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The quantitative relationship between the fraction of UV exposure energy and the retention fraction of tensile strength was investigated on the m-Aramid/p-Aramid blend ratio of spun yarn. An exponential equation to calculate tensile strength from an arbitrary UV exposure energy is evaluated for yarns and fabrics. The spun yarns were exposed to UV light using a xenon-arc weathering meter. The retention fraction of tensile strength decreased exponentially with increasing the fraction of UV exposure energy. Curve fitting of the retention fraction of tensile strength to the fraction of UV exposure energy revealed two groups of degradation coefficients based on the blending ratio of m-Aramid/p-Aramid. The correlation between the degradation coefficients ( α y and α f ) of spun yarn and fabrics can be linearly regressed. The constant of proportionality in linear regression is considered to be the gap between the structure and the breaking mechanism of the fabric relative to yarn breakage. Based on the correlation between the degradation coefficients of spun yarn and fabrics and a mathematical model of the tensile strength of the spun yarn, the tensile strength of fabrics at a given UV exposure energy can be estimated from the tensile strength of the yarn. [ABSTRACT FROM AUTHOR]

This study focused on the m-Aramid/p-Aramid blend ratio of the fabrics, clarified the quantitative relationship between UV exposure and strength retention, and developed a mathematical model to calculate tensile strength from an arbitrary amount of UV exposure energy. The results of tensile strength tests before and after UV exposure showed that the decrease in tensile strength due to UV degradation depended on the combination of p-Aramid and m-Aramid blend percentages. Tensile strength for all blend ratios decreased exponentially with UV exposure energy and was within the range of results for fabrics with p-Aramid 100% and m-Aramid 100%. The retention fraction of tensile strength, which represents the tensile strength after UV exposure relative to the initial tensile strength, decreased exponentially with increasing the fraction of UV exposure energy for all fabrics used in this study. Fitting the retention fraction of tensile strength to the fraction of UV exposure energy, two groups of fabrics were classified based on m-Aramid blends of 40% or more and 60% or less. This model can predict the tensile strength of firefighter clothing fabrics that retain high mechanical strength when exposed to UV light and design the strength of firefighter clothing with consideration of degradation over time. [ABSTRACT FROM AUTHOR]

The existing extinguishment device used in spacecraft is an inert gas (CO2) extinguisher or water mist which is a promising technique to suppress flames, however, the remained production of fume (harmful) gas in the enclosed space was paid little attention, although its removal from the cabin is not an easy task. We propose novel methodology, which can completely resolve this problem; namely, flame is extinguished by "a vacuuming operation" driven by the pressure difference between the suction box and the cabin, whereby toxic gases and even the fire source is drawn into the box, where an effective extinguishment procedure can be separately operated. To convince the effectiveness of this methodology and investigate its performance, a specially-designed test device is developed and an extinction test is examined in this paper. The main experimental parameters are the suction flow rate and the distance between the end of the suction pipe and the burning specimen. The burning specimen used in this study is a small scale electric wire with a polymer sheath. The extinction process via suction operation has been observed carefully. In addition to the direct observation, velocity measurement induced by suction operation as well as the use of the Schlieren imaging technique are introduced. It is found that the vacuuming extinction can be categorized into three types based on the mechanism leading to the extinction. The model of the extinction procedure is proposed and corresponding three non-dimensional numbers as a function of vacuuming volume flow rate (Q) are developed to predict the mode on vacuuming extinction. Afterall, this paper successfully show the concept of a vacuum extinction and how it works. [ABSTRACT FROM AUTHOR]

High-performance yarns are widely used to produce protective fabrics, including stab-resistant materials. The most common approach to studying the mechanism of puncture prevention is to use simulation to assist analysis. However, the anisotropy of the yarn is often overlooked during simulation owing to various factors. In fact, there is a marked difference between the axial and radial properties of a yarn. This may lead to large errors in research. In the present study, a composite material with a grid structure for puncture analysis was designed to investigate the influence of yarn anisotropy on the accuracy of simulation results. The present study combined an actual experiment with a simulation. In the actual experiment, Kevlar yarn/epoxy resin was used to prepare a mesh composite with a spacing of 1 mm. In the simulation, a 1:1 simulation model of composite material was established using finite element software. A simulated puncture experiment was conducted based on the actual experimental conditions and material parameters. After considering yarn anisotropy, the simulation results were closer to the actual experimental results. The simulation revealed that the main failure modes of the mesh material were the fracture of the resin and the bending deformation of the yarns at the junctions, while the surrounding areas were almost unaffected. [ABSTRACT FROM AUTHOR]

We studied the near-limiting behavior of various thicknesses of thermoplastic materials under a candle-like burning configuration; followed by an ISO 4589-2 protocol. The motivation for this work is to understand the sensitivity of the sample thickness on the limiting oxygen concentration in the range from 0.5 mm to 10 mm. In the first place, the effect of heating time on successive ignition was discussed. Through a simple analysis, it was suggested that a 30 s heating time, regulated in ISO 4589-2, might be insufficient to achieve a successful ignition when the specimen becomes thicker. Second, the effect of the thickness of the test specimen (PMMA, ABS) on the limiting oxygen concentration was examined. Flames formed over thicker PMMA (>4.0 mm thickness in this study) at near-limiting condition displayed a flickering motion, which then suddenly extinguished when the critical condition was achieved due to temporal acceleration of the surrounding flow. While the flame behavior with a thinner sample (<4.0 mm thickness in this study) at the limiting condition was found to be stationary, a gentle extinction was experienced as approached to the limit. This fact suggests that the key to leading extinction is different between thicker and thinner sample. Third, the temperature distribution over the 4.0 mm PMMA at the near-limiting condition was measured and a strategy to model/predict the limiting behavior is then proposed. [ABSTRACT FROM AUTHOR]

Abstract: Research and development of firefighters’ protective clothing relies on a large number of fire disaster experiments in order to assess the thermal performance. It would be substantially advantageous to substitute a virtual numerical experiment for a real one in terms of time, cost and safety. The present article reports the development of an integrated numerical simulator that makes possible the estimation of burn injuries originating from fire disasters. In the simulator, a general-purpose computational fluid dynamics program computes the fluid flow and heat transfer in an in situ fire event, while a one-dimensional program calculates the radiative–conductive heat transfer through the clothing and human skin. A data interface combines the two simulations by loose coupling so as to give the real-time burn injury progress output. The predicted surface heat fluxes and burn degrees agree with experimental measurements reasonably well. Possible numerical error sources are discussed that call for potential improvements in the future. [Copyright &y& Elsevier]

Abstract: Fire behavior of heptane pool fires were investigated in a small-scale 40cm cubic compartment with wall vents at the ceiling (top vent) and the floor (bottom vent). The measurements included pressure, mass loss, temperature, heat flux, and gas mole fraction. Flame oscillations, ghosting, and burning at the air inlet were seen. The regime of limited ventilation was examined to study the effect of extinction and the influence of oxygen. A theory based on a critical flame temperature showed that extinction depends on heating as well as oxygen concentration. A complete uniform property model was developed and its solution agrees qualitatively with the measurements. [Copyright &y& Elsevier]