Impact Bending Fatigue of Wood
Keywords:Impact bending, fatigue, defect size, Shorea negrosensis Foxw
Repeated impact tests were conducted using a four-point bending method on an impact machine of the dropping type to obtain fundamental information on the impact bending fatigue of a wood board with a circular hole at the center of its width. Test material used was Red Lauan (Shorea negrosensis Foxw.).
Strain distribution along the specimen length due to repeated impact blows is affected by the radius of the hole (r). In the case of the 15-mm-radius specimen, the strain distribution is opposite that of the control specimen (specimen without a hole). Fracture was classified into two types according to r. The relation between the impact fracture load (P1) and the number of impact blows to fracture (N) is expressed by P1 = a·N m (a, m: constant). Fatigue of the 5-, 10-, 15-mm-radius specimen is faster than that of the 2-mm-radius or control specimen. Among the former specimens, the fatigue becomes larger with decrease in r. The notch sensitivity is 0.12-0.32 in the case of the 5-, 10-, 15-mm-radius specimen and only 0.004 in the case of the 2-mm-radius one in the impact bending fatigue test. The ratio of the impact fracture load to that of the control specimen decreases with r and N except for the case of the 2-mm-radius specimen.
Kollman, F. F. P., and W. A. Côté. 1968. Principles of wood science and technology (I). Solid wood. Springer-Verlag, Berlin. P. 379.nKrech, H. 1960. Größe und zeitlicher Ablauf von Kraft und Durchbiegung beim Schlagbiegeversuch an Holz und ihr Zusammenhang mit der Bruchschlagarbeit. Holz Roh- Werkst. 18(3):95.nMiyakawa, H., and M. Mori. 1976. Impact properties of wood and wood based materials. I. Low cycle impact tensile fatigue of wood. J. Japan Wood Res. Soc. 22(2):69-75.nMiyakawa, H. 1977. Impact properties of wood and wood based materials. II. Fatigue proceedings of glued butt-end joint specimens under tensile impact blows. J. Japan Wood Res. Soc. 23(2):69-75.nMiyakawa, H. 1980. Impact properties of wood and wood based materials. VI. Fatigue proceedings of wood, plywood, and particleboard under repeated impact bending. Sci. Bull. Fac. Agr., Kyushu Univ. 34(3-4):81-95.nMiyakawa, H. 1981. Impact properties of wood and wood based materials. VII. Impact bending fatigue of wooden beams with a semi-circular notch on the tensile side. J. Japan Wood Res. Soc. 27(5):372-380.nMoore, H. F. 1945. A study of size effect and notch sensitivity in fatigue tests of steel. Proceedings Am. Soc. Testing Mats. 45:507-531.nNishida, M. 1967. Stress concentration. Morikita Press Company, Tokyo. P. 309.nNishida, M. 1967. opcit. P. 76.nYlinen, A. 1944. Begründung der Abänderungsvorschläge der Prüfnormen für Holz. Silvae Orbis, Berlin-Wannsee 15:99.n
The copyright of an article published in Wood and Fiber Science is transferred to the Society of Wood Science and Technology (for U. S. Government employees: to the extent transferable), effective if and when the article is accepted for publication. This transfer grants the Society of Wood Science and Technology permission to republish all or any part of the article in any form, e.g., reprints for sale, microfiche, proceedings, etc. However, the authors reserve the following as set forth in the Copyright Law:
1. All proprietary rights other than copyright, such as patent rights.
2. The right to grant or refuse permission to third parties to republish all or part of the article or translations thereof. In the case of whole articles, such third parties must obtain Society of Wood Science and Technology written permission as well. However, the Society may grant rights with respect to Journal issues as a whole.
3. The right to use all or part of this article in future works of their own, such as lectures, press releases, reviews, text books, or reprint books.