structures and materials investigation

[HERculina]

hey guys,
I did an experiment that involved simultaneously adding 50g weights on three different materials and then constructing load/extension graphs for each.
So any suggestions for the following practical questions would be really appreciated :
1) Why does nylon stretch more than wool and plastic, and why does wool stretch more than plastic?
2) What does the accuracy of these results depend on?
3) What is the difference between materials deforming elastically and plastically?
4) What has really happens when a material breaks during testing?
5) What further information would you need to convert your graphs into stress-strain graphs?
thanks.

[HERculina]

BUMP!
When you draw a force-extension graph, is the extension when you subtract the recorded distance for that load from the previous distance? Or is extension just the distance of the string in total including how much it's grown?
i did the former, and my graphs are't turning out right force = y axis , extension = x axis yea?
i got for force : 0,0.5,1.0,1.5,2.0,2.5,3.0.... then for extension in mm: 0,2,1,2,2,2,1... :|

[DisaFear]

The extension is calculated from the equilibrium length, that is, the length when the elastic/spring is at rest

If the spring at rest is 1m, and under some force, we record the length of the spring to be 1.4m, the extension would be 0.4m. If I applied some more force, and the recorded length of the spring was shown to be 1.75m, then the extension would be 0.75m

[HERculina]

OHHH OK thanks so much! i get it now
mind asnwering a few of my other question if you can?

[HERculina]

How exactly do you draw 'line of best fit' ?