Understanding the Effect of Lamination Thickness Variations on Bond Integrity + Panel Properties in CLT
Research Team:
Muszynski, Nairn
Graduate Research Assistants:
Samson Idoghor
Ashley McCann (undergrad)
Project Duration:
2023-2026
2023-2026
Facilities:
Richardson Hall
Richardson Hall
Project Goal Statement
Previous research has shown that CLT panels can include areas with a range of adhesive bond strengths, including zones of delamination, within a single panel. This study aims to assess how much of the variation in adhesive bond strength is due to variation in the thickness of individual laminations within the panel layups.
Introduction/Background
Cross-laminated timber panels are typically made from commercially produced dimension lumber that is pressed and bonded together with adhesive. An important factor dictating how strong the eventual panel is, and what it can be used for, is how well the adhesive bonds each piece of lumber within the panel. However, the thickness of dimension lumber can vary from board to board, depending on manufacturing and sorting tolerances, so the pressure used to solidify the adhesive bond can vary within the panel. This research is intended to determine how this inconsistency can affect the structure and strength of the bonding throughout the panel.
Research Methods
To assess the effect of lam thickness variation, the researchers prepared small-scale, dry 3-ply and 5-ply CLT layups samples with known thickness variances between individual boards. They used digital image correlation to assess local vertical displacement and pressure transfer distribution within these samples. These measurements are compared to elastic model of the small-scale layup samples to inform necessary refinements.
Key Findings
The first task for the project was to see how relevant the digital image correlation was to this type of analysis, but early findings indicated that the digital image correlation method is appropriate to identify pressure transfer throughout CLT layups. From the image correlations, the researchers were able to calculate the strain of individual boards and local contact stress between layers under pressure. They are developing numerical models predicting pressure transfer between the laminations in CLT based on these findings.
They have also found that samples made with tighter control of board thickness exhibited better pressure transfer, which is expected to extend to stronger adhesive bonds in future tests.
Future Work
The next stage of work involves fabricating glued cross laminated samples at multiple scales, still with known thickness variations, and subjecting them to similar tests as the dry samples. The samples will then be dissected into specimens suitable for standard bond integrity tests. A set of pilot-plant scale cross laminated specimens with known thickness variations will be subjected to destructive mechanical tests to assess the correlations of known weak bond areas with the actual failure mode propagation.
Publications & Presentations
Idoghor, S. M., Muszynski, L., & Rezaei, F. (2025). Understanding the effect of lamination thickness variations on bond integrity in cross laminated timber (CLT). World Conference on Timber Engineering 2025, 311–317. https://doi.org/10.52202/080513-0039
Muszynski, L. (2025, October 24). Understanding the Effects of Lamination Thickness Variations on Bond Integrity and CLT Properties. 2025 Mass Timber Research & Design Innovation Symposium, Corvallis, OR. https://www.youtube.com/watch?v=iTbqbbSpAEc
Funding & Acknowledgements
TDI/ USDA ARS