Mechanical behavior of carbon fibers reinforced PEEK laminates under fire conditions
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Julie VACANDARE (FRANCE), Benoit VIEILLE (FRANCE), Fabrice BARBE (FRANCE)Abstract :
The current environmental crisis (CO2 emissions and energy needs) reveals that one of the main issues of aeronautics is the light-weighting design [1]. Thus, the integration of polymer matrix composites in structural parts is increasing. But their behavior significantly depends on their working conditions because of their polymer matrix. Especially, fire issue is a primary concern for aircraft manufacturers [2]. Understanding the thermomechanical behavior of composite in critical conditions (fire) is therefore essential. To study the thermo-mechanical properties of composites materials, a kerosene burner is used, which is meant to mimic the conditions of certification fire tests of aeronautical structural parts: flame temperature of 1100°C and heat flux of 116 kW/m². Preliminary works have investigated the residual mechanical properties in tension and compression of two composites materials (C/PEEK and CG/PEEK) after a kerosene flame exposure [3], [4].
In this study, the thermo-mechanical behavior of PEEK reinforced with a carbon fiber fabric is investigated. The first step consists in the characterization of its thermal properties. Some isothermal and anisothermal thermo-gravimetric analyses have been realized under different atmospheres (N2, O2 and air). The second step consists in the characterization of the decomposition of the material when it is exposed to the kerosene flame. From the first minutes of exposure, matrix decomposes and porosities appear in the material as can be seen on Figure 1. The kinetics of porosity formation plays a major role on the evolution of the composite’s thermomechanical properties: beneficial for thermally insulating the material away from the flame, but detrimental to mechanical properties. Different methods, using the geometry of the samples or X-Ray tomography (Figure 2) for example, can be used to characterize this kinetics.
In a second time, the residual tensile and flexural properties after fire exposure are studied. Two types of thermal aggression are then concerned: a kerosene flame and a hydrogen flame. This latter corresponds to a flame at 2000°C and a heat flux of 600 kW/m². The difference between the two lies not only in the input energy, but also in the nature of the thermal transfers, one involving char formation and the other involving H2O. The kinetics of decomposition and the residual properties in tension and flexion have then been characterized according to the nature of the flame and the time of exposure.
In this study, the thermo-mechanical behavior of PEEK reinforced with a carbon fiber fabric is investigated. The first step consists in the characterization of its thermal properties. Some isothermal and anisothermal thermo-gravimetric analyses have been realized under different atmospheres (N2, O2 and air). The second step consists in the characterization of the decomposition of the material when it is exposed to the kerosene flame. From the first minutes of exposure, matrix decomposes and porosities appear in the material as can be seen on Figure 1. The kinetics of porosity formation plays a major role on the evolution of the composite’s thermomechanical properties: beneficial for thermally insulating the material away from the flame, but detrimental to mechanical properties. Different methods, using the geometry of the samples or X-Ray tomography (Figure 2) for example, can be used to characterize this kinetics.
In a second time, the residual tensile and flexural properties after fire exposure are studied. Two types of thermal aggression are then concerned: a kerosene flame and a hydrogen flame. This latter corresponds to a flame at 2000°C and a heat flux of 600 kW/m². The difference between the two lies not only in the input energy, but also in the nature of the thermal transfers, one involving char formation and the other involving H2O. The kinetics of decomposition and the residual properties in tension and flexion have then been characterized according to the nature of the flame and the time of exposure.