Composites Flashcards
Composites
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
Particulate Composites
Examples: particle board, concrete, glass filled epoxy, foam
Polymer Matrix
Lightest
Best corrosion resistance
Lowest matrix strength, stiffness, and service temp
Metal Matrix
Heaviest
Best fracture toughness
Excellent matrix strength and stiffness in all loading modes, including tension
Intermediate service temp
Variable oxidation and corrosion resistance
Ceramic Matrix
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
Composites with aligned. directional reinforcement
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
Composites with randomly oriented reinforcement and/or roughly spherical particle reinforcement
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
Volume Fraction
f1≡V1/Vtotal =V1/Vc
Note that the sum of the volume fractions of all phases must always be 1
Density
ρc=f1ρ1+f2ρ2
=f1ρ1+(1-f1)ρ2
The equation for density is identically true regardless of the shape of the reinforcement
Modulus Parallel to Reinforcement
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
Modulus Perpendicular to reinforcement
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