength of 11.60 MPa was achieved with a parallel-line scanning strategy and an average laser power of 3 W, hatch spacing of 50 μm and scanning velocity of 700 mm/s, representing a three-fold increase over standard primed joints. Laser-textured joints prepared with the same parameters exceeded the fatigue performance of atmospheric pressure plasma, mechanical abrasion and primer pre-treatments at both high and low maximum average cyclic shear stress, implying that laser texturing is an appropriate solution for improving bonding at high cyclic shear stress and prolonging the crack propagation phase at low cyclic shear stress.