Section 5: Materials Flashcards
What is meant by a plastic deformation?
If a deformation is plastic, the material is permanently stretched (after the force has been removed). Some atoms in the material move position relative to one another. When the load is removed, the atoms don’t return to their original positions. (Past the elastic limit)
What is Hooke’s Law?
The extension of a stretched wire,is proportional to the force applied.
How is energy conserved in springs ?
When a vertical spring with a mass suspended vertically below it is stretched, elastic strain energy is stored in the spring, when the mass is released, the stored energy is transferred to kinetic energy as the spring contracts and GPE as the mass gains height. The spring then begins to compress and the kinetic energy is transferred to elastic strain energy.
What is breaking stress? What is ultimate tensile stress?
Breaking Stress - The stress thats big enough to break the material.
Ultimate Tensile Stress -The maximum stress that the material can withstand.
How is energy conserved in stretching?
When a material is stretched, work has to be done in stretching the material. If the deformation is elastic, all the work done is stored as elastic strain energy in the material, when the force is removed, the stored energy is transferred to other forms. If the deformation is plastic, the energy is dissipated as heat.
What is the elastic limit and the limit of proportionality?
There’s a limit to the force you can apply for Hooke’s Law to stay true - the limit of proportionality, at this point, the graph of force against extension begins to curve. If you increase the force beyond the elastic limit, the material will be permanently stretched, when all force is removed, the material will be longer than at the start.
What is meant by density of a material? What it’s equation?
Density is a measure of the ‘compactness’ of a substance. It relates the mass of a substance to how much space it takes up.
Stress strain graphs:
1) What is the limit of proportionality?
2) The elastic limit?
3) The yield point?
4) The maximum?
5) The area under the straight part?
1) Past the limit of proportionality the graph begins to curve, the material stops obeying Hooke’s law but would still return to its original size and shape.
2) At the Elastic limit, the material starts to behave plastically. From this point onwards the material no longer returns to its original shape.
3) At the yield point the material suddenly starts to stretch without any extra load. The point at which a large amount of plastic deformation takes place with a constant or reduced load.
4)The ultimate tensile stress. (The highest Y value)
5)The energy stored in the material per unit volume.
Which type of force is needed for Hooke’s Law?
The law stays true for both compressive forces and tensile forces. For a spring, k is constant for compression and extension. (Below the limit of proportionality)
What is elastic strain energy?
What a material is stretched, work has to be done in stretching the material. Before the elastic limit, all the work done in stretching is stored as potential energy in the material - called elastic strain energy.
What is tensile strain?
The change in length, divided by the original length of the material. Or the ratio.
How do you find the Young Modulus from a stress against strain graph?
Gradient.
What is tensile stress?
The force applied, divided by the cross-sectional area. When a material is stretched.
What is meant by elastic deformation?
If a deformation is elastic, the material returns to its original shape once the forces are removed - so it has no permanent extension.
What is the young modulus?
A constant given by
