Deformation Of Solids Flashcards
Describe deformation of solids.
Solids change their shape under the action of forces
Change may be large in the case of springs
Change may be hardly noticeable in some structures
Properties of solids:
Compressive and tensile forces
Describe tensile strength.
Force at which a material breaks under a tension force
Also describes how materials break in bending
Describe Hooke’s law.
A material obeys Hooke’s Law if the extension produced in it is proportional to the applied force (load) provided the limit of proportionality has not been exceeded.
F = ke
F -> Force
k -> spring constant
e -> extension
What is the gradient of the Force-extension graph?
Spring constant (k)
Describe the energy stored in a deformed material.
When a wire is stretched by a load (force), work is done on the wire and strain (elastic potential energy)
Energy stored within
The work done in stretching is equal to Fe. -> this is the elastic energy potential energy of the wire.
F is not the maximum but an average force, which is 1/2 F.
Elastic potential energy = 1/2 Fe
Describe stress.
The stress in a material is the ratio of the force acting through the material divided by the cross section area through which the force is carried
The metric unit of stress is the pascal (Pa)
1 Pa = 1Nm-2 (kg m-1 s-2)
Sigma (stress) = Force / Area
Area = pi r2 = pi d2 / 4
Therefore, stress = 4F / pi d2
Describe strain.
Epsilon (strain) = extension / original length = e / L
Sometimes expressed as percentage.
Describe Young Modulus.
Young Modulus -> E -> constant for a particular material
Ratio doesn’t depend on shape/size of material.
Young Modulus = stress / strain
E is a scalar quantity
Defined as ratio of tensile stress to the tensile strain if the proportionality limit has not been exceeded.
Unit = Pa, also quoted as MPa or Gpa
E = (F/A) / (e/L) OR (F/A) x (L/e) OR FL / Ae
Define the elasticity of solids.
Property of material that enables them to return to their original dimensions after an applied force (stress) has been removed.
Define stiffness.
Resistance of a material to changes in shape and size
Define strength.
Ability of a material to withstand a force without breaking
Define elasticity.
Ability of a material to return to its dimensions once force is removed.
Define ductility.
Tendency of a material to change its size and shape considerably before breaking.
Define brittleness.
Tendency of a material to break without deforming.
Name 3 elastic materials.
Sponge
Spring
Rubber
