Help Solving an Easy Stress and Displacement Problem
Help Solving an Easy Stress and Displacement Problem
(OP)
Hi,
I'm an Entry Level engineer fresh out of college. I'm still having problems learning how to apply the basics to real world problems because they did not do a good job teaching us that in school.
I was hoping someone could tell me how I go about solving the problem below by using hand calculations. I need to find the max stress and max displacement and am not sure how to go about solving this. I don't need the exact solution but I provided a picture in hopes someone could teach me how to set it up and solve it myself.
I realize this is probably a really easy problem but I do appreciate any help I can get. Thanks.
I'm an Entry Level engineer fresh out of college. I'm still having problems learning how to apply the basics to real world problems because they did not do a good job teaching us that in school.
I was hoping someone could tell me how I go about solving the problem below by using hand calculations. I need to find the max stress and max displacement and am not sure how to go about solving this. I don't need the exact solution but I provided a picture in hopes someone could teach me how to set it up and solve it myself.
I realize this is probably a really easy problem but I do appreciate any help I can get. Thanks.






RE: Help Solving an Easy Stress and Displacement Problem
RE: Help Solving an Easy Stress and Displacement Problem
Thank you for your help and I'm sorry that I wasn't very clear in the first post. If this still isn't enough info I'm very sorry, but please let me know and I can tell you whatever I'm missing.
Thanks for your help!
RE: Help Solving an Easy Stress and Displacement Problem
RE: Help Solving an Easy Stress and Displacement Problem
Step 1 - free body diagram. I simplified it as a simple beam spanning 6" with an 8.333 lb/in dist load
Step 2 - shear diagram = 25-8.33x; moment diagram = 25x-4.167x^2; Rotation diagram = Ct+12.5x^2-1.388x^3; Deflection diagram = Ct x + 4.17x^3-0.3472x^4
Step 3 - Calculate max stress due to max moment = Mxx y/Ixx
Step 4 - Calculate max deflection (x=3)
Step 5 - Check assumptions - bc of step 1 simplification, the rotation at each end amplifys the deflection at the center so add a little on to the max deflection calculated (ie cut with axe).
RE: Help Solving an Easy Stress and Displacement Problem
RE: Help Solving an Easy Stress and Displacement Problem
RE: Help Solving an Easy Stress and Displacement Problem
BA
RE: Help Solving an Easy Stress and Displacement Problem
"I'm still having problems learning how to apply the basics to real world problems because they did not do a good job teaching us that in school." That, to me, sounds like an unfair assessment. They can teach you beam theory in college, but they also expect you to do your own thinking to apply this stuff. You're not expected to have a course on "Analysis of Little Bent Plates".
You might notice also that the type of analysis appropriate to this problem depends on the application. It could be analyzed in great detail via finite element methods, or treated as a frame, or as a beam. If it's something that should take 5 minutes to analyze and 5 minutes to build, the beam method is probably the way to go. If it's part of an airplane or if you're going to make a million of them, then maybe the FEM is appropriate. Actually building and testing one would be another approach that might or might not be justified by the application.
RE: Help Solving an Easy Stress and Displacement Problem
RE: Help Solving an Easy Stress and Displacement Problem
Such is not the case with a pinned - roller model where no horizontal force can be generated. The model should be pinn - roller as Tegici suggested.
I am assuming the shape is just sitting on a flat surface here with no special attachment to the next shape. However, if the legs are attached together with horizontal Tek screws, this becomes a different problem with more of a fixed condition in the short legs. Not true fixity, but partial.
Mike McCann
MMC Engineering
RE: Help Solving an Easy Stress and Displacement Problem
( http://en.wikipedia.org/wiki/6061_aluminum )
So it's not going to 'develop' the stresses calculated.
I.e., it will fold like lead or butter before reaching the specified load, and beam theory goes all to hell.
Was this problem presented as some sort of qualifying test?
Mike Halloran
Pembroke Pines, FL, USA
RE: Help Solving an Easy Stress and Displacement Problem
Step 6 - Check allowables against actuals - if it folds like lead then beam theory goes to hell (smile)
RE: Help Solving an Easy Stress and Displacement Problem