The effects of thermal aging on tensile strength of three Kevlar/PBI blends used in the outer shell layer of firefighters' protective clothing were examined using cone calorimeter exposures of 10-70 kW/m² for 30-300 seconds. Lower heat flux exposures of 10-15 kW/m² did not result in significant change in the tensile strength of the fabrics, but significant losses of tensile strength were first observed as the heat fluxes increased to 20-30 kW/m² for two ripstop fabrics, and 45 kW/m² for the third fabric. Further decreases in tensile strength were observed with increasing heat flux until there was almost a total loss of original tensile strength following exposure to 70 kW/m². Decreases in tensile strength were explained by comparing fabric temperature measurements made using an infrared thermometer, key temperatures in thermal gravimetric analysis test results, and the appearance of the three fabrics after the exposures. While duration of exposure had little effect on tensile strength after exposures to 10 kW/m², tensile strength decreased with duration of exposure for heat fluxes of 20-40 kW/m². The effect of duration was greatest for a heat flux of 20 kW/m². These results indicate that one must consider not only the maximum temperature that the fabric reaches, but the complete temperature-time trace, including the time at which the fabric remains at the maximum temperature, when examining the effects of thermal aging on tensile strength.

中文翻译：

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高热通量暴露对消防员防护服抗拉强度的影响

^{使用锥形量热计暴露 10-70 kW/m 2} 30-300 秒，研究了热老化对消防员防护服外壳层中使用的三种 Kevlar/PBI 共混物的拉伸强度的影响。^{10-15 kW/m 2}的较低热通量暴露不会导致织物的拉伸强度发生显着变化，但随着热通量增加到 20-30 kW/m ²两个防撕裂织物，第三种织物为 45 kW/m ²。^{随着热通量的增加，观察到抗拉强度进一步降低，直到暴露于 70 kW/m 2}后原始抗拉强度几乎完全丧失. 通过比较使用红外温度计进行的织物温度测量、热重分析测试结果中的关键温度以及暴露后三种织物的外观来解释拉伸强度的降低。^{虽然暴露时间对暴露于 10 kW/m 2}后的抗拉强度影响不大，但对于 20-40 kW/m ²的热通量，抗拉强度随着暴露时间的延长而降低。^{对于 20 kW/m 2}的热通量，持续时间的影响最大. 这些结果表明，在检查热老化对拉伸强度的影响时，不仅必须考虑织物达到的最高温度，还必须考虑完整的温度-时间轨迹，包括织物保持在最高温度的时间。