page 314

52. COMPOSITE MANUFACTURING

•Each material has desirable properties, but in most situations the perfect material is never found.

•Composites allow mixing of materials to get the best of both.

•BASIC PRINCIPLE: different types of materials are blended together. The materials are often quite different in terms of properties, and the results are a new material that has many of the desired properties of each material.

•Examples

-clay bricks with embedded straw

-reinforced concrete

-samurai swords with steel/iron alternation of layers

-steel belted radials

-graphite tennis racquets

-fishing poles

•for reinforced plastic composites, 2,500,000,000 pounds of plastic based composites were shipped in a wide variety of products in the mid 80’s

52.1 FIBER REINFORCED PLASTICS (FRP)

•Typical properties that may be desired are,

-light weight

-stiffness

-strength

-heat resistant

-impact resistance

-electrical conductivity

-wear resistance

-corrosion resistance

-low cost

•Some notable applications are,

-Automotive - engine blocks, push rods, frames, piston rods, etc.

-Electrical - motor brushes, cable electrical contacts, etc

-Medical - prostheses, wheel chairs, orthofies, etc.

-Sports equipment - tennis racquets, ski poles, skis, fishing rods, golf clubs, bicycle frames, motorcycle frames

-Textile industry - shuttles

-etc.

page 315

•Some advantages are,

-composites provide a maximum tensile strength to density ration approximately 4 to 6 times greater than steel or aluminum

-can provide a maximum material stiffness to density ratio of 3.5 to 5 times that of aluminum or steel

-high fatigue endurance limits

-absorb higher impact energies

-material properties can be strengthened where required

-corrosion potential is reduced.

-joints and fasteners are eliminated or simplified

•Some disadvantages are,

-If either material is susceptible to local solvents, the composite cannot be used

-materials can be expensive

-design and fabrication techniques are not well explored and developed.

•fibres are often graphite, glass, aramid, etc.

•the fibres are supported in the matrix, quite often a polymer, epoxy, etc.

•The polymer matrix is often referred to as the resin

•The matrix transfers the load to the reinforcement fibres, and it protects the fibres from environmental effects.

•Resins tend to be thermosetting, or thermoplastic

Thermoplastics - melt, and harden with temperature

Thermosets - undergo a chemical change, and cannot be “recast”. The setting is often heat activated.

• Polyester resins are quite common. The process often begins with molecules like a dialcohol, and diacid. These then cure into a solid polymer.

page 316

O

O

H

O

C

CH

CH

C

O

H

Maleic Acid (A diacid)

HO

CH2

CH2

OH

Ethylene Glycol

(A dialcohol)

an ester

ester linkage

O

O

+

H

O

C

CH

CH

C

O

CH2

CH2

OH

H2O

water is a

byproduct

these ends now link in similar ways

• These reactions create very long chains of polymers in a sort of gel, but the next step involves cross-linking them to make things stiff

page 317

polyester

O

O

C

CH

CH

C

O

CH2

CH2

O

n

peroxide initiator

Reactants

RO

Cross linking Agent

(styrene)

CH

CH2

O

O

Initiation step

C

CH

CH

C

O

CH2

CH2 O

n

O

R

O

O

Bridging Step

C

CH

CH

C

O

CH2

CH2

O

n

OR

CH

CH2

O

O

Crosslinked

C

CH

CH

C

O

CH2

CH2

O

n

OR

polymers

CH

CH2

O

O

C

CH

CH

C

O

CH2

CH2

O

n

page 318

•Various chemical reactions, and physical properties can be altered by changing the chemicals above. Rates of reaction can be accelerated with higher temperatures.

•The initiator is often stored separately from the other reactants to prevent cross linking before use. This may happen spontaneously, and so the chemicals should be discarded if too old.

•Epoxies can also be used, they can be expensive and toxic, but they generally have better overall performance than polyesters.

•Other general categories are,

-Polymides and Polybenzimidazoles

-Phenolics and Carbon matrices

-Thermoplastics

-Ceramic matrices

-Metal matrices

•Polyesters are generally inexpensive, and can be modified for other properties.

•Epoxies are used when the matrix must have good adhesion, strength and corrosion resistance in severe environments.

•Polyimides are used for high temperature applications (up to 600 F/316 C) but are difficult to process

•Phenolics are good for thermal insulation

•Ceramics are used for high temperature, low strength applications.

•Reinforcements in materials can be

-fibres - long directional filaments

-particles - small non-directional chunks

-whiskers - small directional filaments

•Fibres have very long lengths with respect to the surrounding material, and tend to have a significantly higher strength along their length.

•Fibres are often drawn to align the molecules along the fibre length

page 319

Fibre

Drawing

a stretch causing plastic deformation

undirected molecules	directed molecules

•Glass fibres are basically made by,

1.Mixing silica sand, limestone, boric acid, and other minor ingredients

2.The mixture is heated until it melts at about 2300F/1260C

3.Letting the molten glass flow through fine holes (in a platinum plate)

4.The glass strands are cooled, gathered and wound. (protective coatings may be added.)

5.The fibres are drawn to increase the directional strength.

6.The fibres are woven into various forms for use in composites

•There are three common glass types used, E, S, C

E - less expensive

S - 40% stronger than E, and more resistant to temperature

C - well suited to corrosive environments

page 320

	Property			Type of glass
				C	E	S
	Density(g/cc)			2.49-2.50	2.54-2.62	2.48-2.50
	Tensile Strength (ksi)			440-480	500	665
	@72F
				-	380	545-645
	@700F
				-	250	350
	@1000F
	Tensile Modulus (Msi)			10.0	10.5	12.4
	@72F
				-	11.8	12.9
	@1000F
	Coef. of thermal expansion			4.0	2.8	3.1
	(in/in/F)
	Coef. of thermal conductivity			-	72	-
	(BTU-m/hr/sq.ft./F)
				0.188-0.212	0.193-0.197	0.176
	Specific Heat, @72F
				1380-1382	1545-1555	1778
	Softening Point, (F)
				-	262-498	330
	Dielectric Strength, V/mil
	Dielectric Constant			-	0.003-0.005	0.003-0.013
	@ 60 H2
				0.008	0.002-0.0025	0.003-0.0034
	@10	6	H2
				1.532	1.547-1.562	1.523-1.525
	Index of refraction
	Chemical resistance
	(% weight gain after 24 hr expose.)			1.1	0.7	0.7
	In H2O
				4.1	42	3.8
	In 10% HCl
				2.2	39	4.1
	In 10% H2SO4
				24	2.1	2.0
	In 1% Na2CO3

• Carbon Fibres are among the highest strength and modulus materials known.

page 321

Fibre	Typical	Specific	Tensile	Tensile	Strain	Coeff. of	Poisson’s
	diameter	Gravity	modulus	Strength	to	thermal exp.	ration
	(micro m)		(GPa)	(GPa)	failure	(micro m/C)
					(%)	(0 - 100C)
Glass
E glass	10	2.54	72.4	3.45	4.8	5	0.2
S glass	10	2.49	86.9	4.30	5.0	2.9	0.22
PAN-carbon
T-300c	7	1.76	228	3.2	1.4	-0.1to-0.5	0.2
ASd	7	1.77	220	3.1	1.2	-0.5to-1.2
T-40c	6	1.81	276	5.65	2
HMSd	7	1.85	344.5	2.34	0.58
GY-70e	8.4(bilobal)	1.96	483	1.52	0.38
Pitch-carbon
P-55c	10	2.0	380	1.90	0.5	-0.9
P-100c	10	2.15	690	2.2	0.31	-1.6
Kevlar 49f	11.9	1.45	131	3.62	2.8	-2	0.35
Boron	140	2.7	393	3.1	0.79	5	0.2
SiC	133	3.08	400	3.44	0.84	1.5
Al2O3	20	3.95	379.3	1.90	0.4	8.3

• Aramids (Kevlar) fibres are shown below. These do not need to be drawn as they are already in the correct orientation when produced.

O

O

O

O

N

N

C

C

N

N

C

C

n

H

H

H

H

O

O

N

C

C

N

n

H

H

•aramid fibres come in bundles of 134 to 10,000 filaments

•kevlar properties are,

page 322

Kevlar #	29	49	149
Tensile modulus (MPa)	83	131	186
Tensile strength (Mpa)	3.6	3.6	3.4
Elongation (%)	4	2.8	2
Density (g/cc)	1.44	1.44	1.47

• Other popular fibre types are Boron, Silicon, Carbide, Alumina, etc.

•The fibres come in a variety of configurations, Filament - a single fibre

Strand - Could refer to a single fibre, or an untwisted bundle of filaments Tow - A bundle of untwisted fibres, often a predetermined number.

Yarn - A twisted tow

Roving - A number of yarns pulled together without twisting Tape - a thin and wide run of parallel fibres

Woven fabric - yarns and tows are interlaced to create flat cloth Braids - yarns and tows are woven into tubular shapes

Mat - chopped fibres create an undirected pattern in a flat cloth. A binder holds the fibres together.

•There are different weave types used, these provide different workabilities, air removal, distortions, etc.

plain weave

basket weave

page 323

crowfoot satin

long-shaft

•weaves can be made from single fibre types, or combinations

•The relative material properties for composites are seen in the figures below RTW - Rigidity to weight

STW - strength to weight Strain - failure strain

UTS - ultimate tensile strength Yield - yield strength

USS - Ultimate shear strength

UCS - Ultimate compressive strength

page 324

Material	Spec.E	G	UTS	YieldRTW STW		StrainPoissThermUSS UCS
	Grav.(GPa GPa		(GPa)(MPa)			(%)		(MPa)(MPa)
Boron & epoxy 1.99 207		6.4	1585			0.5	.21		2482
(unidirectional, along fiber)
Boron & epoxy 1.99 19			62.7			0.5	.21
(unidirectional, across fiber)
boron 6061 & Al2.35220			1109	na	9.54 48.1	0.5
(unidirectional, along fiber)
carbon & epoxy1.55 137.85.7			1550	na	9.06 101.91.4		.25	60	1172
(high strength, unidirectional, along fiber)
carbon & epoxy1.55 9.0				na			.25
(high strength, unidirectional, across fiber)
carbon & epoxy1.63 215		5.9	1240	na	13.4477.5	0.4	.2	72	620
(high modulus, unidirectional, along fiber)
carbon & epoxy1.63 13.8			86.2	na			.2
(high modulus, unidirectional, across fiber)
carbon & epoxy1.55 45.5			579	na	2.99 38
(quasi-isotropic)
E-glass & epoxy1.8039.3 4.8			965	na	2.16 53.2	5	.3	83	620
(unidirectional, along fiber)
E-glass & epoxy1.804.8			96.5	na		5	.3
(unidirectional, across fiber)
GY-70 & epoxy 1.69 276		4.1	586			0.3	.25	96.5	517
(unidirectional, along fiber)
GY-70 & epoxy 1.69 8.3			41.3			0.3	.25
(unidirectional, across fiber)
kevlar49 & epoxy1.3875.82.1			1378	na	5.60 101.83.1		.34	60	276
(unidirectional, along fiber)
kevlar49 & epoxy1.385.5			28.3	na		3.1	.34
(unidirectional, across fiber)
S-glass & epoxy1.8243			1241	na		5		83	758
(unidirectional, along fiber)
T300 & epoxy 1.55 138		6.5	1448			1	.21	62	1448
(unidirectional, along fiber)
T300 & epoxy	1.55 10		44.8			1	.21

•Composites are sensitive to temperature and humidity during curing.

•When dealing with cyclic loading over a million cycles

-Aluminum and steel design with 0.1 of the normal yield strength

-Composites design with 0.5 of normal yield strength

•Composites in general are very easy to shape, and form, this is not always possible with other high strength materials

•Composites are anisotropic and have good strength along the fibre length, but reduced strength across the fibre axis.

•Elongation of composites is typically linear up to fracture at 1% to 2% elongation