# Simple 1D Stress FE Model

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 March 23, 2010, 17:15 Simple 1D Stress FE Model #1 Member   Jonny Join Date: Aug 2009 Posts: 62 Rep Power: 9 Hello, I am reading a book about finite elements with regards to stress analysis. I'm pretty sure the book is full of mistakes, which makes following and doing the examples fairly difficult. I have posted a 1D analysis from the book, I'm not even sure how he comes up with some of the numbers in the calculations. I do understand the method but what hasn't exactly "clicked" is the sign convention or the displacement of each node equating to the change in element length. The author has (u1-u2), then on the last element he switches to (u4-u3), is there a reason for this or is it because u4 is the last node? Would someone mind having a really quick look at the images I posted to give their oppinion. But definetely his answers do not satisfy the simulataneous equations. Thanks a lot for your time. http://img2.imageshack.us/img2/3816/scan0001xo.jpg http://img203.imageshack.us/img203/8407/scan0002r.jpg http://img242.imageshack.us/img242/3311/scan0003e.jpg http://img43.imageshack.us/img43/5510/scan0004al.jpg

 March 25, 2010, 06:22 FEM beams #2 Member   Marco Evangelos Biancolini Join Date: May 2009 Location: Rome - Italy Posts: 79 Rep Power: 10 Hi Jonny, just a quick glance to the rod in compression (I'm sorry but I haven't time to go in the details of formulas, especially for debug an error!). If you are interested in beams I have developed a solver. First for FSI of cantilever beams in 2D and then a general one valid for 3d space frame. You can take a look to this paper (in Italian) http://www.pcm.unifi.it/Aias/XXXI_CO...TI/PDF/149.pdf. I have also a MathCAD worksheet implementation for 3d space frame (but I still haven't published a pdf version on the web); the version valid for plane stress is here: http://www.uniroma2.it/didattica/TCM..._piano_TCM.pdf. We have also used 3d beam in FSI in the past: in this case you have to create an interface between the FEM nodes at the centre of the cross section and the CFD nodes on the actual skin. MEB

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