An experimental and numerical investigation of the machining of anisotropic materials including wood and a wood composite (particleboard).

摘要

This research investigated the machining of wood and particleboard through experimental and numerical approaches to develop the fundamental understanding of the machining of anisotropic materials.; A microscope-video-cutting experimental setup was developed to examine the chip formation processes. It was found that the machining of anisotropic materials is very complex and different from the machining of isotropic materials. The material anisotropy plays a very important role in the chip formation process. Four modes of chip formation mechanisms were identified in the machining of wood and particleboard. They are Mode I crack fracture, Mode II shear failure, Mode III compression failure and uniquely for particleboard Mode IV debonding. The material orthotropy and the cutting conditions determine the principal chip formation mode.; An elastic-plastic orthotropic homogeneous material model was established. A nonlinear finite element (FE) model was developed to simulate both Mode I and Mode II chip formation processes. It simulated the chip formation process from the incipient nonsteady state cutting to the steady state cutting for Mode II and to the cyclical state cutting for Mode I. A geometric chip separation criterion was used and was proved valid.; Both experimental and numerical results revealed that for Mode II chip formation a shear zone is formed. Grain orientations determine the shear angles. All shear zones were found to lie almost parallel to the weakest shear strength directions. With grain orientation angles varying from 0° to 90°, the predicted shear mode cutting forces follow a bell curve and agree with experimental results very well.; An othotropic linear elastic fracture mechanics (LEFM) criterion was developed for wood. The mixed mode stress intensity factors were evaluated using the finite element method. The predicted results agree with experimental observations very well and show that large depth of cut favors Mode I chip formation.; The characteristics of different chip formation processes are well captured in FE simulations. The predicted cutting forces closely agree with the experimental results. These results suggest that the newly developed material model and the FE model are successful and well suitable for studying the machining of orthotropic materials.