Question

strengths

Answer 1

Your calculation is correct, for k=2.
Question asks k=1.7, so you would get (5(pi) D)/(272)

Answer 2

how do you know k = 1.7?

Answer 3

Dx1.7D I was looking at the appendices trying to locate a table with properties for this piece. Wrong way going about finding K?

Answer 4

Question did not say k=1.7, but said cross sectional dimensions D*1.7D. lol
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Answer 5

Where are you getting 5*pi*D/272?

Answer 6

for t I have D*pi/64

Answer 7

I have
tau_circ=T(D/2)/(pi D^4/32)
and
tau_hollow=T/(2At)
where A=D(kD)=1.7D^2
Then I equated
tau_circ=tau_hollow
and solved for t to get t=5piD/272.

Answer 8

I got 2.88mm and it's correct.

Answer 9

Yep, I got 2.8875, but 2.88 is within 2%, so should be ok.