Youngs Modulus - an extension to Hookes LawMain Questions:Why
are mechanical properties important for engineers?How is Youngs
modulus related to Hookes Law?How do scientists test materials to
calculate the Youngs modulus?What is the difference between
materials with high Youngs modulus vs. materials with a low
Duration: 3-5 days
Amazing footage on of it here.
The main causes of engineering disasters are:human factors
(including both 'ethical' failures and accidents) design flaws
materials failures extreme conditions or environments and, of
course, any combination of any of these
Mechanical Propertiesnumerical value used to compare benefits of
one material vs. anotherspecific unitsserves to aid in material
Hookes LawThe amount of force applied is proportional to the
amount of displacement (length of stretch or compression).
The stronger the force applied, the greater the displacement
Less force applied, the smaller the displacement of the
F - applied force k spring constant x - amount of
k = 60 N/m 60 N will produce a displacement of 1 m
What force will make the spring stretch a distance of 5 m?
Which spring will have a greater spring constant, aluminium
spring, or steel spring? Why?
Hooke's Law applies to all solids: wood, bones, foam, metals,
Youngs modulusMeasures resistance of material to change its
shape when a force is applied to it
Related to atomic bonding
Stiff - high Young's modulus
Flexible - low Young's modulus
Same as Hookes Law the stretching of a spring is proportional to
the applied forceF = -k x
Stress vs. strain graphsYoung modulus is large for a stiff
material slope of graph is steepIs a property of the material,
independent of weight and shapeUnits are usually GPa (x109 Pa)
How do scientists calculate Youngs Modulus???
opened on July 1st 1940The 3rd longest suspension span in the
world Only four months collapsed in a windstorm on November 7,1940.
An important aspect of design for mechanical, electrical, thermal,
chemical or other application is selection of the best material or
materials. Systematic selection of the best material for a given
application begins with properties and costs of candidate
materials. For example, a thermal blanket must have poor thermal
conductivity in order to minimize heat transfer for a given
temperature difference.Systematic selection for applications
requiring multiple criteria is more complex. For example, a rod
which should be stiff and light requires a material with high
Young's modulus and low density. If the rod will be pulled in
tension, the specific modulus, or modulus divided by density E / ,
will determine the best material. But because a plate's bending
stiffness scales as its thickness cubed, the best material for a
stiff and light plate is determined by the cube root of stiffness
divided density .How does it help in the design of structures?Some
structures can only be allowed to deflect by a certain amount (e.g.
bridges, bicycles, furniture). Stiffness is important in springs,
which store elastics energy (e.g. vaulting poles, bungee ropes). In
transport applications (e.g. aircraft, racing bicycles) stiffness
is required at minimum weight. In these cases materials with a
large stiffness are best.
*At first, if you remove the load, the spring returns to its
original length. This is behaviour.Eventually, the load is so great
that the spring becomes permanently deformed. You have passed the
elastic limit and the material has become plastic.
Teacher: explain hooks law equation, simulation, extrapolate
data from 2 springs, graph data, calculate spring
constants.*Explain why force per area with two rulers different
lengths, same materialThe initial straight-line part of the graph
shows that the strain is proportional to the stress.After the
elastic limit or yield point, the graph is no longer linear. Remove
the load, and the wire is permanently stretched.From the initial
slope of the graph, we can deduce the Young modulus.