中文摘要：

利用MTS万能试验机和MTI微型拉伸试验机分别研究了Kevlar 29纤维束与纤维单丝在不同标距下（纤维束：25 mm、50 mm、100 mm、150 mm、00 mm和300 mm;纤维单丝：12.5 mm、25 mm和40 mm）的力学性能。结果表明,Kevlar 29的拉伸强度随着结构尺度（从纤维单丝到纤维束）的增加而降低;标距对Kevlar 29纤维单丝力学性能的影响并不显著;但对纤维束而言,拉伸强度随着标距的增加而降低,呈明显的尺寸效应。利用Weibull模型进行统计分析,量化了不同标距下纤维单丝拉伸强度的随机变化程度。这些统计参数将用于有限元模型以模拟静载下Kevlar 29纤维束的拉伸行为。该模型基于ANSYS中的用户自定义子程序（USERMAT）,并考虑了纤维单丝的随机破坏。模型的预测结果与试验结果相吻合,并讨论了关键参数对模拟结果的影响。

英文摘要：

The material mechanical properties of Kevlar 29 yarns and filaments with different gage lengths（yarns： 25 mm, 50 mm, 100 mm, 150 mm, 200 mm and 300 mm; filaments： 12.5 mm, 25 mm and 40 mm） were investigated by quasi-static testing utilizing a MTS load frame and a MTI miniature tester. The results manifested that the material mechanical properties of Kevlar 29 are dependent on the structural scale. The tensile strength decreases with the structural scale altering from fiber to yarn. For filament, the gage length exerts little influence on the tensile properties; but for yarn, the tensile strength decreases with increasing gage length, indicating an obvious size effect. Weibull statistics were used to quantify the degree of variability in strengths of filaments and yarns at different gage lengths. These data were then used in a finite element model considering the probabilistic failure of filaments, which was established by utilizing a user-defined subroutine（USERMAT） in ANSYS to simulate the stress-strain responses of Kevlar 29 single yarn under pseudo-static loading. The predictions of the finite element model agree reasonably well with the experimental data. Parameteric study was also carried out to investigate the effect on the simulation results.