Contactless temperature monitoring and boundary conditions determination of the back surface of a woven-ply laminate under fire exposure
Topic(s) : Experimental techniques
Co-authors :
Tanguy DAVIN (FRANCE), Mouldi BEN AZZOUNA (FRANCE), Julie VACANDARE (FRANCE), Fabrice BARBE (FRANCE), Benoit VIEILLE (FRANCE)Abstract :
Composites materials are widely spread for the lightening of structures for transport parts because of high specific properties. For aeronautics applications, an important issue is the fire resistance [1]. Thermoplastic composites have shown a very high degree of mechanical performance under severe environmental conditions (high temperature or flame exposure) [2-3]. But better understanding and control of their mechanical behavior evolution under a localized severe thermal aggression requires an accurate knowledge of the thermal fields, both through the thickness and within the laminate planes.
Critical service conditions as mechanical loading under flame exposure induce difficulties to stick probes such as thermocouples and they are intrusive. Two contactless techniques are of promising to determine the 2D surface temperature. With thermal coating including Thermographic phosphors [4], the temperature signal can be extracted from the radiation disturbance on the exposed surface but the method is complex and remains slightly intrusive. IR thermography, though the exposed surface cannot be visualized due to the lack of emission signal compared to flame’s, can be implemented on the back surface.
The main objective of this study is to correctly represent the back-surface temperature and thermal conditions. The results have 2 interests: (1) assess the mean back temperature and (2) evaluate the heat transfer conditions.
The determination of the temperature (1) from IR emission, in severe or critical service conditions, raises two issues: the intrinsic heterogeneity of the emission of the composite sample, and its emissivity with respect to the temperature. The surface state might change due to its thermal decomposition during the test, in terms of aspect (transition states of the matrix) and geometry (swelling) [5]. The study will primarily focus on the results of fire test on a quasi-isotropic C/PPS laminates.
The assessment of the heat transfer boundary conditions (2) will be based on a heat transfer model from which parameters, namely the emissivity and convection coefficients, are identified analogously as was previously proposed [6]. Experimentally, the IR technique on a representative isotropic material will be considered to characterize the limit conditions of a sample exposed to the kerosene flame. This identification method will firstly consist in monitoring the sample temperature homogeneity during heating to adapt the fluxes (especially conductive) to be represented in the heat transfer model. The homogeneous heat flux of the kerosene-flame (previously quantified [7]) will be assumed to identify the back-surface convection.
This identification approach will be extended for various air jet cooling conditions at the back-surface, representative of a composite laminates exposed to a flame. The heat transfer coefficients will be compared to literature values [8] and the previous kerosene-flame exposed surface assumptions will be verified.
Critical service conditions as mechanical loading under flame exposure induce difficulties to stick probes such as thermocouples and they are intrusive. Two contactless techniques are of promising to determine the 2D surface temperature. With thermal coating including Thermographic phosphors [4], the temperature signal can be extracted from the radiation disturbance on the exposed surface but the method is complex and remains slightly intrusive. IR thermography, though the exposed surface cannot be visualized due to the lack of emission signal compared to flame’s, can be implemented on the back surface.
The main objective of this study is to correctly represent the back-surface temperature and thermal conditions. The results have 2 interests: (1) assess the mean back temperature and (2) evaluate the heat transfer conditions.
The determination of the temperature (1) from IR emission, in severe or critical service conditions, raises two issues: the intrinsic heterogeneity of the emission of the composite sample, and its emissivity with respect to the temperature. The surface state might change due to its thermal decomposition during the test, in terms of aspect (transition states of the matrix) and geometry (swelling) [5]. The study will primarily focus on the results of fire test on a quasi-isotropic C/PPS laminates.
The assessment of the heat transfer boundary conditions (2) will be based on a heat transfer model from which parameters, namely the emissivity and convection coefficients, are identified analogously as was previously proposed [6]. Experimentally, the IR technique on a representative isotropic material will be considered to characterize the limit conditions of a sample exposed to the kerosene flame. This identification method will firstly consist in monitoring the sample temperature homogeneity during heating to adapt the fluxes (especially conductive) to be represented in the heat transfer model. The homogeneous heat flux of the kerosene-flame (previously quantified [7]) will be assumed to identify the back-surface convection.
This identification approach will be extended for various air jet cooling conditions at the back-surface, representative of a composite laminates exposed to a flame. The heat transfer coefficients will be compared to literature values [8] and the previous kerosene-flame exposed surface assumptions will be verified.