Stress & Strain: Exploring Copper Wire Properties

In summary, the graph shows how stress decreases as weight is added to an experiment, but the theory is that this is due to the wire becoming thinner as the stress strain curve enters the "necking region." There is a difference between the "enginering" stress-strain curve and the "true" stress strain curve, and if the slope of the curve in the elastic region up to the proportional limit were to be determined, copper would have a YM of about 110-128 Gpa.
  • #1
greener1993
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http://www.ami.ac.uk/courses/topics/0123_mpm/images/met_mpm_imgb.gif [Broken]
[PLAIN]http://i859.photobucket.com/albums/ab152/Greener1011/Untitledpicture.png[/PLAIN]

First off I am sorry about the massive size. The top graph is how a stress strain graph of a metal should look. However i can't seem to think why Mpa of stress decreases as it enters the "necking region". My graph is the one below and although it shows simular trend (limit of proportionality, small yeild point and showing it going into plastic deformation)it was uncompleted because the hoop the weight was attached to snaped and was not time to redo ( will be redoin tomorrow) Every point is a 100g weight being added to the experiment. However my logic is this. how can stress decrease when you are adding more weight and force every time? I thought maybe i had done something wrong i measured the diameter of the wire and used that for all calulations, but if it was thinning then the diameter would be smaller and so would the area.

Same big number / Smaller number = bigger number

It is a theory that has hit me for ages now, I am clearly missing something. Also as one additional question Copper wire has a YM of about 110 - 128 Gpa, where was this measured from? Is it using the highest stress and strain vaules? so the tensile stress or something different like the mean of them all?
 
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  • #2


There is a difference between the 'enginering' stress-strain curcve and the 'true' stress strain curve. The first sketch is the engineering stress strain curve, which does not account for the 'necking down' of the specimen in the plastic region, creating a smaller area. If it were accounted for (true stress), you wouldn't see that dip in the curve as the stress approaches ultimate. I wouldn't worry about that tiny dip beyond yield, that's some slippage in the microscopic structure of the material.
As far as determining YM fior copper, that's the slope of the stress strain curve in the elastic region up to the proportional limit.
 
  • #3


First off sorry about the werid title i had put a randm bunch of letters in so i could see if the images had worked on preview.

Thanks you so much mate youve helped me understnad it alot, cheers :)
 

1. What is stress and strain?

Stress and strain refer to the physical changes that occur in a material when it is subjected to an external force. Stress is the force per unit area applied to a material, while strain is the resulting deformation or change in shape of the material.

2. How is stress and strain measured?

Stress is typically measured using units of force per unit area, such as pounds per square inch (psi) or newtons per square meter (Pa). Strain is measured as a unitless ratio of the change in length or shape of a material compared to its original length or shape.

3. What are the properties of copper wire that affect its stress and strain?

Copper wire has several properties that can affect its stress and strain, including its diameter, length, and composition. The type of copper used, as well as any impurities or defects in the wire, can also impact its stress and strain behavior.

4. How does temperature affect the stress and strain of copper wire?

Temperature can have a significant impact on the stress and strain behavior of copper wire. As temperature increases, the wire may expand and become more pliable, leading to increased strain under the same amount of stress. At extremely high temperatures, the wire may even melt and break, causing a sudden increase in strain.

5. What applications can the study of stress and strain in copper wire have?

The study of stress and strain in copper wire can have numerous applications, including in electrical and mechanical engineering, material science, and product design. Understanding how different factors affect the stress and strain behavior of copper wire can help improve the design and performance of various products and systems that use this material.

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