MatE exam 3 composites, corrosion, and thermal properties

composite

multiphase materials that exhibit properties from their constituent phases

how many types of composites are there?

2

3 multiple choice options

what are the two types of particle-reinforced composites (PRC)?

large particle composites and dispersion strengthened composites

large particle composites

particles are larger than 1 μm; properties are an average of the matrix and particle phases

dispersion strengthened composites

particles are smaller than 1 μm; strengthening occurs at the atomic level, enhancing the matrix

what are the two types of fiber-reinforced composites (FRC)?

discontinuous fiber composites and continuous fiber composites

discontinuous fiber composites

short fibers that slightly enhance properties

continuous fiber composites

long fibers that significantly improve strength and modulus, especially in tension

matrix phase

continuous phase that binds and protects fibers or particles

dispersed phase

provides strength and enhances properties of the composite

rule of mixtures

allows estimation of properties based on volume fractions

corrosion

degradation of materials, typically metals, through chemical reactions with their enviornment

how many types of corrosion are there?

4

3 multiple choice options

galvanic corrosion

occurs when two dissimilar metals are in electrical contact in a corrosive medium

crevice corrosion

happens in confined spaces where stagnant fluid creates localized attack

erosion corrosion

combination of chemical attack and physical abrasion by a moving fluid

stress corrosion

cracking that results from tensile stress in a corrosive environment

how many corrosion prevention methods are there?

4

3 multiple choice options

galvanizing

applying a sacrificial layer (ex. zinc) to prevent oxidation

coating

paints, polymers, or ceramics to isolate form the environment

cathodic protection

electrically charging the metal to prevent oxidation

material selection

using corrosion-resistant materials like stainless steel or alloys designed for specific environments

anode

- positive electrode

- oxidizes

cathode

- negative electrode

- reduces

thermal properties

describes how materials respond to changes in temperatures, including heat capacity, expansion, and conductivity

heat capacity (C)

the amount of thermal energy required to increase temperature, related to atomic vibrations

thermal expansion (α)

the change in material dimensions with temperature

- linear expansion (αL)

- volumetric expansion (αV)

thermal conductivity (k)

the ability of a material to conduct heat

- metals have high conductivity due to free electrons

- ceramics and polymers have lower conductivity

thermal stress

when a material is constrained and heated

fracture

rapid temperature changes can induce thermal shock, leading to potential fractures

how does bond strength influence thermal properties?

stronger atomic bonds resist expansion

how does crystallinity affect thermal properties?

more crystalline materials have more consistent thermal properties

how does porosity affect thermal properties?

more porosity generally reduces thermal conductivity