US Army Research Laboratory, Maryland City, MD, 21005, USA.
Department of Chemistry, Duke University, 124 Science Drive, Durham, NC, 27708-0346, USA.
Macromol Rapid Commun. 2021 Jan;42(1):e2000449. doi: 10.1002/marc.202000449. Epub 2020 Oct 21.
The molecular processes that accompany dynamic mechanical response to large deformations at high strain rate (≈1000 s or higher) underlie the early stages of damage in materials, but understanding of material response in this regime is typically limited to macroscopic constitutive equations. Here, spiropyran mechanophores are embedded in very short, stress-bearing strands in silicone elastomers, and their mechanochromic response to uniaxial compression is explored in a Split Hopkinson Pressure (or Kolsky) Bar. At strain rates of 1000 s , the onset of mechanochromism occurs at lower strains, but higher stresses, than in the same materials under quasi-static loading. Similar to quasi-static loading, however, a negligible effect of mechanophore structure on the critical strain for colorimetric onset is observed. The results suggest that nonequilibrium, inhomogeneous local tension distributions in the elastomers lead to greater stress in individual strands than at the same strains under equilibrium loading, but that within the regions of force concentration, mechanochromic onset is determined primarily by a limiting local strain threshold.
伴随大应变速率（≈1000s 或更高）下的动态力学响应的分子过程是材料早期损伤的基础，但在该区域内对材料响应的理解通常仅限于宏观本构方程。在这里，螺吡喃机械敏感剂嵌入在硅酮弹性体中的非常短的受力链段中，并在分离式 Hopkinson 压杆（或 Kolsky 杆）中探索它们在单向压缩下的压致变色响应。在 1000s 的应变速率下，机械变色的开始发生在较低的应变，但更高的应力，比在准静态加载下的相同材料中。然而，类似于准静态加载，机械敏感剂结构对比色起始临界应变的影响可以忽略不计。结果表明，弹性体中不平衡、不均匀的局部拉伸分布导致单个链段中的应力高于在平衡加载下相同应变时的应力，但在力集中区域内，压致变色的开始主要取决于一个限制的局部应变阈值。
