Fracture Morphology of Hickory (Carya Spp., Juglandaceae) Under Single-Blow Impact Loading

Abstract

Wood specimens of the true hickory group were tested for their shock resistance with the single blow impact method. From this test series 10 pieces with a uniform fracture mode, 'brash' and 'tough' , were selected for electron microscopy to examine the fracture mode of individual fibres in the tensile zone. 'Brash' specimens are characterized by well defined transverse or slightly oblique fracture lines across the entire cell wall, or a stepped-up course preferably within the secondary wall. Stepping-up mainly occurs along the interface between S1 and S2 layer or between primary wall and S1 layer. The smooth fracture of fibres in 'brash' specimens appears to be caused by compression-induced pre-slip planes which do not occur in 'tough' specimens. Individual fibres of 'tough' specimens mostly display a conspicuous and irregular zigzag course of the fracture line due to the tearing apart of fibrillar bundles . In addition, 'tough' specimens are characterised by the regular development of microcracks at a distance of up to several millimeters from the fracture plane. Such microcracks were not observed in 'brash' specimens. The described micro morphological differences between both fracture modes help to explain the considerable variation in shock resistance between specimens of similar density and gross wood structure.

Ultrastructure of Transwall Fracture Surfaces in Radiata Pine Wood using Transmission Electron Microscopy and Digital Image Processing

“…Since fracture across the microfibril axis involves breaking chemical bonds within the individual cellulose molecules, any offset in the alignment of those bonds could contribute to a preferred angle of cleavage across the microfibril. This effect was consistently observed in all secondary wall layers and has also been reported in Hickory by Schmitt et al (1996).…”

“…In addition, ultrastructural features such as lignin distribution, have been related to the position of fracture in the cell wall (Donaldson 1995), although little information is available on the detailed ultrastructural features of wood fracture surfaces (Schmitt et al 1996).…”

Study on wood fracture parallel to the grains based on fractal geometry

“…This makes it difficult to quantitative morphology of wood fracture surface and the fracture mechanisms. Thus, researchers are trying to look for a new index in quantitative morphology of wood fracture surfaces and expect to predict wood intensity and understand its fracture mechanism with it (Schmitt and Richter 1996). Therefore, fractal offers a new theory for developing a better understanding of fracture mechanics of wood.…”