In this article, (and video above), we calculate the total elongation of a mixed-marital assembly to give you a better understanding of what you can expect during the FE exam. This week’s problem was created and solved by Enrique Ivers, an Engineer in Training.
A solid round steel rod 6 mm in diameter and 400 mm long is rigidly connected to the end of a square brass rod 25 mm on a side and 350 mm long. The geometric axes of the bars are along the same line. An axial tensile force of 5 kN is applied at the extreme ends of the assembly. For steel, E = 200 Gpa and for brass, E = 90 Gpa. Determine the total elongation for the assembly.
You can rely on the FE guidebook for this problem, however, you must be careful. Note that the loading of the assembly is uniaxial, given that “the geometric axes of the bars are along the same line.” Additionally, if you search for “elongation”, you will not find the proper equation. You should search for other terms, like “Uniaxial loading” or “Deformation” within the Mechanics of Materials section. Ultimately, you will find the section below:
The deformation equation is:
The total deformation of the assembly will be the deformation of the steel rod plus the deformation of the brass rod:
The Correct Answer is A.
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I hope you found this week’s FE Environmental engineering exam prep question helpful. In upcoming articles, I will answer more FE Exam questions and run through more practice problems. We publish videos bi-weekly on our Pass the FE Exam YouTube Channel. Be sure to visit our page here and click the subscribe button as you’ll get expert tips and tricks – to ensure your best success – that you can’t get anywhere else. Believe me, you won’t want to miss a single video.
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I’ll see you next week.
Anthony Fasano, P.E.
Engineering Management Institute
Author of Engineer Your Own Success