Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 1 Lecture 5 & 6-2 F-35 The Navy’s affordable tactical aircraft for the 21 st century. The first all-aspect stealth platform, all weather precision strike capability. Its simplified, low- cost maintenance and quick turnaround generates striking power. Carbon Fiber (cont.)

Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 2 Carbon Fiber (Cont.) Turbine blades (wind energy generators) have great length of carbon/glass hybrids (56.5 m). They use carbon fibers and curved back edge to optimize blade performance

Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 3 Carbon Fiber (Cont.) The pleasant plain road bridge (composites)

Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 4 Carbon Fiber (applications) Kflf9fpe0e-e0e[rtl6Kflf9fpe0e-e0e[rtl6 Graphite fiber reinforced composites have found applications in a variety of areas: -Aerospace/aircrafts- wings, empennage (tail), fuselage, space, missiles. -Leisure: golf clubs, tennis rackets, finishing rods. -Agriculture -Materials handling equipment -Medical applications -Industrial-weaving machine

Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 5 4- Aramid (Kevlar) Fibers  another important class class of fibers.  Aramid is the generic name for aromatic polyamide.  Organic fiber that posses high strength and stiffness as a result of high aligned, rod like polymeric molecules.  The high strength and stiffness are combined with a relatively low density to give very high specific properties.  Most important aramid fibers are DuPont’s Kevlars, which were introduced in  used quite often to replace glass fibers in many applications due to their high strength and moduli plus ease of handleability.  Were not satisfactory to replace glass fibers in amy applications due to their high strength.  Combined with gr to give hybrid composites to take advantage of toughness and for damage resistance.  Aramid fibers are produced by an extrusion/ spinning process:

Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 6 Aramid (Kevlar) Fibers -aromatic polyamides are made in solution- a polycondensation of diamines and di-acid halides at low temperatures. -Polymers are spun from strong acid solution by a”dry-jet wet spinning process”.

Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 7 Aramid (Kevlar) Fibers -Has low longitudinal shear modulus and poor transverse properties which would result in low resistance to axial compressive failure. -Great in tension bad in compression (buckling has been observed) Fiber properties: -Three types of Kevlar (29, 49 and 149) 29 is used widely as tire cord—has low properties but 49/149 is in our interest for high performance. -Aramid fibers possess high tensile strength and moduli combined with low density: giving then vey high specific properties. -Also possess good retention of properties to elevated temperature. -Good chemical resistance -Good fatigue resistance - high moisture regain is a problem for processing composites- can cause adhesion/wetting problems for the resin-fiber must be dried prior to resin application.

Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 8 Aramid (Kevlar) Properties Reinforcement Forms -Kevlar 49 is available in a variety of forms: -Yarns -Roving -Fabrics -Filaments are available in a variety of deniers -Yarns and roving are available in different cross-sectional size depending on numbers and sizes of filaments per strand. -Fabrics come in all verities of weave and etc. -Composites can be fabricated from a variety of starting materials. -Preimpregnated tapes, fabrics, yarns -Roving can be impregnated in-situ with the process as filament winding. -Most starting materials for gl are available for Kevlar. Composite fabrication is dictated by material form and resin system

Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 9 Aramid (Kevlar) Properties

Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 10 Aramid (Kevlar) Properties 200 not good enough

Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 11 Composite Properties -typical composite properties attainable with Kevlar as shown in the table for unidirectional continuous fiber reinforced epoxy composites: -The high tensile strength and moduli and low density are translated into composites with high specific strength (4x10^6 in) and high specific moduli (2.2 x 10^8 in.) -Also, in addition to above, Kevlar composites possess good fatigue resistance. -Another major characteristic material is very tough impact/damage (hard to machines) -Has two major drawbacks: - very low compression properties make them unsuitable for compression critical structures. Low inter-laminar shear (poor adhesion to resin) is also bad for non-tension critical applications Best suited for tension-critical applications such as filament-wound pressure vessels.

Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 12 Kevlar Applications  Due to high specific tensile properties and ease of handling, Kevlar, Kevlar 49 is well qualified for filament winding of pressure vessels.  Large amount of work in this area.  In addition to pressure vessels also have applications in  Aerospace– secondary structures, interiors, helicopters, rocket motor cases, engines.  Leisure—boats, sails  Protective clothing vests, helmets.  Automotive—tires  Another very important use– hybrid composites  Is used with other advanced composites reinforcements to achieve an optimum balance of properties  Combined with kev/gr/ep  Major usage is as glass replacement