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The increase in strength of gold-nickel brazed joints, with increasing joint gap is explained by considering the mode of failure of the joints. Failure occurs in an apparently semi-brittle manner by crack initiation and propagation. Crack propagation is considered to be the controlling factor in joints brazed at 970°C. On raising the brazing temperature to 1000°C the controlling factor changes to one of crack initiation. This is the result of changes in the braze alloy microstructure due to pick up of small amounts of alloying elements from the steel. The effects of alloying between braze material and steel, on the joint microstructure, are considered and a corner of the gold-nickel-silicon ternary is calculated, silicon having been found to have a large effect on the joint microstructure.

The thesis presents the findings of a programme of research into the design and performance of variable displacement axial piston pumps of the swashplate type with integral controls. The work is principally concerned with developing a systematic design and performance prediction method for use at the design stage. The method developed outlines stage by stage the problems which arise and give guidance on the decisions which have to be made during the design process. Existing theory and technological data is integrated in the method and is augmented by the author's own contributions in the area of force analysis and contact stresses in the cylinder bores. Graphical optimisation methods are employed and the effects of manufacturing tolerances and .pump working ranges are investigated. The effectiveness of the method is demonstrated by designing a pump to the same specification as that of an existing industrial pump and by making a critical comparison of the two designs. Various regions of power loss are identified and equations derived for estimating these losses. The equations are developed and integrated into a performance prediction method which is novel in that unlike any known method, pump performance can be predicted without the need to test a similar pump. Using data readily available at the design stage the method is used to compare the performance of the existing pump with predicted values. Close agreement is claimed as an indication of the reliability of the method. The thesis gives an account of the historical development of the axial piston pump, a survey of published work on design and performance and a description of axial piston pumps and hydrostatic transmissions. Also included is an analytical treatment for the frequency response of servo controlled pumps by manual and electrohydraulic control.

The objective of the study was to examine factors that influence the strength of butt welds and gain an understanding of the process of failure. The study was divided into several sectors. The first and primary part of the programme was to determine the extent to which the pipe system's long-term strength under both internal fluctuating and constant pressure is reduced by the presence of axially misaligned butt welds. The second objective was to examine fracture initiation sites and crack propagation paths of the failed aligned and misaligned butt welded samples in relation to the melt flow zone and the weld bead in order to establish the cause of failure. Finally the project considered the influence of selected welding parameters on the fatigue performance of aligned butt fusion welds and an investigation into the influence of elevated temperature (79°C) testing technique on the basic material's properties. Fatigue and stress-rupture lifetimes were found to decrease significantly with increasing axial misalignment at the butt fusion weld in 63,90 and 125mm MDPE pipe systems at 79°C in a water environment. In the butt fusion weld having axial misalignment of 20 per cent of the wall thickness and above, the reduction in the fatigue and stress-rupture lifetime was greater than 50 per cent compared to the aligned weld. It was not clear whether there is a pipe size effect or not; there was no marked change in the fatigue performance of misaligned butt welds for the three pipe diameters examined. However, the fatigue performance of the aligned butt welds in 90 and 125mm was noticeably better compared to 63mm pipe systems. The stress rupture performance of misaligned butt welds in 90 and 125mm MDPE pipes was more than halved compared to those in 63mm pipe systems. Both the fatigue and stress rupture performance of misaligned butt welds could be explained in terms of amplified axial stress and in general, the Ory expression for evaluating the increase in axial stress due to misalignment appears to be valid. The temperature dependence of the fatigue performance of aligned and misaligned butt fusion welds in 63 and 90mm MDPE pipe systems suggests that if continuous internal fluctuating pressure under the conditions examined is maintained, then the butt fusion welds with axial misalignment of below 10 per cent of the wall thickness may well meet the design lifetime of 50 years at the service termperature. Under stress-rupture conditions, all the misaligned butt welds considered in the three pipe diameters surpassed the minimum specified requirement of 170 hours at 79°C. The fatigue was the most aggresive condition of the two for minor misalignment. Examination of the circumferential butt weld failures revealed that the crack invariably initiated from the notch located at the inner weld bead and no preferred crack propagation path was taken in relation to the melt flow zone. It was proved that the notch was responsible for the observed circumferential failure of aligned butt welds in 63mm MDPE pipes by testing these butt fusion welds where the internal weld bead was machined off. The failure site for the internal weld bead machined off sample was in the pipe remote from the weld inferring that the material in the melt flow zone does not constitute any weakness. The effect of elevated temperature (79°C) testing in 63mm HDPE pipe was found to increase the density (and crystallinity) signifying a slow annealing process in the material. However, the changes in these parameters were not of sufficient scale to strongly influence the performance. The main effect of elevated temperature testing in water environment appears to be the extraction of stabiliser from the base polymer as was indicated by the rapid decrease in oxidation induction time with the ageing times.

Fibre reinforced structural members are currently being produced using the pultrusion process. The mechanical properties of these members are fundamentally different from those of conventional metallic ones. Therefore, the approximate theories which are suitable for designing the latter elements have to be revised before they are applied to pultrusions. An important aspect of the design of building frames is that of joints. The bolting technique is considered as the most suitable method for on-site jointing. Accordingly, experimental investigations are undertaken in order to establish the behaviour of bolted joints in pultrusions. Numerical and analytical methods are used to investigate the stresses in these joints. Single and two-bolt joints were the subject of experimental investigations. It is shown that materials with high percentage of axial fibres do not develop bearing failure. However, provided the end distance is sufficient, the resulting shear failure will be ductile. The load distribution in joints with two bolts is measured and it is found that it varies with the load on the joint. The theoretical investigations compare the use of the laminated plate theory with three dimensional analyses. Because the use of the laminated plate theory is found to be reasonably accurate, an improvement for the case of a symmetrical laminate is proposed where the laminated shell theory is used to model half the plate only. This technique is based on the assumption of a bi-linear variation of the stress through the thickness of the laminate. The effect of the fastener is an important part of the behaviour of the joints. Three dimensional analyses are performed to assess its effect. To avoid the complications of performing three dimensional analyses, a two dimensional model for considering the effect of the washer on the joint is devised. In addition, a method which avoids iteration when considering the effect of friction is formulated. A finite element formulation for the non-linear and failure behaviour of uniaxial composite materials is developed to investigate the behaviour of the joints. Finally, a closed form analytical formula for calculating the tangential stress around a hole in an infinite orthotropic plate loaded on the hole is generated to simplify the design procedures.

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