Force extension graph for copper wire

[shk]

Homework Statement

Using scientific words to describe the properties of materials

Relevant Equations

K=F/x

I have attached the homework with some of the solution.
I have ciuple of questions about it.
For part b, what else I can say?
I think the copper wite is ductile . Elastic and plastic behaviour have already been mentioned. I need to add another word to describe it. Can say it's hard ? Or should I say it's maleable? The question doesn't make it clear that whether the copper wire is under tention or pressure though. The topic on top of the page says
Tensile testing so I assume it's not under pressure and that's why I think "malaeble " may not be the right word and hard might be better.

In the part c, should I find the gradient of the straight line ?

In part e, should I draw another graph which is less steep in the beginning and generally it's lower than tge first graph and also end at a smaller deformation?
This is because I think if the wite is thinner can tolerate less deformation for the same force and it will have a smaller value for the stiffness and hence a smaller gradient for the straight line .

I appreciate your help.
Thanks

 

[Merlin3189]

Homework Statement:: Using scientific words to describe the properties of materials

For part b, what else I can say?
I think the copper wite is ductile . Elastic and plastic behaviour have already been mentioned. I need to add another word to describe it. Can say it's hard ? Or should I say it's maleable? The question doesn't make it clear that whether the copper wire is under tention or pressure though. The topic on top of the page says
Tensile testing so I assume it's not under pressure and that's why I think "malaeble " may not be the right word and hard might be better.

In the part c, should I find the gradient of the straight line ?

I can't see the red & blue, so assume you got the elastic and plastic ok.

Part b is about your understanding of the terms. It might be worth checking any definitions you've been given, or can look up.

Ductile is certainly true and could reasonably be inferred from the graph showing a large plastic region. What other property usually goes along with ductility? Although the graph is a tensile test, they ask only for words that can be applied to Copper and I wouldn't worry too much about distinguishing between pressure and tension in respect of material properties (as opposed to structural properties.)

Part c What do you understand by stiffness? You started to find k from force and extension. If k is a constant, then F/x is the gradient of a straight line. You quoted k=F/x, but didn't say what it meant.

Part e " should I draw another graph which is less steep in the beginning and generally it's lower than the first graph and also end at a smaller deformation?
This is because I think if the wire is thinner can tolerate less deformation for the same force and it will have a smaller value for the stiffness and hence a smaller gradient for the straight line ."
That's a pretty good idea of this.

Have you come across Young's modulus, stress and strain yet? If you have, then you could be a bit more precise about how much less steep and lower the line should be.

The F vs x graph applies to a particular piece of wire. When converted to stress vs strain the graph should be the same for all pieces of wire with those material properties. From that general graph you can work back to the F and x for any size of wire. This would also show your one slight misconception.

If you haven't done this yet, you could simply imagine the original wire is two of the thiner wires side by side in the experiment. How is the force shared between them ? How is the extension shared between them?