Assessment of laser cutting parameters and heat-affected zone on microstructure and fatigue behaviour of carbon fibre-reinforced epoxy

In this study, the effects of laser cutting on the fatigue properties of carbon fibre-reinforced polymers are investigated. For this purpose, unidirectional carbon fibre-reinforced epoxy laminate is cut by laser. The material to be cut evaporates directly in the laser beam and the laser beam can produce thermally induced damage, which is referred to as heat-affected zones. Specimens are cut with two different parameters (varying cutting velocity and break time between passes) to widths up to 15 mm for investigation of the heat-affected zones effects on fatigue behaviour. Prior to fatigue tests microstructure is evaluated using light and scanning electron microscopy with regard to cutting geometry and heat-affected zones. Fatigue tests are performed using multiple amplitude tests with a stress ratio of 0.1, instrumented with a video extensometer system and thermocouples for strain and temperature measurements to determine the influence on mechanical properties and evaluate the sensitivity of the used testing method and measurement instrumentation for this use case. Lower cutting velocities and break time passes lead to a larger edge angle and thus in different specimen widths on front (laser inlet) and bottom (laser outlet) of the carbon fibre-reinforced epoxy laminate. Therefore, the resulting true geometry was considered using statistical approaches to eliminate possible cross-sectional errors regarding mechanical stress application. The results show that the specimen widths and process parameters impact the fatigue properties, highlighting the importance of knowledge about heat induction and the detection of inflicted laminate damage.