#### Stress Engineering Interview Questions Part 1: Technical

Stress Engineering Interview Questions Part 1: Technical

Did you ever wish there was one place where you could go to on the web and get a list of interview questions AND answers that could help you ace a stress engineering job interview? This post is part 1 in the series of posts that are intended to serve that exact need.

These posts can be most helpful to junior engineers and fresh graduates, but they can also serve as a good reference for experienced engineers.

#### Q: What is a free body diagram?

Answer: A free body diagram is a simple sketch of an isolated section or member of a part or a system with applied loads and reaction loads that satisfy the equations of static equilibrium in the principles of statics.

Want to know more about classical hand calculations that use free body diagrams as part of the analysis? Click this link: Classical Hand Calculations.

Here, by ‘loads’ we mean externally applied forces and moments. Assuming inertia forces (due to mass and acceleration, F=ma) do not have to be accounted for, the free body diagrams are typically used to balance the externally applied loads with reaction loads that keep the part in static equilibrium.

For example, consider a simple L angle bracket that connects a flat panel to a vertical panel loading it with a vertical load P. The bracket’s FBD is shown below.

A freebody diagram like this will help you understand the mechanics and also give you confidence in any FEM results, so this one is a critical skill. To get better at this try to draw more FBDs of this same example with other loads in other directions and understand how to balance them (shear loads for instance).

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#### Q: What are SFDs and BMDs for beams?

Answer: SFDs and BMDs are Shear Force Diagrams and Bending Moment Diagrams of loaded beams.

These diagrams are helpful in understanding the shear and moment load distribution along the length of a beam and to determine where the peaks are. These diagrams are particularly important in the primary structure industry for the floor beams for instance. So what does a simple SFD and BMD look like?

The following figure illustrates the SFD and BMD for a pinned and roller supported beam along with the formulas for the reactions, moments and deflections. Sign convention used here for shear is that the summation of reactions and applied loads immediately to the left of the point of interest is positive upwards.

In order to get better at this, practice drawing SFDs and BMDs with multiple supports and loads, any reputed engineering mechanics and statics text book will contain detailed instructions on constructing SFDs and BMDs from scratch. Search on youtube for videos.

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#### Q: Draw the SFD and BMD for the beam above with a mid span moment load

This is one of the trick questions you could be asked intended to judge your knowledge of SFD and BMD variations of simply supported beams.

So in this case there are no forces, just a mid span moment load and reaction loads at the ends. Imagine the physics of this moment trying to pull up the left side and push down the right side of the beam. The only reaction on the left side is down, and stays that way all the way to the right until another force (reaction at the right) shows up, hence the SFD is a constant negative reaction at A and goes back to zero at the right at B. As far as the moment is concerned, it jumps suddenly at the point where the moment is applied and reverses in sign. The following figure illustrates the SFD and BMD of such a beam.

Here is a video that explains a similar situation:

With me so far? Awesome, in the NEXT PART we will explore some more questions. However, it would be even more awesome if you can share your own experience below and let us know what kinds of questions you were asked and what answers you provided. If you interviewed someone for a stress engineer position, what questions did you ask the candidate? Comment below.

Cheers...

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Surya Batchu

Surya Batchu is the founder of Stress Ebook LLC. A senior stress engineer specializing in aerospace stress analysis and finite element analysis, Surya has close to a decade and a half of real world industry experience. He shares his expertise with you on this blog and the website via paid courses, so you can benefit from it and get ahead in your own career.