What is Strength of Materials?
- katerinabiryukova
- 11 minutes ago
- 4 min read
What does it mean to be strong?
When going to the gym, being strong means being able to lift a heavier weight with the proper form. However, materials have to do much more than just withstand a heavier weight.
Instead, you can think about the strength of materials as all aspects of an athlete’s performance. Similarly to how certain sports require some skills more than others, higher specific “strengths” of materials make them useful for certain specific applications. There is a multitude of parameters that engineers consider as “strength” of materials, the most common ones being:
Compressive Strength is
... the ability of a material to withstand being “squeezed”. In buildings, concrete or wood must bear the weight of the entire building and not break. Concrete, for instance, has such a high compressive strength because its microscopic structure is very dense (with little empty space) and there are strong bonds between cement and water particles. Therefore, you need to “squeeze” concrete a lot to break it. The best parallel to compressive strength is weightlifting, where athletes have to raise a weight overhead and keep their body stable while holding the weight there.
Tensile Strength is
... stretching the material to see how much stress it can withstand without breaking. This parameter is critical when building bridges or reinforcement beams as they bend inwards due to the weight on their top but must sustain their structure regardless. Imagine rock climbers: they stretch to reach the next rock/climbing hold and must maintain their entire body in tension to anchor themselves on the surface.
Yield Strength is
... how much stretching a material can bear before it deforms permanently. This is like stretching a rubber band. Usually, a rubber band goes back to its original shape, but if you apply too much force and then let go, the rubber band stays elongated. The type of stress applied to measure tensile and yield strengths is the same: yield strength just measures force until the rubber band deforms permanently, while tensile strength – until it breaks. As an example, high yield strength is crucial for ship hulls, so that the pulling forces of waves don’t deform the ship’s structure. Thinking about gymnasts, their goal is to improve flexibility – how much they can stretch and then return to their starting pose.
Shear Strength is
... the resistance of a material to having its internal structure sliding against itself. A popular parameter is torsional strength - when a material is twisted. High torsional strength is required from pillars in skyscrapers. This ensures that when the wind blows or an earthquake happens, the pillars do not twist, so that the building itself doesn’t collapse. We can think about dancers, who, despite their fluid and often twisting movements, keep their muscles engaged to precisely control their position.
Fatigue Strength is
... in any long-term applications, materials must be able to handle fluctuations in the stresses described above again and again. Fatigue strength is the measure of how many cycles (one complete sequence of applying and removing load) occur before a material is severely weakened or broken. Picture turbine blades: they undergo high bending stresses from steam repeatedly with 10-20 full rotations per minute. Thus, materials for turbine blades must be resistant to the constant changes in stresses, and nickel alloys are the most widely used for the job. In a sense, resistance to fatigue is tested for many different athletes at the end of the game (be it football, hockey or beach volleyball), when they have to execute excellent technique in spite of accumulated tiredness.
What else can you tell me about material strength?
Apart from these, there are about 10 more strength parameters, each of which informs engineering decisions in many different contexts. What this also means is that we CANNOT name the single 'strongest' material on Earth. No material has the highest values for all strength measurements.
The acclaimed leader for tensile strength is graphene, which is essentially one layer of carbon atoms. You can get it by isolating a single 2D layer from graphite, which is the “lead” in our pencils. It was theoretically calculated that a bag of graphene can hold up to 2 tons of weight, though we cannot yet produce those. Defects in the crystal structure arise if we manufacture a larger material, which in turn compromises its strength. In our everyday world, we often use steel for construction and titanium alloys for aircraft. This is because these materials offer high performance across all the strength parameters.
So, the next time you find yourself saying that something is “strong”, try to ask yourself: “What type of strength is it?” And “Why did engineers choose a material with this strength property for this object?”
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