Abstract
Cleaving or riving of wood is an efficient method of cutting, but is usually restricted to veneer cutting or low-quality products such as fence-palings, due to the poor surface finish that occurs on thicker offcuts. If the release of strain energy during fracture could be controlled then the surface finish and dimensional tolerance of cleaved wood products would be improved. A series of experiments were carried out on Pinus radiata to split it in the r.l. direction by mode 1 (crack opening) using both single cantilever beam bending and cleaving by a wedge. The offcut thickness, and the blade thickness and grinding angle were varied and the fracture, plastic and friction energies measured. When the offcut was 15 mm or greater the fracture surface energy from both types of cutting were similar and the friction and plastic energies were much larger; all energies were unaffected by blade dimensions? The mode of fracture of the 5 mm offcut was not simple crack opening and consequently the surface energy was a more significant proportion of the total energy, which is why smaller thickness offcuts may be cleaved in a controlled manner.
Zusammenfassung
Spalten oder Brechen ist eine effektive Methode zum Auftrennen von Holz; allerdings ist diese Methode wegen der geringen Oberflächenqualität und der Dicke der Produkte auf minderwertige Furniere und Umkleidungen beschränkt. Wenn man die Freisetzung der Spannungsenergie während des Bruchs kontrollieren könnte, sollten sich Oberflächenqualität und Dickentoleranz der Spaltprodukte verbessern lassen. In einer Reihe von Experimenten wurde Kiefernholz (Pinus radiata) in RL-Richtung gespalten (Mode 1), zum einen durch einfachen Biegebruch zum andern mit Hilfe eines Keiles. Die Dicke der Spaltproben, der Klinge und der Schnittwinkel wurden variiert und die Energie für Bruch, plastische Verformung und Reibung gemessen. Wenn die Spaltprodukte 15 mm oder dicker sind, ist die Bruchenergie bei beiden Verfahren ähnlich, und die Energie für Reibung und plastische Verformung sind größer als die Bruchenergie. Bruch-, Verformungs- und Reibungsenergie waren unabhängig von den Messerdimensionen. Bei Dicken von 5 mm verläuft der Bruch nicht nur durch einfaches Spaltöffnen; daher ist der Anteil der Oberflächenenergie an der Gesamtenergie hier deutlich höher. Dies ist der Grund dafür, daß das Abtrennen dünnerer Spaltprodukte besser kontrolliert werden kann.
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King, M.J., Vincent, J.F.V. Fracture energy during cleaving of Pinus radiata . Holz als Roh- und Werkstoff 56, 259–265 (1998). https://doi.org/10.1007/s001070050315
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DOI: https://doi.org/10.1007/s001070050315