应变率、温度和尺寸对纤维束机械行为的影响
Strain-rate, temperature and size effects on the mechanical behavior of fiber bundles
AI总结：
研究应变率、温度和尺寸对纤维束机械行为的影响，通过纤维束模型分析热激活作用，揭示应变率和温度对强度、应变和弹性模量的影响，指出传统降尺度方法需谨慎使用。
摘要：
纤维（各种材料）及纤维束的机械特性对纺织品或纤维复合材料的设计和机械行为至关重要。这些特性通常通过应变率控制的拉伸测试确定，通常假设热激活对损伤和断裂过程的作用可忽略。在此假设下，可通过降尺度方法从宏观机械行为推导单根纤维的强度分布。然而，许多实验证据表明应变率和温度对单根纤维或纤维束的机械行为有显著影响，甚至在恒定载荷下也会发生蠕变。这表明热激活在这些过程中起重要作用。本文通过等载荷共享的纤维束模型，引入热激活的纤维断裂动力学蒙特卡罗算法，以分析这些效应。这有助于解释应变率或温度效应，如降低束强度、峰值应力应变和表观杨氏模量。此外，传统用于从束尺度机械行为估计单根纤维强度分布的降尺度程序应谨慎对待。如果在促进热激活的条件下（如低应变率）进行束机械测试，该程序可能严重低估纤维强度分布的固有（无热）韦布尔参数。同一模型还用于探讨尺寸（纤维数量）对束机械响应的影响。
英文摘要：
The mechanical characteristics of fibers (of various materials), as well as of fiber bundles, are of primary importance for the design and the mechanical behavior of textiles, or of fibrous and composite materials. These characteristics are classically determined from strain-rate controlled tensile testing, generally assuming a negligible role of thermal activation on damage and fracturing processes. Under this assumption, the distribution of individual fiber strengths can be deduced from a downscaling of the macroscopic mechanical behavior at the bundle scale. There are however many experimental evidences of strain-rate and temperature effects on the mechanical behavior of individual fibers or bundles, which can also creep under constant applied load. This indicates a strong role of thermal activation on these processes. Here, these effects are analyzed from a fiber-bundle model with equal-load-sharing, in which thermal activation of fiber breakings is introduced from a kinetic Monte-Carlo algorithm adapted for time-varying stresses. This allows to rationalize these rate or temperature effects, such as a decrease of bundle strength, strain at peak stress, and apparent Young's modulus with decreasing strain-rate and/or increasing temperature. This also shows that the classical downscaling procedure used to estimate the distribution of individual fiber strengths from the mechanical behavior at the bundle scale should be considered with caution. If mechanical testing of the bundle is performed under conditions favoring the role of thermal activation (e.g. low applied strain-rate), this procedure can strongly underestimate the intrinsic (athermal) Weibull's parameters of the fiber strengths distribution. The same model is used as well to explore size (number of fibers) effects on bundle mechanical response.
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