Sub-static mechanical behaviour of BTG plastic alloy was researched and its accurate fractional derivative model was also established in this paper.The experiment of tensile stress relaxation was carried out during 1000s at 20、40、60、80 and 100℃.The data of relaxation modulus was acquired according to timetemperature equivalence principle and above-mentioned experiment data within 440 000 s at 20℃.Kelvin model of fractional derivative was established by parameter identification,and by which the evolvement law of modulus of bar specimens under constant load 20 N within 1 160 000 s can be accurately represented.Results show that time-temperature equivalence principle and Kelvin model of fractional derivative are suitable for BTG plastic alloy.%为研究BTG塑料合金的准静态力学性能,并建立准确描述其力学性能的分数导数模型,通过DMA242进行了20、40、60、80和100℃下1000 s时长拉伸松弛实验,以此实验数据为基础,根据时温等效原理获得了20℃下440 000 s时长的时间松弛模量.以此识别参数获得了BTG塑料合金的分数导数Kelvin本构模型,同时在20℃下进行了条块形状试样在恒载荷20 N下的1 116 000 s的长时间实验拉伸实验.结果表明：建立的分数导数Kelvin模型能准确描述DMA实验数据和恒载下的拉伸模量变化规律;时温等效原理适用于BTG塑料合金,用分数导数Kelvin模型来描述BTG塑料合金的粘弹松弛特性合理.
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