Composite materials discontinuous fibres

As noted earlier in this handbook, continuous fibre composites with fibres accounting for 50% or more of the material volume present the highest properties possible. Unfortunately, continuous fibres make forming - and sheet forming in particular - difficult to control. Before specifying continuous fibre components made by sheet forming, a designer should determine whether a discontinuous fibre product could meet the need. 

In this application, the fibre volume content must exceed the critical volume in order to obtain both strengthening and toughening. Composites with this level of fibre content can be produced in a number of ways. The early work on such materials involved hand lay-up of continuous fibrillated polypropylene mats [10,26], However, since then a number of processes suitable for industrial applications have been developed using short, discontinuous fibres ... 

Another classification of composite materials is based on the morphology of the reinforcement introduced into the matrix. The composites therefore could be categorised into two main groups continuous reinforced system and discontinuous reinforced system. In the former, the matrix contains continuous fibres or filaments, which typically distribute in a uniaxial direction and enhance the strength and creep resistance of the matrix. In the latter, the matrix contains particulates, whiskers or chopped fibres, which distribute in the matrix uniformly in random orientations. Moderate toughening and reasonable levels of strengthening can be achieved. 

For this reason, considered at present are possibilities of creating essentially more cheap materials, namely discontinuously reinforced Ti-matrix composites - so called DRTi. According to Miracle [20], the reinforcement with TiB fibres is the most effective one. For example, incorporation of reinforced phase up to 40 vol. % allows a combination of properties (especially stiffness) to be essentially increased. 

Within the field of materials science, the term composite is appUed to a material that consists of a combination of phases. Typically, there are two phases, a continuous one, known as the matrix, and a discontinuous one, dispersed within the matrix phase [1]. The majority of composites consist of an inorganic filler, either particles or fibres, dispersed in a matrix of organic polymer. However, other technically useful composites exist, including all-ceramic composites [2] and metal matrix composites [3]. 

Morton, J., Groves, G. W. (1974) The cracking of composites consisting of discontinuous ductile fibres in a brittle matrix - effect of fibre orientation , /o r a/ of Materials Science, 9 1436 5. 

In the case of material optimization, the variables are volume fractions, kinds and qnalities of components, their distribution in space, their reciprocal relations like adherence, etc. The variables may be defined as continuous or discontinuous (discrete) ones. Quantities (e.g. volume contents) characterizing particular components are the continnous variables. A few discrete kinds of components represent discontinuous variables, that is, only a discrete list of available types of Portland cement and different kinds of fibres may be used in the composition. Methods of production may also be considered as discrete variables provided that they determine final or transitory material properties. 

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