形变导致的蜘蛛大壶状腺丝力学行为的记忆与变异

Strain Induced Memory and Variation in the Tensile Behavior and Property of Spider Major Ampullate Gland Silk

纤维材料的形变与力学行为之间的关系密切。在自然条件下蛛丝会被反复拉伸,但其被拉伸后的力学行为被搁置的时间与形变效应鲜见报道。为此,本工作采用METS电子万能试验机测试研究了反复定伸长拉伸松弛后的间隔时间与形变对蜘蛛大壶状腺丝的力学行为的影响。结果表明,不论天然的还是经水最大限度超收缩干燥后的大壶状腺丝被定伸长反复拉伸过屈服点和屈服区甚至拉至加强区的力学行为曲线都能很好地重叠;经长时间(≥20 min)间隔后也只需一次拉伸就能不受拉伸历史的影响重现之前的力学行为,具有良好的纵向拉伸的形状与力学行为记忆。通过增加应变值对蜘蛛大壶状腺丝进行一系列的加载-卸载循环试验,并分析这些循环中其应力-应变曲线,计算每个循环中它的弹性模量、屈服应力、吸收和耗散的能量,以评估这些力学性能参数随循环增加的微观进化与演变。研究表明,蜘蛛丝力学行为的记忆与变异可以通过不可逆和可逆两种变形微观机制及其组合来解释,其中材料的粘弹性起主导作用。这些研究对人们进行新型功能纤维材料的仿生设计具有重要的指导意义。

There is a close relationship between the shape change of fiber materials and their mechanical properties.In the nature,spider silk is repeatedly stretched during performing biological functions,but the shape strain and time effect on structure and tensile behavior properties after stretching by constant elongation is rarely reported.Therefore,the effects of interval and deformation on the mechanical behavior and properties of spider major ampullate gland silk(abb.Mas)were investigated via METS electronic universal testing machine.The results show that the tensile behavior curves of spider Mas whether natural or dried by maximum supercontraction overlap well after stretched over the yield point and even over yield region to the hardening region,the previous mechanical behavior can be reproduced without the influence of the previous stretching history only via being stretched once after long interval(≥20 min)and that spider Mas presents a good shape and mechanical behavior memory of longitudinal stretching.The elastic modulus,yields stress,energy absorbed and energy dissipated in each cycle were computed by performing a series of loading-unloading tests at increasing values of strain and subsequent analysis of the true stress-true strain curves obtained from these cycles in order to evaluate the microevolution of these mechanical parameters with the cycles.It was found that this variation in the mechanical performance of spider silk can be accounted through a combination of irreversible and reversible deformation micromechanisms in which the viscoelasticity of the material plays a leading role.These findings and a new field of research may be helpful to guide the biomimetic design of novel fiber materials.