Stress: material science and you

stressGod created you and everything around you. As an engineer, it thrills me when I see the fingerprint of God in both nature and me. Let me show you an example related to stress.

In engineering, stress is the result of applying a force to an object. Stress, S, is this force, F, divided by the area, A, over which it acts.

S = F/A

A larger force generates more stress. Similarly, a smaller area increases stress.

In you and me, stress is again a reaction to environment. Difficult circumstances increase stress, which can negatively affect both our mental and physical well-being.

In engineering materials, stress results in two very different phenomena:

dislocationStrain hardening is the strengthening of a metal by permanent deformation. This strengthening occurs because all metals have atomic-level imperfections within their microstructure. These are referred to as dislocations. When stress is applied, these dislocations move within the crystallographic microstructure until they reach a grain boundary. When these dislocations “pile up” and entangle at the grain boundaries, the material becomes stronger.

spring_fatigue

Fatigue failure, on the other hand, occurs over time when a material is subjected to repeated stress through a force that loads and unloads the structure. If the force is above a certain level, microscopic cracks eventually begin to form. At some point, a crack reaches a critical size, it suddenly propagates, and fracture (or failure) occurs. In most cases, the crack initiates at a local imperfection (such as a surface scratch) or at a sharp corner (called a stress riser).

We have similar responses to stress. When difficult circumstances point us toward God, even though we may be under tremendous stress, we find that we are strengthened through the trial. We become stronger when the stress moves our imperfections toward the surface. James described this strain hardening process in James 1:2-4.

Consider it pure joy, my brothers and sisters, whenever you face trials of many kinds, because you know that the testing of your faith produces perseverance. Let perseverance finish its work so that you may be mature and complete, not lacking anything.

Without God, repeated stress produces a crack, a local weakness, that will not heal. Rest does not fix fatigue failure — it only delays it. As the stress continues, even if it is small, that crack grows until eventually we fracture. The small internal crack propagates to a complete failure at the surface.

Here’s what relates the two responses. They are both the result of tiny imperfections which all materials possess, just like you and me. Because we will inevitably face stress and we are all imperfect, there are two options for your future: strain hardening or fatigue failure.

Choose God. Get strong! There is truly strength in your weakness when you offer it to God.

 

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About Tony Schmitz

Tony Schmitz received his BS in Mechanical Engineering from Temple University in 1993, his MS in Mechanical Engineering from the University of Florida in 1996, and his PhD in Mechanical Engineering from the University of Florida in 1999. He is a mechanical engineering professor at the University of North Carolina at Charlotte.
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