6 Materials Flashcards
What are the two forces that can act on a spring
Tensile and compressive
What is the point called where plastic deformation begins to take place
Point of elastic limit
Point of elastic limit
The point where a spring goes from deforming elasticity to plasticly
Hookes law
The extension of the spring is directly proportional to the force applied
F = kx
Force = springs constant x extension
Springs constant unit
Nm^-1
What happens during plastic deformation
Some of the word done on the material has gone into moving atoms to new permanent positions
W = Fx
Work done = force x extension
Force extension graph area under the graph
Work done
E = 1/2 k x^2
Elastic potential energy = 1/2 x force constant x extension^2
Hysteresis loop
Energy lost when stretching an elastic band ( thermal energy )
Polythene
Stretches easily but undergoes plastic deformation under a relatively small force
Tensile stress
The force applied per unit cross-sectional area of a wire
Lower case sigma = F/A
Tensile stress = force / cross-sectional area
Tensile strain
The fractional change in the original length of the wire
Lower case epsilon = x/L
Tensile strain = extension / original length
Stress strain graph p
Limit of proportionality
Stress strain graph E
End of elastic deformation
Stress strain graph Y1-Y2
Upper and lower yield points ( material extends rapidly )
Stress strain graph UTS
Ultimate tensile strength ( maximum stress a material can stand before breaking )
Stress strain graph B
Breaking point
