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Title:Premočrtno odrezavanje kot metoda za določevanje lomnih značilnosti orientiranega lesnega tkiva
Authors:ID Merhar, Miran (Author)
ID Bučar, Bojan (Author)
Files:.pdf PDF - Presentation file, download (576,79 KB)
MD5: 8D0DADC65F3947FA4001791A3672195A
PID: 20.500.12556/dirros/c27eb886-c4c7-4190-a6ec-07e85fb9ceee
 
Language:Slovenian
Typology:1.01 - Original Scientific Article
Organization:Logo SciVie - Slovenian Forestry Institute
Abstract:Prikazana je metoda določevanja kritične koncentracije napetosti na podlagi dolžine segmenta odrezka tipa I, nastalega v procesu premočrtnega ortogonalnega odrezavanja bukovine (Fagus silvatica) v smeri 90°-0°. Eksperimentalni rezi so bili narejeni na 10 mm debelih vzorcih pri cepilnem kotu 31° in 42°, debelina odrezka pa se je spreminjala v območju med 0,1 in 0,3 mm. Z metodo končnih elementov smo modelirali reprezentativni segment odrezka različnih dolžin in debelin. Spreminjali smo obremenitev segmenta ter vsakič izračunali koncentracijo napetosti na konici razpoke ter tlačno napetost v hipotetičnem odrezku. Ob predpostavki, da se razpoka pri ločevanju tkiva širi zgolj v primeru, ko je koncentracija napetosti v njenem korenu kritična, ter da se tlačne napetosti v nastajajočem odrezku nenehno povečujejo vse do mejne vrednosti, lahko na osnovi znane dolžine reprezentativnega segmenta odrezka in tlačne trdnosti vzdolž poteka tkiva izračunamo kritično koncentracijo napetosti oziroma določimo lomno togost aktualnega materiala. Razpoka napreduje namreč vse dokler tlačna napetost ne doseže porušne vrednosti, kar se zgodi na mestu loma odrezka. Kritične koncentracije napetosti, ki smo jih določili na osnovi dolžine reprezentativnega segmenta odrezka debeline 0,3 mm, se zelo dobro ujemajo z vrednostmi, dobljenimi s klasičnim frakturnim testom. Pri manjših debelinah odrezka prihaja do manjših odklonov, kar je najverjetneje posledica povečane asimetrije vzorca. Prikazano metodo lahko nedvomno označimo kot učinkovito in verodostojno, kar je tudi najbolj pomembno. Metoda je zelo enostavno in hitra, kajti lomne lastnosti aktualnega materiala je praktično moč določiti že z enim samim premočrtnim rezom. Treba je tudi poudariti, da je priprava vzorčnega materiala nezahtevna, kajti edino, na kar moramo paziti, je usmerjenost tkiva.
Keywords:premočrtno odrezovanje, odrezek, fraktura, frakturni način, koncentracija napetosti
Publication status:Published
Publication version:Version of Record
Year of publishing:2010
Number of pages:str. 49-56
Numbering:Vol. 92
PID:20.500.12556/DiRROS-7735 New window
UDC:630*81
ISSN on article:0351-3114
URN:URN:NBN:SI:doc-MQW5NF95
COBISS.SI-ID:3048102 New window
Publication date in DiRROS:12.07.2017
Views:4663
Downloads:1991
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Record is a part of a journal

Title:Zbornik gozdarstva in lesarstva. forest and wood science & technology
Shortened title:Zb. gozd. lesar.
Publisher:Gozdarski inštitut Slovenije, Biotehniška fakulteta, Oddelek za gozdarstvo in obnovljive gozdne vire, Biotehniška fakulteta, Oddelek za lesarstvo
ISSN:0351-3114
COBISS.SI-ID:6206978 New window

Secondary language

Language:Undetermined
Title:Oblique cutting as a method for determination of the fractural properties of oriented wood tissue
Abstract: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.


Collection

This document is a part of these collections:
  1. Acta Silvae et Ligni

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