Question

Combine loads

Answer 1

part b

Answer 2

@mathmate

Answer 3

I am here but I am cooking. lol I will be checking back and forth.

Answer 4

okay I am back.

Answer 5

@mathmate k back.

Answer 6

Yes, I'm here now.

Answer 7

okay so what about part b?

Answer 8

I checked you A,I,J and they're correct.
and the moments Mx,My,Mz are good, including sign.

Answer 9

Are you working with H or K?

Answer 10

Oh, you're working with H.
Let me look at the stresses.

Answer 11

For Mx, I have 3.4 kN-m (not 3.46, perhaps just a typo)

Answer 12

let me look

Answer 13

3.46x10^6 N-mm

Answer 14

yes I have 3.40 KN-m

Answer 15

What formula did you use to calculate the transverse shear (not torsional)?

Answer 16

Which one is the transverse?

Answer 17

So I get sigma_z=91.99 MPa (instead of 93)

Answer 18

Direct shear due to Px or Py.

Answer 19

look under summary of stresses at H

Answer 20

that is how i calculated the 93.775

Answer 21

Yes, that's the one I am asking, the 26.757. I do not find the calculations for it.

Answer 22

looking

Answer 23

tau shear = tau xz = Fx*Q/Ix*d_outer

Answer 24

I got 26.757MPa

Answer 25

ok, so they both have the same sign.

Answer 26

for bending and shear i made them both negtaive

Answer 27

tau_xz = -26.757 MPa - 59.241 MPa = -85.9MPa

Answer 28

Using Mx=3.4x10^6, I get sigma_z=100.704, while you have 102.488. Wonder which one should be used.

Answer 29

BTW this question had multiple steps. I have everything right.

Answer 30

Mine would give total sigma_z=100.704-8.712=91.992

Answer 31

Like 14 questions. So I know my work is good.

Answer 32

ok, so you had all of them corrected already?

Answer 33

yes, everything was accepted except I can't figure out part b (question I posted)

Answer 34

Do you want to see all the questions?

Answer 35

this is 90 degrees to the principal stress (max or min), so this is the pure shear plane(at 45 degrees in real life, not mohr circle). I expect the sigma to be zero.

Answer 36

well that is what I thought too but it's wrong. I thought the sigma was zero. I have already tried this before.

Answer 37

Did you put +0 or -0 or without sign?

Answer 38

just 0

Answer 39

I tried + or -, didn't like it.

Answer 40

I am asking my friend what he got.

Answer 41

I will wait to see what he came up with. I am going to the next problems. Thanks for looking at it.

Answer 42

my friend said it's suppose to be principal stress 2.

Answer 43

that makes sense. It's suppose to be -51 MPa

Answer 44

Then they are referring to the real angles, not on the Mohr's circle.
I agree with that, because at 45 degrees, you had the pure shear plane, which means that at 90 degrees, we have the other principal stress of -51.

Answer 45

I should have spotted it because both parts (a) and (b) do not have shear stresses! lol

Answer 46

and part (c) is just the sigma_av and max. shear.

Answer 47

Ah no worries. lol

Answer 48

I only realized afterwards that you guys are not working with the Mohr circle, but the real cube.

Answer 49

Honestly, I am glad we are not working with the Mohrs circle... lol

Answer 50

That was an interesting problem.
Mohr circle is actually simpler in the sense that a circle is more concrete than a bunch of equations and formula. It can be visualized mentally and hence avoid certain mistakes.

Answer 51

So it looks like you're at the last stretch of the course.
Guess pressure vessels are next!

Answer 52

Nope, already did pressure vessel homework assignment. It was 3 problems. Super easy. lol

Answer 53

Yeah, that true! But that's good. Did you do the three-(Mohr) circle part? lol

Answer 54

the what? what do you mean three-(Mohr) circle?

Answer 55

There is a kind of problem where we're looking at sigma in all three directions, but sigma is always zero, so that ends up with three morh circles, two of which is inside the third.
If you don't do Morh circles, then that would be done differently or not at all.

Answer 56

*sigma z is always zero (z is along thickness of vessel)

Answer 57

Ah I see. Hmmm probably discussed in lecture, but I have not seen one of those problems yet.

Answer 58

Better not than yes. It could be confusing! lol

Answer 59

I'll let you go then! lol

Answer 60

take care and have a good weekend!

Answer 61

Good weekend to you too!