Bending Moment question

  • Thread starter mzha109
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  • #1
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Homework Statement


The problem can be found here:
2422006-1.png


Sorry the picture is so small. I guess you can download it and then zoom in or something. The main question I'm interested in 2b. Calculating the moment.

position of neutral axis: 37.14mm
Second moment of area: 2.83 x 10^(-6)


Homework Equations


The flexure formula.


The Attempt at a Solution


My answers for maximum compression : 58.4MPa and maximum tension: 34.5MPa. They're off by about 4Mpa respectively.
 

Answers and Replies

  • #2
PhanthomJay
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I get your numbers also.
 
  • #3
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Sorry I should have made it more obvious. The answers are:

Stress tensile=30.93 MPa, Stress compressive=-61.99 MPa.

I can't figure out why I'm wrong.
 
  • #4
PhanthomJay
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:smile:Me neither,so maybe they're wrong?
 
  • #5
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I hope not. It was an exam question. I'd imagine they'd be more careful.
 
  • #6
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Your answers are correct for bending alone, but there is an additional 3.6 MPa for the axial compression. In other words apply the combined stress formula N/A +- M/Z
 
  • #7
PhanthomJay
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Your answers are correct for bending alone, but there is an additional 3.6 MPa for the axial compression. In other words apply the combined stress formula N/A +- M/Z
Nice catch, thanks, we completely overlooked that.
 
  • #8
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Your answers are correct for bending alone, but there is an additional 3.6 MPa for the axial compression. In other words apply the combined stress formula N/A +- M/Z

Oh of course I can't believe I forgot that. Thankyou so much.
 

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