Composite Structures Particle, fiber, and structural composite.
TERMINOLOGY/CLASSIFICATION • Composites : --Multiphase material w/significant proportions of ea. phase. • Matrix : --The continuous phase --Purpose is to: transfer stress to other phases protect phases from environment --Classification: MMC, CMC, PMC • Dispersed phase : --Purpose: enhance matrix properties. MMC: increase y , TS, creep resist. CMC: increase Kc PMC: increase E, y , TS, creep resist. --Possible Classifications: Particle , fiber , structural metal ceramic polymer Reprinted with permission from D. Hull and T.W. Clyne, An Introduction to Composite Materials , 2nd ed., Cambridge University Press, New York, 1996, Fig. 3.6, p. 47.
Types of composites (MMC, PMC, CMC) Wood (cellulose fibers with stiffer lignin matrix) Bone (soft collagen and brittle apatite) Clay (particles and glass naturally form when fired) We will focus on artificial composites. Natural composites include:
For any composite, regardless of the selection of matrix and disperse phase (material and type), there are many options that will affect properties:
Each option will impart different benefits to the final part. Also surface coatings on the dispersed phase
Particle Reinforced Composites Particle-reinforced • Examples: Adapted from Fig. 10.10, Callister 6e . (Fig. 10.10 is copyright United States Steel Corporation, 1971.) Adapted from Fig. 16.4, Callister 6e . (Fig. 16.4 is courtesy Carboloy Systems, Department, General Electric Company.) Adapted from Fig. 16.5, Callister 6e . (Fig. 16.5 is courtesy Goodyear Tire and Rubber Company.)
Involves large particles that are harder or stiffer than matrix.
The matrix transfers applied stress to the particles, which thus bear a fraction of the load.
Bonding at the interface is necessarily important.
Particles should be:
Properties generally determined by the rules of mixtures.
Upper bound: Lower bound:
COMPOSITE SURVEY: Particle-II • Elastic modulus, E c , of composites: -- two approaches. Particle-reinforced Adapted from Fig. 16.3, Callister 6e . (Fig. 16.3 is from R.H. Krock, ASTM Proc , Vol. 63, 1963.)
So, as fibers get longer and thinner, the overall properties of the composite are improved.
Optimal fiber lengths are usually about 30*L c .
Poorer fiber efficiency Better fiber efficiency fiber diameter shear strength of fiber-matrix interface fiber strength in tension • Ex: L c is 1mm for fiberglass, so the optimal fiberglass length is >=30mm.