6. Materials (3.4) Flashcards
Tensile force
Force pulling a material apart
Compressive force
Force pushing a material inward
Shear force
Force that acts at an angle
Tensile deformation
When something gets stretched apart
Compressive deformation
When something gets squeezed inward
Hooke’s law
The change in length due to a force is proportional to the force. This is valid up until the elastic limit.
Formula for extension
F = kx
Formula for energy required for extension (spring constant one)
E =1/2 kx^2
What does the stiffness of an object depend on? (2)
- the type of material
- the object’s dimensions
Look at force-extension and force-compression graphs for springs.
Look at the practical for investigating hooke’s law
What does the area under a force-extension graph represent?
Work done
Formula for energy with force and extension:
E=1/2 Fx
What is elasticity?
The ability of a solid to regain its shape after being deformed
Ductile
The ability of a solid material to elastically deform to a large extend before fracture when subjected to tensile loading.
Brittle
The material undergoes little to no plastic deformation before fracture when subjected to tensile loading
Stress (or Tensile stress)
Definition:
Formula:
The force per unit area of the cross section when a material is stretched.
sigma = F/A
Strain (or tensile strain)
Definition:
Formula:
The ratio for change in length over initial length
epsilon = x/L
Ultimate tensile stress
The maximum stress a material can withstand before it breaks
Limit of proportionality
The point until which the material obeys hooke’s law
Elastic limit
The point until which all deformation was elastic
Which comes first, limit of proportionality or elastic limit?
Limit of proportionality
What happens after a metal passes the ultimate tensile stress?
The material becomes longer and thinner at its weakest point (necking)
The material eventually snaps at the breaking point
Breaking strength
The stress value at the breaking point
Young’s modulus formula
E =sigma/epsilon
Young’s modulus = stress / strain
The Young’s modulus is the gradient of the stress/strain graph when it obeys hooke’s law
Learn stress-strain graphs for typical materials.
Look at the method of determining the Young’s modulus of a material
