D.Ing. / This thesis studies the application of newer generation engineering materials, specifically carbon fibre reinforced polymers, as bone plates in cases of fractured bones. The application of bone plates subsequent to bone fracture is a very old orthopaedic technique that has always rendered some problems. The rigidity of the bone plate, and thus the plated system as a whole, is of advantage during the healing phase, but of disadvantage later. Bone remodels itself to most efficiently perform the load bearing required of it. In a plated system, the load is born primarily by the plate and therefore protects the underlying bone, leading to osteoporosis and eventual atrophy. All bone plates are made of a material that is totally foreign to the body, and in most cases these are removed after some healing of the bone had occurred. The majority of current research programmes with respect to bone plates are directed towards biodegradable bone plates that reduces in mechanical strength at approximately the same rate as bone gains in its ability to sustain loads. The principle of stimulating bone growth in cases of delayed union and non-union has been studied since the early 1960's. The studies revealed that bone healing can in fact be enhanced by the introduction of a very small electric current to the fracture site. Variations to the mechanisms and position of application of the current, alternating or direct, are well documented. Although the physiological healing process associated with electrical stimulus remains largely unknown, the principle is well established. The phenomenon of galvanic corrosion has been known since the tum of the century. Where two dissimilar materials are in the presence of a conducting media, the more "reactive" of the two materials will react as an anode or electron donor to the other material. An electric current thus will flow from the one material to the other. Having three existing and known phenomena, namely bone plating, bone healing stimulation and galvanic corrosion raises the question of whether these can be combined to yield a solution superior to any current plating mechanism - a plate that would render sufficient mechanical support but act as an electron source and thus as a bone healing stimulus. The purpose of this study is to assess the biological criteria determining the choice of bone plates (inclusive of mechanical, physiological and electrical criteria) and thereafter selecting a material suitable for this dynamic requirement.

<p>A crush test fixture for measuring energy absorption of flat plate specimens from an earlier study was redesigned to eliminate the problem of binding of the load transfer platen with the guide posts. Further modifications were to increase the stroke, and combine the two scaled test fixtures into one. This new crush test fixture was shown to produce load displacement histories exhibiting well developed sustained crushing loads over long strokes.</p> <p> An experimental study was conducted on two material systems: AS4/3502 graphite/epoxy, and a hybrid AS4-Kevlar/3502 composite. The effect of geometric scaling of specimen size, the effect of ply-level and sublaminate-Ievel scaling of the stacking sequence of the full scale specimens, and the effect of trigger mechanism on the energy absorption capability were investigated.</p> <p> The new crush test fixture and flat plate specimens produced peak and sustained crushing loads that were lower than obtained with the old crush test fixture. The trigger mechanism used influenced the specific sustained crushing stress (SSCS). The results of this study indicated that to avoid any reduction in the SSCS when scaling from the 1/2 scale to full scale specimen size, the sublaminate-level scaling approach should be used, in agreement with experiments on tubes. The use of Kevlar in place of the graphite 45° plies was not as effective a means for supporting and containing the 0° graphite plies for crushing of flat plates and resulted in a drop in the SSCS. This result did not correlate with that obtained for tubes.</p> / Master of Science

Heat transfer in turbulent flow from external surfaces has been investigated extensively in the past. Most of the theoretical and experimental work deals with a two dimensional boundary layer on isothermal or uniform heat flux surfaces with longitudinal temperature variation. However, little attention has ever been paid to the case in which the temperature of the plate varies transversely. This is a three dimensional problem due to the spanwise variation of the thermal boundary layer. The most elementary example of this is the boundary formed by the sudden temperature impulse that acts transversely across a flat plate as shown in Fig. 1. Theoretically, this spanwise boundary increases the heat transfer coefficient. A knowledge of this is important in the field of heating and cooling system design. It is also important for the investigation of spot-heat flux measurement.

The welding of steel plays an important role as a major fabricating process in industry. In the field of welding metallurgy, much attention is given to the effects which a welding arc or flame will have on the structure and properties of the metals being joined. The engineer is interested in the intensify and extent of physical changes brought about by the unavoidable heat treatment which accompanies the execution of a weld. In order to gain some quantitative appreciation of the way in which the metallurgical effects of welding depend on welding variables, geometry, and physical properties, considerable attention has been given to the unique heat-transfer phenomena associated with the movement of heat sources in or on metal surfaces.

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A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering, August 2019 / An extension to classical lamination theory (CLT) is presented to analyse the natural fre- quencies and critical buckling loads of simply supported functionally graded plates. The variation of the through-thickness properties of the plate is governed by a power law which is subsequently represented by a polynomial series of su cient order and varies according to the law of mixtures or the Mori-Tanaka Homogenization method. The sti ness matrices are found, from which the position of the neutral plane is established which allows for the governing equations for the natural frequency and critical buckling load to be derived using the Rayleigh-Ritz method. The natural frequency and critical buckling loads are determ- ined for various volume indices, aspect and span ratios and the accuracy thereof is validated against 2D, 3D and quasi-3D solutions found in literature. A comparison with CLT found that the present study produces natural frequencies and critical bucking loads which are more accurate and which converge faster than CLT. / NG (2020)

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