Chapter 16: Composite Materials ISSUES TO ADDRESS... • What are the classes and types of composites? • Why are composites used instead of metals, ceramics, or polymers? • How do we estimate composite stiffness & strength? • What are some typical applications?

Composites Combine materials with the objective of getting a more desirable combination of properties Ex: get flexibility & weight of a polymer plus the strength of a ceramic Principle of combined action Mixture gives “averaged” properties Don’t always get what you want Ex: combine ferret (pet) + mink (fur) Desire a mink with good disposition but got a nasty ferret

Terminology/Classification • Composites: -- Multiphase material with significant proportions of each phase. woven fibers cross section view 0.5 mm • Matrix: -- The continuous phase -- Purpose is to: - transfer stress to other phases - protect phases from environment -- Classification: MMC, CMC, PMC metal ceramic polymer • Dispersed phase: -- Purpose: enhance matrix properties. MMC: increase sy, TS, creep resist. CMC: increase Kc PMC: increase E, sy, TS, creep resist. -- Classification: Particle, fiber, structural

Matrix and Disperse phase of composites

Composite Survey Composites Particle- reinforced Fiber-reinforced Structural Large- Dispersion- Continuous Discontinuous Sandwich Laminates particle strengthened (aligned) (short) panels Randomly Aligned oriented

Composite Survey: Particle-I Particle-reinforced Fiber-reinforced Structural • Examples: - Spheroidite steel matrix: ferrite (a) (ductile) particles: cementite ( Fe 3 C ) (brittle) 60 mm - WC/Co cemented carbide cobalt WC (brittle, hard) V m : 10-15 vol%! 600 mm - Automobile tires rubber (compliant) (stiffer) 0.75 mm

Composite Survey: Particle-II Particle-reinforced Fiber-reinforced Structural Concrete – gravel + sand + cement - Why sand and gravel? Sand packs into gravel voids Reinforced concrete - Reinforce with steel rerod or remesh - increases strength - even if cement matrix is cracked Prestressed concrete - remesh under tension during setting of concrete. Tension release puts concrete under compressive force - Concrete much stronger under compression. - Applied tension must exceed compressive force threaded rod nut Post tensioning – tighten nuts to put under tension

Composite Survey: Particle-III Particle-reinforced Fiber-reinforced Structural • Elastic modulus, Ec, of composites: -- two approaches. c m upper limit: E = V + p “rule of mixtures” Data: Cu matrix w/tungsten particles 20 4 6 8 10 150 250 30 350 vol% tungsten E(GPa) (Cu) ( W) lower limit: 1 E c = V m + p • Application to other properties: -- Electrical conductivity, se: Replace E in equations with se. -- Thermal conductivity, k: Replace E in equations with k.

Composite Survey: Fiber-I Particle-reinforced Fiber-reinforced Structural Fibers very strong Provide significant strength improvement to material Ex: fiber-glass Continuous glass filaments in a polymer matrix Strength due to fibers Polymer simply holds them in place

Composite Survey: Fiber-II Particle-reinforced Fiber-reinforced Structural Fiber Materials Whiskers - Thin single crystals - large length to diameter ratio graphite, SiN, SiC high crystal perfection – extremely strong, strongest known very expensive Fibers polycrystalline or amorphous generally polymers or ceramics Ex: Al2O3 , Aramid, E-glass, Boron, UHMWPE Wires Metal – steel, Mo, W

Fiber Alignment aligned continuous aligned random discontinuous

Composite Survey: Fiber-III Particle-reinforced Fiber-reinforced Structural • Aligned Continuous fibers • Examples: -- Metal: g'(Ni3Al)-a(Mo) by eutectic solidification. -- Ceramic: Glass w/SiC fibers formed by glass slurry Eglass = 76 GPa; ESiC = 400 GPa. matrix: a (Mo) (ductile) fibers: g ’ (Ni3Al) (brittle) 2 mm (a) (b) fracture surface

Composite Survey: Fiber-IV Particle-reinforced Fiber-reinforced Structural • Discontinuous, random 2D fibers • Example: Carbon-Carbon -- process: fiber/pitch, then burn out at up to 2500ºC. -- uses: disk brakes, gas turbine exhaust flaps, nose cones. (b) fibers lie in plane view onto plane C fibers: very stiff very strong C matrix: less stiff less strong (a) • Other variations: -- Discontinuous, random 3D -- Discontinuous, 1D

Composite Survey: Fiber-V Particle-reinforced Fiber-reinforced Structural • Critical fiber length for effective stiffening & strengthening: fiber strength in tension fiber diameter shear strength of fiber-matrix interface • Ex: For fiberglass, fiber length > 15 mm needed • Why? Longer fibers carry stress more efficiently! Shorter, thicker fiber: Longer, thinner fiber: Poorer fiber efficiency Better fiber efficiency s (x)

Composite Strength: Longitudinal Loading Continuous fibers - Estimate fiber-reinforced composite strength for long continuous fibers in a matrix Longitudinal deformation c = mVm + fVf but c = m = f volume fraction isostrain Ece = Em Vm + EfVf longitudinal (extensional) modulus f = fiber m = matrix

Composite Strength: Transverse Loading In transverse loading the fibers carry less of the load - isostress c = m = f =  c= mVm + fVf  transverse modulus

Composite Strength • Estimate of Ec and TS for discontinuous fibers: Particle-reinforced Fiber-reinforced Structural • Estimate of Ec and TS for discontinuous fibers: -- valid when -- Elastic modulus in fiber direction: -- TS in fiber direction: Ec = EmVm + KEfVf efficiency factor: -- aligned 1D: K = 1 (aligned ) -- aligned 1D: K = 0 (aligned ) -- random 2D: K = 3/8 (2D isotropy) -- random 3D: K = 1/5 (3D isotropy) (TS)c = (TS)mVm + (TS)fVf (aligned 1D)

Composite Production Methods-I Pultrusion Continuous fibers pulled through resin tank, then preforming die & oven to cure

Composite Production Methods-II Filament Winding Ex: pressure tanks Continuous filaments wound onto mandrel

Composite Survey: Structural Particle-reinforced Fiber-reinforced Structural • Stacked and bonded fiber-reinforced sheets -- stacking sequence: e.g., 0º/90º -- benefit: balanced, in-plane stiffness • Sandwich panels -- low density, honeycomb core -- benefit: small weight, large bending stiffness honeycomb adhesive layer face sheet

Composite Benefits • CMCs: Increased toughness • PMCs: Increased E/r E(GPa) G=3E/8 K=E Density, r [mg/m3] .1 .3 1 3 10 30 .01 2 metal/ metal alloys polymers PMCs ceramics fiber-reinf un-reinf particle-reinf Force Bend displacement • MMCs: Increased creep resistance 20 30 50 100 200 10 -10 -8 -6 -4 6061 Al w/SiC whiskers s (MPa) e ss (s-1)

Summary • Composites are classified according to: -- the matrix material (CMC, MMC, PMC) -- the reinforcement geometry (particles, fibers, layers). • Composites enhance matrix properties: -- MMC: enhance sy, TS, creep performance -- CMC: enhance Kc -- PMC: enhance E, sy, TS, creep performance • Particulate-reinforced: -- Elastic modulus can be estimated. -- Properties are isotropic. • Fiber-reinforced: -- Elastic modulus and TS can be estimated along fiber dir. -- Properties can be isotropic or anisotropic. • Structural: -- Based on build-up of sandwiches in layered form.

Material Selection

Material Classification

The Materials Selection Process Processes Composition Mechanical Electrical Thermal Optical Etc. Structure Shape Materials Properties Environment Load Applications Functions

PRICE AND AVAILABILITY • Current Prices on the web: e.g., http://www.metalprices.com -- Short term trends: fluctuations due to supply/demand. -- Long term trend: prices will increase as rich deposits are depleted. • Materials require energy to process them: -- Energy to produce materials (GJ/ton) -- Cost of energy used in processing materials ($/MBtu) Al PET Cu steel glass paper 237 (17) 103 (13) 97 (20) 20 13 9 elect resistance propane oil natural gas 25 17 13 11 Energy prices from http://www.npga.org/i4a/pages/index.cfm?pageid=914 Energy using recycled material indicated in green.

RELATIVE COST, c, OF MATERIALS Graphite/ Ceramics/ Semicond Metals/ Alloys Composites/ fibers Polymers Relative Cost (c) pl. carbon Au Si wafer PET Epoxy Nylon 6,6 0.05 0.1 5 100000 10000 2 0000 000 1 00 0.5 Steel high alloy Al alloys Cu alloys Mg Ti Ag Pt Tungsten Al oxide Concrete Diamond Glass-soda Si carbide Si nitride PC LDPE,HDPE PP PS PVC Aramid fibers Carbon fibers E-glass fibers AFRE prepreg C FRE prepreg G Wood • Reference material: -- Rolled A36 plain carbon steel. • Relative cost, , fluctuates less over time than actual cost. Based on data in Appendix C, Callister, 7e. AFRE, GFRE, & CFRE = Aramid, Glass, & Carbon fiber reinforced epoxy composites.

STIFF & LIGHT TENSION MEMBERS F, d L c • Bar must not lengthen by more than d under force F; must have initial length L. -- Stiffness relation: -- Mass of bar: (s = Ee) • Eliminate the "free" design parameter, c: minimize for small M specified by application • Maximize the Performance Index: (stiff, light tension members)

STRONG & LIGHT TENSION MEMBERS F, d L c • Bar must carry a force F without failing; must have initial length L. -- Strength relation: -- Mass of bar: • Eliminate the "free" design parameter, c: minimize for small M specified by application • Maximize the Performance Index: (strong, light tension members)

STRONG & LIGHT TORSION MEMBERS • Bar must carry a moment, Mt ; must have a length L. -- Strength relation: -- Mass of bar: • Eliminate the "free" design parameter, R: specified by application minimize for small M • Maximize the Performance Index: (strong, light torsion members)

DETAILED STUDY I: STRONG, LIGHT TORSION MEMBERS • Maximize the Performance Index: • Other factors: --require sf > 300 MPa. --Rule out ceramics and glasses: KIc too small. • Numerical Data: material CFRE (vf = 0.65) GFRE (vf = 0.65) Al alloy (2024-T6) Ti alloy (Ti-6Al-4V) 4340 steel (oil quench & temper) r (Mg/m3) 1.5 2.0 2.8 4.4 7.8 tf (MPa) 1140 1060 300 525 780 P [(MPa)2/3m3/Mg] 73 52 16 15 11 • Lightest: Carbon fiber reinforced epoxy (CFRE) member.

DETAILED STUDY II: STRONG, LOW COST TORSION MEMBERS • Minimize Cost: Cost Index ~ M ~ /P (since M ~ 1/P) where M = mass of material cost/mass of low-carbon steel cost/mass of material = relative cost = • Numerical Data: material CFRE (vf = 0.65) GFRE (vf = 0.65) Al alloy (2024-T6) Ti alloy (Ti-6Al-4V) 4340 steel (oil quench & temper) 80 40 15 110 5 P [(MPa)2/3m3/Mg] 73 52 16 11 ( /P)x100 112 76 93 748 46 • Lowest cost: 4340 steel (oil quench & temper) • Need to consider machining, joining costs also.

SUMMARY • Material costs fluctuate but rise over the long term as: -- rich deposits are depleted, -- energy costs increase. • Recycled materials reduce energy use significantly. • Materials are selected based on: -- performance or cost indices. • Examples: -- design of minimum mass, maximum strength of: • shafts under torsion, • bars under tension, • plates under bending,