Abstract


Composite materials are replacing day by day theconventional metallic materials due to their light weight, high strength,design flexibility and long life. This article covers classification of compositematerials, multilayer woven reinforcements in textile composites which are moreand more employed in textile composites, especially for aeronauticalapplications due to their relatively higher strength, more uniform propertiesand reduced manufacturing cost and a note on thermoplastic and thermo-setresins.


Key words: Textile composites, laminated composites, 3-D wovenfabrics, Multilayer fabrics


Composite Material


Two inherently different materials are mixed to form a newmaterial called composite material which is different to both but better inproperties. The two constituents of the composites are called matrix and resin.


Matrix


It is the main constituent of composites materialsmainly responsible for its mechanical properties. Its percentage in the compositemay be up to 70% by volume.

 


Adhesive /Resin


Normally it is a synthetic polymer with an objective to bindthe matrix elements.


Why composites materials?


Composites materials are preferred over contemporarymetallic materials due to their

  • High strength
  • Light weight
  • Long life
  • Net shape manufacturing
  • Design flexibility


1. Classification of Composite Materials


Composites materials can be classified on the basis of typeof resin and type of reinforcement as well.


1.1 Classification on the basis of resin


On the basis of type of resin used, composite materials canbe classified into two categories.

  • Thermoplastic Composites
  • Thermo-set Composites


Thermoplastic composites


This is type of composite material with thermoplastic resinlike polyester, HDPE etc. They are lesser used as high-tech materials due totheir higher viscosity which cause problem during their penetration into the reinforcement.Their manufacturing required equipment that can withstand at high temperatureand pressure which increases the manufacturing cost. But they have someadvantages too. For examples they are not toxic and can be recycled.


 

Thermo-set composites

In these composites thermo-set polymers like epoxy, unsaturated polyester and vinyl-ester are used as resin.


They are most used type of composites materials in automotive, naval, aeronautical and aerospace applications.


They are preferred over thermoplastic resin due to their lesser viscosity (normally lesser of order of 103 times than thermoplastics) which help them to penetrate in reinforcement easily even at room temperature. Moulding equipments used are relatively cheaper as there is no need to rise till very high temperature and pressure. They have disadvantages of being toxic, non-recyclable, lesser availability for penetration time once polymerisation starts.


1.2 Classification on the basis of reinforcements


The reinforcements used during manufacturing may be in form of laminates which are combined to get certain thickness or in the form of thick woven cloth. So on the basis of reinforcement composites can be categorised in two categories

  • Laminated Composites
  • 3-D woven Composites


Laminated composites:


In laminar composites the layers of reinforcement are stacked in a specific pattern to obtain required properties in the resulting composite piece [3]. These layers are called plies or laminates.


Laminates can be composed of reinforcement material which may be

  • Non woven
  • Braided
  • Fiber reinforced
  • Matt
  • 2D-woven
  • Uni-directional fibers or UDs


Advantages of laminated composites are relatively well defined position of fibres in final composite piece, higher strength, higher fiber to volume ratio and their disadvantages are relatively poor through the thickness properties [4][5] and problems of process induced deformations. For high-tech applications UDs are mostly used in the form of pre-preg for carbon/epoxy and in the form of non-crimp fabric in case of glass/polyester.


3D woven composites


These composites have reinforcement of 3D woven or 2D+ multilayer interlock fabric. These composites have much better through the thickness properties as compared to laminated composites and have no chance of inter layer slippage which is common in laminated composites when subjected to mechanical constraints [6][9].


3D woven composites are largely employed in the structures subjected to heavy vibration i-e helicopter rotors. As no machine is being developed yet that can produce true 3D woven fabrics on commercial scale so 2D+ multilayer fabrics are largely employed as reinforcements in 3D-woven fabrics.


Multilayer fabrics for 3D woven composites


In multilayer performs weaving is done such that number of threads from a specific fabric layer are used to bind it with the other fabric layer and so on. It has been shown that the in-plane properties of multilayer woven structures are inferior to those of equivalent structures made from tape, because of crimping of the fibres, resin rich areas due to the weave design, and possibly because of damage to the fibre tows during the weaving process. These geometrical flaws have been shown to play an important role in the failure process of composites reinforced by multilayer woven preforms.

For aerospace applications, the decrease in strength in itself is not a great concern because the design allowable are normally determined by the compression after- impact strength. The decrease in stiffness due to fibre crimping may, however, be important where stiffness is the critical design parameter. The mechanical performance of the composite will therefore depend upon the final fibre architecture, so adequate control over the architecture is of prime importance [7].
Multilayer woven fabrics can be classified into four types depending on the binding pattern of the layers and the penetration depth on biding threads into the layers. [8]



1. Multi-layer angle interlock through the thickness Fig.3.

2. Multi-layer angle interlock layer to layer Fig.4.

3. Multi-layer Orthogonal through the thickness Fig.5.

4. Multi-layer Orthogonal layer to layer Fig.6.


In multilayer fabrics through the thickness properties improve considerably but absence of binding threads at certain areas decrease the in-plane properties and also resin rich areas Composites with layer to layer binding may have more fibre volume fraction than through the thickness binding also angle interlock binding fabrics have better delaminating properties in the composites than orthogonal fabrics.[8]


References


  1. http://www.addax.com/technology/properties.html, dated 09/12/2009
  2. http://www.zoltek.com/carbonfiber/, dated 09/12/2009
  3. 3-D textile reinforcements in composite materials by Antonio Miravete Page-02.
  4. K.H.Tsai, C.H.Chiu, T.H.Wu, Fatigue Behaviour of 3D Multi-Layer Angle Interlock Woven Composite Plates, Composites Science and Technology, Vol. 60, pp 241-248, 2000
  5. Potluri, P., I. Parlak, et al. (2006). "Analysis of tow deformations in textile performs subjected to forming forces." Composites Science and Technology 66(2): 297-305.
  6. Bannister, M., et al., The manufacture of glass/epoxy composites with multilayer woven architectures. Composites Part A: Applied Science and Manufacturing, 1998. 29(3): p. 293-300.
  7. Yi, H. L. and X. Ding (2004). "Conventional Approach on Manufacturing 3D Woven Preforms Used for Composites." Journal of Industrial Textiles 34(1): 39-50.
  8. De Luycker, E., et al., Simulation of 3D interlock composite preforming. Composite Structures, 2009. 88(4): p. 615-623.

Yasir Nawab is associated with Université de Nantes, France and Salma Yasir is with Université de Caen, France