# young’s modulus - an extension to hooke’s law main questions: –why are mechanical properties...

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• 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 value?

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 selection

• 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 is.

Less force applied, the smaller the displacement of the spring.

• F - applied force k spring constant x - amount of displacement

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, plastics, etc...

• 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???

http://www.msm.cam.ac.uk/doitpoms/tlplib/thermal-expansion/simulation.php

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.

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