Dynamic tensile mechanical properties and constitutive equation of Kevlar29 yarn
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摘要: 为了能够清晰地表征芳纶纱线在不同应变率下的力学行为，进行了Kevlar29纱线的准静态和动态拉伸试验，结合分离式霍普金森拉杆理论和运动目标追踪法，获得了Kevlar29纱线在不同应变率下的应力-应变曲线，分析了纱线动态拉伸的变形与断裂过程，揭示了Kevlar29纱线力学性能的应变率效应；通过最小二乘法拟合得到了基于纱线应变率效应的黏弹性本构方程，分析了三元件和五元件本构模型的差异及适用性。结果表明：随着应变率升高，Kevlar29纱线的断裂应变减小，拉伸强度和韧性先增大后减小，拉伸模量先增大后趋于稳定；五元件黏弹性本构模型能够较好地表征纱线力学性能的应变率效应。Abstract: In order to clearly characterize the mechanical behavior of Kevlar29 yarn at different strain rates, this paper reports quasi-static and dynamic tensile tests on Kevlar29 yarn. Combined with the split Hopkinson tensile bar (SHTB) theory and motion target tracking method, the stress-strain curves of Kevlar29 yarn at different strain rates are accurately obtained, and then the deformation and fracture process of yarn dynamic tension are analyzed, revealing the strain rate effect of Kevlar29 yarn mechanical properties. Based on the strain rate effect of yarn, a viscoelastic constitutive equation is obtained through the least squares fitting method, and the differences and applicability between the three-element and five-element constitutive models are analyzed. The results show that when the strain is calculated by identifying the coordinates of the marker points on the yarn by the motion target tracking method, it is more accurate than the strain calculated directly from the waveform measured by SHTB. The quasi-static mechanical properties and dynamic mechanical properties of Kevlar29 yarn differ significantly, e.g., the dynamic tensile modulus and tensile strength are higher than those of quasi-static, and the dynamic fracture strain is smaller than that of quasi-static. In the strain rate range of 0.001–700 s−1, with the increase of strain rate, the breaking strain of Kevlar29 yarn decreases, and the tensile strength, tensile modulus and toughness all increase first, but at higher strain rates, the tensile strength (higher than 497.5 s−1) and toughness (higher than 330.7 s−1) decrease, while the tensile modulus (higher than 330.7 s−1) tends to be stable. The viscoelastic constitutive equation can better characterize the strain rate effect of the mechanical properties of Kevlar29 yarn, but the viscoelastic constitutive model cannot reflect the nonlinear stress-strain relationship of the yarn before fracture. Relatively speaking, the fitting effect of the five-element viscoelastic model is better than that of the three-element viscoelastic model.
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图 3 纱线拉伸过程中夹持部位标记点观测
Figure 3. Observation of marked points at the clamping location during yarn stretching process
图 12 去除初始非线性段的应力-应变曲线
Figure 12. Stress-strain curves after removing initial nonlinear section
图 14 应变率为279 s−1时纱线的拉伸过程
Figure 14. Stretching process of the yarn when the strain rate is 279 s−1
图 15 应变率为279 s−1时纱线的应力-应变曲线
Figure 15. Stress-strain curve of the yarn when the strain rate is 279 s−1
图 21 黏弹性本构模型的理论值与试验值对比
Figure 21. Comparison between the theoretical values of viscoelastic constitutive models and experimental results
图 22 三元件模型与五元件模型对比
Figure 22. Comparison between three-element model and five-element model
表 1 三元件黏弹性本构模型参数
Table 1. Parameters for the three-element viscoelastic model
E1/GPa E2/GPa η2/（MPa·s） 82.5 54.7 2.218 
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表 2 五元件黏弹性本构模型参数
Table 2. Parameters for the five-element viscoelastic model
E1/GPa E2/GPa E3/GPa η2/（MPa·s） η3/（MPa·s） C1 82.5 43.7 42.3 1.326 0.989 1416
下载: 导出CSV
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