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

IIE：探索不同热膨胀产生的剪切应力对 CLT 板分层的影响

• 批准号: 2734870
• 金额: --
• 依托单位: University of Edinburgh
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2734870
• 关键词: IIE; Exploring; impact; shear; stresses

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.

交叉层压木材（CLT）是一种工程质量木材建筑材料，由木材层用粘合剂粘合在一起形成。暴露的工程质量木材产品（如CLT）的使用由于其高度理想的、美学的和可持续的品质而继续增加。由于燃料负荷的增加以及CLT在车厢内容物燃烧结束后继续燃烧的能力，暴露的CLT的使用增加对车厢的防火安全提出了挑战。为了保持木材的燃烧，热量必须从热燃烧气体传递到木材内的热解区，将木材热解成挥发性气体。如果传递到热解区的热量不足，则热解速率将降低，并且火将衰减并自动熄灭。如果暴露的木材自动熄灭，则在车厢内的内容物完成燃烧后，车厢将被烧毁。自动熄灭的关键部分是在热燃烧气体和原始木材之间形成厚的焦炭层，该焦炭层提供热阻。然而，如果CLT层之间的结合失败，CLT将分层。这会去除烧焦的外层，并暴露出下面的层，从而提高燃烧速度，延迟或防止自动熄灭。粘合强度被认为是板材抗分层性的主要因素。然而，我假设，在胶层之间的剪切应力引起的层之间的热膨胀差的层也起着关键的作用，在分层的CLT。为了验证这一假设，我提出了一系列的实验来比较样品之间的分层的大小与不同的热膨胀之间的差异。为了引起一系列的热膨胀差异，我建议测试一系列的CLT面板，其中每层的晶粒之间的角度在0度（平行）和90度（垂直）之间变化。这将在产生一系列的剪切应力，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，我建议结合一系列的数据源。首先，质量损失率和火灾威力将是数据收集的重点。我假设在分层发生后将观察到质量损失率和功率的增加。质量损失率将通过质量平衡测量，火灾的威力将通过分析抽油烟机抽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。