Quality Aspects of Sliced Oak Lamellae in Development of Engineered Wood Flooring

Sammanfattning: Valuable hardwoods, such as oak, although renewable, present limitations in product realisation in terms of their cost and availability, often attributed to production waste and sub-optimal product design factors. The slicing technique facilitates the production of thin wood lamellae, minimising waste and ensuring optimal material conversion. This study explores the application of sliced lamellae in engineered wood flooring, focusing on quality aspects and control. The performance of sliced lamella-based engineered flooring was compared with traditional parquet flooring elements through standard performance tests, which scrutinised the characteristics of appearance, delamination, and dimensional stability under varying climate conditions. The climate tests highlighted the significant flaws of sliced lamella-based flooring elements: surface-checking. Despite diminished delamination resistance, the dimensional stability excelled for the sliced lamella–based flooring. Primary observations indicated that the study’s constraints are related to a lack of surface-checking quantitative measurements and an absence of sliced lamellae quality control. The subsequent research characterised sliced lamellae quality using the properties of slicing checks and mechanical performance perpendicular to the grain. Slicing thickness is considered a critical variable in both lamella-processing and product performance factors. A detection method using image processing and analysis was developed to characterise slicing check occurrence. The method considered slicing check characteristics, check depth ratio and check frequency. The results of the slicing check inspection indicated a decrease in the check depth ratio and check frequency with increased slicing thickness. Mechanical testing revealed that oak sliced lamellae exhibited considerably lower strength and stiffness compared to sawn solid wood. The slicing check depth ratio was found to be negatively correlated with the sliced lamellae’s tensile strength and strain at break.A novel method for detecting surface-checking was developed and employed. It utilised digital image correlation and analysis of full-field strain data. The novelty of the method is advancing the surface-checking quality index that considers the check length over the inspected area. This method was applied to engineered wood flooring to evaluate the impacts of core type and sliced lamellae nominal thickness on surface-checking results. Significant interactions between the studied variables were found, indicating that the surface-checking tendency could not be attributed to a single factor. Especially notable was the reduced surface-checking outcome in standard core specimens paired with a low lamella thickness. This thesis offers new insights into using sliced lamella in engineered wood flooring realisation. Although the assumed sliced lamellae quality aspects, slicing check depth and check frequency, were shown not to impact surface-checking, the significant interactions between engineered wood flooring construction parameters highlight the need for a broader perspective concerning this subject. Future research should focus on further refining the sliced lamellae quality analysis and developing new methods that consider other quality aspects.