Polymeric materials with reinforcement fiber are classified as composites with two or more different stages. Normally, are formed by two stages: One mold of polymeric resin and continuing fiber of reinforcement carbon. This fiber forms the backbone of the material and determines his strength and resistance in his direction. The mold protect from graze and impacts, supported by fiber that transmit the strain between all the fibers.
The fiber chain interweaves formatting a flat structure of fabric in one or more layers of fiber. This layers keep joined with mechanic unions between fibers or with a secondary material used for tied up fixing all in his place. In this way, is possible gives consistency at the fiber phase to be able for industrial process.
These kinds of fabric are classified according to the orientation of the fibers in the mold and his molding way to fix the fibers connected to each other. The main categories of the orientations of the fiber are: Unidirectional, bidirectional and multiaxials.
Unidirectional fabric (UD)
In this fabric, the majority of the fibers are oriented in one direction and let the structure of the composite be designed for the fiber orientation transforms the major loads in strains to the fiber. So the UD fiber are completely flat and without imperfections because doesn’t exist the interweave fiber. In this way, the maximum benefits are just in the fiber direction. Generally, this fabric is used for reinforce laminate putting it in the orientation of the loads.
Interweave fabric (Bidirectional)
These fabrics are used when the load is complex and requires more than one orientation in the fiber. The interweave fabric are the result of the intersection of the vertical fibers (0º) and horizontals (90º) in a regular pattern. The integrity of the fabric is made by the mechanic fixation of the fiber. There are different types of regular pattern but the most used is called “twill”. It presents a disposition of normal fibers interweaved in scaled way in pairs regularly. This provides a flat order of fiber with less waves, as results a free irregularity fabric with mechanic characteristics little higher than a flat interweave. Sometimes is possible see a rib on the fabric to increase the isotropic behavioural because himself has very good answer to vertical and horizontal strain but with different angles needs being reinforced.
Layout de un tejido bidireccional tipo Twill
Multiaxial fabric
The multiaxial fabric are used for reduce the time of fabrication of wide laminate. In this kind is possible use more thicken fabric and reduce the number of layers than in normal laminate. These fabrics are formed by one or more layers of large fiber fixed by a secondary net no structural. The main fiber can be any kind of structural fiber in any combination. The process of weave let use any orientation of the fiber, beside of the 0/90º fabric, the triaxial is the most common to be combined in a fabric. These fabrics offer better mechanical properties than interweave because always are flat and without imperfections and its possible put more orientations of fiber to support de loads. The number of layers of fabric increase but the behaviour is near to be likely isotropic material.
Teixit Tri axial 0/45º/-45
Mechanical characteristics
It’s possible study different levels:
- Mechanical characteristics of constituents (fiber, mold and interface)
- Mechanical characteristics of a layer (combination between fiber and mold)
- Mechanical characteristics of the laminate (succession of layers in different orientations)
The mechanical characteristics of different layers of composites are determined by the combination of the properties of the reinforce fiber, the mold, the interface and the volumetric proportions. Finally the mechanical characteristic of a pile of layers (laminate) depends of the combination of the mechanical characteristic of the different layers that compose it.
Given the crowd of combinations of different fibers and molds its difficult generalizes but in comparative terms its possible expose the next estimations of tensile and strength.
The absolute data are enough interesting, but the differentiation of the compounds of carbon is to take the density, the resistances and specific rigidities into account:
This excellent resistance/weight relation and rigidity/weight makes that it is a very good choice for pieces that combine the mechanical demand with the needs of low weight.