The method for determination of critical stress intensity factor based on chip segment length of chip type-I originating from orthogonal oblique cutting of beech wood (Fagus silvatica) in the 90°-0° direction is shown. Experimentalcuts on 10 mm thick specimen with rake angles 31° and 42° were made, and the chip thickness varied between 0,1 mm and 0,3 mm. Using the finite element method, we modelled a representative chip segment of varying length and thicknesses. We varied the load at the chip segment and calculated,for each case, stress intensity at the crack tip and compressive stress in hypothetical chip. On presumption that the crack propagates during tissue separation only when the stress intensity at the crack tip equals the critical stress intensity and the compressive stress rises in chip formation process up to the limit strength, we can calculate the critical stress intensity factor by knowing the chip segment length and compressive strength in longitudinal direction. Specifically, the crack propagates until the compressive stress reaches the strength, which occurs at the place of chip break. Critical stress intensity factor calculated from representative 0.3 mm thick chip segment length agrees well with values obtained with classical fracture tests. The results obtained from thinner chip segments deviates to a lesser extent, which is most probably a consequence of highly unsymmetrical specimen. The method has been undoubtedly shown as effective and reliable, which is the most important. The method is very simple and fast, enabling us to determine the fracture properties practically with a single oblique cut. It has to be emphasized, that the specimen preparation is also undemanding, for the only thing we have to pay attention to is the tissue orientation.
|
