热老化弹性体中的不变断裂粘聚长度
Invariant fractocohesive length in thermally aged elastomers
AI总结：
研究发现热老化过程中断裂粘聚长度保持不变，为预测老化弹性体断裂韧性提供了新方法。
摘要：
断裂粘聚长度——断裂韧性与断裂功的比值——提供了一个材料特定的长度尺度，用于表征原始弹性体的尺寸依赖性断裂行为。然而，其在热老化材料中的相关性仍不清楚，因为在热老化材料中，韧性和断裂功都会显著下降。在这里，我们证明了尽管存在严重的热脆化，断裂粘聚长度在热老化过程中保持不变，与温度或持续时间无关。我们对两种弹性体系统（苯乙烯丁二烯橡胶和硅橡胶）在多个老化温度和长达八周的老化时间下进行了实验验证。这一发现填补了老化聚合物断裂力学中的关键空白：虽然断裂功的演变可以从已建立的本构模型中预测，该模型跟踪网络变化（交联密度和链断裂），但断裂韧性的发展缺乏预测框架。断裂粘聚长度的不变性使能够从预测的断裂功直接计算断裂韧性，消除了对老化弹性体进行大量断裂测试的需求，并为计算断裂预测提供了关键的缺失链接。
英文摘要：
The fractocohesive length - the ratio between fracture toughness and work-to-fracture - provides a material-specific length scale that characterizes the size-dependent fracture behavior of pristine elastomers. However, its relevance to thermally aged materials, where both toughness and work of fracture degrade dramatically, remains unexplored. Here, we demonstrate that despite severe thermal embrittlement, the fractocohesive length remains invariant throughout thermal aging, independent of temperature or duration. We verify this invariance experimentally for two elastomer systems (Styrene Butadiene Rubber and Silicone Rubber) at multiple aging temperatures for aging times up to eight weeks. This finding bridges a critical gap in fracture mechanics of aged polymers: while the evolution of work-to-fracture can be predicted from well-established constitutive models that track network changes (crosslink density and chain scission), the evolution of fracture toughness has lacked predictive frameworks. The invariance of fractocohesive length enables direct calculation of fracture toughness at any aging state from the predicted work of fracture, eliminating the need for extensive fracture testing on aged elastomers and providing a crucial missing link for computational fracture predictions in aged elastomeric components.
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