Thermo-mechanical analysis of a fire door for naval applications

P. Boscariol, F. De Bona, A. Gasparetto, L. Moro
DIEGM, University of Udine

Fires doors are subjected to standard fire tests in order to evaluate their fire resistance. The certification process of fire doors, according to FTP code of the International Maritime Organization, requires to verify that the door, subjected to a standard fire endurance test, satisfies some requirements: as an example, the mean temperature on the surface which is not exposed to the fire should not exceed a defined value. Therefore a realistic simulation of the heating process is needed during the design phase in order to reduce as much as possible the number of fire tests. The problem of defining a Finite Element model (FEM) of a fire door and of its supporting frame is then dealt with. In ship structural design the frame plays an important role and therefore it should be included in the analysis. The door is constituted by a steel box filled with some insulation material, while the frame is composed by a steel wall which is insulated by means of a layer of mineral wool. The door is connected to the frame by a structure made of steel profiles with a quite complex geometry. Since the problem can be considered uncoulpled, the temperature field resulting form the thermal analysis can be used as the input for a subsequent structural analysis. Two different types of thermal anlysis are considered: a transient analysis and a steady state analysis. A non linear structural analysis follows to predict the displacement field which occurs at the end of the heating phase. The temperature dependency of the constituent materials is considered in the thermal model and a suitable elasto-plastic model is also implemented. This choice allows to investigate also the unloading phase, i.e. the cooling at room temperature. This feature is needed to evaluate the correct functionality of the door after the exposure to a fire.
The two Finite Elements Models are here validated trough a comparison with experimental data. The experimental setup includes 12 thermocouples and a thermographic camera in order to record the temperatures on both side of the system. A laser sensor has been adopted to monitor the displacements in several points of the unexposed side. The comparison between simulated and measured data confirms that the proposed approach can be a valid tool for the prediction of thermo-mechanical performances of a naval fire door. Moreover the effective evaluation of different design improvement strategies can be also achieved.