Abstract

A persistent issue in adhesively bonded wood-based composites is their moisture durability. A key question, therefore, is: what is the best approach to assessing moisture durability of wood composites? Previous work has focused on failure initiation (e.g. internal bond strength) and therefore, could not consider effects of moisture on subsequent damage propagation. This research addressed that knowledge gap by using crack propagation fracture experiments to study moisture effects on medium-density fiberboard (MDF), oriented strand board (OSB), and particleboard (PB). Fracture toughness vs. crack growth curves (i.e. material R curves) were measured for MDF, OSB, and PB after immersing them in water for immersion times up to one week. Experiments were done immediately after immersion to record crack propagation in states of increasing moisture content. Trends in experimental results could be characterized by a three-point model for MDF and PB or a linear model for OSB. Experiments and modeling showed that all composites degraded in both initiation toughness and in their ability to inhibit crack growth by fiber bridging mechanisms. Summary plots compare how R curves for MDF, OSB, and PB changed from control conditions to water saturation conditions and compare their moisture degradation rates.

摘要

粘合木基复合材料的一个长期存在的问题是它们的耐湿性。因此，一个关键问题是：评估木质复合材料耐湿性的最佳方法是什么？以前的工作主要集中在故障萌生（例如内部结合强度）上，因此无法考虑水分对后续损坏传播的影响。本研究通过使用裂纹扩展断裂实验来研究水分对中密度纤维板 (MDF)、定向刨花板 (OSB) 和刨花板 (PB) 的影响，从而解决了这一知识缺口。断裂韧性对比 裂纹扩展曲线（即材料R曲线）在将它们浸入水中长达一周后测量 MDF、OSB 和 PB。浸泡后立即进行实验，以记录水分含量增加状态下的裂纹扩展。实验结果的趋势可以用 MDF 和 PB 的三点模型或 OSB 的线性模型来表征。实验和建模表明，所有复合材料的初始韧性和通过纤维桥接机制抑制裂纹扩展的能力都会降低。汇总图比较了MDF、OSB 和 PB 的R曲线如何从控制条件变为水饱和条件，并比较了它们的水分降解率。