Hybrid Composites 234p5d

TECHNICAL SEMINAR ON

HYBRID COMPOSITES BY

NITHIN K [email protected]

COMPOSITE MATERIAL What is composites? It is manufactured (except wood) It consists of two or more physically and/or chemically distinct, suitably arranged or distributed phases with an interface separating them.

WHAT IS HYBRID COMPOSITES? •

Composites containing more than one type of fiber called hybrid composites.

Mixing of fibrous and particulate fillers in a single resin or metal matrix produces another species of hybrid composite. • Two types of hybrid processing , 1. Intimately mingling the fibers in a common matrix. 2. Laminating alternate layers of each type of composites.

FEATURES OF HYBRID COMPOSITES • Hybrides extend the idea of tailor making a composite material to meet specific property requirements. • Partial replacement of expensive fibers by cheaper but adequate fiber types is another attractive feature of hybrid composites. • Additionally, there is the possibility of obtaining a synergistic effect in the fatigue behaviour of hybrid composites.

Holes in Material Property Space Is it possible to create  a material to fill this empty space? (A compliant- high thermal conductivity material ??)

big empty area

E

HYBRIDS

Typical examples: 1. Carbon/Aramid 2. Glass/Carbon 3. Glass/Aramid 4. Carbon/ Kevlar 5. Aluminium/Aramid etc.

The advantages of hybrids is that in some weaves and braids, the best properties of each of the types of reinforcements can be utilized with cost reduction. •Hybrid composites provide wider opportunities to control material stiffness, strength, and cost. • A promising application of these materials is associated with the so-called thermostable structures, which do not change their dimensions under heating or cooling. •For some composites, e.g., with glass or boron fibers, the longitudinal coefficient of thermal expansion is positive, whereas for other materials, e.g.,with carbon or aramid fibers, it is negative. •So, the appropriate combination of fibers with positive and negative coefficients can result in material with zero thermal expansion.

Ehybrid = EAVA + EBVB + ECVC + ............................................................... where EA , EB , EC ...... are the moduli of the individual component unidirectional composites VA , VB , VC are the volume fractions of the components VA + VB + VC + = 1.

HYBRIDS: CONFIGURATION

fiber by fiber mixtures

skin-core-skin structures

tow-by-tow mixtures

internal ribs

Layer-by-layer mixtures

External ribs

Carbon glass hybrid composite

ARAMID -ALUMINIUM LAMINATES • If hybrid composite is made of alternating layers of high strength aluminium alloy sheets and unidirectional aramid fibres in an epoxy matix is called aramid aluminium laminates(ARALL). • Properties: Excellent fracture & fatigue resistance, high strength, good formability, machinability, toughness & impact resistance. cracks can grow only a short distance before being blocked by the aramid fibers spanning the crack tip. 15-30% weight saving over conventional construction. • It can be formed, punched riveted or bolted like a metal. • Applications: • Tension dominated fatigue and fracture critical structures such as aircraft fuselage, lower wing and tail skins.

ARAMID ALUMINIUM LAMINATES (ARALL)

GLASS- ALUMINIUM LAMINATES • Other type: If a glass fiber reinforced epoxy sheet is used instead of an aramid /epoxy sheet, then it is called GLARE. • Another version: metallic outer skins with a viscoelastic core material (polyethylene, nylon, polypropylene, paper or cork). • Application: sound and vibration damping (Viscoelastic layer provides a high loss factor,i.e, a high capacity to convert vibrational energy to heat).

Study of a journal paper

•Hybrid consisting lamianted layers of carbon fibers and glass fibres was studied.(Volume fraction ratio 1:1) •Two types of hybrid were made.(bonded and un bonded).

LOAD-STRAIN DIAGRAM OF CFRP & GRP

s taken Specimen

Load-strain curves for unbonded layered hybrid specimens consisting of two layers of CFRP and two of GRP

Load-strain curves for bonded layered hybrid specimens consisting of two layers of CFRP and two of GRP

Discussions •The extension at breaking point is greater than the breaking extension of the CFRP tested alone. •After initial fracture, which occurs at the weakest point of the CFRP layer, the well-bonded samples behaved in a manner quite unlike the unbonded material. • The load/elongation curves were not like those predicted by any model that considers only the independent properties of the separate constituents. •The bond between layers ensures that the CFRP continues to carry a share of the applied load and to contribute to the overall stiffness of the hybrid. • Because of the bond, load transfer occurs between the GRP and CFRP and there is a critical length for effective reinforcement by the stiffer layers similar to that in the ordinary theory of composites. •It is therefore possible, with a good bond between the different layers of fiber reinforced materials, to produce light engineering materials with controlled stressstrain behaviour. •The load elongation curves obtained for the hybrid materials described here were similar to that proposed as being desirable for a strut (Fig. 1).

References 1. Hybrid carbon and glass fiber composites by A.R.Bunsell & B.Harris 2. Composites materials-Science and Engineering by K.K.Cawla 3. Http://www.google.co.in 4. PPT on Hybrid composites by John Summerscales.