Specimens of high-density low-density polyethylene were uniaxially compressed at nominally constant strain-rates ranging from 0.000066 to 0.66 sec-1 at temperatures from 77° to 350°K and hydrostatic pressures from 0.001(latm) to 4 K bar. It was shown that there were significant effects of temperature, pressure and strain rate on both polyethylenes. At small strains (O.O1), the time-temperature and time-pressure superpositions were used successfully to construct the master curves of stress versus reduced strain-rate. These master curves, which were found to have been taken in the range of linear-viscoelastic behaviour of the polymers, were employed to derive the stress-relaxation moduli and the relaxation spectra. The viscoelastic response to temperature and pressure of high-density polyethylene in the transition zone between the γ and α relaxations, and that of low-density polyethylene in the transition zone between the γ and β relaxations have been found to be controlled by the same molecular motion. This motion, an Arrhenius-type activated process, was identified as involving molecular segments of six to eight carbon atoms with an activation energy of 22 Kcal/mole and an activation volume of 110 cm3/mole.

Research in radio astronomy at the University of Aucklan School of Engineering has been in progress for a period of six years. The program was initiated primarily to provide a variety of topics for post-graduate research in the Department of Electrical Engineering, and at the same time to develop a useful radio telescope installation. Initial work was concentrated on the development of antenna arrays (Lim, 1968) and low noise receivers at a frequency of 42MHz, utilising both phase-switched and correlation interferometer principles (Irving, 1966; Yarrall, 1968; Saunders, 1968). At the beginning of 1969, the Department moved from its former country site into the centre of Auckland city. As no alternative field site was available, the telescope was also moved, but space limitations meant that the city site was inadequate for any useful observations at 42MHz. It became clear that to utilise the site more fully a higher observation frequency would be necessary, and a frequency of 200MHz was chosen, as this was the upper limit of most of the available laboratory equipment, yet still within the range of semiconductor devices. In view of the inadequacies of the site, it was obvious that the performance of the system could be significantly improved by processing the output in a digital computer.

The investigation reported in this thesis is an extension of an earlier investigation of the stress/strain behaviour of β-brass single crystals under static and dynamic loading. It was aimed at elucidating the mechanisms of deformation, using optical microscopy to examine slip habits and transmission electron microscopy to examine dislocation substructures. Marked differences were observed in the stress/strain response, slip behaviour, and the substructural rearrangements of single crystals of β-brass when widely different rates of uninterrupted compressive loading were used. Under static loading (strain rates = 10-4 sec-1) the crystals workhardened in a parabolic manner, slip being confined to either of the two (101) [111] or (211) [111] systems. Cross-slip in the statically deformed crystals was evidenced by the wavy appearance of the slip traces. Under dynamic loading (strain rates > 103 sec-1) the crystals exhibited large yield drops followed by a linear rate of work-hardening which was lower than the static work-hardening rate. Slip on the four (-101) [111], (-110) [111], (101) [-11l] and (110) [-111] systems occurred simultaneously. The traces on any one dynamically deformed specimen were both coarser and finer than those observed on specimens statically deformed. The coarse traces belonging to a given {110} <111> slip system always bounded the finer traces of another {110} <111> system. No wavy slip was observed on the dynamically deformed specimens. The substructures present in the statically deformed crystals were consistent with a single mode of slip and exhibited features indicative of high rates of hardening on the active slip planes. The important features of the statically induced substructures were as follows:- (a) There was a predominance of dislocations with Burgers vectors of a[111]. Many of these lay in non-screw high-energy orientations, consistent with the occurrence of cross-slip and the observed high hardening rates of the crystals. (b) Strong tangling developed on the slip planes as a result of a[111] edge segments interacting with other a[111] segments and with loop and dipole debris produced on the slip planes. (c) A partially developed cell structure resulted from this tangling. The dynamically induced substructures were consistent with the simultaneous operation of the four {110} <111> slip systems. It was inferred from the substructural investigations that the lower rates of hardening in the dynamically deformed crystals arose from the distribution of slip over the four systems with a consequent reduction in hardening on each individual system. The interactions between dislocations on intersecting slip planes appeared to be less important in contributing to hardening than the influence of the four systems in reducing the hardening on any one system. A series of interrupted tests indicated that behaviour under staticstatic, dynamic-dynamic and dynamic-static loading sequences was consistent with the uninterrupted static and dynamic behaviour, but that the dynamic reload stress/strain and slip behaviour, and the associated substructural changes were greatly modified by static preloading. The crystals deformed by a "static" type slip mechanism, but exhibited "dynamic" type stress/strain behaviour during the dynamic reload in this sequence.

An investigation is made into the coupled lateral-torsional response of torsionally unbalanced “shear” buildings to horizontally directed earthquake excitation. Attention is confined to analytical models that have linearly elastic, viscously damped responses. The investigation involves three separate analyses: Firstly, in a preliminary study, the earthquake response of an asymmetric single storey building model is analyzed and general expressions are derived for the location of the centre of stiffness and the orientation of the principal axes. Secondly, an analysis is made of the coupled lateral-torsional response of a partially symmetric single storey building model to a single component of earthquake excitation. A modal solution of the two equations of motion is developed and a general criterion is derived for the existence of full modal coupling. By employing the design spectrum concept, together with conservative rules for the combination of modal maxima, analytical results in dimensionless form are evaluated for an equivalent static shear and an equivalent static torque. The combination expressions are then modified to include an allowance for modal coupling before the final results are computed and tabulated. The results substantiate previous findings which have pointed to a possible link between strong modal coupling and severely coupled lateral and torsional responses. In particular, they indicate that those nominally symmetric buildings which exhibit strong modal coupling are liable to respond more strongly in torsion than has hitherto been recognised by most building codes. This effect has not in the past been quantified in analytical terms. Although the results have practical applications in design, the analysis concerns itself primarily with the determination of realistic estimates for the dimensionless response quantities and no attempt is made to derive design rules. Finally, the partially symmetric single storey model is extended to a special class of partially symmetric multistorey "shear" buildings. The importance of this final analysis derives from the similarity between the results for the single storey model and those for the continuous multistorey model.

The causes and effects of water pollution are Listed and the mechanisms of stream self-purification described. The parameters for which mathematical models have been developed are described and the success of the various previous models for predicting them is discussed. The equations governing the concentration of dissolved oxygen in a polluted waterway are developed and a review is made of the various finite difference schemes which available for solving them. Models are developed for predicting dissolved oxygen concentrations in two polluted New Zealand rivers, the Waikate and the Tarawera. It was found that the models used previously in other waterways were not adequate for either of these rivers. The model of the Waikato River uses the well-known Streeter-phelps equation to model the exertion of BOD but includes the effects of the macrophyte and phytoplankton communities on the concentration of dissolved oxygen. The model of the Tarawera River uses the Monod equations to predict the concentrations of active biomass in the porous pumice sediments on the river bed, and successfully accounts for the high rate of oxygen uptake which has been observed. The way in which these models could profitably be developed is also discussed.

The work described in this thesis represents the results of an investigation undertaken with the dual intention of (a) establishing the apparatus and techniques necessary for carrying out investigations into the work-hardening behaviour of metals under-going plastic deformation, and (b) examining the work-hardening behaviour of polycrystalline copper during interrupted tensile testing. The first part of the investigation required the development of the basic apparatus for investigations of the type envisaged. This apparatus included a tensile testing-machine, apparatus for the production of meta1 single crystals, apparatus for the determination of the orientation of metal single crystals and apparatus for the strain-free machining of metal single crystals. Details of the design and construction of this apparatus are presented. The second part of the investigation required the assessing of the existing knowledge of work-hardening and the establishment of a programme aimed at contributing further to this knowledge. A review is presented of information which pertains to the results of interrupted tensile tests such as those where the temperature dependence of the flow stress is examined, or the yield phenomenon produced by unloading is examined. Some omissions and anomalies in this information are noted and a programme of interrupted tests of the types described in the review is outlined for polycrystalline copper. As a result of this programme, the following conclusions are made concerning the work-hardening behaviour of polycrystalline copper during interrupted tensile testing: (a) polycrystalline copper obeys the Cottrell-Stokes law irrespective of the grain size or purity. (b) copper single crystals of polyslip orientations obey the Cottrell-Stokes law. (c) polycrystalline copper exhibits a yield phenomenon produced by unloading at all temperatures and strains. The magnitude of the change in flow stress associated with the yield phenomenon increases with decreasing temperature and is not significantly dependent on grain-size or purity. The magnitude of the change in flow stress increases with increasing strain and passes through a maximum. (d) the magnitude of the change in flow stress associated with the yield phenomenon produced by unloading in polycrystalline copper increases as the amount of unloading increases.

One of the most important process operations in the pulp and paper industry is the transport of pulp in pipe lines. Because pipe friction losses are much higher than with water under comparable conditions, accurate design correlations for each pulp are important to the industry. The purpose of this investigation was to design and build a flow rig suitable for investigating a wide range of pulp conditions, to obtain pipe friction loss data for New Zealand pulps, and to produce design correlations and procedures for the industry. This thesis is therefore concerned primarily with describing the experimental equipment and procedures, presenting pipe friction loss data for a variety of New Zealand pulps, including a design correlation for them, and developing design methods for computing friction losses. It includes, in addition, data on drag reduction observed at high velocities of flow, and a discussion of flow mechanisms in each regime of flow. The equipment was designed to produce friction loss data from three pipe diameters simultaneously for each consistency of pulp. Flow rate was controlled without throttling the flow. Pipe friction loss data are presented for five Kraft pulps and one neutral sulphite semi-chemical pulp. Data were obtained from 1,2,3 and 4 in. diameter PVC pipes for a wide range of consistencies and flow rates up to 0.8 ft3/sec. Standard Lampen mill evaluations on hand sheets made from the pulps are presented, as well as data on the characteristics of the fibres. The Kraft pulps exhibited the characteristic maxima and minima but the semi-chemical pulp did not exhibit these turning points. For Kraft pulps head losses before the respective maxima were increased by refining the pulp and using rough pipe; and decreased by adding short-fibre Tawa and by drying and reslushing the pulp. In comparison with maxima for the unbeaten Kraft Pulp, the maxima of the head loss curves for all Kraft pulps were shifted to lower velocities by the above-mentioned operations. This would reduce the friction loss in many practical cases. In particular, rough pipe lowers the magnitude of friction loss in this regime, and can therefore yield a considerable economic advantage. A single design correlation for Kraft pulps is presented for the regime of flow before the maxima in the head loss curves. The limits of the correlation are given. Friction losses of New Zealand pulps were found to be lower than those previously reported in the literature. Two methods of design are presented for the regimes at velocities above the maxima in the head loss curves. A procedure is suggested for pulp and paper mills to obtain their own limits for the design correlation and to verify the correlation proposed in this investigation for their own pulps. A design correlation for the Tawa NSSC pulp is also presented. Mechanisms of flow are discussed for Kraft pulps and a semi-chemical pulp. Visual observations in an artificially roughened pipe for the regime of flow before the maxima of the head loss curves have confirmed fibre-wall contact in this regime. Data obtained at the first sign of permanent plug disruption have been correlated with data at the onset of drag reduction. Fully developed turbulence was found to occur at the maximum level of drag reduction. Some velocity profiles are reported for the transition regime using a modified annular-purge probe. In addition the disruptive shear stress of fibre networks has been correlated by three different methods. Data for the onset of drag reduction are presented and compared with data previously obtained from large diameter pipes from other investigations. This correlation is used as a method for designing piping systems at high flow rates.

This thesis presents a report of an analytical investigation of the characteristic features of the transient response of fully yielding structures to a dynamic exciting force. The study was concerned with an estimation of the maximum possible peak-to-peak amplitude of simple idealised models subjected to pulses of a sinusoidal nature. The study was mainly centred around the maximum response of the single degree of freedom elastoplastic system and the effect upon it of viscous damping and a transition region between the elastic and plastic states. The extension of the approach to the two degree of freedom elastoplastic system was also investigated. The study was undertaken within the context of the earthquake engineering field. The investigation shows up certain basic characteristics of the transient response of fully yielding structures which appear to be common for widely varying types of exciting function. It also shows that the response of fully yielding structures to earthquake motions is probably a function of the characteristics of the largest pulses of an earthquake. A brief review of the study of the inelastic response of structures in the earthquake engineering context is also presented.

The relationship between heat treatment, microstructure, fracture topography and room temperature fracture toughness has been determined for a high strength low-alloy steel, En 25. 0ptical, transmission and scanning electron microscopy were used to characterize the structure and morphology while fracture toughness, notched impact and tensile tests were used to determine the mechanical properties. The as-quenched microstructure was predominantly autotempered lath martensite. A little retained austenite was observed in all as-quenched martensite. Austenitizing at 1200°C instead of the conventional 850°C resulted in a 30 percent increase in as-quenched fracture toughness with no loss in tensile strength. Step quenching from 1200 to 850°C for 15 minutes before oil quenching resulted in embrittlement of the austenite grain boundaries and consequently a loss of fracture toughness. The superior fracture toughness of the coarse grain l200°C material was maintained for tempers up to 200°C. Severe intergranular embrittlement and a considerable reduction in toughness were observed when the coarse grain 1200°C material was tempered in the 300-400°C tempered martensite embrittlement range. The fine grain 850°C material also exhibited a drop in toughness in the 300-400°C tempering range but in this case the fracture mode was mainly transgranular cleavage. Transgranular cleavage fracture was tentatively associated with the precipitation of lath boundary cementite, Fe3C. Tempering the fine grain material above 400°C eliminated cleavage and brittle intergranular fracture and resulted in a significant increase in toughness. A little brittle intergranular fracture was observed in the coarse grain material tempered at 500°C. The transverse fracture toughness for material of yield strength less than 1200 MPa was controlled by the major MnS stringer population. The fracture profile was zig-zag, each peak or trough terminating at a MnS stringer. A shear fracture mechanism has been proposed to account for the observed zig-zag fracture mode. The longitudinal fracture toughness was significantly greater than the transverse fracture toughness for tempers of 400°C and above. Mixed microstructures containing lower bainite and martensite did not have inferior relative toughness to wholly martensitic structures. Relationships were found between relative toughness and yield strength and relative toughness and shear lip thickness. There was no meaningful relationship between notched bar impact and fracture toughness data.

The plane strain fracture toughness of a high strength low alloy steel, En 25, tempered from the as-quenched state to 650°C, and a high strength aluminium alloy, 7075-T6, have been determined using compact tension specimens of varying thicknesses from 4 to 25mm. The size of the shear lips, BSL, measured at the free surfaces of the specimens was found to be independent of the specimen thickness and to be related to the true plane strain fracture toughness, KIC, through the expression BSL = 0.41(KIC/σ ys)2.02, where σys is the 0.2% proof stress of the material. A rationale for this behaviour is that BSL is approximately equal to the size of the plane stress plastic zone, ry, at the surfaces of a plate specimen, which from theoretical analysis, has been shown to be rY = Π/8(KIC/σYS)2. The ASTM standard plane strain fracture toughness test method has been proven to be insensitive to detect excess yielding in the specimens tempered at temperatures higher than 450°C. At high tempers, yielding fracture mechanics approaches were used to determine the true KIC values. The fracture toughness versus shear lip size relationship is believed to have considerable importance in the analysis of service failures and in the preliminary study of specimen size effect in plane strain fracture toughness determination.