In situ tensile behavior of hybrid carbon and glass fibers reinforced PEEK laminates: Isothermal or fire testing conditions

This work aims at investigating the thermo-mechanical coupling under critical temperature conditions in hybrid carbon/glass fibers reinforced Poly Ether Ether Ketone (PEEK) laminates. Two testing conditions have been considered: (i) isothermal and (ii) fire condition. A tensile loading was applied in homogeneous and isothermal temperature distribution (Room temperature – 350 and 500 °C) by means of a high-temperature furnace to quantify the influence of temperature on the mechanical response and properties. Regarding the fire conditions, a one-of-a-kind bench-scale fire test combining an in situ tensile mechanical loading and a kerosene burner (a flame temperature of 1100 °C ± 80 °C and a heat flux of 116 kW/m2 ± 10 kW/m2) has been designed and instrumented to induce anisothermal temperature conditions. This prototype allows the evolution of various physical quantities to be tracked as a function of the flame exposure time (5-10-15 min). These include temperature, loss of mass, deformation, stress, which are fundamental for understanding the mechanisms brought into play. The decrease of the tensile properties under isothermal conditions is −38% ± 0.6% (axial stiffness) and −54% ± 0.3% (axial strength) with respect to the values obtained at room temperature. The tensile response under fire is similar to the one obtained in isothermal conditions at 500 °C. The creep behavior of CG/PEEK laminates was also investigated with different boundary conditions (with or without a protective shield reducing the delirious effect of flame in terms of damages within the laminates). Compared to virgin specimens, the residual tensile mechanical properties significantly decrease as a function of the flame exposure time (5-10-15 min): 30% ± 1.1% and −55% ± 1.6% in axial stiffness and strength, respectively.