The deformation behaviour of copper, reinforced with iron and steel fibres has been investigated. Parameters studied include: fibre diameter, matrix mean free path, and relative strength of fibre and matrix. No strengthening effect has been observed which can be attributed to fibre size alone. However, it is suggested that the strength of metal fibre-reinforced metal, composites are greatly influenced, by a "size effect" in the matrix. A modification of the theory of combined action has been proposed for predicting the strength of a fibre-reinforced composite, viz: [ Equation omitted ] where A is volume fraction, f refers to fibre, m refers to matrix, df is fibre diameter, and K is a constant whose value depends on the hardness of the fibre. Weakening of the matrix-fibre interface in composites of copper and steel fibres has been attributed to segregation of carbon to the interface. Alloys containing 6 to 8 weight per cent copper in iron have been shown to exhibit a martensitic transformation when cooled from the ɣ region of the Fe-Cu phase diagram. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The deformation characteristics of continuous tungsten fibre-reinforced zinc composites have been investigated. Composites with a single crystal matrix containing up to 4.5 volume per cent of tungsten fibres were studied. The stress-strain curves of W-Zn composites showed positive deviations from the "rule of mixture" predictions. Theoretical work attributes the positive deviations to matrix hardening due to either one of the phenomena: (a) the difference in the lateral contractions of the fibre and the matrix; (b) the pile up of dislocations in the matrix at the matrix-fibre interface. In the present work the positive deviations in the elastic-plastic region of the stress-strain curves of the composites have been attributed to both (a) and (b). The positive deviations in the ultimate tensile strengths of the composites have been attributed to (b). Composites containing up to 0.08 volume per cent of the tungsten wires deformed even after the fracture of the fibres. Dissolution of the matrix of these deformed composites showed that multiple necking had occurred in the fibres fractured to 1-5 mms length. Composites containing greater than 0.08 volume per cent of tungsten fibres fractured by cleaving through the basal plane of the matrix. No fibre fracture inside the matrix was seen except at the fracture end of the composite. Multiple necking of the fibres near the fractured end has been seen only in those composites which have deformed more than the free fibres tested individually. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The compression of fairly short solid cylinders under axial load is considered. A preliminary investigation examines the displacements produced by the superposition of a prescribed surface loading. This is followed by the more interesting problem in which the radial displacement is prescribed over part of the surface, the remaining part of the surface being stress free. Two types of elastic materials are considered; firstly, rubber-like materials governed by a strain energy function of the Mooney form, and secondly, metals which have a quadratic strain energy function. In the former case a finite axial compression is permitted prior to imposing any constraint on the outer curved surface of the cylinder. In all cases the irregularities introduced by the constraints are sufficiently small that they can be described by infinitesimal elasticity theory. The analysis utilizes displacement potential functions and the main problem is reduced to solving a set of dual cosine series. The particular case of the contact problem in which the cylinder height is equal to the radius is examined in detail and the contact stresses are given graphically. / Science, Faculty of / Mathematics, Department of / Graduate

The new shear machine enforces more uniform deformations than the conventional triaxial test. A low compliance pore pressure measuring device is an integral part of the machine. The machine described is capable of applying cyclic normal stress up to 1000 lb. per sq. in. and alternating cyclic shear stress up to ± 500 lb. per sq. in. Static loads can be taken 50 percent higher. The test specimen can be cut from an ordinary undisturbed drill hole sample, being 2 ins. square and 1 1/8 in. high. Height variation of ± 1/8 in. is permitted during testing, but there is no "dead" zone; the entire sample is subjected to the applied shear. An analytic solution is presented, for the boundary value problem of an anisotropic elastic sample in the tests to be described. This solution shows the variation of the stress field and deformations throughout the sample. For the benefit of any future simple shear machine designs, the theoretical relationship was also examined between the ratio of sample length to height and the uniformity of stresses and displacements within the sample. In comparing test results from the new machine with conventional triaxial tests, it was found that the measured strengths are different. Some of the results suggest that the triaxial test could over-estimate the strength of undrained sand. The difference between simple shear and triaxial conditions is, therefore, of more than theoretical interest. Liquefaction of undrained sand was readily induced by alternating shear in the new machine. It was found that liquefaction alters the structure of a sand sample, rendering it more susceptible to re-liquefaction. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The deformation behaviour of the intermetallic CsCl-structure compound β'AuZn has been investigated over a wide range of metallurgical variables. The plastic deformation, specifically the stress-strain relation, has been characterized in terms of the effects of composition, temperature, strain-rate, and grain size. The constitutional defect structure was investigated using lattice parameter measurements and annealing experiments. Polycrystalline AuZn was found to behave in a ductile manner, over the temperature range 77 to 533°K and composition range 48.0 to 52.0 a/o Au. In addition to slip on the planes of the <001> zone, slip on planes of the <111> zone was also suggested by the slip trace analyses. This may account for the observed ductility and high work hardening rate. The composition dependence of the yield stress exhibited the following behaviour; 1) a minimum at the stoichiometric composition, 2) a linear dependence of hardening on the deviation from stoichiometry, 3) approximately equal hardening due to both excess Au and Zn atoms, and 4) a temperature independent hardening-composition slope (except at 77°K where a hardening minimum was observed at 50.5 a/o Au). The existing order strengthening theories and solid solution hardening mechanisms were found to be unsatisfactory for AuZn. The temperature dependence of the yield stress was similar to that observed for bcc metals and alloys with a rapid increase in yield stress at temperatures below 200°K. The excess Au atoms decreased the temperature dependence significantly in the composition range 50.1 to 51.6 a/o Au The temperature dependence of the yield stress was investigated using the thermally activated flow parameter analyses. The magnitude of the activation volume, activation energy, frequency factor and shear stress extrapolated to 0°K were consistent with the predictions of either the thermally activated cross-slip mechanism developed by Escaig or the Peierls-Nabarro force mechanism proposed by Rajnak and Dorn. The Peierls mechanism was found to provide a more satisfactory explanation of the solid solution softening phenomena. The defect structure of AuZn was determined to be antistructural. The larger Au atom expanded the lattice more than the smaller Zn atom constricted it. The as-extruded Zn-rich wire exhibited an anomalous increase in resistivity during annealing experiments. The increase and subsequent decrease were attributed to a variation in the degree of long-range order. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

A Sn - 1% Bi alloy has been studied to determine the effects of superplastic deformation on the grain growth kinetics. Using both constant crosshead speed and creep tests, the grain size was measured as a function of deformation time and strain over a wide range of strain rates. It was found that during deformation, considerable increases in the grain growth rates occurred when compared to static annealing. The effect was most pronounced at intermediate strain rates (≃10⁻²/minute) in the high strain rate sensitivity region. However, the grain growth rates on annealing after deformation were found to be less than static rates. To aid in understanding the mechanism of the enhanced growth, alternating tension-compression tests were performed. The amount of grain elongation and the changes in preferred orientation with deformation were also measured. Grain type and grain size distributions after deformation and after annealing were established and analyzed in terms of a grain coalescence mechanism. However, the most favourable mechanism appears to involve the production of excess vacancies in the grain boundary region leading to increased boundary mobility. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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