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The mechanical properties of aluminium have been studied for many years and are well documented under standard loading conditions. However, the properties of the material at elevated temperatures and under transient loading conditions (high heating rate and high strain rate), have not been widely researched and the data available is therefore limited. This type of data is becoming increasingly important as the physical requirements that have to be met and the service environments materials have to withstand are continually increased. This investigation studied the individual and combined effects of temperature, strain rate and heating rate on the mechanical properties of a 6082 aluminium alloy. To allow the behaviour of the material to be examined under a wide range of testing conditions several different test methods had to be employed. These ranged from standard tensile tests to novel testing methods at high strain rates using a Gleeble 1500 thermomechanical simulator. Using Finite Difference based computer-modelling techniques specimens were designed specifically for the high strain rate testing of the 6082 alloy on the Gleeble 1500. These specimens were designed to produce a specific thermal profile during heating, which allowed accurate stress/strain data to be recorded. In addition to uniaxial tensile testing, the viability of miniature disk bend tests for the calculation of tensile properties of 6082 aluminium was investigated. Empirical relationships were produced for the calculation of yield and UTS data for the testing of the 6082 aluminium alloy. The main test program produced data that mapped the behaviour of the 6082 alloy over a wide range of temperature, heating rate and strain rate conditions, from which empirical relationships for proof stress and UTS were produced. These relationships made possible the calculation of mechanical properties of the 6082 alloy for a broad range of test conditions.

This thesis addresses the understanding of the static strength and behaviour of internally ring stiffened T- and DT-joints under axial brace loading. Initial numerical work verifies the appropriateness of the Finite Element (F.E.) modelling technique and the use of the F.E. Method as an analysis tool. This was achieved through a validation study on both unstiffened and ring stiffened T-joints and on unstiffened DT-joints. There follows four substantial parametric studies on ring stiffened T- and DT-joints which investigate the effect of the variation of the stiffener dimensions of plain and T-shaped stiffeners along with the joint geometrical parameters β and γ on the strength and behaviour of the stiffener and the stiffened joint. Also the number and position of the ring stiffeners are investigated. Findings of the study enabled, where appropriate, the proposal of two methods of strength prediction for the ring stiffener. One uses Plastic Theory to postulate a ring model which is based on a five- or six-hinge failure mechanism for the stiffener, resulting in a virtual Work Equation. For this method it is assumed that a portion of the chord interacts with the stiffener in producing the strength enhancement. The stiffener cross-section is then considered as a T- and an I-section for the plain and T-shaped stiffeners respectively. The other is an empirical equation based on the variation of the non-dimensional stiffener strength with the various influencing non-dimensional parameters. It has been shown that the theoretical method can be compromised when the stiffener parameters exceed the validity range of the predictive method whereas the empirical method appears to be more robust to extrapolation of the validity ranges. Both methods provide accurate predictions of stiffener strength when compared to the newly created FE database and existing test and numerical results.

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In response to frequent calls during the last few years for research into overlapped joints in steel circular hollow sections, this thesis addresses the static strength and behaviour of axially loaded overlapped K joints. A review of previous research and design guidance indicates the dearth of reliable, representative data and a general lack of knowledge of the behaviour of these joints, which are widely recognised as being potentially more cost effective than typical canned or stiffened gap joints. Preliminary, non-linear, numerical analyses, including thorough calibration of the Finite Element modelling strategy, are followed by a substantial parametric study investigating the effects of variation of the principal geometrical parameters on the behaviour and capacity of both overlapped and, for comparison, small-gap K joints. The results are compared with the design guidance of CIDECT (1991), which, for the overlapped joints, fails to predict all the interactive effects of the geometry variations and, consequently, is excessively conservative for some geometries. A new strength equation for overlapped K joint capacity is therefore proposed, based on the results of the numerical study. The equation has limited use in practice at present because of the limited scope of the parametric study. Nevertheless, it provides a robust platform onto which the results of future selective research (the requirement of which are discussed) may be added. Some important findings within the field of strength of tubular joints also emerge, namely: a) the effects of different boundary conditions on isolated joint tests - for replicating frame effects and the consequences for database screening, b) the reliability of the on- and offshore codes for gap K joint capacity, and c) the effects of chord can length on gap K joint capacity.

Carbon brushes used for the collection of current from rotating electrical machines are made from mixtures of natural and by-product carbons by bonding with a secondary coke formed by the thermal decomposition of a temporary hydrocarbon binder. When heat treated to a temperature of some 1200K-1400K the composition of the body is essentially the element carbon but with the constituents in various degrees of atomic structural order. On further heat treatment to about 3000K some carbons will change dramatically in their response to applied mechanical forces,and this is accompanied by improved resolution in their electron and X-ray spectra. Use is made of this behaviour for composite carbons to be used as electrical brushes as after the high temperature heat treatment they are stronger than natural graphite but have satisfactory self lubricating properties to run against a slip ring or commutator and are good conductors of electricity for current collection. The choice of ingredients and method of manufacture have a profound influence on the performance in practice and one particular aspect of this is the ability of a carbon brush to remain in good electrical contact with its counterface in the prescence of mechanical vibration. This report describes work carried out on two series of electrographitic carbons where in 1) the matrix composition and structure have been kept constant and the volume fraction porosity varied and 2) the porosity was kept constant and a range of petroleum cokes known to reach different states of structural order after heat treatment were used as matrices. These materials have been examined by microscopic and diffraction techniques to achieve a method of characterising their state of strucure numerically to relate with their static mechanical properties and damping capacity ability. It has been found that the mechanical damping capacity of these materials is very strongly amplitude dependant, and is a function of both the atomic order of the carbon ingredients and of the volume fraction porosity present.

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