Comparison of the Tensile Behavior of Carbon Fibers Reinforced Laminates Exposed to Fire Conditions
摘要
This study investigates the influence of a kerosene flame aggression (characterized by a 116 kW/m2 heat flux and an 1150 °C flame temperature) and a tensile loading (monotonic or creep) on the deformation and damage mechanisms of quasi-isotropic carbon fibers reinforced laminates consisting of different thermosetting matrix systems (epoxy and bismaldeide). The influence of the carbon fibers reinforcement (unidirectional and woven fibers) along matrix nature were examined on both the fire and mechanical responses of the laminates. A specific fire bench was used to conduct such tests while monitoring the changes in the axial stress and strain as well as temperature along flame exposure time. First, from monotonic testing conducted under fire conditions, the axial strength is about 50 and 30% lower than woven ply C/BMI laminates, in unidirectional (UD) and woven ply C/Epoxy laminates, respectively. These results agree with the tendency observed in virgin specimens. After a 300 s exposure, the axial strength decreases by 40 to 60% of their initial values for studied materials with respect to their virgin state. After a 900 s exposure, the drop has almost stabilized at about 30 to 40% of their initial values. Woven ply laminates being characterized by matrix-rich areas at the crimp, the thermal decomposition primarily occurs in these areas. As a result, the thermally-induced damages (porosities formation and extensive delamination) in these areas contribute the thermal transfers to be modified within the laminates Second, creep testing under fire conditions were performed to comply with the fire certification standards. The underlying idea of these tests is to identify the axial creep stress to be applied to ensure that the loading bearing capabilities of the composite part are preserved for 900 s. With respect to C/BMI laminates, under the same fire conditions, the maximum applied stress is 30 and 20% lower in UD and woven ply C/Epoxy laminates, respectively. Based on the changes in the time-to-failure as a function of the creep tensile force, it is possible to get analytical expressions, which are the first step towards the definition of simple design rules useful to engineers willing to meet safety requirements.