Composites

Question 1

Composites

Answer 1

Materials created by combining two or more materials in order to obtain combinations of properties not normally achievable by a single material

Offer the widest range of properties of any class of materials

In general: more expensive, more difficult to manufacture, and more difficult to design with any other class of materials

Question 2

Particulate Composites

Answer 2

Examples: particle board, concrete, glass filled epoxy, foam

Question 3

Polymer Matrix

Answer 3

Lightest

Best corrosion resistance

Lowest matrix strength, stiffness, and service temp

Question 4

Metal Matrix

Answer 4

Heaviest

Best fracture toughness

Excellent matrix strength and stiffness in all loading modes, including tension

Intermediate service temp

Variable oxidation and corrosion resistance

Question 5

Ceramic Matrix

Answer 5

iNTERMEDIATE DENSITY

wORST TOUGHNESS

highest SERVICE TEMPERATURES AND BEST HIGH TEMPERATURE STRENGTH, CREEP RESISTANCE

Highest service temperatures and best high temp strength, creep resistance

Excellent oxidation resistance, mixed corrosion resistance

Matrix very hard and very strong in compression, weak in tension

Question 6

Composites with aligned. directional reinforcement

Answer 6

Strongest and stiffest in that single direction but weak and compliant in other directions

Best for situations in which direction of stress is reliable and well understood

Question 7

Composites with randomly oriented reinforcement and/or roughly spherical particle reinforcement

Answer 7

Will be less strong/stiff than aligned composites in their optimum direction

Best for parts with stresses in many directions, unpredictable loads, or when it is desirable to minimize design effort and validation

Question 8

Volume Fraction

Answer 8

f1≡V1/Vtotal =V1/Vc

Note that the sum of the volume fractions of all phases must always be 1

Question 9

Density

Answer 9

ρc=f1ρ1+f2ρ2
=f1ρ1+(1-f1)ρ2

The equation for density is identically true regardless of the shape of the reinforcement

Question 10

Modulus Parallel to Reinforcement

Answer 10

Ec,parallel=f1 E1+ f2 E2

Identically true for laminated composites parallel to the lamina

Good approximation for aligned fiber composites in direction of fiber

Represents an upper bound to the composite modulus for given volume fractions, regardless of the shape of the reinforcement

Question 11

Modulus Perpendicular to reinforcement

Answer 11

Ec,perp=[f1/E1 +f2/E2 ]^(-1)

Identically true for laminated composites perpendicular to the lamina

Poor approximation for aligned fiber compsites perpendicular to the direction of the fiber, but still most common used

Represents an lower bound to the composite modulus for given volume fractions, regardless of the shape of the reionforcement