Strengthening methods

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. 

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Composite Strengthening. An alternative strengthening method which holds great promise for producing advanced high temperature aUoys involves the incorporation of fibers or lamellae of a strong, often brittle phase, in a relatively weak, ductile, metallic matrix. This technique has been... 

The result is work-hardening the steeply rising stress-strain curve after yield, shown in Chapter 8. All metals and ceramics work-harden. It can be a nuisance if you want to roll thin sheet, work-hardening quickly raises the yield strength so much that you have to stop and anneal the metal (heat it up to remove the accumulated dislocations) before you can go on. But it is also useful it is a potent strengthening method, which can be added to the other methods to produce strong materials. 

It is adequate to assume that the strengthening methods contribute in an additive way to the strength. Then... 

Summary of Strengthening Methods. In practice, few alloys are strengthened by only one or merely a few of Ihe mechanisms described, as shown in Iable 2. 

M. Ashby, in Strengthening Methods in Crystals, ed by A. Kelly, R.B. Nicholson (Applied Science Publishers, London 1971), p. 137... 

By the mid nineteenth century, as the weakened condition of the collections of paper materials in major European and American libraries and archives began to attract increased concern, new strengthening methods were developed (3). The most significant of these was silking— the application of a silk gauze to both sides of a document. The process seems to have been adopted first at the National Archives of France,... 

A.Kelly and R.B. Nicholson, Strengthening Methods in Crystals, John Wiley and Sons, New York, 1971, 553. 

Figure 8. Principal strengthening methods currently used (a) modified flitch upgrading (b) tension zone upgrading (c) compression and tension zones upgrading (d) reinforcement of beams or joints above decorative ceilings [15] (reprinted with permission from Rotafix Ltd.).

A. Kelly and R. B. Nicholson, eds.. Strengthening Methods in Crystals, Applied Science Publishing, London, 1971. 

However, for MHS in seismic regions, which are to be inhabited the value safety is of first priority. Therefore, strengthening methods are selected to be technical and cost-effective, as well as less invasive (Tassios and Mamillan 1985). 

Strengthening method is to use external posttensioning as shown in Fig. 13a. Steel jackets bonded to the sides of the joint and anchored to the bent cap are also effective (Thewalt and Stojadinovic 1995). Finally, FRP jackets in the form of an ankle wrap have been tested (Gergely et al. 2000) and used to strengthen column to cap beam-colunm joints as shown in Fig. 13b (Pantelides et al. 2004). The nominal principal tensile stress developed in the beam-column joint is used to design the carbon FRP composite layers. When strengthening of these joints is required to improve the longitudinal response, transversely prestressed bolsters may be used. 

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