Solids under stress

Solids under stress

1. Elastic Potential Energy

   • Found by area under graph/0.5 x Force x extension

2. Material

   • Elastic material - returns to normal after stretching
   • Plastic material - Permanently deform after stretching
     • Materials will have an elastic limit, after this is exceeded the material will not return back to it's normal structure. This will be shown on a graph when it begins to plateau.
   • Ductile - can be drawn into wires. Strecthes under tensile stress
   • Malleable - Hammered into sheets. Compresses under pressure
   • Brittle - breaks without significant deformation from stress. Can absorb low amounts of energy

3. Stress (Nm-2) (o)

   • Small cross section will take less force to stretch, therefore has a lower tensile stress
     • Stress = Force/Cross-sectional area

4. Strength

   • Depends on: material, thickness, heaviness on object
   • An object will yield before it deforms due to tense stress

5. Strain (e)

   • Strain = Extension/Original length

6. The Young Modulus (E)

   • Found by gradient of stress-strain graph
     • Area under graph is the energy stored
       • Proven by:  Shaded area = Force/Area  X  Extension/Original length                           stress                       strain                                           = Force X Extension/Area X original lenthEnergy           = Work Done/Volume
       • Tougher the material - more energy to break so bigger area under graph
   • Young Modulus = stress/strain
   • Measures the force that is needed to stretch or compress a material
     • For materials with a high young modulus such as steel you would need a very long, thin sample to get any measurable extension or compression.
     • Keep in mind effects of room temperature an the sagging of ceiling.

7. Hooke's Law: Force needed to extend or compress a spring by some distance is proportional to the distance

8. Density

   • The amount of matter in a certain volume
   • Density = mass/volume

9. Crystal Structure

   • Atoms are placed in a crystal lattice structure
     • Slip plane: Happens when an atom moves out of place
       • This happens when bonds are broken - plastic deformation.
     • Edge dislocation: Distorted rows near a dislocation where half plane atoms are introduced midway through the crystal
       • When there is a dislocation atoms will fill in where other atoms are missing, causing constant making and braking of bonds in one direction.
     • Alloy: Foreign atoms in a lattice that hinder movements and dislocations
       • The different sizes of atoms make it harder for atoms to slide across surfaces of the crystal lattice. Making slip plane less likely.
   • Faults in Crystals
     • Slip Plane: when an atom moves out of place when bonds are broken
       • When a bond between two atoms breaks, the atoms will bond to the next best atom. This will cause a short in a certain direction where bonds are constantly being broken. Eventually resulting in edge dislocation.
     • Edge dislocation: two neighbouring rows distorted near a dislocation, atoms move into areas where there's room
   • Alloy: Mixture of different shaped and sized atoms
     • Means no dislocations or grain boundaries

10. Polycrystaline

Imagens e arquivos do mapa