Unit 5, Solids Under Stress Flashcards
What is the point at which a spring starts to become deformed
The elastic limit
Hooke’s law
The tension in a spring or wire is proportional to its extension from its natural length provided the extension is not too great
What is the equation for the spring constant
F = kx
how would you calculate work done with a force-extension graph
Calculate the area under the graph
What is the equation for work done using Hooke’s law
W = 1/2kx^2
What is Young’s modulus used to compare
Different materials of various lengths and cross-sectional areas
What is the equation for Young’s modulus in word form
E is equal to Stress divided by Strain
Stress
The force per unit cross-sectional area when equal opposing forces act on a body
What is the equation for stress
sigma = Force/Area
Strain
The extension per unit length due to an applied stress
What is the equation for strain
Epsilon = Change in length / original length
What are the units of stress
Pascal, Pa
What are the units of Strain
There are no units
What are the three types of solids
Crystalline
Amorphous
Polymeric
Crystalline
Is a solid in which atoms are arranged in a regular array, there is a long rand order within the structure
Amorphous
A solid in which there is no regular order, atoms are arranged randomly
Polymeric
A solid that consists of chain-like molecules
On an annotated stress-strain graph what does the P point stand for
Limit of Proportionality, Where Hooke’s law stops being followed
On an annotated stress-strain graph what does the E point stand for
Elastic Limit, beyond this point all extension is plastic strain
What is the difference between plastic and elastic strain
in elastic strain the material will return to it’s original point after the force is removed, with plastic strain the material no longer returns to the original point
On an annotated stress-strain graph what does the Y point stand for
Yield Point, Beyond this point a small increase in the force applied will cause a larger than before extension
On an annotated stress-strain graph what does the X point stand for
Breaking Point, The stress at this point is known as the breaking stress
Dislocation
A gap in a plane of atoms where one plane is incomplete
How to reduce dislocations and there effects
Introduce impurities into the material
What is necking
Local thin`ning due to dislocations, which increases the stress around the area
What are the two methods to increasing the breaking stress of brittle materials
Reduced the number of cracks within the material
Form the material under compression
When does rubber obey Hooke’s law
When the force is small
Why is more work done when stretching rubber than when contracting it
Due to the extra energy used to stretch being transferred to vibrational energy in the rubber molecules. The vibrations re tangle the chains.
