Compact reinforced composite

Bache, H.H. Introduction to Compact Reinforced Composite. Nordic Concrete Research, Publ. No 6, 1987, pp. 19-33. 

H.H. Bache, Compact Reinforced Composite, Basic Principles, CBL Report No. 41, Aalborg, Denmark, 1987. 

As a general rule, self-reinforced composites consist either of layers of highly-oriented thermoplastic textiles [4-7] or of a combination of self-reinforced textiles and a similar thermoplastic matrix material, which is added in the form of a film, powder or melt [1]. These are then hot-compacted to structurally consolidated mono-composites under pressure and temperature in a pressing process. For the most part, the fiber composite concept relies upon the embedding of stretched endless fibers or tapes made of PP into a chemically identical matrix. 

The first step in the production of self-reinforced composites is the primary shaping of films and tapes directly from the melt. While doing so, a mono-, and also a co-extrusion of the said products, can be targeted. In contrast to coextrudates, mono-extruded films and fibers require extremely precise temperature control during later hot-compaction and molding processes. However, they can be purchased for a lower price. 

Figure 22.2. Production of self-reinforced composite via selective melting of the outer surface of the oriented PP-tapes during hot-compaction under temperature and pressure according to [7,43]...

Figure 22.4. Schematic pressure and temperature dependent processing window for the hot-compaction of self-reinforced composites [22]...

In the case of fibre reinforced composites a special measure of workability was proposed by ACI 544.2R-89 called inverted slump cone. A standard Abrams cone is suspended upside down and filled with tested material without any compaction. The internal vibrator is activated and the bottom cover of the cone is removed, then the time of flow out of the material is recorded, which is usually between 10 and 30 seconds. This method is still in use, but is subject to some criticisms. Other methods of the flowability of the fresh mix with dispersed fibres are proposed by Laboratoire des Fonts et Chaussees in France (cf. Section 12.5). 

In this study, 7 mm diameter rod shaped SiC reinforced composites produced by pressure infiltration technique were examined. A schematic of the pressure infiltration apparatus used in this study is illustrated in Figure 1. A fused silica tube was used as a compact holder. The mean diameter of the SiC particles compacted in the silica tube was 23 pm. Commercial pure Al and Al-8 wt% Mg alloy melts were infiltrated into the compacts under argon pressure of 765 kPa at a melt temperature of 750 "C. Details of the infiltration procedure were explained in [14]. 

The further development of three-dimensional textiles is the main focus of current research projects in this area. Compared to the very compact reinforcement tex-tiies for composites, the textile reinforcement of cement-bonded matrices needs a more open-meshed textile structure. For economic reasons, textile structures should be arranged only in the cross sections of components in which tractive forces have to be transferred that cannot be absorbed by the concrete. Areas of compressive stress and zones with a low mechanical stress should be widely free of textiles. The advantages of textile-reinforced concrete are as follows ... 

Hot pressing produces compacts that have superior properties, mainly because of higher density and finer grain size. Closer dimensional tolerances than can be obtained with pressing at room temperature are also possible. Hot pressing is used only where the higher cost can be justified. It has been usehil in producing reactive materials. One use is the combination of P/M and composites to produce hot-pressed parts that are fiber reinforced. 

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