Simulation of green wood milling with discrete element method

Abstract

During the primary transformation in wood industry, logs are faced with conical rough milling cutters commonly named slabber or canter heads. Chips produced consist of raw materials for pulp paper and particleboard industries. The process efficiency of these industries partly comes from particle size distribution. However, chips formation is greatly dependent on milling conditions and material variability. Numerical simulation of chip fragmentation can allow some useful chip thickness prediction. In this complex situation in wood cutting, the utilization of the Discrete Element Method (DEM) is relevant. In this method, solids are modeled with spherical discrete elements linked by cohesive bonds. However the Discrete Element Method requires a previous calibration step with simple mechanical loading. For example the nature and the mechanical properties of the cohesive bonds must be determined. After an analysis of the different mechanical loadings in green wood milling, a complete study of green wood compression is carried out. This experimental study covers the strain rates range of 10-3 to 103 s-1 using a hydraulic compression machine and the Split Hopkinson Pressure Bar technique. Wood specimens at different moisture content states are compressed longitudinally. This study enables us to observe the viscoelastic and hygroscopic behaviour of wood. The experimental and qualitative simulation results show that elastic brittle beams are not well adapted to be used in quantitative green wood milling simulations.