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post #1 of 9 (permalink) Old 10-24-2005, 10:31 PM Thread Starter
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Engineers in Here

I know there's a few engineers here so I thought I would throw this out there. Mechanics of materials class, having a heck of a time on this problem.

A 1 in diameter steel (E=30,000 ksi and v=0.30 (Poison's ratio)) bar (rod) is subjected to a tensile load P and a torque T. Determine the axial load P and the Torque T if the strains indicated by gauges a and b on the bar are Ea=+1084 micro and Eb=-754 micro

The pic is a shaft laying horizontal with the strain gauges aligned (a) 45 degrees ccw from the horizontal axis (x) and (b) 45 degrees cw from the horizontal axis (still x). The axial load P is a tension and the torque is up on the right end and down on the left end (give an idea of the shearing stress) There is no gauge in the x direction.

The final answers are supposed to be P=11.11 kip and T=4.16 in kip

Just a start or how to set up would be very helpful, and if anyone happens to be in this class with the same book (Mechanics of Materials, Riley, Sturges, and Morris) it's ch. 6-103

TIA

Joe

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post #2 of 9 (permalink) Old 10-24-2005, 11:09 PM
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Say what? Is that the stuff I'm gonna need to solve once I start taking ME classes?

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post #3 of 9 (permalink) Old 10-25-2005, 02:44 AM
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Quote:
Originally Posted by SVT2888
Say what? Is that the stuff I'm gonna need to solve once I start taking ME classes?
Yeah, solid mechanics (or mechanics of materials, same thing) is a second or third year ME course.

As far as the problem is concerned...way too complicated for me at this hour...I'll take a look at it tomorrow though. Just one little thing to split hairs on, the units of the torque should be kip-ft (or kip-in or lb-ft or something), not just kip.

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Last edited by Palmguy; 10-25-2005 at 02:54 AM.
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post #4 of 9 (permalink) Old 10-25-2005, 06:23 AM
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[QUOTE=Palmguy]Yeah, solid mechanics (or mechanics of materials, same thing) is a second or third year ME course.

This also sounds like a strength of materials class early in a civil engineering program.

I've done problems like this before, but it has been about 4 years since then. It would take a while for me to figure out. Hopefully, someone else will help you out before I'm able to get to it.
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post #5 of 9 (permalink) Old 10-25-2005, 06:26 AM
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Lordy that brings back BAD memories!!!

The very first "ME question" I got in Physics class was something like this:

You have a 6' x 6' x 6' solid block of reinforced concrete, with 1/2" rebar on a 1 foot three dimensional grid. If you apply 100 tons psi to the top of the block, what will the temperature increase be of a 1" cube in the middle of the block?

It then went on to give all the pertinent information of all the materials. Like it friggin mattered!!!

But I guess it does matter to people building bridges. (And by the end of the quarter, we had solved that problem)

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post #6 of 9 (permalink) Old 10-25-2005, 06:43 AM
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Can you scan in the figure for the problem? Or snap a digital pic of it...you're description of the setup ain't getting it with me. I'm visual.

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post #7 of 9 (permalink) Old 10-25-2005, 09:10 AM Thread Starter
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Can't post pics, but I'll try to describe it a little better.

Imagine the rod being held in your hands, one cut end in the right hand and the other in the left. The x axis goes from your left to right hand. The strain gauges so that normally they would be parallel with the x axis, on the axis. Now simply rotate the gauges a ccw from the axis 45 degrees and b cw from the axis 45 degrees.

Hope this helps a little more. If I get time I will try to post a rough sketch later on today if I don't get it figured out.

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post #8 of 9 (permalink) Old 10-25-2005, 10:09 AM
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[QUOTE=Bull]
Quote:
Originally Posted by Palmguy
Yeah, solid mechanics (or mechanics of materials, same thing) is a second or third year ME course.

This also sounds like a strength of materials class early in a civil engineering program.
Yeah, it is...at my school for the Mech/Aero dept it is called solid mechanics, and for civil it is mechanics of materials and has a different course number, but the course curriculum and instructor are the same. When I had the class I was actually in a study group of all civil majors.

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post #9 of 9 (permalink) Old 10-26-2005, 03:11 PM
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I took that class. You still use some of that in Computer Aided Machine Design (Finite Element Analysis Class). I'll be a senior after this semester.


As far as the question goes, scan it and it would probably make a lot more sense

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