数字散斑分析技术在定向刨花板水分吸放循环中的应用

Effect of water on the mechanical performance of OSB in compression tests

【目的】旨在深入研究水分对定向刨花板(oriented strand board, OSB)力学性能的影响规律。【方法】选取13和19 mm共2种厚度的OSB为研究对象,调整试件含水率及对试件进行吸放水循环处理,使用万能力学试验机压缩试件,同步使用数字散斑相关分析技术记录试件的面内应变分布。【结果】含水率和吸放水循环次数增加,均会增加试件厚度和压缩变形。压缩载荷作用下,压缩和剪切应变均多始于OSB试件厚度方向上的中心区域。吸放水循环会释放OSB表层内应力,造成试件表层区域结构疏松和载荷作用下表层压缩应变集中。含水率为20%时,试件压缩变形增加70%,且面内应变分布规律改变,具体表现为试件中心区域应变集中现象弱化。吸放水循环使试件面内应变增加,但对应变分布规律影响较小。8次吸放水循环后,试件压缩变形增加约30%。【结论】含水率和吸放水循环次数的增加均使OSB的抗压强度下降和厚度方向上的应变增加,含水率增加会造成应变分布改变但吸放水循环对应变分布影响不明显。

[Objective] Oriented strand board(OSB) is an environmental-and eco-friendly material produced with renewable, mainly fresh wood from logs with either small or large diameter logs. Composed of crossoriented layers consisting of thin and rectangular wooden flakes or strands that are compressed and bonded together with synthetic resins, it is an important engineered wood product widely applied in load bearing situations and its mechanical performance is largely dependent on the moisture content(MC) and water sorption/desorption. Therefore, with an investigation of the compressive strength(CS) of samples at different MC and water sorption/desorption cycles, this study is aimed to research the effect of water on mechanical performances of OSB. [Method] With samples selected from two types of OSB panels with different thicknesses, conditioned to three different MCs and treated with multiple water sorption/desorption cycles,supervision was conducted of the dimensional changes, CS and strain distribution of samples were monitored.Then the CS was measured using an Instron universal testing machine with the strain distribution recorded using digital image correlation(DIC) simultaneously. [Result](1) An increase in both MC and water sorption/desorption cycle could lead to an increase in thickness and compressive deformation;(2) The CS of the samples was significantly decreased when they were conditioned with a relative humidity of 95% and a MC of approximately 20%;(3) High MC could reduce the final thickness of OSB after compressing whereas water sorption/desorption cycles could slightly decrease the final thickness of OSB after compressing;(4) High MC and multiple water sorption/desorption cycles were able to change the relationship between CS and displacement from two domains linear to almost linear which attributed to the disappearance of the samples’ plastic deformation domain;(5) High MC can soften wood strands and enlarge internal voids, which could lead to strain increase and the change of strain distribution profile while water sorption/desorption cycles degraded the internal structure of samples and(6) Water sorption/desorption cycles might cause compression strain accumulation in surface layers. [Conclusion] Water affects the CS of OSB in various aspects including the softening of wood strands, enlargement of voids among wood strands, diminishing of trapped stress from hotpressing with different MCs. Such findings will help with the generation of effective manufacturing strategies that aim at good mechanical performance of OSB at different water conditions as well as optimizing the application methods and extending the application fields of OSB. [Ch, 7 fig. 1 tab. 23 ref.]