Composite Materials Chapter 8. Carbon Fiber Composites Prof. Song-Hee Kim Department of Advanced Materials Engineering

8.1 Fabrication of Carbon Fiber Composites Fig 8.1 A helicopter windshield post made of carbon fiber/vinyl ester resin by pultrusion. Krishan K. Chawla, Composite materials science and engineering, Springer-Verlag, (1998)

8.1 Fabrication of Carbon Fiber Composites Fig 8.3 Schematic of carbon/carbon composite manufacture starting from pitch on phenolic resin Krishan K. Chawla, Composite materials science and engineering, Springer-Verlag, (1998)

8.1 Fabrication of Carbon Fiber Composites Three main routes to obtain c/c composites 1.Woven carbon fiber preform is impreganted under heat and pressure with pitch from coal tar. → pyrolysis. The cycle may be repeated for densification. 2. C fiber/polymer composites are pyrolyzed to decompose the resin, generally phenolics because they give high char strength → reimpregnation and repyrolysis to get a carbonaceous matrix bonded to carbon fibers. 3. Cvd from gaseous phase (methane+N2+H2) onto and between the C fibers in a preform.

8.2 Properties Table 8.1 Typical mechanical properties of some carcon fiber epoxy composites Krishan K. Chawla, Composite materials science and engineering, Springer-Verlag, (1998)

8.2 Properties Fig 8.3 Fickian moisture absorption in caborn/epoxy laminate. Krishan K. Chawla, Composite materials science and engineering, Springer-Verlag, (1998)

8.2 Properties Damages of Carbon fiber/polymer matrix composite come from Ⅰ Ultraviolet rays ← Painting the exterior of the composite. Ⅱ Moisture reduces Tg, plasticize the polymer matrix. Moisture absorption and ∆T increase causes (1)Compressive stresses in resin (2)tensensile stresses in fibers

8.2 Properties Fig 8.6 Creep strains at ambient temperature for a +-45 and for a 0℃/ 90℃/ +-45℃ carbon /epoxy laminate. (after T.B.Sturgeon, in Creep of Enginering Materials, a Journal of strain Analysis Monograph, 1978, p.175)

8.2 Properties The types of reinforcements • Fibers- A general term for a material which has a long axis that is many times greater than its radius. • Filament- A single fiber. This is the unit formed by a single hole in the spinning process. • Strand- A general and somewhat imprecise term. Usually refers to a bundle or group of untwisted filaments but has also been used interchangeably with fiber and filament. • Tow- An untwisted bundle of continuous filaments, usually with a specific count (such as 12,000 filaments).

8.2 Properties • Roving- A number of yarns or tows collected into a parallel bundle without twisting. • Tape- A collection of parallel filaments (often made from tow) in which the filaments are held together by a binder (usually the composite matrix). The length of the tape, in the direction of the fibers, is much greater than the width and the width is much greater than the thickness. • Yarn- A twisted bundle of continuous filaments; hence a twisted tow. Often used for weaving. • Woven Fabric- A planar material made by interlacing yarns or tows in various specific patterns. • Braiding- The interlacing if yarns or tows into a tubular shape instead of a flat fabric.

8.2 Properties Fig . Fabric consturection forms: (a) plain weave (b) basket weave (c) crowfoot stain (d) long-shaft, and (e) leno weave.

8.2 Properties Table 8.2 Mechanical properties of c/c composites at room temperature. Krishan K. Chawla, Composite materials science and engineering, Springer-Verlag, (1998)

8.2 Properties Fig 8.9 Stress-strain curves of 1-D, 2-D, 3-D, c/c composites Change in fracture mode from semibrittle (1-D) to non-brittle (3-D) ∵ Continuous crack pattern in the 1-D composite. Krishan K. Chawla, Composite materials science and engineering, Springer-Verlag, (1998)

8.3 Interface Fig 8.8 Structure of Carbon fiber, interface, and epoxy matrix. ( after R.J.Dieferdorf, in Tough Composite Materials, Noyes Park Ridge, NT, 1985, p.191) Krishan K. Chawla, Composite materials science and engineering, Springer-Verlag, (1998)

8.3 Interface Fig 8.12 Interlaminar shear strength (ILSS) as a function of weight less on oxidation. A high weight loss corresponds to a high degree of oxidation. Max ILSS corresponds to less than a 10% weight less in both cases. A: High modulus type, B: High-strenghth type ※Overoxidation results in a less of fiber strength and lower ILSS. Krishan K. Chawla, Composite materials science and engineering, Springer-Verlag, (1998)

8.3 Interface Liquid Phase Oxidation. Treated in nitric acid, sodium hypochlorite, potassium permanganate, and anodic etching. ⇒ increase in interfacial area and formation of oxygenated surface groups due to fiber etching.

8.3 Interface Carbon Fiber Surface Treatment Promote adhesion to epoxy materials through a Two-prolonged mechanisms (a) remove a week outer layer which is present initially. (b) add chemical groups to the surface which increase interaction with the matrix.

8.4 Applications Fig 8.13 A louvered door made of carbon fiber(40%Vf/)nylon thermop[lastic used on the engine naceele of the Boeing 757 aircraft(courtesy of LNP Coporation ) Krishan K. Chawla, Composite materials science and engineering, Springer-Verlag, (1998)

8.4 Applications Applications of c fiber composite Ⅰ. Aerospace Industry : Light weight structure ( c fiber PMCs) eq. helicopter rotor blade engine nacell of Boeing 757 Ⅱ. Road Transport Industry Ⅲ. Medical Application X-ray film holder, Tables for X-ray equipment. Ⅳ. Sports Goods: fishing rod, tennis racket, skis, etc

8.4 Applications Fig 8.14 Schematic carbon/epoxy helicopter rotor blades[from Mayer(1974)] Krishan K. Chawla, Composite materials science and engineering, Springer-Verlag, (1998)