尼龙1010应力松弛行为研究

Stress Relaxation Behavior of Nylon 1010

尼龙1010样品在初始应变为1%、2.8%和5.1%的条件下,在不同的恒温环境中分别进行不少于10 h的应力松弛实验,得到20-80℃范围的应力松弛曲线.研究了不同应力、温度下的应力松弛速率、松弛过程的残余应力、活化体积以及相关参数的数学关系.结果表明,尼龙样品在松弛过程中存在一定的形变残余应力,体系存在恒定的长时模量.不同初始应变的尼龙样品松弛过程表现出相似的规律,当松弛速率-d（σ/σ0）/dlnt达到最大值后,在一段时间内聚合物内部活化单元发生松弛,-dσ/dt与作用于样品的有效应力σ＊为指数关系.随着松弛过程的进行,应力减小到一定程度后,活化体积V逐渐增加,此时独立的活化单元运动受到限制,聚合物内部依靠多个活化单元的协同运动将内应力逐渐松弛,应力辅助功Vσ＊为常数,-dσ/dt与σ＊满足幂律关系,幂指数为σ＊V/（k T）.

The stress relaxation behavior of nylon 1010 samples with the initial strain of 1%,2. 8% and5. 1% were investigated under various temperatures for not less than 10 h. The samples were measured at 20,40,60 and 80 ℃ separately. The stress relaxation rate,the residual stress and the activation volume under different experimental conditions were obtained. The results show that there was a certain permanent residual stress in the relaxation process. The reason is that the effect of the crystalline regions in the semi-crystalline nylon leads to a permanent modulus of the system. During the relaxation process,nylon samples with different initial strains showed similar trends. When the relaxation rate reached the maximum,the values of activation volume remained constant for a short period of time,which is in accordance with the principle of stress-aided thermal activation. At this stage the activation unit of the polymer was relaxed,and the relaxation rate- dσ/dt and the effective stress σ＊showed an exponential relation. With further relaxation,the stress decreased to a certain threshold,activation volume would gradually increase and the independent movement of activation unit was restricted. The internal stress of the polymer gradually relaxed by the cooperative movement of multiple activation units. At this final stage,the value of stress assisted work was constant. The relaxation rate- dσ/dt and the effective stress σ＊exhibited power-law relation and the power exponent is σ＊V /（ k T）.