Stress: For Brains and Beams
Engineers are well-acquainted with stress. What type? One could definitely make the case for both physiological and structural. However, for these purposes, let’s start with engineering. A simple mathematical definition for stress is that it is the force applied over a given area. When we apply stress to structures, they respond differently based on material and design properties. Even without much engineering, we can all imagine what happens when there’s too much stress applied in the wrong direction: failure. Structures break, bend, crack, and deform in all kinds of different ways. Stress also has a counterpart, known as strain. Strain accounts for the change in length of a material. A typical example of this is a bar increasing in length as it is pulled from both ends, as well as the behavior it demonstrates when it eventually breaks in two.
Stress and strain are among the most basic concerns of any engineer. We design parts to perform tasks, all of which will involve dealing with some stress and strain on the components. Our job is to make our creations functional and able to deal with all the stressors they encounter, something we as people have to do all the time. One way we can mathematically quantify this preparedness is by calculating the margin of safety. We do so by first defining the load we need our creation to be capable of bearing. In the design phase, the most basic conditions and needs are considered to determine this load. After the design phase, material properties and testing determine how much load the structure can actually bear. The quantity of the maximum load minus the design load divided by the design load is the margin of safety. It is our measure of how well-equipped something actually is to do its job successfully.
Now that you have patiently sat through engineering definitions and math, it is time to address the human element. Why should we care about how engineers evaluate stress in structures? The short answer is, if you aren’t an engineer, you absolutely do not need to know how engineers are evaluating stress. A longer answer is that the thought process behind it is rather applicable to the human experience. By our personal brain mechanisms, we are all capable of dealing with a certain maximum load of stress. On a daily basis, we probably have an idea in mind for how much stress we are expecting to encounter. So from our maximum and design loads we can reimagine the margin of safety as a sort of happiness index with intangible quantities. Mathematically, how well are we coping, and what do we do with that information?
Recently in class, we were asked to evaluate a basic aerospace structures question that involved a plane making a banked turn. This maneuver creates specific relationships between load, lift, velocity, bank angle, etc. The end result of this is increased bank angles in a fixed radius turn lead to increases in load. We were asked what kind of failure this could cause and how to prevent it. It seemed such a turn put stress on the wings and other parts of the structure. And budding engineers that we are, we all came to the same conclusion: well, just don’t bank the plane that severely. Technically, that is mathematically correct, but it’s not the only answer. We could also reinforce the structure to take the extra load. At the end of the day, it was about perspective and understanding there is more than one right way to improve a plane. And in some cases, certain ways are definitely better than others.
We are all well aware of the effects that too much stress can have on the human body. It can negatively affect our health and our overall happiness, especially if we do not have resources available to help us (DeLongis et al). Stress and stress-related disorders have been linked to decreased immune function, which even includes the body’s ability to fight against certain cancers (Reiche et al). However, it is even more complicated because the time in our lives when we experience stress can affect the kind of stress-related problems we have at a later phase in life. It’s intimidating to think that stress during our teenage years can have lingering effects during adulthood. (Lupien et al). If there’s a way to start feeling stressed about stress, it’s definitely reading stress studies.
So, maybe it is time we start thinking about ourselves like a plane. We should view our own lives like an engineer. Just like the question of the banked turn, we cannot avoid everything that increases our stress load. Some stresses are just temporary additions that come as a result of us functioning properly and it would be impossible to eliminate all of that. Therefore, it comes back to the other idea, that we need to reinforce our wings so we can keep flying. As an engineer, I am not equipped to say how exactly we should do that. However, as a person and a fellow plane reinforcing my wings, I can say that we all need to look at the load we can really carry. And we should all be aware of the resources available that can help us. Who are the skilled and professional engineers in our lives who can reinforce our wings? Increased awareness of ourselves and our options can help us improve our own margin of safety and keep us all flight ready.
A. DeLongis, S. Folkman, and R. S. Lazarus, “The impact of daily stress on health and mood: Psychological and social resources as mediators,” Journal of Personality and Social Psychology, vol. 54, pp. 486-495, March 1988. [Online]. Available: https://psycnet.apa.org/doiLanding?doi=10.1037%2F0022-35184.108.40.2066 [Accessed September 12, 2019].
S. J. Lupien, B. S. McEwen, M. R. Gunnar, and C. Heim, “Effects of stress throughout the lifespan on the brain, behaviour and cognition,” Nature Reviews Neuroscience, vol. 10, pp. 434-445, April 2009. [Online]. Available: https://www.nature.com/articles/nrn2639#abstract.
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E. M. V. Reiche, S. O. V. Nunes, and H. K. Morimoto, “Stress, depression, the immune system, and cancer,” The Lancet Oncology, vol. 5, issue 10, pp. 617-625, October 2004. [Online]. Available: https://www.sciencedirect.com/science/article/pii/S1470204504015979. [Accessed September 12, 2019].