超高分子量聚乙烯纤维束低速拉伸下的应变率效应及其统计损伤本构关系

Strain Rate Effect and Statistical Damage Constitutive Relationship of Ultra-High MolecularWeight Polyethylene Fiber Bundles Under Low Speed Stretching

基于轴向拉伸实验研究超高分子量聚乙烯(UHMWPE)纤维束低速下(包含准静态)应变率效应对其力学性能及破坏模式的影响,阐述了其弹-黏塑性特性和分子链断裂在纤维束变形过程中的贡献。在10^(-5)~3.3×10^(-2)s^(-1)应变率范围内,对UHMWPE纤维束进行5种不同应变率工况的拉伸实验,得到了各工况下的力学性能参数及应力-应变曲线。结果表明,UHMWPE纤维束的拉伸强度和失效应变与应变率之间分别存在指数增长和指数衰减关系,随着应变率的提升,二者的应变率效应逐渐削弱。室温下,UHMWPE纤维束具有较为复杂的力学行为,呈现2种不同的损伤特性,分别为黏弹性主导的宏观整体性脆性断裂和黏塑性主导极具韧性且包含蠕变的塑性变形。基于实验结果并结合现有文献结论,推断UHMPWE纤维束发生脆-韧转变的临界应变率在10-5量级。最后,根据实验数据拟合了计及应变率且包含修正项的纤维束低速统计损伤本构方程,通过与实测值对比,验证了该方程的准确性。

At low speed(including quasi-static),the influence of the strain rate effect on mechanical properties and failure modes of ultra-high molecular weight polyethylene(UHMWPE)fiber bundles was investigated by axial tensile experiments.The contribution of elastic-viscoplastic properties and molecular bond fracture to fiber bundles’deformation was illustrated.In the strain rate range of 10^(-5)~3.3×10^(-2)s^(-1),tensile experiments of UHMWPE fiber bundles were carried out under five different strain rate conditions,and the mechanical parameters and stress-strain curves were obtained.The findings demonstrate an exponential growth and decay relationship between the tensile strength,failure strain,and strain rate of UHMWPE fiber bundles,respectively.The strain rate effect of the two parameters is gradually weakened as strain rate rises.At room temperature,UHMWPE fiber bundles exhibit complex mechanical behaviors,showing two different damage characteristics,namely,viscoelastic-dominated macro-integrity brittle fracture and viscoplastic-dominated plastic deformation that is extremely tough and includes creep.Based on the experimental results and conclusions of existing literatures,it is concluded that the critical strain rate of brittle-toughness transition of UHMPWE fiber bundles is on the order of 10-5.Finally,according to the experimental data,the low-speed statistical damage constitutive equation of fiber bundles,including the strain rate effect and correction function,was fitted,and the accuracy of the constitutive equation was verified by comparing with the measured values.