Thesis Topic

Innovative industrial transformation of oak into technical components for structural and non-structural use in construction

Research fields

This CIFRE PhD thesis is the result of a partnership between the LABOMAP (Laboratoire des Matériaux et des Procédés de Cluny) and the Ducerf Group, a Charolais-based sawmill that has specialized in oak for over 140 years.

The current landscape is defined by the new RE2020 regulations, which strongly encourage architects to adopt bio-sourced materials. As a result, the demand for structural timber is skyrocketing. However, softwood resources are already heavily exploited. The solution lies in the strategic use of hardwoods, particularly oak. While oak represents a quarter of the standing timber volume in French forests, it accounts for only 16% of the annual harvest. The challenge is significant: utilizing the available resource means processing "secondary quality" timber—wood that is often smaller, knottier, and more twisted.

How can we transform this resource into high-performance products? Manufacturing a reconstituted oak beam requires a specific approach. Unlike softwoods, defects must be purged more intensively. This involves cutting the timber into much shorter elements—2 to 10 times smaller than those used for softwoods. The process then consists of finger-jointing these short sections (known as "courçons") to form laminations, which are then glued together to produce panels, scantlings, glulam (glued laminated timber), or CLT.
Today, the glulam industry is dominated by softwoods, supported by tailored standards and standardized, automated production lines. The goal of my research is to bridge this technical and regulatory gap for oak. This involves adding value through optimized machining processes, finer mechanical grading, and, above all, a deep understanding of the mechanical behavior of these complex assemblies.

To better grade this heterogeneous oak, it is essential to characterize it more accurately upstream. We use industrial scanners that combine color, laser, and density sensors. However, the key to predicting mechanical performance (strength and stiffness) lies in measuring the grain orientation.
To measure this critical characteristic, we utilize dot laser technology. The principle is physical: by observing how the laser light scatters on the wood surface (the Tracheid effect), we can deduce the local orientation of the fiber. This information is invaluable; it allows us not only to predict mechanical properties but also to define precise machining criteria to limit finger-jointing defects, such as tear-outs or cracking during the gluing of the joints.
The final phase of my thesis focuses on material optimization within the reconstituted beam itself. The guiding principle is to understand the influence of the geometry of small wood elements and, crucially, their mechanical variability. By mastering these parameters, we can develop intelligent placement strategies—for instance, positioning the highest-performing elements where the stresses are greatest. The ultimate goal is to optimize the assembly to increase the overall mechanical properties of the beam while utilizing a heterogeneous raw material.

 

Doctoral Advisors :

• Guillaume Pot, director
• Joffrey Viguier, supervisor
• Thibault Chastagnier (ext. DUCERF Groupe)

Partners :

DUCERF Groupe (Les Bois Profilés)

Funding :

Private, CIFRE ; Public Ademe

Start

17th March 2025

Expected end

31th March 2028

Distinctions and awards

Winner of the Alban Tixier Prize 2025