Research in Mechanical Engineering

MATERIALS

Staff Involved: G. Leadbeater, K.K. Teh, I.J. Davies

Project Description(s):

The influence of welding parameters on induced residual stresses and fatigue properties of thin aluminium plates

From the standpoint of certain industries in Western Australia, there is a constant need for ongoing research and development in welding, particularly for exotic materials such as Stainless steels, Titanium alloys, and Aluminium alloys. This project focuses on Metal Inert Gas (MIG) welding of thin (<6mm) Aluminium alloy plate, with the purpose of investigating the effects of variations in welding parameters on the induced residual stresses and fatigue properties of the welds. An important aim of the work is to optimise the welding conditions for various design configurations and specific alloys related to the marine and automotive industries. A MEng project commenced in 2001, in which appropriate automated MIG welding equipment has been developed and initial residual stress analysis by the hole drilling method has been carried out.

Stainless steels and exotic alloys

A number of regionally based industries, eg. offshore, mining, refining, process and power, are regular, though not high-quantity, consumers of stainless steels and exotic alloys, particularly for critical components used in severe environments. In order to optimise the selection and application of these materials, work has begun aimed at predicting their behaviour in specific service conditions using FEA modelling. Testing equipment to simulate elevated temperature/corrosive-erosive service environments will be developed in the next stage of the project. Support for this work has come from both local and national industrial organisations.

In a separate project, again in collaboration with a local organisation, work is being done to develop a mathematical model to predict the operation of a Vacuum Arc Remelting (VAR) furnace, used in the production of Nickel based superalloys. This work is in the early stages, but seeks to establish an understanding of how small variations in process parameters can affect the quality and specification of the finished alloy product.

Biomaterials

Work is envisaged which will establish more clearly the tribological and interfacial behaviour of a number of hard coatings on traditional prosthesis materials. Loading conditions and performance of appropriate test specimens will be modelled initially by finite-element methods (FEM), followed by analysis in simulated in-situ environments. The project has clear multi-disciplinary potential; drawing on elements from mechanical and materials engineering, health sciences, and applied sciences.

Ceramic Materials

Ceramic materials may be tailored to possess a wide variety of physical and mechanical properties, making them useful for applications such as high temperature structural materials, electronic materials, and biomaterials. Examples of ceramic materials include silicon nitride (Si₃N₄) and silicon carbide (SiC) (high temperature structural materials), alumina (Al₂O₃) and aluminium nitride (AlN) (electronic materials), and hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) and zirconia (ZrO₂) (biomaterials). Future projects will involve the manufacture and characterisation of advanced ceramic materials.

Ceramic matrix composites (CMCs)

One potential disadvantage of ceramics when compared to other materials is their relatively poor fracture toughness. The introduction of ceramic matrix composites (CMCs), in which ceramic particles, whiskers, or fibres are embedded within a ceramic matrix, has improved the fracture toughness of ceramic materials by an order of magnitude. High fracture toughness CMCs typically comprise of continuous silicon carbide (SiC) or carbon (C) fibres in their respective matrices, i.e., SiC/SiC and C/C. Applications of high strength, high fracture toughness CMCs include high temperature (>1200 ^oC) space and aerospace structures. Future projects will involve the manufacture and characterisation of CMCs.

Polymer matrix composites (PMCs)

Polymer matrix composites (PMCs), comprising of particles, whiskers, or fibres embedded within a polymer matrix, possess significantly higher fracture toughness and stiffness values compared to standard polymeric materials. The most utilised types of PMCs are the glass fibre reinforced polymer (GFRP) and carbon fibre reinforced polymer (CFRP) composites, with applications including the reinforcement of civil engineering structures and lightweight aerospace structures. One particular group of PMCs is known as a "hybrid" composite and contains two or more types of fibre reinforcement, e.g., glass/carbon and carbon/aramid. Future projects will involve the manufacture and characterisation of PMCs.

Failure of Brittle Materials 

The standard theory of failure for brittle materials normally assumes a large number of randomly oriented flaws, leading to a Weibull distribution for cumulative failure versus strength. However, in many cases the flaw population within a brittle material does not conform to this ideal, such as the case of most ceramics which contain two distinct flaw populations, i.e., surface flaws and internal flaws. Another example might be that of anisotropic materials in which the flaw population is preferentially oriented. Future projects will involve theoretical considerations and statistical simulations of failure within brittle materials containing non-ideal flaw populations.

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