Lisachem 2010

[Akirus]

Few solutions in materials and structures detailed study that I disagree with, someone prove me wrong:

1. Which of the following means that copper has a tensile strength of 2.5 * 10^8 Nm^-2?

Solution says B: "A sample will become permanently deformed if subjected to a stress greater than 2.5 * 10^8 Nm^2". Doesn't that describe the elastic limit?

I selected A: "A sample of copper will probably break if subjected to a stress of 2.5 * 10^8 Nm^-2", which falls more in line with the definition of 'strength'.

3. You'd have to look at the diagram for this question, it's a graph. None of the curves have a clearly marked breaking point, so I selected D (i.e. impossible to tell as maximum tensile strength is unknown); for all we know, isoprene may break where it is whereas neoprene and urethane could extend a lot further.

4. If neoprene is stretched 7 times its original length, then change in length = 6l (since 1l + 6l = 7l) => strain = 6l/l = 6. I don't see how it could be 7.

[m@tty]

Tensile strength is the maximum stress the sample withstands, ie. the maximum on the stress-strain curve. B is the yield strength. A seems more correct here.

With 4 it says that it stretched 7 times its length, this is the length of the actual stretch ie. the entire length is now 8l. It was not stretched to 7 times its length. 

[ghadz7]

Encountered the same problem with question one:

Tensile strength - the force required to pull something such as rope, wire, or a structural beam to the point where it breaks.

Yield strength - The stress a material can withstand without permanent deformation.

Aremy definitions wrong?

[Elnino_Gerrard]

Sorry i still don get q 4...once u get the change in L then what?how to fin the stress?  Youngs modulus =stress/strain?

[ghadz7]

Read it of the graph! The y-axis represent the stress.

[Akirus]

Tensile strength is the maximum stress the sample withstands, ie. the maximum on the stress-strain curve. B is the yield strength. A seems more correct here.

With 4 it says that it stretched 7 times its length, this is the length of the actual stretch ie. the entire length is now 8l. It was not stretched to 7 times its length. 

"Neoprene is stretched to 7 times its original length."

=/

[Elnino_Gerrard]

Read it of the graph! The y-axis represent the stress.

LOL thanks hahaha i cant belive i asked that question

[m@tty]

Tensile strength is the maximum stress the sample withstands, ie. the maximum on the stress-strain curve. B is the yield strength. A seems more correct here.

With 4 it says that it stretched 7 times its length, this is the length of the actual stretch ie. the entire length is now 8l. It was not stretched to 7 times its length. 

"Neoprene is stretched to 7 times its original length."

=/

Ok, then you're right.