Material Properties: Study Guide

• Study notes for review
• The notes cover material properties, material selection, failure, fracture, crystal structures, sustainability, and crystalline defects

Material Tetrahedron

• Illustrates the relationship between a material's properties, structure, processing, and performance

Material Properties

• Describes how a material responds to external forces, depends on the material, not size
• Intensive quantity doesn't depend on size
• Extensive quantity depends on size.

Classification of Materials

• General properties include cost and density
• Mechanical properties include strength (yield), stiffness, and toughness (fracture)
• Thermal properties include conductivity, diffusivity, and heat capacity
• Electrical properties include dielectric constant and conductivity
• Magnetic properties include remanence, saturation, and magnetization
• Optical properties include refraction and absorption
• Chemical properties include corrosion resistance, fouling, and surface energy
• Biological properties include biocompatibility and hemocompatibility

Classes of Materials

• Divided into metals, ceramics, polymers, glasses, elastomers, and hybrids

Metals

• Characterized by metallic bonding
• Strong, ductile, and fracture-resistant
• Electrically and thermally conductive
• Includes steels, cast irons, aluminum alloys, and titanium alloys
• Formed by machining, cold working/annealing, and surface treatment

Ceramics

• Bonded by a combination of ionic and covalent bonds
• Generally, inert
• Hard, stiff, and strong, but brittle and prone to fracture
• Insulative to heat and electricity
• Includes alumina, zirconia, silicon, and carbides

Polymers

• Characterized by covalent bonding
• Have immense variety and tuneability
• Composition and structure can be controlled
• Structures comprised of repeating units known as monomers
• Includes polyethylene, polystyrene, polyesters, and epoxies

Glasses

• Types include Silica glass, Soda glass, and Borosilicate glass

Elastomers

• Types include natural rubber, silicones, neoprene, and isoprene

Hybrids

• Include composites, foams, and lattices

Mechanical Properties (LEC 41)

Stress-Strain Behavior

• Materials deform in response to stress
• Strain can be permanent or non-permanent

Elastic Strain

• Is non-permanent and recovers when stress is removed

Plastic Strain

• Is permanent and does not recover when stress is removed

Mechanical Stress

• SI unit is MPa (megapascals)
• Experienced when a tensile force is applied
• Normalizes for the size effect of cross-sectional area

Mechanical Strain

• Results in material extending
• Normalizes the size effect of specimen length

Young's Modulus (E)

• Unit is GPa (gigapascals)
• Ratio of stress to strain when a solid is elastically deformed
• High Young's Modulus corresponds to higher stiffness

Poisson's Ratio

• Applies for uniaxial stress and an isotropic material

Plastic Deformation

• Is non-reversible deformation
• Occurs when applied stress exceeds the yield strength

Yield Strength

• The stress required to produce plastic strain
• Yielding is the onset of plastic deformation

Ultimate Tensile Strength

• Is the maximum stress the material can withstand while being stretched

Elongation to Failure

• Is the strain at which a tensile specimen fails

Ductility

• Refers to how much a material plastically deforms before it fractures

Brittleness

• Is when material experiences minimal plastic deformation

Material Selection (LEC 42)

Material Index

• Combination of material properties that characterize performance

Property Limit

• Sets limits on material properties

Material Selection Process

• Translation of design requirements into material specifications
• Screening of materials that fail to meet specifications

Material Selection - Continued

• Ranking by the ability to meet objectives using material indices
• Search for supporting information for promising candidates

Additional Notes on Material Selection

• Highest MPI = nearest to slope in Ashby chart
• Functional requirement, geometric parameter, and material performance index are important

Material Performance Index

• Elastic modulus, yield strength, and density

Failure and Fracture (LEC 43)

Fracture

• Separation of a body into two or more pieces in response to an imposed stress
• Applied stresses can be tensile, compressive, shear, or torsional

Fracture Modes

• Brittle fracture: crack spreads rapidly with little plastic deformation
• Ductile fracture: extensive plastic deformation in the vicinity of an advancing crack

Stress Concentrations

• Measured fracture strengths for most materials are lower than theory

Ductile Fracture (necking)

• Materials have defects that act as stress concentrators

Brittle Fracture

• No deformation and rapid crack propagation

Fracture Toughness

• Material property that determines whether a material fails in a brittle or ductile manner

Fracture Types

• Brittle fracture when K > KIC and ductile fracture when K < KIC

Ductile to Brittle Transition

• Thermoset retains form when heated and generally brittle
• Thermoplastic can melt under heat; may be brittle or ductile

Crystal Structures (LEC 44)

Arrangement Types

• Crystalline (ordered), amorphous (no order), and mixed (semi-crystalline)

Crystal Structure by Material

• Metals are usually crystalline, ceramics are often crystalline, polymers are never fully crystalline

Unit Cell

• The basic repeating unit of a crystal structure

Simple Cubic Unit Cells

• Composed of 1/8 atoms at each corner
• Coordination number is 6

Body-Centered Cubic (BCC)

• Atoms at all eight corners and one in the center

Face-Centered Cubic (FCC)

• Atoms at all eight corners and one at each face

Hexagonal Close Packed (HCP)

• Atoms at the corners of the top/bottom faces, 2 face atoms, and 3 interior atoms

Polymorphism (Allotropy)

• Ability of materials to exist in multiple crystal structures

Filtration in WWTPs (LEC 45)

Primary Treatment

• Removes physical contamination

Secondary Treatment

• Removes biological contamination

Tertiary Treatment

• Filtration process

Types of Filtration Processes

• Granular filtration, adsorption, and membrane filtration

Adsorbent Materials

• Zeolites, synthetic polymeric adsorbents, and activated carbon

Adsorption – Ion Exchange

• Contaminated water goes in the filtration pipe and NO3 & Cl exchange process

Important Adsorption Factors

• Surface area, pore size, adsorption sites, and accessibility

Membrane Filtration

• Outsite-in filtration for contaminants screened outside and Inside-out for contaminants screened inside.

Sustainability in Engineering (LEC 46)

Ecological Footprints

• Measures the amount of nature's resources consumed

Carbon Footprint

• Total amount of greenhouse gases generated by our actions

Life Cycle Assessment (LEC 47)

• To evaluate potential environmental impacts

Design for Environment

• Reduce, reuse, and recycle

Reduce the mass energy

• Used in the production of technology

Reuse

• Materials and equipment required for production

Recycle

• Waste products produced during manufacturing and operation

Crystalline Defects (LEC 48)

Porosity

• Volume fraction of a solid that is empty

Defects

• Does not always imply a negative effect on properties

Point Defects

• Vacancy is a lattice position that is vacant because the atom is missing
• Interstitial is an atom that occupies a place outside the normal lattice position

Vacancies

• Enable material properties for ionic compounds

Line Defects

• Dislocations are extra, also missing half plane

Planar Defects

• Surface atoms have higher energy than bulk atoms

Planar Defects - Grain Boundaries

• Most solids are polycrystalline and contain many grains separated by transition regions

Properties Enabled by Grain Boundaries

• Grain boundaries influence strength, toughness, and creep rate

Bulk Defects

• Voids, porosity, and cracks