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) 是一种工程大体积木材建筑材料，由用粘合剂粘合在一起的多层木材组成。由于其非常理想的、美观的和可持续的品质，诸如 CLT 等裸露工程木材产品的使用持续增加。在考虑隔间的消防安全时，由于燃料负载的增加以及隔间内容物燃烧完毕后 CLT 继续燃烧的能力，暴露的 CLT 的使用增加带来了挑战。为了维持木材的燃烧，热量必须从热燃烧气体传递到木材内的热解区，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，则热解速率将降低，火将衰减并自动熄灭。如果暴露的木材自动熄灭，则隔室中的内容物燃烧完毕后，隔室将烧毁。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厚的炭层，从而提供热阻。然而，如果 CLT 层之间的粘合失效，CLT 将分层。这会去除烧焦的外层并暴露下面的层，导致燃烧速率增加并延迟或防止自动熄灭。粘合强度已被确定为面板抗分层的主要因素。然而，我假设层间热膨胀差异引起的层间胶层剪切应力在 CLT 分层中也起着关键作用。为了验证这一假设，我提出了一系列实验来比较分层的程度每层之间热膨胀差异不同的样品之间。为了引起一系列热膨胀差异，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）和 90 度（垂直）之间变化。这将产生一定范围的剪切应力，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。为了量化分层程度，我建议组合一系列数据来源。主要是质量损失率和火灾威力将是数据收集的重点。我假设发生分层后会观察到质量损失率和功率的增加。将通过质量平衡测量质量损失率，并通过分析抽油烟机抽出的烟雾成分来计算火力。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。