Fibre composites -joining

Composite materials can be prepared for bonding in several ways. Common procedures include mechanical abrasion of the cured composite surface and the use of a peel ply. This is a removable layer that is applied prior to curing the composite and then stripped to reveal a textured surface prior to adhesive bonding abrasion is sometimes used in addition to remove residues that may have been left by the peel ply (see Fibre composites - joining). There are also other surface treatments available, but aU aerospace bonding and pretreatment processes will require high standards of control. 

Several articles are included on different aspects of Fibre-matrix adhesion in these materials. Special techniques are required for Fibre composite joining. 

Some of the main constituents nsed in these materials are discussed under Fibre composites - matrices and fibres and practical aspects are considered under Fibre composites - joining and Fibre composites - processing techniques. 

Some other practical aspects of the use of these materials are discussed under Fibre composites - joining. 

A selection of these techniques is also applicable to polymer composites (see Fibre composites - joining). However, since composites gain their superior properties from the reinforcement, the weld is inevitably the weak point in the system as the fibre will be discontinuous across the joint interface. All the welding processes are governed by the parameters time, temperature and pressure. In order to achieve high-quality welds, careful optimization of the welding parameters is required for each application. 

Fibre composites - joining K B ARMSTRONG Thermoset matrices, peel-ply, abrasion thermoplastic matrices, corona discharge... 

Wooden airframes have historically been bonded, originally with glues such as casein or synthetic urea-formaldehyde systems, but today most aerospace structures are made from fibre composites (glass fibre and carbon fibre, predominantly) and metals (mostly aluminium but also titanium). Adhesives are well suited for joining composite materials since the need to drill holes through the composite can be avoided and, in some cases, the... 

The world of advanced fibre composites is changing rapidly. Technical and commercial battles take place in the composites arena, where big chemical companies have joined the show. The diagram shows a basic idea behind these involvements. The chemical industry thinks volume. Commodities and energy, products with a relatively low added value, have been their business over the past decades. Nowadays, however, High Tech is the message. Specialities with a high added value seem attractive. This is demonstrated by the amount of recent take overs of relatively... 

Wacker M, Moser L, Schlarb A K and Tradt H-R (2008) Flexible 3D joining process for complex fibre composite components, Joining Plastics 2 266-271. 

Because different materials are joined in composites, there are a large number of possible combinations. Metal, ceramic, or polymer matrix composites can be strengthened with different kinds of particles or fibres. Composites may be classified either by the geometry of the strengthening particles (fibres, fabrics, etc.) or by the matrix material used. 

McCarthy MA, Lawlor VP, Stanley WF. An experimental study of bolt-hole clearance effects in single-lap, multi-bolt composite joints. J Compos Mater 2005 39(9) 799—825. Hart-Smith LJ. Design and empirical analysis of bolted or riveted joints. In Joining fibre reinforced plastics. Elsevier Science 1987. pp. 227—69. 

As with aluminium extrusions, so with pultruded fibre reinforced composite profiles. The limit to the size and complexity of these profiles suggests that a modular approach could be adopted towards forming alternative structural configurations from the basic or standard profile shapes by bonding together individual lengths. Composite materials lend themselves to being joined with resin adhesives because they are themselves formed with vinyl ester, polyester or epoxy resins. Cursory surface treatments only, such as mild abrasion, often suffice. 

Laminated joints are formed by laminating fibre layers on cured composite parts, often by hand lay-up. The resin used is typically identical to that used in the components to be joined. However, different resins may also be used for fabricating laminated joints, for example epoxy on polyester parts. 

Hart-Smith, L.J., Design and analysis of bolted and riveted joints in fibrous composite structures, Douglas paper 7739, presented to International Symposium on Joining and Repair of Fibre-reinforced Plastics, Imperial College, London, 1986. 

Davies P, Cantwell WJ, Jar PY, Bourban PE, Zysman V, Kausch HH, Joining and repair of a carbon fibre reinforced thermoplastic. Composites, 22(6), 425-431, 1991. 

Morgan joined RK Textiles Composite Fibres Ltd. in 1981 as Technical Director and became involved with the design, building, erection and transfer of technology for the sale of carbon fiber plants in Israel, South Korea and India, as well as plants for in-house use. 

Fig. 7 illustrates Chapman s treatment of the mechanics of this composite system. The system is treated as a set of zones consisting of fibril and matrix elements. Originally, this was introduced as a way of simplifying the analysis, but, the later identification of the links through IF protein tails makes it a more realistic model than continuous coupling of fibrils and matrix. Up to 2% extension, most of the tension is taken by the fibrils, but, when the critical stress is reached, the IF in one zone, which will be selected due to statistical variability or random thermal vibration, opens from a to P form. Stress, which reduces to the equilibrium value in the IF, is transferred to the associated matrix. Between 2% and 30% extension, zones continue to open. Above 30%, all zones have opened and further extension increases the stress on the matrix. In recovery, there is no critical phenomenon, so that all zones contract uniformly until the initial extension curve is joined. The predicted stress-strain curve is shown by the thick line marked with aiTows in Fig. 6b. With an appropriate. set of input parameters, for most of which there is independent support, the predicted response agrees well with the experimental curves in Fig. 6a. The main difference is that there is a finite slope in the yield region, but this is explained by variability along the fibre. The C/H model can be extended to cover other aspects of the tensile properties of wool, such as the influence of humidity, time dependence and setting.

From a conceptual point of view, welded connections seem to be the most suitable method to join composite materials, with potential economic and technical advantages. However, the use of this technique is restricted to FRP materials containing thermoplastic resins which, as previously discussed, are more limited technically than thermoset resins (in terms of fibre adhesion and impregnation, processing and mechanical properties). Therefore, this technique is not often used in civil engineering applications. 

Hollaway, L. C., Zhang, L., Photiou, N. K.,Teng, J. G. and Zhang, S. S. (2006), Advances in adhesive joining of carbon fibre/polymer composites to steel members for repair and rehabilitation of bridge structures . Advances in Structural Engineering, Vol. 9, Issue 6, pp. 791-803. 

---