Experimental and numerical study on open-hole tension/compression properties of carbon-fiber-reinforced thermoplastic laminates

The stress-strain responses and damage initiation/propagation mechanisms of T700G/LM-PAEK, an open-hole carbon-fiber-reinforced thermoplastic were investigated experimentally and numerically. To obtain the mechanical properties necessary for numerical simulations, uniaxial tensile/compressive, double cantilever beam, and end notched flexure tests were conducted. T700G/LM-PAEK was found to have comparable or higher Young's modulus, strength, and interlaminar fracture toughness relative to thermoset CFRPs with carbon fiber of a similar grade. These superior mechanical properties are mainly attributable to the higher toughness and ductility of the thermoplastic resin. The interfacial fracture toughnesses were evaluated by finite element analysis with the cohesive zone model to determine the interlaminar fracture toughnesses for crack initiation and propagation. Based on the above experimental and numerical results, the stress strain response and damage evolution of open-hole specimens were analyzed by a quasi-3D extended finite element method (XFEM) and compared with the experimental results. The computational model with the elastoplastic constitutive law provided an accurate prediction of the stress-strain response in both open-hole tension and compression (OHT and OHC, respectively), suggesting that the elastoplastic constitutive law should be considered in XFEM to guarantee the accuracy of strength prediction for both OHT and OHC. The OHT model showed that the Weibull criterion was satisfied without any delamination at the failure strain, corresponding to the brittle failure mode due to fiber breakage. For the OHC simulation, the damage initiation of 0 degrees-ply kinking was observed at 88% of the peak stress. These predicted damage mechanisms agreed reasonably well with the experimental observations.