ارزیابی مدل مواد چوبی برای ارزیابی های عددی نیروی برش در فرآیند های ورقه سازی Evaluation of wood material models for the numerical assessment of cutting forces in chipping processes

Introduction When calculating structural stress in components subjected to heavy loads using modern, standard finite element analysis, it is of great importance to define load cases and scenarios. Misconceptions lead to incorrect results and furthermore, a possible non-conservative assessment may occur (Blaauwendraad 2010). Wood as a quite complex, anisotropic material, exhibits properties that vary enormously, depending on the direction of fibre orientation. Previous studies in the field of woodworking provide an insight into acting forces on low chip thickness. For cutting depths of about 1 mm, the loads on the operating blades are on a comparably low level. Hereby, the main focus is on the fabrication of wooden products like furniture or semifinished materials for the construction industry. Many influences on the cutting force in woodworking have firstly been researched by Kivimaa (1950) and include blade geometry and sharpness, machining speed, wood density, moisture and temperature. Further investigation on an experimental basis to analytically calculate the acting forces is shown by Porankiewicz et al. (2011) and Axelsson et al. (1993). Moreover, analytical methods to calculate forces caused by sawing rather uncommonly processed tropical woods have been investigated by Cristo´va˜o (2013). Machining in the forest industry means significantly more cutting service, in turn leading to higher mechanical loads on the structural parts. In this case, the closest attention is devoted to the cut chip itself. Large industrial heating boilers that generate more than 1 MW require chips approximately 35 mm in size (Kofman 2006). Research on measurements of such cutting dimensions is quite rare and difficult to put into practice. Recently, Pfeiffer et al. (2015a, b) and Hatton et al. (2015) utilized huge pendulums with applied force sensors to measure loads acting during the chipping process or to simulate the chip building process with the discrete element method (DEM). Another method to measure forces on such scales is possible with machine built-in sensors shown in Hellstro¨m et al. (2011) and Hellstro¨m (2010). On the basis of the aforementioned investigations as well as preliminary studies presented in Pichler et al. (2016a, b), this paper deals with the determination of the cutting resistance of wood by numerical methods, whereby experimental tests on small-scale samples are conducted to help customize the parameters for the material models in explicit finite element analysis (Fig. 1). The aim of this work is to achieve a model, which allows an assessment of the cutting force distribution for greater cutting depths and additionally deals with an approach to numerically estimate the resulting mechanical stresses caused by the dynamic chipping process.