The fracture of wood under torsional loading
- 191 Downloads
A series of experiments have been carried out on hardwood (red lauan) and softwood (sitka spruce) test pieces using static and cyclic torsional loading under displacement control. Measurements of the applied torque, the corresponding angle of twist and the number of cycles to failure were recorded. It was found that under static torsional loading, the strength of both hardwood and softwood reduced as the grain orientation of the sample to the axis of twist increased from 0° to 90° with a corresponding decrease of elastic modulus. Hardwood is stronger than softwood. In the fatigue test, when the torsional load is plotted against cycle number, the results showed that under displacement control stress relaxation occurs. The S–N curve for softwood has a shallower gradient than that of hardwood, indicating that the torsional strength of softwood is less affected by fatigue loading than hardwood. In both static and cyclic torsional loading tests, the failure mode of hardwood is slow and incomplete, whereas, softwood fails suddenly and completely. The crack growth is along the tangential direction in the hardwood cross-section and in the radial direction in the cross-section.
KeywordsFatigue Hysteresis Loop Tangential Direction Test Piece Grain Orientation
The authors wish to thank Dr P. Bonfield, of the Building Research Establishment(UK), for supplying the Sitka spruce and Scots pine used in this work.
- 2.Bonfield PW (1991) In: Fatigue evaluation of wood laminates for the design of wind turbine blades, Ph.D Thesis, University of Bath, UK, p 46Google Scholar
- 3.Thompson RJH (1996) In: Fatigue and creep in wood based panel products, Ph.D Thesis, University of Bath, UK, 1996, p 18Google Scholar
- 4.Lark RF (1983) In: Proceedings 28th Meeting of National Society for the Advancement of Materials and Process Engineering, p 1277Google Scholar
- 5.Sekhar AC, Sukla NK, Gupta VK (1963) J Natl Building Organization 8:36Google Scholar
- 6.Sekhar AC, Sukla NK (1979) J Indian Acad Wood Sci 10(1):36Google Scholar
- 8.Koran Z (1984) Wood Fibre Sci 16:12Google Scholar
- 9.Bodig J, Jayne BA (1982) In: Mechanics of wood and wood composites. Van Nostrand Reinhold Company Inc., New York, USA, p 158Google Scholar
- 13.Dinwoodie JM (1981) In: Timber, its nature and behaviour. Van Nostrand Reihold Company Ltd, New York, USAGoogle Scholar
- 14.Chen Z (2002) In: Torsional fatigue of wood, Ph.D Thesis, University of London Southbank University, UK, p 198Google Scholar
- 16.Lewis WC (1962) US Forest Product Laboratory Report, No. 2236Google Scholar