Periodic Reporting for period 1 - HEFESTO (Helicopter Engine Deck - Multifunctional layered insulation for CFRP fire andthermal protection)
Período documentado: 2018-10-01 hasta 2020-06-30
The main objective of the HEFESTO project is to develop and demonstrate the effectiveness of a novel coating configurations which thermally isolates and fireproofs carbon fibre reinforced plastics (CFRP) to resist the operating conditions and fire hazards in aircrafts. The multilayer concept. The project also covers the redesign the various primary structures, made in metal, towards CFRP in order to benefit from all the advantages of this material such as low weight and fatigue resistance, while complying with the thermal and the fireproof requirements in aviation.
To achieve a solution which is applicable to manned aircrafts it is needed to start in parallel with both, materials survey studies, and novel redesigning concepts, from metal to CFRP, while successfully anticipate integration routes for the fire protection layers within the new produced parts.
The fire conditions imposed by aviation are contemplated in various standard (long/small aircrafts, helicopters etc). In particular, the multilayer protective coating should be able, not only to avoid the burn out of the CFRP part, but to keep it below safety temperatures sufficient time not to diminish the mechanical strength of the structure, all under a continuous fire rain of kerosene, and in the presence of heavy mechanical vibration.
The sought multilayer configuration should appear to behave optimally in terms of thermal isolation, fireproofing and firefighting requirements. It also should be of easy of application, low cost and weight while maintaining its effectiveness. The project also looks at the process of removal and replacement if it is found to degrade or gets damaged under operating conditions in anticipation of maintenance related problems as well as long term environmental deterioration.
To achieve a solution which is applicable to manned aircrafts it is needed to start in parallel with both, materials survey studies, and novel redesigning concepts, from metal to CFRP, while successfully anticipate integration routes for the fire protection layers within the new produced parts.
The fire conditions imposed by aviation are contemplated in various standard (long/small aircrafts, helicopters etc). In particular, the multilayer protective coating should be able, not only to avoid the burn out of the CFRP part, but to keep it below safety temperatures sufficient time not to diminish the mechanical strength of the structure, all under a continuous fire rain of kerosene, and in the presence of heavy mechanical vibration.
The sought multilayer configuration should appear to behave optimally in terms of thermal isolation, fireproofing and firefighting requirements. It also should be of easy of application, low cost and weight while maintaining its effectiveness. The project also looks at the process of removal and replacement if it is found to degrade or gets damaged under operating conditions in anticipation of maintenance related problems as well as long term environmental deterioration.
After the selection of most appropriate fireproof materials, different layer assemblies are done using coupons of CFRP plates of different sizes. Fig. 1.
The pathway from metal to CFRP requires new designs principles. Load distributions, joinings, fittings and other auxiliary parts need to be reconfigured or relocated. Fig. 2.
A laboratory for fire testing has been upgraded in AIN facilities in Pamplona (Spain) to adapt to ISO 2685. In an initial phase, the preliminary multilayer screening has been made in a purpose rebuilt rig consisting on a support frame for the tested 200×200 mm coupons. The coupon is then exposed to a flame of an impinging diameter at least ½ the area of the coupon, assuring a temperature of 1100ºC and a heat flux of 116 kw/m2 (Fig. 3); to attain the indicated values, a heat flux gauge has been constructed and tested. The coupons are then monitored during its exposition to the flame using a set of thermocouples (up to 12), located at the interface between the CFRP base plate and the multilayer protective coating. The temperature monitoring as a function of time has been measured using a data recorder. A signal adaptor circuit is used to convert the signal into temperature recording datasets.
All phases of fire testing are being complemented with thermal simulations based on the test arrangements, using Finite Element models. The parameters which influence the conduction and convection modes of heat transfer have been defined in the FEM as temperature dependent (non-linear analysis). A complementary Computational Fluid Dynamic model (CFD) has also been constructed. It simulates the natural convection between the composite and the environment and from this, the distribution of convection coefficients as a function of temperature is obtained and then used as input parameter for the FEM. Additionally, the layer thicknesses are modelled parametrically making it easier to study variations on the same configuration. The fire test simulated consists of a CFRP plate with protective coating only at the face exposed to the flame. The simulated plate is then exposed to a reduced circular flame modelled as a fixed surface temperature input of 1100oC at the center of the plate which is applied for fifteen minutes to correspond with the duration of an ISO 2685 fire test.
The most promising combinations of fireproof are then tested under certified aviation conditions (Fig. 4).
The pathway from metal to CFRP requires new designs principles. Load distributions, joinings, fittings and other auxiliary parts need to be reconfigured or relocated. Fig. 2.
A laboratory for fire testing has been upgraded in AIN facilities in Pamplona (Spain) to adapt to ISO 2685. In an initial phase, the preliminary multilayer screening has been made in a purpose rebuilt rig consisting on a support frame for the tested 200×200 mm coupons. The coupon is then exposed to a flame of an impinging diameter at least ½ the area of the coupon, assuring a temperature of 1100ºC and a heat flux of 116 kw/m2 (Fig. 3); to attain the indicated values, a heat flux gauge has been constructed and tested. The coupons are then monitored during its exposition to the flame using a set of thermocouples (up to 12), located at the interface between the CFRP base plate and the multilayer protective coating. The temperature monitoring as a function of time has been measured using a data recorder. A signal adaptor circuit is used to convert the signal into temperature recording datasets.
All phases of fire testing are being complemented with thermal simulations based on the test arrangements, using Finite Element models. The parameters which influence the conduction and convection modes of heat transfer have been defined in the FEM as temperature dependent (non-linear analysis). A complementary Computational Fluid Dynamic model (CFD) has also been constructed. It simulates the natural convection between the composite and the environment and from this, the distribution of convection coefficients as a function of temperature is obtained and then used as input parameter for the FEM. Additionally, the layer thicknesses are modelled parametrically making it easier to study variations on the same configuration. The fire test simulated consists of a CFRP plate with protective coating only at the face exposed to the flame. The simulated plate is then exposed to a reduced circular flame modelled as a fixed surface temperature input of 1100oC at the center of the plate which is applied for fifteen minutes to correspond with the duration of an ISO 2685 fire test.
The most promising combinations of fireproof are then tested under certified aviation conditions (Fig. 4).
The major achievement so far is to demonstrate the capability of a multilayer stack to protect the CFRP against fire, not only avoiding the combustion of the plastic but also to preserve its temperature low enough not to cmpromise its mechanical strength. Fig. 5 shows the IR image of the back side of a 500x500 mm CFRP coupon protected with a multilayer. The temperatures recorded at the back side of the coupon did not exceeded 130ºC.