Calculating Bending Moment: 2b Question and Solution | Homework Equations

[mzha109]

Homework Statement

The problem can be found here:

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.

 

[PhanthomJay]

I get your numbers also.

 

[mzha109]

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.

 

[PhanthomJay]

Me neither,so maybe they're wrong?

 

[mzha109]

I hope not. It was an exam question. I'd imagine they'd be more careful.

 

[pongo38]

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

 

[PhanthomJay]

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.

 

[mzha109]

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.