Simulation of the burning and dripping cables in fire using the particle finite element method
(2022)
The behavior of the cable jacket in fire characterized by the tendency to melt and drip constitutes a major source of fire hazard. The reason is that the melted material may convey the flame from one point to another, expanding fire and contributing to the fire load. In this article, the capability of a new computational strategy based on the particle finite element method for simulating a bench-scale cables burning test is analyzed. The use bench-scale test has been previously used to simulate the full-scale test described in EN 50399. As the air effect is neglected, a simple combustion model is included. The samples selected are two cables consisting of a copper core and differently flame retarded thermoplastic polyurethane sheets. The key modeling parameters were determined from different literature sources as well as experimentally. During the experiment, the specimen was burned under the test set-up condition recording the process and measuring the temperature evolution by means of three thermocouples. Next, the test was reproduced numerically and compared with a real fire test. The numerical results show that the particle finite element method can accurately predict the evolution of the temperature and the melting of the jacket.
An experimental and numerical investigation of the effect of bisphenol A bis(diphenyl phosphate) (BDP) and polytetrafluoroethylene (PTFE) on the fire behaviour of bisphenol A polycarbonate/acrylonitrile butadiene styrene (PC/ABS) in the vertical UL 94 scenario is presented. Four PC/ABS blends were discussed, which satisfy different UL 94 classifications due to the competing effects of gasification, charring, flame inhibition and melt flow/dripping. For numerical investigation, the particle finite element method (PFEM) is used. Its capability to model the complex fire behaviour of polymers in the UL 94 is analysed. The materials' properties are characterised, in particular the additives impact on the dripping behaviour during thermal exposure. BDP is an efficient plasticiser; adding PTFE prevents dripping by causing a flow limit. PFEM simulations reproduce the dripping and burning behaviour, in particular the competition between gasification and dripping. The thermal impact of both the burner and the flame is approximated taking into account flame inhibition, charring and effective heat of combustion. PFEM is a promising numerical tool for the investigation of the fire behaviour of polymers, particularly when large deformations are involved. Not only the principal phenomena but also the different UL 94 classifications and the extinction times are well predicted.
Melt flow and dripping of polymeric materials can be both beneficial and detrimental during fire. It reduces flame spread and result in extinction, as mass and heat are removed from the actual pyrolysis zone. In contrast, melt flow and dripping can provide an additional ignition source, additional process of flame spread and has the potential to start a pool fire. In the vertical UL 94 test, a well adjusted dripping behaviour of flame retarded polypropylene (PP-FR) resulted in a non-flaming dripping V-0 classification. For the polymer samples and their drops collected in UL 94, the decomposition and viscosity was investigated. Particle finite element method (PFEM) was successfully used to simulate the material behaviour in the UL 94 test and increased the understanding of the complex behaviour of polymeric materials during fire.