Characterising pull-out of thermoplastic expander dowels from particleboard through 4D X-ray microtomography

Abstract

This thesis was conducted in collaboration with IKEA Components AB and aims to assess the potential of X-ray computed microtomography (μCT) and four-dimensional (4D) μCT for use in product development. The thesis examines the interaction between particleboard and thermoplastic expander dowels during pull-out testing.

An experimental methodology was developed combining mechanical pull-out testing with μCT imaging. Specimens were subjected to different testing conditions, including continuous and incremental pull-out, using different machinery, and the influence of these conditions on the results was analysed. In addition, a subset of specimens was prepared to investigate relaxation effects. The interaction between the dowel and the material was captured by μCT imaging of the specimens both before and after ex-situ loading and, for some specimens, multiple times during in-situ loading. The internal deformation was analysed using digital volume correlation (DVC) applied to the three-dimensional μCT image volumes. This enables the mapping of the three-dimensional displacement and strain tensor fields.

The results show that the pull-out behaviour is strongly influenced by the heterogeneous structure of the particleboard. The mechanical tests for different samples showed similar global responses, but with variations arising from differences between specimens and testing setups. The in-situ tests, and associated μCT and DVC, provided insight into the internal deformation. The results from the three-dimensional analysis showed that the material did not deform uniformly. Instead, most of the movement and damage were concentrated in a cone-shaped region surrounding the dowel. The analysis also showed that the dowel teeth play a key role in resisting pull-out and transferring load to the surrounding material. In addition, most of the material returned to its original shape after the dowel was removed, while small areas around the dowel teeth remained permanently damaged. The thesis demonstrates that μCT and DVC can be used to relate global pull-out behaviour to internal structure and deformation mechanisms, making them useful tools for understanding product performance and supporting future development.

Popular Abstract

What keeps your furniture together and how?

What makes a piece of furniture feel sturdy and reliable? Surprisingly, the answer may depend on a small plastic component hidden inside the structure. Although rarely seen, this tiny connector plays an important role in keeping furniture together. In this thesis, X-ray imaging was used to reveal what happens inside such a connection as it is pulled out from the furniture component, as might happen under excessive loading or disassembly during house-moving.

Many furniture products are assembled using small connectors that become almost invisible once the furniture is put together. One example is the thermoplastic expander dowel. It works by first inserting the dowel into a furniture component and then pushing a pin into it, causing the dowel to expand. Small teeth on the surface of the dowel press into the surrounding material, helping to hold the furniture parts together.

Traditional mechanical testing can measure how much force is required to pull the dowel out of the furniture component. However, it cannot reveal why the connection behaves as it does, since the damage and deformation occur inside the particleboard, hidden from view.

To look inside the furniture connection without needing to destroy it, X-ray computed microtomography (μCT) was used. Similar to a medical CT scan, but at a much smaller scale, μCT provides three-dimensional (3D) images of the dowel and the particleboard around it. The images were further analysed using digital volume correlation (DVC), a method that compares 3D scans taken at different loading stages. This made it possible to track tiny movements and changes within the material. By combining these measurements with the mechanical testing, the response could be linked to local deformation inside the board.

The results from the 3D analysis showed that the material did not deform uniformly. Instead, most of the movement and damage were concentrated in a cone-shaped region surrounding the dowel. The analysis further revealed that the dowel teeth play a key role in resisting pull-out and transferring load to the surrounding material. In addition, most of the material returned to its original shape after the dowel was removed, although small regions around the dowel teeth remained permanently damaged.

Together, μCT and DVC provide insights that cannot be obtained from mechanical testing alone. By revealing how damage develops inside furniture connections, these techniques help explain why some connections fail and how small design details influence strength and reliability. This knowledge can support the development of stronger, more durable furniture in the future.

• author: McAuley Skriver, Isabella
• supervisor: Stephen Hall
• organization: Department of Construction Sciences; Solid Mechanics
• course: FHLM01 20261
• year: 2026
• type: H3 - Professional qualifications (4 Years - )
• subject: Technology and Engineering
• keywords: x-ray computed microtomography, ex-situ pull-out, in-situ pull-out, digital volume correlation, particleboard, thermoplastic expander dowel
• report number: TFHF-5273
• other publication id: LUTFD2/TFHF-26/5273-SE(1-78)
• language: English
• id: 9243758
• date added to LUP: 2026-06-25 15:18:32
• date last changed: 2026-06-25 15:18:32