IIE: Exploring the impact of shear stresses from differential thermal expansion on the delamination of CLT panels

交错层压木材(CLT)是一种由多层木材用胶粘剂粘合而成的工程化的大量木材建筑材料。露天的工程木材产品，如CLT，由于其高度可取、美观和可持续的品质，继续受到越来越多的欢迎。当考虑到由于燃料负荷的增加以及CLT在舱室内容物完成燃烧后继续燃烧的能力而导致的舱室的火灾安全时，暴露的CLT的使用的增加带来了挑战。为了保持木材的燃烧，必须将热量从热的燃烧气体转移到木材内的热解区，以将木材热解成挥发性气体。如果传递到热解区的热量不足，那么热解率就会降低，火就会衰减并自动熄灭。如果裸露的木材自动熄灭，车厢内的物品燃烧完毕后，车厢就会烧毁。自动熄火的一个关键部分是在热燃烧气体和原始木材之间形成一层厚厚的炭层，这提供了耐热性。然而，如果CLT各层之间的结合失败，CLT将剥离。这会去除烧焦的外层，暴露下面的层，导致燃速增加，并延缓或防止自动消光。粘合强度已被认为是面板抗分层的主要因素。然而，我假设，层与层之间的差热膨胀引起的层间粘结线上的剪应力也在CLT的分层中起着关键作用。为了验证这一假设，我提出了一系列实验来比较不同层之间热膨胀差异的样品之间的分层程度。为了引起一定范围的热膨胀差异，我建议测试一系列CLT面板，其中每层颗粒之间的角度在0度(平行)到90度(垂直)之间变化。这将产生一定范围的剪应力，因为在木材中，平行于纹理的热膨胀系数比垂直于纹理的热膨胀系数小一个数量级。为了量化分层的程度，我建议结合一系列数据源。主要的质量损失率和火灾的威力将是数据收集的重点。我假设在分层发生后会观察到质量损失率和功率的增加。质量损失率将通过质量天平测量，火灾功率将通过分析抽油烟机排出的烟雾的成分来计算。我还建议对实验进行录像，并使用嵌入式热电偶记录CLT面板的内部温度，以帮助进一步证明我的发现是正确的。

Cross-Laminated Timber (CLT) is an engineered mass timber construction material formed of layers of timber bonded together with an adhesive. The use of exposed engineered mass timber products such as CLT has continued to increase in popularity due to their highly desirable, aesthetic, and sustainable qualities. The increased use of exposed CLT poses a challenge when considering the fire safety of compartments due to the increase in fuel load and the capability for the CLT to continue to burn after the contents of the compartment have finished burning.To maintain the burning of timber, heat must be transferred from the hot combustion gases to the pyrolysis zone within the timber to pyrolyze the timber into a volatile gas. If the heat transferred to the pyrolysis zone is insufficient then the rate of pyrolysis will decrease, and the fire will decay and auto-extinguish. If the exposed timber auto extinguishes, the compartment will burnout after the contents of the compartment have finished burning.A key part of auto extinction is the formation a thick char layer between the hot combustion gases and the virgin timber, which provides thermal resistance. However, if the bond between the layers of CLT fails, the CLT will delaminate. This removes the charred outer layer and exposes the layer beneath, leading to an increased burning rate and delays or prevents auto extinction.The adhesive strength has been identified as a major contributor to a panel's resistance to delamination. However, I hypothesise that the shear stresses in the glue line between layers induced by differential thermal expansion of the layers also plays a key role in the delamination of CLT.To test this hypothesis, I propose a series of experiments to compare the magnitude of delamination between samples with varying differences in thermal expansion between each layer. To induce a range of thermal expansion differences, I propose testing a range of CLT panels in which the angle between the grain of each layer is varied between 0degrees (parallel) and 90degrees (perpendicular). This will work in producing a range of shear stress as in wood the coefficient of thermal expansion parallel to the grain is an order of magnitude smaller than perpendicular to the grain.To quantify the extent of delamination, I propose the combination of a range of data sources. Primarily the mass loss rate and the power of the fire will be focus of the data collection. I hypothesise that an increase in mass loss rate and power will be observed after delamination occurs. The mass loss rate will be measured through a mass balance and the power of the fire will be calculated by analysing the composition of the smoke extracted by the extraction hood. I also propose that the experiment is videoed and the internal temperatures of the CLT panel recorded using embedded thermocouple to aid in further justifying my findings.