Coniform-shape tool for splitting of wooden logs

Abstract

Bodnár F., Minárik M. (2015): Coniform-shape tool for splitting of wooden logs. Res. Agr. Eng., 61: 29-34.The article deals with design of a coniform tool with rotary motion for splitting of logs. The tool is proposed using a fracture mechanics theory. The approach of energy balance during crack growth in a split wood log is applied for construction design of the shape of the splitting tool. The proposal of the tool shape is based on the experimental fracture methods. The only used criteria it is the demand of the minimum quantity of the consumed energy.Keywords: fracture mechanics; wedge splitting test; fracture energy Splitting of wood is a process when wood is separated along wood fibres through action of a working tool. The tool causes initiation of the crack and its propagation in the wood tissue. The failure mechanism at splitting of the wood is complicated due to anisotropy of wood material, orientation of wood fibres in a log, due to wood heterogeneity of earlywood and latewood, due to different dimensions and shapes of the split log and also due to shape of the splitting tool. All these factors influence the initiation and propagation of cracks in the log, which in the final stage entails splitting of the log. The problems of crack initiation and propagation are basic questions of fracture mechanics. Researchers with various backgrounds investigate fracture mechanics especially for purposes of design and reliability of structures against the failure. Here the fracture mechanics is used to design a splitting tool with rotation motion which is applied for splitting of wooden logs. A portable tool is proposed for splitting of reclining logs, without need to manipulate with them. A driving gear of the splitting tool is an electromotor and the splitting tool is a wedge with a straight circular cone shape. The penetration of the tool in the wooden material is caused through the medium of a thread on the coniform surface of the rotating splitting tool. The basic idea at design of the splitting tool was to attain min. energy consumption.Pioneering studies regarding fracture mechanics were developed by Griffith (1921) andIrwin (1948). Griffith developed a theory for an infinite plate containing a crack and subjected to uniform stress. Drawing upon the concept of potential energy, Griffith showed that for every level of applied stress, there is a critical value for the crack length. At this value, the system is at a max. of potential energy, meaning that if the stress or the crack length is increased above this condition, the system will reduce its potential energy by increasing the crack length, basically developing a failure. Irwin introduced the concept of stress intensity factor and strain energy release rate. Critical values of stress intensity factor and strain energy release rate are material attributes that characterize the resistance to elastic fracture. The critical strain energy release 29