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yusongpan

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专业: 机械摩擦学与表面技术

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聚合物的应力松弛过程主要表现为高分子链段的运动和重排以及键角的改变。从高聚物分子链段运动理论来说，高聚物应力松弛实际上是其分子链段沿着外力的方向作运动以减小或消除应力的过程，分子链段运动快慢直接制约应力松弛速率的大小。在应力松弛试验过程中，初始加载时试样产生的形变主要包括两部分：键长键角变化的普通弹性形变和高分子链段运动变化的高弹形变。试样的初始形变主要为普通弹性形变，普通弹性形变的模量很高。在初始形变自发回弹的内应力的作用下，随着时间的延长，那些拉伸时间较长的链段，先后沿着力的方向逐渐由卷曲分子构象向伸展分子构象运动，发展成为高弹形变。由于高弹形变模量远低于普通弹性形变模量，使得试样内维持相同应变的内应力减小，发生了应力松弛。由于高弹形变逐渐取代了普通弹性形变，宏观上就观察到了应力随时间的增加而减小的现象，随着观察时间的延长，应力松弛发展到与恒定应变相平衡的应力值时，应力松弛将停止达到稳定。

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Polymer stress relaxation process is mainly manifested in the polymer chain segment of the movement and rearrangement, as well as bond angle changes. From the kinetic theory of polymer chain segments, the polymer stress relaxation is actually the molecular chains along the direction of external forces for campaigns to reduce or eliminate stress in the process of fast and slow movement of molecular chain segments directly hinders the stress relaxation rate size. In the stress relaxation experiment, the initial load the specimen deformation resulting from two main parts: the bond length and bond angle changes in the ordinary elastic deformation and changes in polymer chain segment motion high-elastic deformation. The initial sample deformation is mainly ordinary elastic deformation, normal elastic deformation of high modulus. Spontaneous rebound in the initial deformation under the action of internal stress, with time, those who stretch longer chain segment, has gradually along the direction of force by the coil molecular conformation to the extended molecular conformation movement, developed into a high-elastic deformation. Deformation due to the high elastic modulus much lower than the average modulus of elastic deformation, allowing the specimen to maintain the same strain of the internal stress reduced stress relaxation took place. Due to the high elastic deformation gradually replaced the ordinary elastic deformation, macroscopic stress on the observed increase over time reduce the phenomenon, with the extension of observation time, stress relaxation and constant strain developed to balance the stress values, stress relaxation will cease to stabilize.