The Integrity of Polymer Composites during and after Fire

Abstract

This paper reports on changes to the mechanical properties of woven glass laminates with polyester, vinyl ester and phenolic resins during fire exposure. Two sets of experiments were carried out. First, unstressed laminates were exposed to a constant one-sided heat flux (50 kW m 2) for various times, and the residual post-fire strength at room temperature was reported. In a second series of experiments, laminates were tested under load. The times corresponding to a given loss of properties were 2-3 times shorter than in the previous case. It was found in both cases that modes of loading involving compressive stress were more adversely affected by fire exposure than those involving tension. A simple ‘two-layer’ model is proposed, in which the laminate is assumed to comprise (i) an unaffected layer with virgin properties and (ii) a heat-affected layer with zero properties. For residual properties after fire, the ‘effective’ thickness of undamaged laminate was calculated using this model and compared with measured values. A thermal model was employed to predict the temperature and the residual resin profile through the laminate versus time. Comparing the model predictions with the measured values of effective laminate thickness enabled simple criteria to be developed for determining the position of the ‘boundary’ between heat-affected and undamaged material. For post-fire integrity of unloaded laminates, this boundary corresponds to a Residual Resin Content (RRC) of 80%, a criterion that applies to all the resin types tested. For polyester laminate under load in fire, the boundary in compressive loading (buckling failure) appears to correspond to the point where the resin reaches 170 C. In tensile loading, significant strength is retained, because of the residual strength of the glass reinforcement. The model was used to produce predictions for ‘generic’ composite laminates in fire.

Modelling Reaction-to-fire of Polymer-based Composite Laminate

“…Since then, these models have been adapted for modelling the heat and mass transfer through fibre-polymer composite material in fire. Several researchers , Henderson & Doherty (1987a), Henderson & Wiebelt (1987b), Florio et al (1989), Sullivan & Salamon (1992a), Sullivan & Salamon (1992b), Perring et al (1980), Mc Manus & Springer (1992a), Mc Manus & Springer (1992b, Dimitrienko (1995), Davies et al (1995a) Dimitrienko (1997), Milke & Vizzini (1991), Gibson et al (1995), Davies & Wang (n.d.), Looyed et al (1997), Gibson et al (2004), Lattimer & Ouelette (2006), Trelles & Lattimer (2007)] have developed different approaches but the most influential work in this area came from Henderson et al (1985). Research on the effects of fire on sandwich composite has used the same principle as single monolithic composite in terms of modelling [Davies et al (1995a), Davies et al (1995b), Looyed et al (2001), Krysl et al (2004), Galbano et al (n.d.), Marquis (2010a)].…”

“…Given the complicated character of the thermal response of a composite material, the mathematical description also uses further assumptions: (1) Pyrolysis kinetics is modeled by a single-step first-order reaction; (2) the composite material forming the skins consists of the volumetric fractions X f (glass fibres), X p (polymer), X m (moisture), and X g (gas and/or vapours); (3) the effective density of each condensed-phase component of the panel is constant whereas the corresponding volumetric fraction varies to take into account chemical and physical transformations occurring during the exposition to fire; (4) the total volume occupied by each skin does not change as a consequence of thermal decomposition and combustion of the polymeric resin; (5) the solid, liquid and gas/vapour phases are in a local thermal equilibrium; (6) the transport by diffusion of volatile species is small; (7) the transport by convection and diffusion of the liquid-phase moisture is negligible; (8) the gas/vapour mixture obeys to the ideal gas law. By applying these assumptions and the formalism of Whitaker (1977), the local energy balance on Figure 2 can be reduced to a single equation following the approaches of Kung (1972) and Kansa & Perlee (1977) [Perring et al (1980), Henderson et al (1983), Florio et al (1989), Gibson et al (2004) Mouritz & Gibson (2006), and Galbano et al (2009). Estimation of the net heat transfer into a composite material leads to a change in energy accumulation E CV within a control volume CV.…”

“…A complete review is given by Ott (1981), Henderson et al (1985), Gibson et al (2004) and Mouritz & Gibson (2006). The temperature dependence of thermal conductivity can also be expressed as a linear combination of the virgin material and char conductivities, weighed by the ratio of the solid material mass to the initial virgin mass or final char density ].…”

“…It is a function of the decomposition rate of polymer matrixṁ ′′ p (x, t) (kg.s −1 ). The heat release rate is dependent on material (chemical composition, fibre content and architecture) geometry, environment condition and external irradiance levels as shown by Gibson et al (2004). The relationship of these two quantities can be expressed as:…”

Two-Dimensional Modeling of Thermomechanical Responses of Rectangular GFRP Profiles Exposed to Fire

“…In 2006, the apparent specific capacity, developed by Lattimer and Ouellette [15], was input into a heat transfer model to predict the temperature profile through E-glass/vinyl ester composite laminates. Gibson et al [16,17] investigated the postfire mechanical properties of polymer composites by combing the thermal model with Mouritz's two-layer mechanical model [18]. In 2012, the thermal responses of FRP laminates subjected to three-point bending and one-side heat flux were experimental and numerical investigated by Gibson et al [19].…”