NUMERICAL SIMULATION OF FIRE SPREAD ON POLYURETHANE FOAM SLABS | NIST
Computational Fluid Dynamics (CFD) models are used extensively by fire protection engineers for performance based design and forensic analysis. The equations of motion describing the gas phase are relatively well known and the approximations in the various gas phase sub-models have been extensively studied. However, coupling of the gas phase and the condensed phase to describe flame spread over a burning solid, has proven to be difficult to model. This is due to a lack of understanding of the underlying physical phenomena that take place during the decomposition of the solid as well as poor characterization of the fundamental material properties that control the burning process. The overall goal of this project is to improve the capability of the fire models to predict flame spread over materials that typically burn in a compartment fire. In this paper, we attempt to simulate fire growth and spread on 10 cm thick slabs of polyurethane foam. A multi-layered, multi-material model was developed to simulate flame spread, and material properties were obtained from various small scale experiments. Model predictions were compared with large scale experiments on polyurethane foam slabs, ignited on one edge. Results indicate that the model is capable of qualitatively predicting the observed trends in heat release rate, flame spread rate and heat fluxes measured in the experiments. This report will describe the progress that has been made to date on modeling fire growth and spread on polyurethane foam slabs and the comparison of these results with experimental data.
Studies on the Thermal Behavior of Polyurethanes
The number of fires appear to be increasing all over the world with some big fires started from burning sofa polyurethane foam (PUF). The general public is quite concerned about the risk of fire due to the extensive use of polyurethane-based materials. Better understanding of the fire behavior of the materials would provide guidelines on fire safety provision. The first step is to review the thermal decomposition mechanisms of polyurethane under different environmental conditions, which will be reported in this paper. Recent studies on the thermal decomposition kinetics and thermal stability of polyurethane are described. Thermal decomposition and combustion reactions of polyether-polyurethane and polyester-polyurethane in air and nitrogen atmospheres investigated by using thermogravimetry analysis will then be outlined. The kinetic processes of polyurethane decomposition studied by the model fitting method are discussed. Polyester-polyurethane was found to be thermally more stable than polyether-polyurethane. The presence of oxygen would significantly affect the breaking down of the polymeric chains. Fire retardants for polyurethane are also briefly reviewed. Results are useful for developing fire retardants for polyurethane-based materials with better fire behavior.
Joint strength of aluminum ultrasonic soldered under liquidus temperature of Sn–Zn hypereutectic solder
Abstract In order to obtain high-strength aluminum joints, ultrasonic soldering of 1070 aluminum was conducted under liquidus temperature of Sn–Zn hypereutectic solder. A device for ultrasonic soldering was assembled, which propagated ultrasonic vibrations in a direction perpendicular to joining surfaces. This device joined 1070-Al using quasi-melting Sn–Zn hypereutectic solder without using any artificial spacers. The strength of the solder joints was evaluated by tensile tests. The optimum joining conditions were determined, and the effects of solder compositions and soldering temperature on the joint strength and the solder layer thickness were examined. In this ultrasonic soldering process, the highest tensile strength was obtained for the solder joints fabricated at 220 °C for the Sn–23Zn and Sn–40Zn solder compositions. The joint strength was equivalent to that of 1070-Al heat treated at 220 °C. The sound joints were obtained at 300 °C using Sn–82Zn solder, the liquid phase volume fraction of which was theoretically only 0.24. The present work also revealed that the thickness of retained solder layer in the joint after ultrasonic soldering could be estimated. Accordingly, ultrasonic soldering under the liquidus temperature of Sn–Zn hypereutectic solder could be a spacer-free soldering method to obtain high-strength aluminum joints.