Materials Flashcards
Hookes law
for a material within its elastic limit, the force applied is directly proportional to the extension of the material
When does Hookes law not apply
Once the elastic limit of the material is reached, Hooke’s law is no longer obeyed and the material will not return to its original shape.
What is denoted by a linear relationship on force-extension graph
this would be elastic deformation as the material would go back to original shape.
What is denoted by the curve relationship after the elastic deformation on a force-extension graph?
Plastic deformation occurs beyond this point therefore it will not go back to its original shape
What does the unloading of a material that has undergone plastic deformation show
often the unloading line/curve has a returning point on the x-axis (extension) which shows permanent deformation of the material
What is represented in the unloading curve of rubber
it is a hysteresis loop, the area represents the energy that was required to stretch the material out
carry out a practical to test for force-extension characteristics
The material is suspended using a clamp adjacent to metre rule
A marker is applied to the ruler to mark the original length of the material. Standard masses are attached to the bottom of the material in increments
and the extension of the spring for each mass is recorded.
use set square for eye level measurements
ensure elastic gradient is calculated
What occurs when work is done to elastically and plastically deform a material
- the energy is converted to elastic potential energy ( area under force extension graph)
- If plastic deformation occurs, then the work done to achieve this deformation is not stored as elastic potential energy, it is used to rearrange the atoms in to their new permanent positions.
define tensile stress
force applied to a material per unit cross-sectional area
Stress (𝜎) = 𝐹/A
Define tensile strain
extension or compression of a material per unit length, it has no units
strain = x/L
