Crystal structures and textures of hot forged Ni48Mn30Ga22 alloy investigated by neutron diffraction technique

A ferromagnetic shape memory alloy of Ni48Mn30Ga22 prepared by induction melting was successfully hot forged. Strong textures and a large anisotropy of in plane plastic flow were developed during the hot forging process. The crystal structures, both in austenitic and martensitic states, were investigated by means of neutron powder diffraction technique. The result suggests that Ni48Mn30Ga22 has a cubic L21 Heusler structure at room temperature, the same as that in the stoichiometric Ni2MnGa. When cooled to 243 K, the Ni48Mn30Ga22 alloy changes into a seven layered orthorhombic martensitic structure. No substantial change of the neutron diffraction pattern was observed upon further cooling to 19 K, indicating that there is no intermartensitic transformation in the investigated alloy, which is different from the transformation processes in the Ni–Mn–Ga alloys with higher martensitic transformation temperatures.

Wild silkworm cocoon as a natural tough biological composite structure

Silk cocoons are biological composites with intriguing characteristics that have evolved through a long natural selection process. Knowledge of structure-property-function relationship of multilayered composite silk cocoon shells gives insight into the design of next-generation protection materials. The current investigation studied the composite structure and mechanical performance of a wild silkworm cocoon (Chinese tussah silkworm cocoon, Antheraea pernyi) in comparison with the domestic counterpart (Mulberry silkworm cocoon, Bombyx mori). 180º peel and tensile tests were performed on the cocoon walls to understand both their interlaminar and in-plane mechanical properties. The fracture surfaces were investigated under SEM. The wild cocoon showed substantially higher toughness over the domestic cocoon, which explains their unique capability to tackle severe environmental adversaries.

Constitutive modelling of high strength titanium alloy Ti-6Al-4 V for sheet forming applications at room temperature

To enable the design and optimisation of forming processes at room temperature the material behaviour of Ti-6Al-4 V needs to be accurately represented in numerical analysis and this requires an advanced material model. In particular, an accurate representation of the shape and size of the yield locus as well as its evolution during forming is important. In this study a rigorous set of experiments on the quasi-static deformation behaviour of a Ti-6Al-4 V alloy sheet sample at room temperature was conducted for various loading conditions and a constitutive material model developed. To quantify the anisotropy and asymmetry properties, tensile and compression tests were carried out for different specimen orientations. To examine the Bauschinger effect and the transient hardening behaviour in - plane tensile - compression and compression - tensile tests were performed. Balanced biaxial and plane strain tension tests were conducted to construct and validate the yield surface of the Ti-6Al-4 V alloy sheet sample at room temperature. A recently proposed anisotropic elastic-plastic constitutive material model, so-called HAH, was employed to describe the behaviour, in particular for load reversals. The HAH yield surface is composed of a stable component, which includes plastic anisotropy and is distorted by a fluctuating component. The key of the formulation is the use of a suitable yield function that reproduces the experimental observations well for the stable component. Meanwhile, the rapid evolution of the material structure must be captured at the macro - scale level by the fluctuating component embedded in the HAH model. Compared to conventional hardening equations, the proposed model leads to higher accuracy in predicting the Bauschinger effect and the transient hardening behaviour for the Ti-6Al-4 V sheet sample tested at room temperature.

Conventions of pictorialism (iconic imagery, perceived space and the picture plane) deconstructed and reconstructed as alternative models of perception, embodied in paintings and drawings

This thesis is concerned with conventions of pictorialism, viz. the surface of an artwork or the plane of denotation (in my case paper, canvas or wood); and iconic imagery and the depiction of perceptual space that is connotated by marks, colours and forms upon that surface. Most importantly this thesis is concerned with the relationship between these elements and the deconstruction of them. That the reconstruction of the deconstructed language can create expressive iconic structures that perhaps contain conflicting information and elements, but are simultaneously single and self-contained perceptual models of seeing the world, and the things in it, in another way; is a major focus. The thesis is embodied in the paintings and drawings which are documented in the exegesis that follows.

Plane wave scattering by a spherical di-electric particle in motion : a relativistic extension of the Mie theory

Light scattering from small spherical particles has applications in a vast number of disciplines including astrophysics, meteorology optics and particle sizing. Mie theory provides an exact analytical characterization of plane wave scattering from spherical dielectric objects. There exist many variants of the Mie theory where fundamental assumptions of the theory has been relaxed to make generalizations. Notable such extensions are generalized Mie theory where plane waves are replaced by optical beams, scattering from lossy particles, scattering from layered particles or shells and scattering of partially coherent (non-classical) light. However, no work has yet been reported in the literature on modifications required to account for scattering when the particle or the source is in motion relative to each other. This is an important problem where many applications can be found in disciplines involving moving particle size characterization. In this paper we propose a novel approach, using special relativity, to address this problem by extending the standard Mie theory for scattering by a particle in motion with a constant speed, which may be very low, moderate or comparable to the speed of light. The proposed technique involves transforming the scattering problem to a reference frame co-moving with the particle, then applying the Mie theory in that frame and transforming the scattered field back to the reference frame of the observer.

The distribution of grain boundary and interface plane orientations in transformed microstructures

The properties of interfaces depend not only on the lattice misorientation, but also on the interface plane orientation. Extensive studies of grain boundaries led to the conclusion that in systems evolving by grain growth, the relative areas of different grain boundary planes are inversely correlated to their relative energies. In other words, the low energy grain boundary planes make up a larger part of the population than the higher energy grain boundary planes. The hypothesis of this work is that the interface plane orientation distribution in transformed microstructures depends more on the mechanism of formation than on the relative energy. After a discussion of methods for measuring interface plane orientations, results will be presented for lath martensite in a low carbon steel and for martensite in a Ti-6Al-4V alloy processed in two different ways to promote a displacive transformation in one case and a diffusional transformation in the other.

The role of thermomechanical routes on the distribution of grain boundary and interface plane orientations in transformed microstructures

In the current study, a series of thermomechanical routes were used to produce different microstructures (i.e., ferrite and martensite) in low-carbon low alloy steels. The five-parameter grain boundary character distribution was measured for all microstructures. The thermomechanical processing route altered the texture of the fully ferritic microstructure and significantly influenced the anisotropy of the grain boundary character distribution. Generally, the population of (111) planes increased with an increase in the γ-fiber texture for the ferritic microstructure, but it did not change the shape of the grain boundary plane distribution at specific misorientations. The most commonly observed boundaries in the fully ferritic structures produced through different routes were {112} symmetric tilt boundaries with the Σ3 = 60 deg/[111] misorientation; this boundary also had a low energy. However, the grain boundary plane distribution was significantly changed by the phase transformation path (i.e., ferrite vs martensite) for a given misorientation. In the martensitic steel, the most populous Σ3 boundary was the {110} symmetric tilt boundary. This results from the crystallographic constraints associated with the shear transformation (i.e., martensite) rather than the low-energy interface that dominates in the diffusional phase transformation (i.e., ferrite).