Machining-Induced Subsurface Damage of Wood
As wood is machined, characteristic chip formation mechanisms take place while the workpiece is exposed to severe, but very localized, forces. The result is deformation of the material, concentrated in a narrow zone usually called the shear plane or shear zone. This widely studied deformation/fracture process is perhaps best described as one of tearing. In wood, however, some deformations take place in layers located underneath the freshly generated surface by those forces applied during machining. Although this subsurface deformation has been observed in metals, wood is more susceptible to damage under the stresses caused by machining loads, mainly because of structural heterogeneity and varying material properties. The permanent or semi-permanent compression in woods manifests itself mainly by cell deformation, void crushing, or layers of different density invading one another. This deformation will, to some degree, react with certain applications (like water-based finishes and high ambient humidity among others) and spring back, thus adversely affecting the final surface quality. The result can be fiber-pop, fuzzed grain, and undesired variations in the outer surface of the part. This paper presents the results of a microscopy study regarding the subsurface crushing phenomenon. A taxonomy, with the types and extent of this phenomenon, is also proposed.
Forest Products Journal
Carrano, Andres L.; Taylor, James B.; and Lemaster, Richard L., "Machining-Induced Subsurface Damage of Wood" (2004). Engineering Faculty Publications. 247.
Carrano, A.L., Taylor, J.B., and Lemaster, R.L. (2004). Machining induced subsurface damage of wood. Forest Products Journal. 54(1):85-91.