以时温等效方法研究尼龙1010应力松弛行为及使用寿命预测

以尼龙材料的应力松弛行为作为研究对象, 考察初始应变为1.0%, 2.8%和5.1%的尼龙1010样品在温度区间293353 K的松弛曲线, 采用时间-温度等效叠加方法得到了松弛模量主曲线, 计算出叠加过程中的表观活化能、 松弛过程中的活化体积和应力辅助功. 结果表明, 整个松弛过程中的表观活化能和应力辅助功表现出相同的变化趋势, 体现出松弛过程中克服运动单元位垒的过程. 当293323 K区间的松弛曲线叠加时, 随着初始应变的增加, 表观活化能和应力辅助功均逐渐降低, 有助于聚合物内部的运动单元越过能垒发生松弛, 与松弛过程中的应力辅助热活化理论相一致; 当333353 K区间的松弛曲线叠加时, 不同初始应变样品的表观活化能均为260 kJ/mol, 应力辅助功均为60 MPa·nm³, 说明松弛过程中克服运动单元的能垒与应力作用无关. 根据松弛主曲线, 计算出了尼龙1010在1.0%, 2.8%和5.1% 3种形变下, 长时间范围内应力衰减与时间的关系, 为预测实际使用过程中的应力松弛行为提供了依据.

Long-term Stress Relaxation Prediction for Nylon 1010 Using Time-temperature Superposition Method†

Stress relaxation behavior of plastic has great influence on its service life and safety. The master curves were generated by horizontal and vertical shifts of the short term curves of stress relaxation for Nylon 1010 at temperatures ranging from 293 K to 353 K using proposed time-temperature superposition equivalence method. The apparent activation energy was calculated from the Arrhenius plots of shift factor, and the values of activation volume and stress-assisted work were calculated from the master curves. The time-temperature superposition principle was found to be available for the stress relaxation curves. During the superposition interval of the experimental temperature from 293 K to 323 K, the apparent activation energy and stress-assisted work show a tendency to decrease gradually, which is helpful for the relaxation of the moving units in the polymer over the energy barrier. During the superposition interval of the experimental temperature from 333 K to 353 K, the apparent activation energy of different initial strain samples is about the same value of 260 kJ/mol and the stress-aided work is basically unchanged at the value of 60 MPa·nm³, which indicates that the energy barrier of the moving unit is independent of the stress effect. According to the mater curves of Nylon 1010, the relationship between stress decay and relaxation time in a long time range can be obtained under the strain of 1.0%, 2.8% and 5.1%, which provides a reference for predicting stress relaxation behavior in practical use.