Predictive Modelling of Combustion-Induced Mechanical Property Degradation of Flame-Retardant Structural Composites

Lead Research Organisation: University of Bolton
Department Name: Centre for Materials Res and Innovation

Abstract

This proposal involves mathematical modelling of the burning and degradation of mechanical properties of flame retadant glass fibre reinforced plastic laminates. At Bolton, novel flame - retardant laminates have been developed and patented during an earlier EPSRC project. These laminates contain novel flame retardant chemicals and inherently flame retardant cellulosic fibres as additives in the resin matrix or as additional fabric layer. Some laminates also contain polymer layered silicate nanocomposites with or without conventional flame retardants. The laminates show improved flame reatrdant and residual mechanical properties after fire/heat exposure compared to unmodified laminates. This proposal is a joint attempt by 'Fire and Heat Resistant Materials' group at Bolton Institute and 'Fire Engineering Research Group' at University of Manchester to numerically predict their burning and mechanical behaviour under a fire condition. The Bolton team will focus on the burning aspect and the Manchester team the burning induced degradation of mechanical properties. Results from the Bolton team will provide input of material damage and temperature information to the Manchester team so that the outcome of this project will be an integrated predictive model for combining both burning and burning-induced mechanical behaviour. A limited amount of mechanical tests at elevated temperatures will be carried out to provide data for validation of the numerical models developed.

Publications

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McCarthy E.D. (2012) Application of modeling and simulation in predicting fire behavior of fiber-reinforced composites in Modeling and Simulation in Fibrous Materials: Techniques and Applications

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Kandare E (2007) Global kinetics of thermal degradation of flame-retarded epoxy resin formulations in Polymer Degradation and Stability

 
Description A crucial feature of any fibre-reinforced polymeric composite is the thermal and burning behaviour of its matrix resin, which affects the mechanical performance of the composite at elevated temperatures and may ultimately lead to complete loss of structural integrity. Hence, it is important to understand and predict the thermal, combustion and mechanical behaviour of composite materials at elevated temperatures. At Bolton, novel flame - retardant laminates were developed and patented during an earlier EPSRC project, which showed improved flame retardant and residual mechanical properties after fire/heat exposure compared to unmodified laminates. This collaborative research project between the Universities of Bolton and Manchester, aimed to model these composites' fire and mechanical behaviour, where the Bolton team's focus has been on the burning aspect and the Manchester team on the burning induced degradation of mechanical properties.
To describe how a material decomposes under the action of heat, a thermo-kinetic model was developed, which allowed the modelling of decomposition (mass loss) profiles of different composites and their components at various heating rates. From these mass loss profiles, Arrhenius kinetic parameters, such as activation energies and frequency factors for different steps of decomposition could be obtained, which were used as input data for the heat transfer model. A heat transfer model based on the theory used originally by Henderson et al, was developed. The model was used to predict the temperature profile at any given time and through the laminate thickness. The model could also reasonably predict the mass loss data and time-to-ignition for composite laminates. This data was used by the Manchester team in their micromechanical model to predict the mechanical behaviour of laminates at elevated temperatures. For micromechanical modelling, they developed three micromechanical unit cells, one each for: the resin, the yarn consisting of the resin and unidirectional fibres, and for the woven fabric -reinforced structural composite. The unit cell of the resin required input data of resin mechanical properties at elevated temperatures, which was provided by the Bolton team by carrying out mechanical testing on the resin at elevated temperatures. The micromechanical model using unit cells was incorporated into the commercial FE code ABAQUS and used to simulate a series of tests on flame-retardant fibre-reinforced composite laminates, good agreement between theoretical and experimental results was observed.

Major outcomes of the project include:
1. A global kinetic model capable of predicting mass loss of a polymer without/with additives linked to polymer degradation mechanistic steps of different components.
2. A heat transfer model capable of predicting temperature profile through the thickness of the laminate plus qualitative prediction of ignition time, mass loss, heat release rate and volatile mass flux.
3. A micromechanical finite element model capable of simulating mechanical performance of laminates at elevated temperatures.
4. A methodology to obtain temperature - dependent properties (thermal conductivities, densities and the specific heat capacities) and database of other physical properties for different components of the composites
5. Residual mechanical performance data for epoxy resin and fibre-reinforced composites exposed to both convective and radiative heat environments for a range of temperatures/heat fluxes and times.
Exploitation Route With the methodology developed in this project, a Composites Material Scientist with the right information of the material properties can confidently predict the temperature profiles within a laminate exposed to an external heat flux, from which mechanical behaviour of the laminate under those conditions can be predicted. This information can be used by a Composites Structural Engineer to produce a safe structure with reduced weight and cost.
Sectors Aerospace, Defence and Marine,Education,Transport

 
Description 1. Fire safety of composites is an important factor determining their usage in structural applications. For Material Scientists and Structural Engineers it is important to predict how a particular structure will perform mechanically under extreme environmental conditions, including fire. The project has contributed to that by providing: a) a global kinetic model capable of predicting mass loss of a polymer linked to polymer degradation mechanistic steps of different components , b) a heat transfer model capable of predicting temperature profile through the thickness of the laminate plus qualitative prediction of ignition time, mass loss, heat release rate and volatile mass flux and c) a micromechanical finite element model capable of simulating mechanical performance of laminates at elevated temperatures. 2. The RAs on the project received on-the-job training for many different complimentary techniques and also by attending relevant short courses and conferences. The RAs, Dr Dr. E. Kandare and Dr E McCarthy got positions as Research Fellows at the University of Melbourne, Australia and National Institute of Standards and Technology, USA. 3. Dr E McCarthy also developed part of a post graduate module on damage and repair of composites for the Hefce/NWUA HLSP in advanced materials and engineering, which helped him developing his skills in module writing for his academic career. In addition results from this project have been used in MSc lectures, disseminating knowledge of fire protection of composites to the wider community. 4. During the tenure of the project, 2 visiting researchers were trained in writing codes and developing models. Short and confidential reports for these two small projects are available. 5. All the findings of this research have been published in peer-reviewed journals and presented at national and international conferences, thus informing the scientific community at large about fire safety of materials.
First Year Of Impact 2009
Sector Aerospace, Defence and Marine,Education,Transport
Impact Types Societal