An in-depth investigation is carried out to characterise the damage accumulation mechanisms and fatigue growth in single wood pulp fibres, which may be thought of as concentrically-layered, filamentary composite tubes that are approximately: 1-3 mm long, 20-40 $ mu$m in cross-section. The novel experimental methodology principally consists of the in situ apparatuses, on the one hand, which comprise the in-house designed and built single-fibre tensiometer, in conjunction with the confocal laser scanning microscope (CLSM) and, on the other, the computer hardware and periphery. The tensiometer's prime components, the loading jaws, are specifically designed to best emulate the force actions to which wood pulp fibres are subjected while between the discs of mechanical refiners (viz.: cyclic shear, radial compression and tension); and incorporate a mechanical fixation mechanism to ensure proper mounting of the single fibres. Moreover, the CLSM, which functions by scanning a diffraction-limited spot of light relative to the specimen in a raster-type scan, is a powerful tool for obtaining qualitative information on the morphology of fractured surfaces and structural behaviour of the fibres being fatigued, as well as providing accurate visual records of the history of crack propagation. The entire fully-automated set-up is controlled, in real time, via a computer algorithm specifically written for displacement-control fatigue-testing, while making efficient utilisation in terms of execution time, memory allocation, signal conversion and data acquisition. / The engendered conclusions may be summed up as follows. From a litany of tenuously-oriented microcracks, dominant macrocracks propagate along the axis of the fibre which may sharply deflect in the presence of natural bias (e.g. pits in the fibre wall). The material property degradation characteristics further include: volumetric expansion due to internal fibrillation in the cell wall, extensive external fibrillation, gradual delamination of the layers and partial peeling-off of the cell wall material. Cumulative damage due to cyclic shear is shown to be the most significant, further supported by the high structural collapsibility of the fibre wall layers. The mechanisms of fracture are either due to the development of transverse cracks at regions of high stress concentration (such as bordered pits), or owing to the gradual slippage of the fibre wall layers.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.41604 |
| Date | January 1994 |
| Creators | Hamad, Wadwood Y. |
| Contributors | Provan, James W. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Mechanical Engineering.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001401298, proquestno: NN94629, Theses scanned by UMI/ProQuest. |
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