IFM research seminar series 2012

 Abstract

The alloys of Al and Mg are widely used in the industry. As the main lightweight alloy, they have many excellent properties, such as low density, high ductility, and high specific strength and so on. For these properties, the Mg alloy is better than Al alloy. However, the corrosion of Mg alloy occurs more readily than with the Al alloy, the strength is lower and the post-processing is also more complex. Thus a solution to this problem is to use compound casting to make these two alloys unite to satisfy the requirements from industry. In this study the distribution of residual stresses in the compound casting is determined by numerical simulation. With the increasing of temperature of substrate, residual stresses increase, and the x-direction stresses in the substrate and in the deposit are compressive and tensile, respectively. With the increasing of thickness of deposit, the residual stress in the substrate increases, while they decrease in the deposit. Furthermore, the stresses concentrate near the edge of deposit, which eventually lead to failure of the deposit. In addition, we also use Computational Fluid Dynamics (CFD) that adopts the volume of fluid (VOF) method to study the impact mechanism, and the spreading of the liquidized Mg alloy in the surface of solid Al alloy. The impact process can be described by several steps: spreading step, retracting step, oscillating step, and equilibrium step. We also investigate some main parameters that influence the quality of compound casting products: impact velocities, initial diameter of the droplet, and the temperature of the substrate. We find that the spread diameter of the drop on the substrate changes when the impact velocity and initial diameter of drop are varied. While the impact velocities and initial diameters of drop are larger than the critical value, the liquid may part or appear the bubbles in the film. The higher the temperatures of substrate are, the larger the spread diameters; and they will take more time for oscillating step and equilibrium step to complete.

 Abstract

There has been a growing interest in recent years in the use of natural fibres as reinforcement in the composites because of high specific properties, low mass, environmentally friendly and ability to be incinerated for energy recovery. Natural fibres are normally used in two different forms for composite manufacture i.e. random discontinuous fibres and aligned continuous form. Natural fibre composites made from random discontinuous fibres have low strength and cannot be used for applications where high strength is needed [2]. To be able to use these fibres in structural applications, the fibres must be used in aligned continuous form. These must be converted to a yarn of required properties as per the end application requirements. Besides the required yarn structure, to use these fibre composites for structural applications, these fibres must be strategically placed according to the strength requirements of composites parts and the composite manufacturing process. To address this issue, the first aim of this study is set as follows:

 Abstract

3D characterisation of materials has always been the dream of researcher especially in the field of material science. Thanks to micro-tomography it is possible to obtain 3D images in a non destructive manner since 1995 using synchrotron sources and since 2002 with laboratory tomograph. The main progresses that have been achieved these last years with synchrotron sources are the reduction in the time to acquire a full 3D image keeping a spatial resolution of the order of 1 micron. This allows performing what we call fast-tomography and therefore 3D in situ experiments in various field of material science : phase transformation, damage during thermomechanical testing ... During this presentation we will first show that 3D in situ characterisation is sometimes mandatory. Then we will present the main characteristics of tomography and requirements for in situ micro-tomography. We will after show several examples where in situ tomography can provide interesting information in the field of solidification and damage in materials. Concerning solidification we will focus on intermetallics nucleation and growth in Al-Si-Cu-Fe alloys and hot tearing phenomenon in Al-Cu alloys. Concerning damage in materials we will focus on high temperature damage in AZ31 alloy during superplasticity. Finally we will present the limitation of fast tomography and the benefit of ultra fast tomography in which acquisition time lower than 1s for a full 3D image are obtained.

 Abstract

Aluminium-magnesium (Al-Mg) alloy sheets become widely used in the automotive industry, due to their excellent properties of high strength, corrosion resistance and weld ability. However, although these advantages, their formability at room temperature is lower than that of steel sheets and several material or structural effects are still difficult to predict. For example, Al-Mg sheets are known to experience dynamic ageing during plastic deformation called Portevin-Le Châtelier (PLC) effect, that is characterized by plastic instabilities leading to non-aesthetic stretcher lines on sheet surfaces. While this effect occurs typically during tensile tests, the jerky flow in an Al-Mg alloy during simple shear tests for various strain rates at room temperature is studied with a digital image correlation system. In parallel, an elastoviscoplastic model, proposed by McCormick et al., in which an additional internal variable called ageing time is introduced, is used to predict the propagation of PLC bands in shear tests specimens. The use of aluminium alloy is also slowed down by the springback magnitude which requires the evolution of sheet forming processes, mainly in two trends: the first one consists in the improvement of the numerical simulations at room temperature. The second aspect consists in increasing the formability by performing forming operations at warm temperature in order to modify the stress state in the formed parts thus leading to a decrease of springback. Some experimental and numerical results on springback in aluminium alloys for several forming temperatures will be presented.

 Abstract

This PhD project aims at investigating new ways to prevent wool against photoyellowing. Two main objectives will be achieved: (1) Fabrication of new inorganic UV absorbers with a novel structure, i.e. ZnO@void@SiO₂, TiO₂@void@SiO₂ rattle-type nanoparticles. (2) Successful application of these inorganic UV absorbers on wool fabric to protect the fabric against photoyellowing, with a focus on the enhancement of rubbing fastness and washing resistance of the coated fabric. Wool fibre is well known as a superior natural textile material due to its resilience and softness. However the photodegradation of wool caused by exposure to sunlight, particularly from the UV light, makes the fibre weak and yellow, which is a significant problem for the wool industry. Although commercial bleaching and fluorescent whitening agent (FWA) finishing processes are widely employed to improve the whiteness of wool, the rate of photoyellowing of bleached and FWA-treated fabrics is much faster than the non-treated one, especially in the wet condition. In order to neutralize this destructive attack from ultraviolet light, the most widely used protective method is application of UV absorbers. The most successful UV absorber applied in wool is known as 'Cibafast W', which is an organic conjugated compound and has been commercialised by CSIRO in 1990. It is effective against phototendering rather than photoyellowing[1], and cannot be used on bleached and FWA-treated wool[2]. Compared with the organic UV absorbers, inorganic UV absorbers, such as ZnO and TiO2, are generally non-toxic, more stable and effective. But their strong photocatalysis effect could accelerate the photoyellowing process. The key research question is: is it possible to develop inorganic UV absorbers that have low photocatalytic activity?

 Abstract

In almost every application of ionic liquids, water is present. In some cases, water is an undesired impurity. In others, it is an essential co-solvent, the main solvent, or a dominant phase present during a synthesis reaction or separation process. Because ionic liquids are salts, it has been assumed that they are very hydrophilic, but there is significant evidence that some ionic liquids are quite hydrophobic and that water interacts in various and unpredictable ways with ionic liquids. In this talk, we will describe a number of molecular-level simulation studies that have been directed at understanding the way in which water affects the thermodynamic and transport properties of ionic liquids. We will show how ionic liquids dissolved in a bulk water phase do not necessarily dissociate completely, but rather remain associated even under high dilution conditions. We will also use simulations to show how amino acid analogues partition between an aqueous phase, an octanol phase and an ionic liquid phase, and how the nature of the ionic liquid anions plays a major role in determining this partitioning tendency. Finally, we will show how simulations can enable the prediction of water solubility in an ionic liquid phase, and how these calculations are being used to optimize new ionic liquids being developed for CO2 capture.

 Abstract

John Jonas was born in Montreal and educated at McGill and Cambridge Universities. He began teaching at McGill in 1960 and established a laboratory specializing in the high temperature deformation of metals. He was 35 years old before he published his first paper, now happily forgotten. No one had bothered to inform him of the Eight Basic Laws for success in research. Now he has painstakingly derived these himself and will share them with the audience and with those beginning their research careers. But first, everyone is invited to propose his or her own favorite rules. After suitable discussion, the two lists are compared and the best ones are proposed for adoption by researchers in training. He and his students have won numerous awards for their work and he has been named to the Order of Canada as well as to the Order of Quebec. His current h-index is 56 and he has more than 13,000 citations to his credit.

 Abstract

Cashmere guard hairs are stiff natural keratinous protein fibrous materials. They are segregated as a waste from cashmere fleece during collection of luxurious fine cashmere fibres by the dehairing process in the cashmere industry. Unlike the fine cashmere fibres, they are coarse; contain large medullation, and lack crimp or curvature. Consequently, cashmere guard hairs are not suitable for spinning and often fetch low value applications. As a protein fibre, cashmere guard hair contains different functional sites/groups such as -CO-NH-, -COOH, -SSR, -SH. These reactive groups can be utilized to bind organic and inorganic chemical species, similar to other protein fibres such as silk and wool, targeting specific applications. Recent studies on the powdered wool and silk have shown improved adsorption kinetics towards organic dyes and different transition metal ions, which demonstrated their potential in waste water treatment applications. Cashmere guard hair powder could also be used in similar ways to realise good value addition for the product that otherwise has little use. In the present study, cashmere guard hair has been pulverised into ultrafine powder and its potential in toxic heavy metal ion absorption has been investigated. To explore their application as a functional coating material, powders have been used to coat polyester fabric by electrostatic powder coating technique to impart the natural feel and antibacterial properties to the synthetic substrate.

 Abstract

Low symmetry metallic materials (e.g. titanium, zirconium, etc.) display deformation and failure properties that are quite different from that of typical materials with cubic crystalline structure (aluminium, steels, etc). Rolled or extruded products exhibit a strong anisotropy and very pronounced difference in yielding and work-hardening evolution between tension and compression loadings. In this talk, new multi-scale models for description of the deformation of such materials are presented. These models are based on a detailed multi-scale characterization conducted in order to identify the physical mechanisms at the single crystal level and their effects on the macroscopic response. The effect of texture evolution is explicitly modeled using these experimental data and numerical tests results performed with a crystal plasticity model. Applications of these models to the simulation of the quasi-static and dynamic response of titanium and zirconium are presented. We conclude with the presentation of new analytic plastic potentials for isotropic and anisotropic porous materials containing spherical voids randomly distributed in a matrix displaying tension-compression asymmetry. These anisotropic plastic potential developed depend on all the invariants of stress and mixed stress-anisotropy invariants. It reduces to Benzerga and Besson (2001) criterion, if the matrix material is transversely isotropic and has no strength differential effects. If the matrix material is isotropic and has the same yield in tension and compression, Gurson (1977) criterion is recovered.

 Abstract

I will first introduce the research activities of the sheet metal forming group of the University of South Brittany. These activities deal with (i) the characterization of the mechanical behavior of metallic sheets at room (up to warm) temperatures and under quasi-static conditions and (ii) the design of laboratory devices of sheet forming and assembly processes, like deep drawing, flanging, hemming, twisting and indentation, to validate finite element simulations. I will then focus on the ductile damage characterization of a 6000 series aluminium alloy. Tensile tests on both straight and notched samples at different orientations to the rolling direction, and equibiaxial expansion tests were performed up to fracture. Gurson-Tvergaard-Needleman model, extended to the case of plastic anisotropy described by Hill's 1948 yield criterion, was used to represent the material behavior. The parameters were identified by inverse analysis and by using finite element simulations for inhomogeneous tests and a critical void volume fraction was then determined. This criterion based on a critical void volume fraction was then used to the case of both unconstrained bending of square samples and three-step hemming process of flat surface-straight edge sample. Ductile failure was evidenced with SEM observations and numerical predictions were compared with experiments. In a third step, ductile damage was also investigated at the microstructure scale (i.e. void distribution) by X-ray micro-tomography, for different triaxiality ratios.

 Abstract

Nanotechnology is having a profound effect on the development of new biosensors. Biosensors commonly comprise a biological recognition molecule immobilised onto the surface of a signal transducer to give a solid state analytical devices. The reaction between the biorecognition molecule and the analyte is a heterogeneous reaction and therefore the design of the biosensing interface is all important in determining the final performance of the biosensor. Advances in nanofabrication of biosensing interfaces is one of the two major areas where nanotechology has dramatically impacted on biosensor research in the last few years. With regards to fabricating biosensing interfaces the rise of self-assembled monolayers (SAMs) has been particularly important in giving molecular level control over the fabrication of the biosensing interface. Using SAMs has resulted in not only better performing biosensors but also new opportunities in developing new types of transduction mechanisms in biosensors which are more sensitive, selective or both. The application of new nanomaterials, be they nanoparticles, nanotubes or nanoporous materials, to biosensing is the other major area in which nanotechnology has influenced biosensing research. The use of high surface area nanomaterials has been important in producing biosensors with greater sensitivity and shorter responses times as well as being compatible with in vivo biosensing. This presentation will discuss the importance of nanotechnology on biosensing research drawing from examples from our laboratory. In the first half of the presentation we will concentrate on the advantages of fabricating biosensing interfaces using self-assembled monolayers. The latter half of the presentation will discuss some of the unique opportunities nanomaterials provide for biosensor development.

 Abstract

Solid-state nuclear magnetic resonance (NMR) spectroscopy is an extremely useful and versatile technique for the characterization of materials at the molecular level. It can provide unique, quantitative structural information such as atomic coordinations or bond lengths, and can also be used to probe dynamic processes over a wide range of timescales. I will provide a very brief, basic introduction to NMR spectroscopy and quadrupolar nuclei before outlining several recent methodological developments in this field. In particular, I will focus on techniques for "difficult" quadrupolar nuclei such as sulphur-33 and nitrogen-14, which are challenging to study using solid-state NMR, but, due to their ubiquity, have the potential to provide crucial information on a number of important systems.For sulphur-33, I show that a simple combination of computational methods can be used to generate signal enhancement schemes based on a crystal structure. This approach allows the a priori optimization of the experimental settings for this insensitive nucleus.For nitrogen-14, I show how frequency-swept RF pulses can be used to acquire extremely wide NMR spectra in relatively short timescales, and discuss the application of this approach to probe the proton conduction mechanism in crystalline imidazole. Finally, I describe the magic angle spinning (MAS) overtone experiment which allows the direct acquisition of high-resolution nitrogen-14 spectra from powder samples, something not previously thought possible.

 Abstract

Historically materials research at the University of Wollongong to a large extent focuses on steels as a priority area. This is due to the close links between the University and BlueScope Steel Ltd. (formerly BHP). In this talk a brief overview of the steel-related projects conducted by the BlueScope Steel Metallurgy Centre and Engineering Materials Institute will be presented. In particular, projects on pipeline steels, hydrogen embrittlement and transformation-induced twinning steels will be discussed.