Thermal defect characterization and strain distribution of CFRP laminate with open hole following fiber laser cutting process

Abstract

High power fiber laser cutting of CFRP composites has been proven to be feasible with high efficiency, while there are still several challenges due to different carbon fiber-epoxy resin properties and sensitivity to thermal heat. This paper studied the influence of processing parameters on machined hole quality and quasi-static tensile behavior of unidirectional CFRP laminate with open hole (6.0 mm in diameter) following fiber laser cutting process. Hole surface morphology was analyzed using optical microscope and scanning electron microscopy. The area of heat affected zone and defect factor were quantified to understand the effect of machining parameters on thermal defect. It was found that both cutting speed and laser power were statistically significant with respect to HAZ recorded at hole entry, while cutting speed was the only significant factor for HAZ observed at hole exit. The full-field strain distribution during tensile loading was characterized using 3D digital image correlation (DIC) technique. Surprisingly, laser processing parameters showed limited effect on surface strain distribution (εxx, εxy, εyy) during tensile loading. Some highly localized strain zones were observed on the tangent of transverse edge of the hole, corresponding to final failure mode of splitting due to inevitably slight shear force during tensile loading and weak interface strength between carbon fiber and epoxy resin. Numerical simulation results of strain distribution were in good agreement with the DIC analysis.