Translaminar fracture behavior of hybrid woven-ply PEEK thermoplastic laminates under isothermal and kerosene flame exposure
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Lanhui LIN (FRANCE), Benoit VIEILLE (FRANCE), Christophe BOUVET (FRANCE), Tanguy DAVIN (FRANCE)Abstract :
With regard to the stringent fire safety regulations for thermoplastic-based (TP) composites in aeronautics field [1], it is a critical issue to understand and quantify the fracture mechanisms of degraded laminates, whose behavior is highly heterogeneous and anisotropic. To date, most attention has been given to unidirectional (UD) thermosetting laminates [2,3]. Therefore, this study aims at investigating the influence of different critical thermal conditions (resulting in the decomposition of the polymer matrix) on both the thermally-induced damages and the fracture behavior of hybrid woven-ply carbon/glass fibers reinforced PolyEther Ether Ketone (CG/PEEK) laminates, as a function of heating temperature and fire exposure time.
The Compact Tension (CT) and Compact Compression (CC) specimens are exposed to isothermal conditions (from the melting temperature 350℃ to the decomposition temperature of matrix 550℃ by furnace, for 15 min) and anisothermal conditions (116 kW/m² and 1150℃ one-side kerosene flame by a burner bench, from 5 min to 15 min) respectively. The mechanical tests are then conducted to evaluate the residual mechanical properties of post-exposure laminates at room temperature. Fractographic analysis has been carried out by means of microscopic and tomographic observations using a numerical optical microscope Keyence VHX-5000 and RX Solutions EasyTOM-150 respectively to visualize, classify and quantify the thermally and mechanically damaged areas with 3D representations (Figure 1).
Using a Digital Image Correlation (DIC) system combined with a binarization algorithm [4], the crack tip is located via the discontinuity of the strain field resulting from the crack propagation within material during loading, as shown in Figure 2. Here, the ASTM-399 test standard [5] is applied to determine the value of the critical initiation energy release rate. The evolution of the energy release rate from the force-displacement curve during the crack propagation is monitored by the compliance method. From these tests, the influence of severe heat exposure on the fracture toughness of CG/PEEK laminates has been evaluated. For the isothermal cases, the behavior of laminates is characterized by temperature dependence. When the temperature is approaching to the onset of thermal decomposition, the mechanical properties are severely affected, following by the formation of porosities and delamination within laminates. When the CG/PEEK laminates are exposed to flame, the optical and tomographic observations reveal heterogeneous fire- and mechanically induced damages with the presence of in-plane and through-thickness temperature gradients, contrary to what is observed for the homogeneous conditions. Depending on the thermal decomposition of each ply (function of the exposure time), the bearing capabilities of the plies is gradually degraded.
The Compact Tension (CT) and Compact Compression (CC) specimens are exposed to isothermal conditions (from the melting temperature 350℃ to the decomposition temperature of matrix 550℃ by furnace, for 15 min) and anisothermal conditions (116 kW/m² and 1150℃ one-side kerosene flame by a burner bench, from 5 min to 15 min) respectively. The mechanical tests are then conducted to evaluate the residual mechanical properties of post-exposure laminates at room temperature. Fractographic analysis has been carried out by means of microscopic and tomographic observations using a numerical optical microscope Keyence VHX-5000 and RX Solutions EasyTOM-150 respectively to visualize, classify and quantify the thermally and mechanically damaged areas with 3D representations (Figure 1).
Using a Digital Image Correlation (DIC) system combined with a binarization algorithm [4], the crack tip is located via the discontinuity of the strain field resulting from the crack propagation within material during loading, as shown in Figure 2. Here, the ASTM-399 test standard [5] is applied to determine the value of the critical initiation energy release rate. The evolution of the energy release rate from the force-displacement curve during the crack propagation is monitored by the compliance method. From these tests, the influence of severe heat exposure on the fracture toughness of CG/PEEK laminates has been evaluated. For the isothermal cases, the behavior of laminates is characterized by temperature dependence. When the temperature is approaching to the onset of thermal decomposition, the mechanical properties are severely affected, following by the formation of porosities and delamination within laminates. When the CG/PEEK laminates are exposed to flame, the optical and tomographic observations reveal heterogeneous fire- and mechanically induced damages with the presence of in-plane and through-thickness temperature gradients, contrary to what is observed for the homogeneous conditions. Depending on the thermal decomposition of each ply (function of the exposure time), the bearing capabilities of the plies is gradually degraded.