ES195 Materials for Engineering Flashcards
5 “families” of materials
Metals/alloys (Gold, Steel, Cu alloys)
Ceramics (Alumina, Silicon carbide)
Polymers (Polyester, phenolic)
Glasses (soda glass, borosilicate)
Rubbers (Silicones, EVA)
Hybrids combine 2 or more e.g. GFRP, composites
Purpose of selection methodology
Material properties vary enormously
Multiple factors affect design choice
Function - loading, environment its in.
Commercial - availability of raw materials, required manufacturing volume
Environmental - impact of different materials e.g. embodied energy, pollutants
Three way relationship
Between properties, processing and structure
In manufacturing, we deliberately change
compositions and thermo-mechanically
process materials to change their
structure and properties
Material structures
Crystalline/polycrystallaline - long range order
Amorphous - short range order
Typical values for elastic modulus
Steel ≈ 200GPa
Al alloys ≈ 70 GPa
Ti alloys ≈ 110 Gpa
Ball and spring model of elasticity
Material in tension, bonds stretch and atoms move apart, vice versa for compression.
Also represents how spring gets narrower in the middle
εz = -νεy (poisons ratio)
Primary vs secondary bonds
Primary
Ionic, covalent, metallic
Secondary
Van Der walls (dipolar attraction between uncharged atoms)
Hydrogen - dipole attraction between bonded hydrogen and neighbouring ions
Structure of diff bonding types
Ionic - highly ordered, simple structure e.g. cubic. Stuff, strong and brittle
Covalent - highly ordered, often complex, stiff strong and brittle
Metallic - complex, alloying possible, variety of structures, moderate stiffness, variety of strength and ductility
Why covalent bonds easier to deform
Materials deform when defects propagate through them. Defects move easier along a line/simple plane. Easier in a cubic (ionic crystal) rather than a complex structure (covalent)
Directions denoted by
Square brackets
