Finding the maximum load of a bar from the yield stress

  • Thread starter Lap9387
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  • #1
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Homework Statement


I have a bar, 500mm long (0.05m) 10mm wide (0.01m) and 3mm deep (0.003 m)

The bat has a load applied in the centre of 30n

I know the maximum yield stress is 150 mpa 150x10^6

How do I calculate the maximum load the bar can take?


Homework Equations



I used stress = m y / I



The Attempt at a Solution



I calculated the bending moment to be 3.75 at 250mm (.25m) using a shear bending diagram,

I then reversed the equation above to get:

150x10^6 = 0.0015m/2.25x10^-11

Which gives m as : (150x10^6 x 2.25x10^-11) / 0.0015

M = 2.25

I know the bending moment is at .25 m

So divide 2.25 / .25

I get 9


The answer can't be 9n as the question uses 30n

Can someone please show me how to solve this?.

Thanks in advance x
 

Answers and Replies

  • #2
rock.freak667
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How is the bar supported? Are the two ends simply supported or fixed, etc?

The type of supports affect the maximum bending moment, which will affect your maximum load.
 
  • #3
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Sorry, the bar is simply supported at either end
 
  • #4
rock.freak667
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For a simply supported beam, the maximum bending moment occurs at the center and is given by

Mmax =PL/4 where P= applied load and L= length of beam
 
  • #5
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So I can then use this to find the max load from the yield stress??
If so, how?
 
  • #6
rock.freak667
Homework Helper
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So I can then use this to find the max load from the yield stress??
If so, how?


Use your first equation and rearrange for M.

σ = My/I
 
  • #7
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thank you for this...
 

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