Solids under stress Flashcards
What is the spring constant, k?
The force per unit extension.
What is Hookes law?
The tension in a spring or wire is directly proportional to its extension from its natural length, provided the extension is not too great.
What is the exstention?
The increase in length of an object when put under tension.
What is stress and its unit of measurement?
The force per unit cross sectional area (F/A) measured in Pa or Nm-2.
What is strain?
The extension per unit length.
What is Young’s modulus and it’s unit of measurement?
stress/strain measured in Pa or Nm-2.
What are the properties of crystalline solids?
Have a short and long range order arranged in a regular lattice e.g metals. These can be a single crystal or polycrystalline.
What are the properties of Amphorous solids?
Have little to no range order and molecules are arranged randomly by individual atoms or small molecules e.g glass.
What are the properties of polymeric solids?
Long chains of carbon atoms bonded to other atoms e.g cellulose. There is no range order between molecules but there is order within each molecule.
How to calculate stress?
σ= F/A
How to calculate strain?
ε= Δl / l
How to calculate Young’s modulus?
E= stress / strain or Fl / AΔl
Why does plastic deformation of a ductile metal occur?
Because of dislocation flow, which is an incomplete plane of atoms.
How can metals be strengthened for less plastic deformation?
Smaller grains
Work hardening
Introducing foreign atoms
Why are amorphous solids like glass brittle?
Because cracks can travel through them easily. A small stress can make a crack on the surface grow until the solid snaps. These solids are strong under compression and weak under tension.
