Chapter 6 Materials Flashcards
What is Hooke’s law?
The force-extension graph is a straight line from the origin up to the elastic limit of the spring.
What is the elastic limit and what happens after the force is greater than it?
The elastic limit is the maximum force a spring can withstand without undergoing plastic deformation.
What is the unit for the force constant?
Nm^-1
and it is a measure of the force required to extend and object by a unit length
With a simple force-extension graph how do you calculate the energy stored in the elastic material?
Area under the graph
For a given spring how is the energy stored related to the extension?
The energy stored is directly proportional to the extension^2
Equation for energy stored of a spring?
E = 1/2 Fx
Equation for elastic potential energy?
E=1/2 kx^2
In series how are the force constants combined?
The reciprocals of the force constants are added together just like adding resistors in parallel.
How are force constants combined in parallel?
Force constants are added together
What does brittle mean?
Brittle materials when subjected to stress fractures with little elastic deformation and without significant plastic deformation.
What does ductile mean?
A material that can be stretched into wires or hammered into thin sheets
What is a material which is brittle?
Ceramic or glass
What is an example of a material which is ductile?
Copper or aluminium
Definition of Stress and its unit?
Force applied per cross-sectional area and the unit is Pa
Definition of strain and its unit?
Tensile strain is defined as the fractional change in the original length of a wire.
At what point on a stress-strain graph is the limit of proportionality?
The point at which the stress stops being directly proportional to the strain.
What are the yield points on a stress strain graph?
The yield points are points where the material extends rapidly.
What is the ultimate tensile stress of a material?
The UTS is the maximum stress which a material can withstand when being stretched before it breaks.
What is the definition of a strong material?
A material with a high UTS.
How do you calculate the Young’s modulus of a material?
The gradient of a Stress-Strain graph shows the Young’s modulus.
What is Young’s modulus?
The Young’s modulus of a material refers to its ‘stiffness’.
What is the loop called from the formation of the loading and unloading curves?
The loop is called the hysteresis loop.
What measurements are needed to find out the Young’s Modulus of a material?
Initial length of material
Cross sectional area
extension of material
Tension in material in Newtons
What to mention when describing a graph?
Whether it obeys Hooke’s law or not
What is meant by plastic deformation?
When a material is permanently deformed
Explain why the force constant of two springs in series is halved?
The extension is doubled so the force constant halves.
