WEBVTT

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What does strong actually mean?. A fiber can carry a large stress, stretch far, or absorb substantial energy before breaking. These are different properties.

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Stress compares force with area. Engineering stress is σ = F/A₀. Divide tensile force by the fiber's initial cross-sectional area to compare differently sized fibers.

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Strain compares extension with length. Engineering strain is ε = ΔL/L₀. Divide the change in length by the initial length; a 10% extension means strain 0.10.

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Strength is the peak stress. On a stress–strain plot, tensile strength is the highest stress reached. The horizontal extent shows how far the fiber stretches.

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Toughness needs the whole curve. The area under the stress–strain curve up to fracture gives energy absorbed per initial volume:

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Toughness needs the whole curve. toughness. These curves are schematic, not measurements.

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Compare more than the peak. Inspect the schematic curves. Which peaks higher? Which has more area? Explain why the stronger example need not be tougher.