Ultrastructural Characteristics of Wood Fracture Surfaces


  • W. A. Côté
  • R. B. Hanna


Scanning electron microscopy, compression parallel to the grain, tension parallel to the grain, radial shear, tangential shear, intrawall failure, transwall failure, intercell failure, fracture paths, fracture surface


This study concentrated on the ultrastructural characteristics of hardwood fracture surfaces, but it included southern yellow pine as a representative softwood for comparison. Very small specimens were made, tested for compression parallel to the grain, tension parallel to the grain, shear in the radial plane and shear in the tangential plane, and were then prepared for scanning electron microscopy. Secondary electron micrographs of the fracture zones were recorded singly or in stereo pairs, and a number are used to illustrate the major findings.

Thick-wall cells tend to fail in an intrawall pattern at the S1/S2 interface, while thin-walled cells are more likely to fail with transwall fracture. In tangential shear tests of ring-porous woods, the plane of fracture follows the earlywood vessels which are thin-walled and have wide lumens. Large oak-type rays affect the fracture path in all of the test modes. Certain characteristic types of failure can be related to each of the testing modes utilized.


ASTM. 1976. Annual book of ASTM standards, Part 16, pp. 56-98. Tests for small clear specimens, D-143, Part II. Secondary methods. American Society for Testing Materials.nClark, S. H. 1935. Forestry (London)9:132nDeBaise, George R. 1970. Mechanics and morphology of wood shear fracture. Ph.D. dissertation, Dept. of Wood Products Engineering, State University College of Forestry at Syracuse University.nDeBaise, George R. 1972. Morphology of wood shear fracture. J. Materials7(4):568-572.nDeBaise, George R., A. W. Porter, and R. E. Pontoney. 1966. Morphology and mechanics of wood fracture. Mater. Res. Stand.6(10):493-499.nKeith, C. T., and W. A. Côté. 1968. Microscopic characterization of slip lines and compression failures in wood cell walls. For. Prod. J.18(3):67-74.nKloot, N. H. 1952. A micro-testing technique for wood. Aust. J. Appl. Sci.3(2):125-143.nKollmann, F. F. P. 1963. Phenomena of fracture in wood. Holzforschung17(3):65-71.nKoran, Zoltan. 1967. Electron microscopy of radial tracheid surfaces of black spruce separated by tensile failure at various temperatures. Tappi50(2):60-67.nKoran, Zoltan. Undated. Electron microscopy of tangential tracheid surfaces of black spruce produced by tensile failure at various temperatures. Tech. Report No. 514, PPIRC, Canada.nTiemann, H. D. 1951. Wood technology, 3rd edition. Pitman Publ. Corp., New York.nWardrop, A. B. 1951. Cell wall organization and the properties of the xylem. 1. Cell wall organization and the variation of breaking load in tension of the xylem in conifer stems. Aust. J. Sci. Res., B4(4):391-417.nWardrop, A. B., and F. W. Addo-Ashong. 1965. The anatomy and fine structure of wood in relation to its mechanical failure. Pages 169-199 in "Fracture"—The proceedings of the First Tewksbury Symposium, Univ. of Melbourne. Australia, 26-30 Aug. 1963.nWoodward, Clinton. 1980. Fractured surfaces as indicators of cell wall behavior at elevated temperatures. Wood Sci.13(2):83-86.n






Research Contributions