Thermoplastic adhesives for thermosetting composites

Joining of carbon fibre/epoxy composites with traditional thermosetting adhesives can require extensive surface treatment and processing time to give a high-quality bond, adding to processing costs. A recently developed alternative uses a thermoplastic film as the adhesive incorporated onto the outer layer of the composites to be joined, with the thermoplastic and epoxy forming a semi-interpenetrating polymer network (SIPN) during the cure of the epoxy. When incorporated into the composite manufacturing process, this has the potential to provide a low-cost high-performance alternative to currently used methods.

For the thermoplastic film to be a viable adhesive, it should have a high chemical resistance and provide high-temperature performance, good long-term fatigue and creep performance in a variety of environmental conditions, and the joining process should allow interdiffusion of the thermoplastic polymer at the join while not degrading the composite adherend. However there are several other issues to be addressed. The diffusion rates of the epoxy resin and hardener may differ, giving residual levels of resin or hardener in the thermoplastic and thereby altering performance. The size of the SIPN can be optimised through an understanding of epoxy and thermoplastic compatibility, interdiffusion and curing rates. Joining processes, including localised heating and vibration, may be able to enhance the speed or quality of the bonding process without degrading the composite adherends, requiring an understanding of autohesion and polymer diffusion processes. Finally the influence of processing on the joint, in particular residual stress levels in the thermoplastic, will be of interest for determining long-term performance.

A full-time (Master or PhD) student with a good degree in materials science or polymer chemistry is sought to conduct research projects in this area. The successful candidate will be jointly supervised through the University and the CRC-ACS and will be eligible to apply for a CRC-ACS scholarship top-up of $6000 p.a.

Numerical Modelling and Characterisation of Z-fibre Reinforcement of Advanced Composites

Advanced composite materials manufactured from carbon fibres and epoxy matrix offer significant performance advantages over metals including high strength and stiffness to weight ratios, the ability to tailor properties during design, and resistance to corrosion and fatigue. These superior properties have been utilised by the aerospace industry for a number of years in both secondary and primary structural applications.

Typical advanced composites are manufactured by laminating a number of thin layers of material, which are cured at elevated temperature and pressure. A result of this process is that no fibres are orientated through the thickness of the laminate, making composite materials susceptible to loads applied in this direction. Such loads can be induced at joints, changes in geometry and free edges, or through impact events. The resulting damage often takes the form of delaminations, which seriously reduce the compression strength of the laminate.

A technology to insert fibres through the thickness of laminates, termed Z-fibres, has been proposed. The Cooperative Research Centre for Advanced Composite Structures (CRC-ACS) is currently involved in an international research program investigating the uses of this technology. A full-time research student (Masters or PhD) with good Bachelor degree in aerospace, mechanical or materials engineering is sought to conduct research projects into numerical modelling and characterisation of Z-fibre reinforcement. In particular, numerical procedures will be developed to simulate the effect of Z-fibres on the stiffness and strength, fracture toughness and impact resistance of laminated composites. Experiments will be conducted to verify the numerical modelling techniques developed. The modelling techniques will be applied to the design of composite structures incorporating the Z-fibre technology.

The successful candidate will be jointly supervised through the university and the CRC-ACS, and will spend considerable time at the CRC-ACS working as part of a team of research engineers. The successful candidate is eligible to apply for a $6,000 p.a. CRC-ACS top-up scholarship.

Post-forming of cured or semi-cured composite parts

Current thermoset composites for aerospace applications such as carbon fibre/epoxy composite structures are normally cured at 180C for several hours. This gives an epoxy matrix which is fully -crosslinked, and holds its shape at service temperatures up to for instance 150C. However it is known that if out-of-plane loads are applied to an unsupported structure during any subsequent curing, the composite can creep to some extent, and assume an altered shape. This behaviour is normally undesirable, and the process or tooling changes necessary to avoid it may be very expensive.

On the other hand, there may be considerable manufacturing cost advantages in being able to re-form a composite structure which has been cured into a slightly different shape. In this case the creep behaviour outlined above is highly desirable.

The project will investigate the extent of this "post-forming" behaviour in composite materials used in aerospace production. Among the aspects investigated will be: residual stresses and springback of postformed parts; the effect on laminate mechanical properties; the degree of post forming possible; the relationship between degree of cure and ease of postforming; and the effect of temperature. The project may open up possibilities for new production methods and /or allow manufacturers to avoid costly production fixes.

The Cooperative Research Centre for Advanced Composite Materials (CRC-ACS) conducts research into the effective and efficient production of composite structures for various demanding applications. A full-time (Masters or PhD) research student with a good bachelor degree in aerospace, mechanical or materials engineering is sought to conduct research projects in this area. The successful candidate will work as part of a team of research engineers, have access to a wide range of equipment and expertise, be jointly supervised through the University and the CRC-ACS and will be eligible to apply for a $6000 p.a. CRC-ACS scholarship top-up.

In-line non-destructive inspection of pultruded products

Pultrusion is a process by which composite components of continuous cross-section can be economically manufactured. High performance pultrusions often involve the use of relatively viscous resins systems such as epoxies. This can lead to difficulties in fully "wetting-out" the reinforcement material with the possibility of a dry or voided product. These flaws must be identified and eliminated. In order to achieve efficiency in the production of high integrity parts such as are demanded by the Aerospace Industry, a means must be developed for incorporating the necessary non-destructive inspection (NDI) down-stream of the die and prior to entry into the docking saw.

Traditional methods for inspecting composite parts such as ultra-sonic scanning using a may be possible as may more novel approaches such as on-line dielectric or even chemical monitoring. The NDI signal could also provide feedback for control of the process, through adjustment to parameters such as pulling speed.

The Cooperative Research Centre for Advanced Composite Materials (CRC-ACS) is conducting research into the effective and efficient production of aerospace quality pultrusions. A full-time (Masters or PhD) research student with a good bachelor degree in aerospace, mechanical or materials engineering is sought to conduct research projects in this area. The successful candidate will work as part of a team of research engineers, have access to a wide range of equipment and expertise, be jointly supervised through the University and the CRC-ACS and will be eligible to apply for a $6000 p.a. CRC-ACS scholarship top-up.

Modelling and Characterisation of Knitted Preforms for Advanced Composites

Advanced composite materials manufactured from textile preforms such as woven, braided and knitted fabrics offer significant performance advantages over other more conventional composites in terms of potential cost savings and improved mechanical properties. These superior properties are derived from the ability of textile processes to produce reinforcements that afford parts integration, reduced material wastage, improved formability and z-direction reinforcement.

Knitted composites are of particular interest because of their good formability by affording net-shape or near net-shape preforms. However, due to the nature of the knit architecture, there have been concerns that knitted composites would not have adequate mechanical performance for many engineering applications. Previous work carried out at the Cooperative Research Centre for Advanced Composite Structures (CRC-ACS) has shown that careful design of the knit architecture and structure could help overcome this concern. Further, it has been established through experiments that the overall composite properties could be altered during preforming when the fabric is deformed to accommodate the shape of a component. With this database of mechanical properties, the need now is to develop models tthat can be utilised for design purposes.

A full-time research student (Masters or PhD) with a good Bachelor degree in aerospace, mechanical or materials engineering is sought to carry out the research project into modelling and characterisation of knitted composites. In particular, numerical procedures will be developed to simulate the effects of different knit parameters, such as tuck and float stitches, knit parameters loop length and density, and knit architecture on both the overall formability of a fabric as well as the mechanical properties of the knitted composites. Experiments will be conducted to verify the numerical modelling techniques developed. The modelling techniques will be applied to the design of knitted composite demonstrator structures to assess their effectiveness.

The successful candidate will be jointly supervised through the university and the CRC-ACS, and will spend considerable time at the CRC-ACS working as part of a larger team involved in textile composites. He/she will also have the opportunity to interact with, and complement the work of, overseas researchers currently collaborating with the CRC-ACS in this area of research. The successful candidate is eligible to apply for a $6,000 p.a. CRC-ACS top-up scholarship.

Numerical Modelling of Advanced Composite Manufacturing Processes

Advanced composites are made of high strength fibers and moderately high temperature resins at very high fiber volume fractions. The performance advantages of the advanced composites over metals equivalents include weight reduction, design flexibility, corrosion resistance and reduced noise transmission. These advantages have long been exploited in aerospace industry where the advanced composites have been used in preference to metals for secondary and primary structures including fuselage, wings and power transmission components. Applications of the advanced composites in other areas, such as railway and automobile industries, have also become more popular in recent years.

One of the main barriers to more widespread application of the advanced composites appears to be set by the manufacturing process. All too often otherwise good ideas cannot be produced or cannot be produced at reasonable cost. An advanced composites manufacturing process can be very complex, and often involves a number of coupled physical and chemical phenomena including heat and mass transfer in multi-phase media, resin reaction, and deformation caused by temperature, chemical shrinkage and applied pressure. A fundamental understanding of the process is essential to ensure cost efficient and quality part production. In many cases, this can only be achieved economically through successful numerical modeling,

Research students (Master or PhD) with a good Bachelor degree in aerospace, mechanical or materials engineering are sought to conduct research projects in numerical modelling of advanced composite manufacturing processes. In particular, numerical procedures will be developed to simulate the residual stress development during manufacturing process.

Experiments will be conducted to obtain material properties to be used in the numerical modelling and to verify the numerical procedures developed. The simulation results obtained will be applied to guide tooling and process design for the manufacturing processes. The projects are well balanced between fundamental research and industrial applications. It is expected that the candidates will be jointly supervised by a university and the Cooperative Research Center for Advanced Composite Structures (CRC-ACS) and will spend considerable time at CRC-ACS, working with a team of research engineers in this area. A $6,000 CRC-ACS top-up scholarship may be made available for a University scholarship holder.

Continuous forming processes for composite sections

Most production of fibre-reinforced composite structures is by batch methods, in which the constituent materials are loaded into a forming mould, if necessary placed under heat and pressure, and allowed to cure. These methods allow the production of high quality parts, but are often slow and expensive, especially for high-volume production. An alternative, continuous method of production for composites called pultrusion can be used very effectively to make low-cost structural sections. However the method may be unsuitable for use with aerospace quality resins.

The CRC-ACS is developing alternative continuous or semi-continuous production methods which involve continuous forming methods to produce constant-section parts efficiently from flat composite feedstock. Little is currently known about the forming mechanics of such processes.

The project will examine the forming mechanics of the different types of composite reinforcement materials, in both their pre-impregnated and "dry" forms. The project will examine the optimum material types and conditions for forming, and the feasibility of forming different shapes. It is intended that a major part of the work be the simulation of such forming processes using general-purpose or dedicated computer software.

The Cooperative Research Centre for Advanced Composite Materials (CRC-ACS) conducts research into the effective and efficient production of composite structures for various demanding applications. A full-time (Masters or PhD) research student with a good bachelor degree in aerospace, mechanical or materials engineering is sought to conduct research projects in this area. The successful candidate will work as part of a team of research engineers, have access to a wide range of equipment and expertise, be jointly supervised through the University and the CRC-ACS and will be eligible to apply for a $6000 p.a. CRC-ACS scholarship top-up.

Manufacturing requirements for the moulding and shaping of composites made with reinforcement containing stretch-broken fibre tows, and the structural behaviour of the resulting composites

Current forms of reinforcement for structural composites are normally some form of woven or stitched fabric, or unidirectional tape, all of which incorporate bundles of continuous fibres such as carbon or glass fibres. Composites made from such continuous fibre reinforcement have very good mechanical properties, but there is considerable difficulty in manufacturing doubly-curved shapes using these reinforcements. The major problem is that the only deformation modes available to allow the reinforcement to be fitted to a compound curved surface is in-plane shear (the "trellising" action) and interply slip. To be easily formable, the material needs to be able to undergo inplane plastic deformation (stretching) like metals. Another form of fibre reinforcement, chopped-strand or continuous filament mats, can undergo in-plane stretching during layup or forming, but the resulting composites have much lower mechanical properties as the reinforcement cannot be oriented in the required direction and the fibre volume fractions achievable are much lower.

A new form of reinforcement which may allow a combination of the excellent mechanical properties of continuous fibre reinforcement with some of the formability of mats has recently been developed. This reinforcement consists of continuous fibre bundles in which the fibres themselves are not continuous but are at least several centimetres long, and the fibre breaks are randomly distributed to allow stress transfer between fibres with little effect on the mechanical properties of the resulting composite. The fibre bundle is made from continuous fibre tows by a process of controlled stretch-breaking. This type of fibre bundle, a "staple" yarn, is very common in other types of textiles, with cotton and wool yarns for instance being made up of discontinuous fibres.

This new reinforcement material opens up exciting prospects for the low-cost manufacture of high-performance compound -curved shapes such as car bodies. However at present very little is known about the forming mechanics of these materials, or the mechanic properties of the resulting composites. This project will examine particularly the forming mechanics of reinforcements incorporating stretch-broken fibres, whether "dry" , commingled with thermoplastic resin or impregnated with partially-cured thermoset resins. Forming methods will need to be developed or modified, and the properties of the resultant composites measured. If possible, models or at least guidelines for the forming of the reinforcement will be developed.

The Cooperative Research Centre for Advanced Composite Materials (CRC-ACS) conducts research into the effective and efficient production of composite structures for various demanding applications. A full-time (Masters or PhD) research student with a good bachelor degree in aerospace, mechanical or materials engineering is sought to conduct research projects in this area. The successful candidate will work as part of a team of research engineers, have access to a wide range of equipment and expertise, be jointly supervised through the University and the CRC-ACS, and will be eligible to apply for a $6000 p.a. CRC-ACS scholarship top-up.

Applicability of metal forming technology to forming of composites

A large number of specialised forming processes have be developed for shaping sheet metal, such as stretch-forming, roll-forming, stamping etc. A wide range of equipment and expertise is available to assist with the forming of sheet metal, especially in the car industry. Engineers familiar with this very efficient technology are often surprised to discover that in the aircraft industry, advanced composite panels of similar shapes are manufactured mostly by painstaking and costly hand lamination processes. There are good reasons for this: for example the forming mechanics of composite materials are quite different to those of metals, and the need for weight reduction often results in more complex designs. However it is also apparent that the manufacturing methods used for making composite structures are in many cases somewhat unsophisticated. It is recognised by Australian and international aerospace companies that their manufacturing methods will have to become more sophisticated, automated and above all efficient if they are to survive in this industry.

Some of the processes used in sheet metal forming, such as stamping or roll forming, are beginning to be investigated by the composites industry. This project will examine available metal forming processes, and the manufacturing aids used to predict whether these will work (e.g. forming limit diagrams) for possible applicability to forming of composites. The project will examine the forming of both thermoset and thermoplastic composites, but will concentrate on the use or adaption of current metal forming technology to the manufacture of thermoset prepreg composites. The student will need to be innovative and open to new ideas, and to be able to quickly under stand the differences in forming behaviour of metals and composites. A successful project will make the student very much in demand in the growing composites industry.

The Cooperative Research Centre for Advanced Composite Materials (CRC-ACS) conducts research into the effective and efficient production of composite structures for various demanding applications. A full-time (Masters or PhD) research student with a good bachelor degree in aerospace, mechanical or materials engineering is sought to conduct research projects in this area. The successful candidate will work as part of a team of research engineers, have access to a wide range of equipment and expertise, be jointly supervised through the University and the CRC-ACS and will be eligible to apply for a $6000 p.a. CRC-ACS scholarship top-up.

Diaphragm forming limits of preimpregnated composite preforms

In the aircraft industry, carbon epoxy and glass/epoxy parts have traditionally been made by hand layup followed by curing under heat and pressure in an autoclave. The process is very flexible, and can be used to make quite intricate parts, but relies on individual plies of reinforcement being laid down and shaped one-at-a-time by experienced operators. This means that costs are very high.

One method of mechanising this process is called diaphragm forming. In this method a flat stack of plies is laid up easily by hand or robotic device, and the stack is placed between two extensible diaphragms. The stack is clamped by evacuating the space between the diaphragms, and the stack is then formed over a male mould shape by evacuating the space below the diaphragms or pressurising the space above. The process is being developed by CRC-ACS and is now being introduced into the Australian aircraft industry. However much remains to be discovered about the process.

This project will investigate the importance of the various factors which are thought to influence the diaphragm forming process. Among these are interlaminar friction; resin viscosity; diaphragm stiffness; diaphragm boundary conditions; and reinforcement type. An important aspect of the work will be the identification of the mechanism by which wrinkles can form in the part, causing it to be scrapped. It is likely that computer simulation of the forming process using the PAM-FORM code will be a part of this work.

The Cooperative Research Centre for Advanced Composite Materials (CRC-ACS) conducts research into the effective and efficient production of composite structures for various demanding applications. A full-time (Masters or PhD) research student with a good bachelor degree in aerospace, mechanical or materials engineering is sought to conduct research projects in this area. The successful candidate will work as part of a team of research engineers, have access to a wide range of equipment and expertise, be jointly supervised through the University and the CRC-ACS and will be eligible to apply for a $6000 p.a. CRC-ACS scholarship top-up.