# Homework Help: Mechanics of Materials - Shear and Compression

1. Dec 10, 2011

### Femme_physics

1. The problem statement, all variables and given/known data

http://img62.imageshack.us/img62/9815/mechmatt.jpg [Broken]
P = 235 kN
d = 50mm (diameter of the axis)
t = 20 mm
t1 = 12 mm
Safety coeffecient = 2.0
σy = 320 MPa

Check the axis for strength (shear and compression)

2. Relevant equations

http://img202.imageshack.us/img202/8345/formulas2.jpg [Broken]

3. The attempt at a solution

http://img714.imageshack.us/img714/210/gzira.jpg [Broken]

Last edited by a moderator: May 5, 2017
2. Dec 11, 2011

### I like Serena

I do not know what all your symbols mean, but your calculation for the shear stress and tensile strength is correct.

I do see that your relevant formula mentions 0.5/0.6, while you apply 1.5/2.0.
Is that intentional?
TBH, I do not know what this factor is. Do you?

Last edited: Dec 11, 2011
3. Dec 14, 2011

### Femme_physics

Sorry it took me a while to reply, I had a materials strength lab reports to give.

I was hoping you'd tell me that

Well, so my answer is correct? At any rate, let's interpret the symbols.

Ts [N/mm^2] = max shearing strength in the part
Fmax [N] – Max shearing force
As = Area of shearing
[T] = allowable shearing strength
Safe factory

Sigma/c [N/mm^2] – Max compression strength in the part
Fmax = max compression force
A/c = area of the compression
[Sigma/c] [Mpa] – allowable compression strength
safely coeffecient

4. Dec 14, 2011

### I like Serena

How did the material strengths lab report go?

Well, I didn't study material sciences, so there are a few technical aspects that escape me...

What is $d \cdot t_{min}$?
And your formulas appear to contain $lc$ instead of $/c$...?
What are $[\sigma_t]$ and $\sigma_y$?
What's the difference between shearing strength and compression strength?

I would expect the extra factor to be some type of rule-of-thumb factor, but I have no clue for what...

5. Dec 15, 2011

### Femme_physics

Great! I copied it from the smartest guy in class (specifically said "guy" ) so it have better turned out great. I just don't like to give out reports as much as I like to solve exercises.

I don't see d x t (min)

As far as Ic instead of /c, I might have miscopied! Not sure whether it's "I" or "/"

Sigma y is "yield strength"
Sigma t is (I think) "tensile strength". There's appearing a relation between that and compression or shearing strength.

Last edited: Dec 15, 2011
6. Dec 16, 2011

### I like Serena

I'm certain it would turn out even better if you let the smartest person in class do it!

There it is!
http://img202.imageshack.us/img202/8345/formulas2.jpg [Broken]

Okay... I'll just accept that for now...

Aha!

Last edited by a moderator: May 5, 2017