FRACTURE ENERGY DURING CLEAVING OF PINUS-RADIATA

Cleaving or riving of wood is an efficient method of cutting, but is u sually restricted to veneer cutting or low-quality products such as fe nce-palings, due to the poor surface finish that occurs on thicker off cuts. If the release of strain energy during fracture could be control led then the surface finish and dimensional tolerance of cleaved wood products would be improved. A series of experiments were carried out o n Pinus radiata to split it in the r.l. direction by mode 1 (crack ope ning) using both single cantilever beam bending and cleaving by a wedg e. The offcut thickness, and the blade thickness and grinding angle we re varied and the fracture, plastic and friction energies measured. Wh en the offcut was 15 mm or greater the fracture surface energy from bo th types of cutting were similar and the friction and plastic energies were much larger; all energies were unaffected by blade dimensions. T he mode of fracture of the 5 mm offcut was not simple crack opening an d consequently the surface energy was a more significant proportion of the total energy, which is why smaller thickness offcuts may be cleav ed in a controlled manner.