Materials Flashcards
(17 cards)
Density?
The mass per unit volume
Average Density?
Average density determines if an object floats or sinks. A solid will float on a fluid if its density is lower than the fluid
Tensile Force?
A force which stretches an object
Compressive Force?
A force which squashes an object
Elastic Limit?
The point at which permanent deformation occurs and an object cannot return to its original shape once the load force is removed: indicating plastic deformation.
Atoms behavior in deformation?
In elastic deformation the atoms move small distances relative to their equilibrium positions and once load is removed they return to those positions. If the deformation is plastic atoms don’t return to their original positions once load is removed
Stress?
The force applied divided by the cross-sectional area
Strain?
Change in length divided by the original length of the material
Breaking Stress?
The point at which stress is high enough to break the material. This is because the stress pulls apart the atoms from one another so much they separate completely
Ultimate tensile stress?
The maximum stress a material can withstand
Strain Energy?
The potential energy stored in a material when work has been done to stretch a material. In elastic deformation the work done is stored as strain energy in the material. In plastic deformation work is done to separate atoms so isn’t stored as strain energy and instead dissipates in the form of heat.
Young’s Modulus?
The constant, which up to the limit of proportionality, enables stress and strain to be proportional
Young’s Modulus Experimentally?
Find the cross sectional area of the test wire by finding the diameter at different points along the wire using a micrometer. Clamp the wire to the end of a bench and have a pulley so weights can be hung off the end. Measure the distance between the marker and end of the wire to give the unstretched length. Keep adding intervals of weight and recording the distance and amount of weight each time
Stress-Strain Graph?
The area under the graph is the strain energy per unit volume. The gradient on the linear section of the graph is the equivalent to Young’s Modulus
Yield Point?
The point at which plastic deformation occurs and a small increase in stress results in a large increase in strain
Brittle Material?
There is no plastic deformation and the material snaps at a certain point. A brittle material has no curving on a stress-strain graph. They have a rigid structure as the arrangement of atoms is crystalline or polycrystalline
Brittle Fracture?
Stress results in cracks at materials surface to get large enough they break the material completely
