van der Kooij Hanne M, Dussi Simone, van de Kerkhof Gea T, Frijns Raoul A M, van der Gucht Jasper, Sprakel Joris
Physical Chemistry and Soft Matter, Wageningen University & Research, Stippeneng 4, 6708 WE Wageningen, Netherlands.
Dutch Polymer Institute, P.O. Box 902, 5600 AX Eindhoven, Netherlands.
Sci Adv. 2018 May 4;4(5):eaar1926. doi: 10.1126/sciadv.aar1926. eCollection 2018 May.
Stresses well below the critical fracture stress can lead to highly unpredictable delayed fracture after a long period of seemingly quiescent stability. Delayed fracture is a major threat to the lifetime of materials, and its unpredictability makes it difficult to prevent. This is exacerbated by the lack of consensus on the microscopic mechanisms at its origin because unambiguous experimental proof of these mechanisms remains absent. We present an experimental approach to measure, with high spatial and temporal resolution, the local deformations that precipitate crack nucleation. We apply this method to study delayed fracture in an elastomer and find that a delocalized zone of very small strains emerges as a consequence of strongly localized damage processes. This prefracture deformation zone grows exponentially in space and time, ultimately culminating in the nucleation of a crack and failure of the material as a whole. Our results paint a microscopic picture of the elusive origins of delayed fracture and open the way to detect damage well before it manifests macroscopically.
远低于临界断裂应力的应力在经过一段看似静止的长时间稳定期后，可能会导致高度不可预测的延迟断裂。延迟断裂对材料的寿命构成重大威胁，其不可预测性使得预防变得困难。由于对其起源的微观机制缺乏共识，这一情况更加恶化，因为这些机制仍缺乏明确的实验证据。我们提出了一种实验方法，以高空间和时间分辨率测量引发裂纹成核的局部变形。我们应用这种方法研究弹性体中的延迟断裂，发现由于强烈局部化的损伤过程，会出现一个非常小应变的非局部化区域。这个预断裂变形区在空间和时间上呈指数增长，最终导致裂纹成核和材料整体失效。我们的结果描绘了延迟断裂难以捉摸的起源的微观图景，并为在损伤宏观显现之前很久就检测到它开辟了道路。
