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

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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.