Today, fibre reinforced polymer (FRP) materials are extensively used for building lightweight hull structures of vessels with length up to about 50 metres, whereas in longer vessels their use is limited to secondary structures and components. In the European FIBRESHIP research project, innovative FRP materials are evaluated, new design and production procedures and guidelines are elaborated, and new validated software analysis tools are developed. As a result of the project, a comprehensive set of methods will be compiled, enabling the building of the complete hull and superstructure of over 50-metre-long ships in FRP materials. The results enhance significantly the use of FRP materials in shipbuilding and strengthen the competitiveness of the European shipbuilding industry on the world market.
In Task 2.4 of the FIBRESHIP project, an extensive experimental campaign was performed in two phases to characterize the fire performance of FRP materials and solutions.
For the first phase, seven commercially available resins or resin systems were selected for examination of fire performance. Laminates with glass fibre reinforcement and cured resins without reinforcement were produced for cone calorimeter tests and thermogravimetric analyses, respectively. From these seven candidates, two materials were down-selected on the basis of the mechanical performance, manufacturability and impact (including cost, claimed fire retardancy, worker health impact and recyclability).
The two material solutions chosen to continue to the second phase were LEO vinylester resin system and SR1125 epoxy resin system. The fire tests of the first phase showed that an intumescent coating on the surface of these laminates is essential for providing adequate fire performance.
In the second phase, a more comprehensive evaluation of thermal and fire properties was performed by carrying out more cone calorimeter tests, as well as dynamic mechanical thermal analysis, microscale combustion calorimetry, differential scanning calorimetry and transient plane source tests. Simultaneously, data for pyrolysis modelling, thermomechanical modelling and fire simulation was produced.
In cone calorimeter test at the irradiance of 50 kW/m2, the times to ignition of coated LEO and SR1125 were 75 and 52 seconds on the average, respectively. The maximum heat release was 261 kW/m2 for SR1125, but only 69 kW/m2 for LEO indicating good reaction-to-fire performance. The total heat release and the total smoke production were ca. 40 MJ/m2 and 9 m2, respectively, for both systems.
Cone calorimeter tests of coated laminate specimens were run also at the irradiance levels of 25 and 35 kW/m2 and for specimens representing different production batches. The results were not consistent in all cases. In addition, DSC tests revealed changes of the glass transition temperature when the specimens were re-heated, referring to incomplete curing in the manufacturing process. These observations highlight the importance of repeatable and well- controlled manufacturing process. The whole process must be carefully instructed, monitored and reported. The laminates and coatings must be of uniform quality to ensure the fire performance claimed on the basis of fire tests performed. Precise specifications and quality control play a key role in securing the fire safety of materials and products.
Thermogravimetric analyses and micro-scale combustion calorimetry showed that the mass loss of cured resins typically starts slightly above 300 °C both in inert (N2) and oxidative (air) atmosphere. The reactions in these atmospheres differ, the oxidative atmosphere revealing reactions such as char oxidation. At about 300 °C, however, a structure made of these FRP materials starts to produce combustible gases and contribute to fire.
Dynamic mechanical thermal analysis showed that the glass transition temperature is ca. 111 °C for LEO, and ca. 95 °C for SR1125. In general, the glass transition temperatures of FRP materials are typically about 100 °C. At this temperature, the material softens and loses its loadbearing capacity.
Structures made of FRP materials have a tendency to heat up locally, due to their relatively low thermal conductivity. In the case of a local fire, combustible gas production and heat release are the main concerns in terms of fire safety. If the fire threatens a large structure, like in the case of a compartment fire, the main problem is the softening of the material and the loss of the loadbearing capacity.