Laser Ablation of Machined Wood Surfaces. 1. Effect on End-Grain Gluing of Pine (Pinus silvestris L.) and Spruce (Picea abies Karst.)

Abstract

Summary This report describes two attempts to test the effect of removing the layer of damaged cells—the mechanical weak boundary layer. In both trials, the wood has been laser ablated using different types of lasers with different wavelengths. The goal has been to determine whether the glue joint strength is influenced by the mechanical weak boundary layer and to show how the laser wavelength affects the glue joint strength. The statistical evaluation of the results shows however no great differences between glue joints made of ablated and glue joints made of unablated surfaces. Nor are there any real differences between the different lasers and different wavelengths. This may be because there are indeed no differences between ablated and unablated surfaces, in terms of a mechanical weak boundary layer, but it may also be due to cracks which occurred in the wood specimens, and it is also possible that the glue itself was too weak. An ESEM (Environmental Scanning Electron Microscope)—analysis showed that fracture occurred primarily in the glueline and not in the boundary layer. In addition to the ESEM analysis and the statistical evaluation, a theoretical FEM (Finite Element Method)—analysis has been used to explain the crack initiation in the second trial.