Uniaxial tensile creep experiment and creep model of fabric for airship structures
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摘要: 聚酯纤维织物类膜材因其轻质高强、耐候性好等特点常被用于飞艇结构的蒙皮材料,其在高应力水平下的蠕变失效行为决定飞艇结构长期安全性能,但目前尚未有相关的性能测试标准及研究。为研究此类膜材的蠕变性能,选用以Vectran纤维为基布材料的膜材在极限应力的85%、80%、75%、70%四组应力水平下进行单轴拉伸蠕变试验,分析了蠕变过程中膜材应变、模量及蠕变破坏时间等参数随应力水平的变化规律,并给出基于应力水平的蠕变强度包络线拟合公式;通过牛顿迭代法建立了参数化的四单元蠕变模型及蠕变破坏准则,可以较准确地反映材料在高应力水平下的蠕变破坏规律。Abstract: Polyester fabrics are often used for airship structures because of their light-weight, high-strength and environmental resistance properties, their creep failure behavior under high stress levels determines the long-term safety performance of airship structures, but there is no relevant test standard or research at present. In order to study the creep properties of polyester fabrics, a membrane material composed of Vectran fibers was selected to carry out uniaxial tensile creep tests at 4 high stress levels: 85%, 80%, 75% and 70% of ultimate stress. The variation laws of creep strain, creep modulus and creep failure time with respect to stress level were summarized, and the fitting formulas of creep rupture envelopes were given through Newton iterative calculation. When the stress level is lower than 63% of the ultimate stress, the fabrics will not reach the creep rupture point. Based on the experimental data, the parametric four element creep model and creep failure criterions are established. It is found that the fitting model can generally reflect the creep failure reactions under high stress levels.
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Key words:
- fabric membrane material /
- creep strength /
- creep model /
- viscoelasticity /
- nonlinearity
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图 10 聚合物的四单元蠕变模型
Figure 10. Common creep model of polymers based on combination of spring elements and dashpot elements
ε1—Universal elastic strain; ε2—High elastic strain; ε3 —Viscosity strain; E1, E2—Elastic modulus of different spring elements in the model; η2, η3—Viscosity coefficient of different sticky pot units in the model; σc—Load holding stress value; t—Time
表 1 Vectran-PVF膜材蠕变试验设备及参数
Table 1. Instruments parameters of Vectran-PVF fabric creep testing
Test equipment Measuring range Accuracy Error Electronic universal testing machine 0-5000 N 0.1 N ±0.5% Displacement meter 0-800 mm 0.008 mm ±1% Thickness gauge 0-12.7 mm 0.001 mm ±1% 表 2 Vectran-PVF膜材模型预测带与试验结果的极限应变值对比
Table 2. Comparison of ultimate strain values of Vectran-PVF fabric between model prediction zone and test results
Stress Ultimate strain/% Error/% Experiment Creep model 85%σu 2.40 2.33-2.55 0.0 80%σu 2.33 2.29-2.37 0.0 75%σu 2.22 2.04-2.10 5.4 70%σu 2.11 1.78-1.89 10.4 -
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