Mechanical Properties Mostly Metals Flashcards
How is the mechanical behaviour of a material derived?
from chemical bonding present
How can mechanical properties be measured and tested
Measured by separating atoms from each other but this is difficult due to size of atoms
Materials are large, so mechanical testing is carried out on these
Mechanical testing involves separating the atoms in a material by applying a force
We need to know the force and the distance that the atoms are separated by for testing
What is the stress and strain?
Values of force and extension need to be normalized against the material geometry cause a thin copper wire will need less force than a thick copper sheet.
Force needs to be normalised against cross sectional area to give stress
Stress = F/A
Extension needs to be normalised against the original length to give Strain
Straub = Change in length / Original length
What are some forms of stress
A Torsion - form of shear/drive shaft a type of stress(twisting)
Simple tension
Simple compression
Bi-axial tension
Hydrostatic Compression
What is elastic modulus aka Hookes law?
A linear relationship between session and strain. The gradient of stress/strain is hookes law
What is poisons ratio
Metals - 0.33
Ceramics - 0.35
Polymers - 0.4
What is plastic deformation
Plastic behaviour is when the stress increase falls with increasing strain . In elastic deformation they come back to their original position while in plastic they do not return to their original position and a permanent change has occured
What’s the difference between ductile and brittle materials
Materials that show palatial deformations up to large strains are called ductile materials
Materials that show little or no plastic deformation and break at small strains are brittle materials.
What is toughness
Describes the amount of energy absorbed by an object before deformation.
If we consider a force versus displacement plot for a material that is linear elastic
what is ultimate strength vs yield strength
Ultimate strength is the maximum amount of force per unit area that the material can sustain
Yield strength is the maximum force per unit area that a material can sustain before plastic deformation
What is hardness?
Resistance to permanently indenting the surface. Large hardness means resistance to plastic deformation or cracking in compression - better weather properties. It is directly related to ensure strength
What does Rockwell indentation use? What is MOHshardness
Each items has a number B is based on what scratches what
