6.2.1Work, energy, power and deformation
Elastic and Plastic Behaviour
5 min read 7 parts Lesson 14 of 17 1 quiz
Lesson summary
6.2.1 Elastic and Plastic Behaviour — AS PHYSICS 9702 notes: Distinguish elastic and plastic deformation and brittle and ductile materials using force–extension and stress–strain graphs.Elastic deformation — when the load is removed, the object returns to its original natural len…
- Elastic limit
- Linear portion
- Limit of proportionality
- Brittle materials
- Graph of a brittle material
- Graph of a ductile material
Section 1 of 7Types of deformation
Types of deformation
Elastic deformation
- Elastic deformation when the load is removed, the object returns to its original natural length.
Plastic deformation
- Plastic deformation when the load is removed, the object does not return to its original length.
Elastic limit
- Elastic limit the point beyond which the object does not return to its original length when the load is removed.
- Plastic deformation occurs beyond the elastic limit.
Section 2 of 7Regions of a force–extension graph
Below the elastic limit
- Below the elastic limit the material shows elastic behaviour and returns to its original shape.
Above the elastic limit
- Above the elastic limit the material shows plastic behaviour.
Linear portion
- Linear portion the loads at which force and extension are directly proportional.
Limit of proportionality
- Limit of proportionality the upper end of the proportional relationship.
Section 3 of 7Elastic limit and limit of proportionality
Limit of proportionality
- Limit of proportionality beyond it the material is no longer defined by Hooke’s law.
Elastic limit
- Elastic limit the furthest point a material can be stretched and still return to its previous shape.
Position
- Position the elastic limit is at a slightly higher extension than the limit of proportionality, so they are not the same point.
Section 4 of 7Brittle and ductile materials
1Brittle materials
- Brittle materials they have very little or no plastic deformation.
- Glass and concrete are examples.
- A brittle material breaks with little elastic and insignificant plastic deformation.
2Ductile materials
- Ductile materials they have a larger plastic region and stretch into a new shape before breaking.
- Copper is an example.
3Graph of a brittle material
- Graph of a brittle material a straight line through the origin with no or negligible curved region.
4Graph of a ductile material
- Graph of a ductile material a straight line through the origin, then curving towards the x-axis.
Section 5 of 7More from the specification
1Elastic Potential Energy
- The elastic potential energy stored in a stretched spring or wire obeying Hooke’s law is equal to the work done on the sample: Ep = 0.5 * F * x = 0.5 * k * x2.
2Area Under a Force-Extension Graph
- On a force-extension graph for a metal sample, the area under the curve represents the strain energy stored during elastic deformation or the total work done during plastic deformation.
3Elastic versus Plastic Behaviour
- Elastic deformation is reversible upon removing the deforming tensile force,
- whereas plastic deformation causes permanent structural rearrangement of atoms beyond the elastic limit.
4Elastic Potential Energy
- The elastic potential energy stored in a stretched spring or wire obeying Hooke’s law is equal to the work done on the sample: Ep = 0.5 * F * x = 0.5 * k * x2.
5Area Under a Force-Extension Graph
- On a force-extension graph for a metal sample, the area under the curve represents the strain energy stored during elastic deformation or the total work done during plastic deformation.
6Elastic versus Plastic Behaviour
- Elastic deformation is reversible upon removing the deforming tensile force,
- whereas plastic deformation causes permanent structural rearrangement of atoms beyond the elastic limit.
7Trapezium
- A shape with two parallel sides, giving the area under a uniformly accelerating v-t line.
8Potential energy
- Energy stored by the configuration of a system.
9Energy stored
- W = ½QV = ½CV²What the symbols mean: W or E = energy stored (J) · Q = charge (C) · V = p.d. (V) · C = capacitance (F)
10Significant figures
- Digits carrying meaningful information in a number.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Elastic deformation | Deformation where the object returns to its original length when the load is removed. |
| Plastic deformation | Deformation where the object does not return to its original length. |
| Elastic limit | Point beyond which the object does not return to its original length. |
| Brittle | Material with very little or no plastic deformation before breaking. |
| Ductile | Material with a large plastic region that stretches into a new shape before breaking. |
Section 7 of 7Exam technique
1
Treating the elastic limit and limit of proportionality as the same point — the elastic limit is slightly higher.
2
Thinking elastic means stretchy — it means returning to the original shape.
3
Saying brittle materials stretch a lot before breaking — they show little plastic deformation.
4
Assuming any point on the straight line is plastic — a straight line means elastic behaviour.