A cellular finite element model for the cutting of softwood across the grain

In this paper, the mechanics of cutting wood across the grain are reexamined. A hybrid cellular/macroscopic finite element model of wood was developed to simulate the effects of cell collapse during the cutting process. Initially, the model was used to simulate the compression test across the grain. The linear elastic and cell collapse behaviours of the compression tests were sucessfully simulated. The model was then used to simulate two orthogonal cutting processes, wedge cutting and chip-forming cutting. The cellular/macroscopic model revealed that during the cutting process, the load compresses the wood until cell wall buckling occurs ahead of the tool. The collapse of the supporting cell wall results in a localized tensile stress in the longitudinal direction of the cell at the tip of the tool. It is postulated that this longitudinal tensile stress would lead to microfibrils being pulled out of the matrix and hence to failure of the cell wall. Therefore, the cellular/macroscopic model has been used to explain the mechanics of severing wood fibres during the process of cutting wood across the grain.