4.1 Deformation of Solids Flashcards
(16 cards)
State
Hooke’s Law
The extension of an elastic material is directly proportional to the stretching force applied up to a maximum load known as the limit of proportionality.
Equation
Hooke’s Law
F = kx
Define
Limit of Proportionality
Beyond this point the extension is no longer proportional to the applied force.
Define
Elastic Limit
If the applied force is greater than this value it will cause permanent deformation.
Define
Yield point
Beyond this point small increases in the applied force cause large increases in extension.
Define
Elastic Deformation
The object will return to its original shape and length when the applied force is removed.
Define
Plastic Deformation
The object will be permanently deformed when the applied force is removed.
Define
Stress
Stress is defined as the force acting per unit cross sectional area.
Equation
Stress
Stress = F⁄A
OR
Stress = Applied force⁄Cross sectional area
Unit Nm-2 or Pa
3 Types
of Stress
Tensile stress - Stresses which stretch an object causing tension in the object.
Compressive stress - Stresses which squash or compress an object casuing compression in the object.
Ultimate Tensile Stress - The maximum stress that can be applied to a wire without it breaking.
Define
Strain
The extension (or change in length) per unit length.
No unit.
Equation
Strain
Strain = x⁄l or e⁄l or ∆l⁄l
OR
Strain = Change in length⁄Original length
Define
Young Modulus, E
The ratio of stress to strain.
Equation
Young Modulus, E
E = FL⁄Ax
OR
E = Stress⁄Strain
Unit Nm-2 or Pa
Equation
Elastic Potential Energy
Es = 1⁄2F ∆x
OR
Es = 1⁄2kx2
Unit J
k is the force constant.
Define
Strain Energy
In a deformed state any object will possess an additional potential energy known as the strain energy.
