Calculating stiffness
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Flip to reveal answersState the three formulae for stiffness.
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All 4 Flashcards — Calculating stiffness
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Question
State the three formulae for stiffness.
Answer
σ = F ÷ A using the original area; ε = ΔL ÷ L using the original length; E = σ ÷ ε taken on the straight part of the graph.
Question
Why does strain have no units?
Answer
It is a length divided by a length, so the units cancel. A 200 mm bar stretched 0.4 mm has a strain of 0.002.
Question
Where on a stress-strain graph is Young's modulus taken?
Answer
From the straight part only, before the yield point. Past yield the line curves and a gradient taken there is not the modulus.
Question
Give four typical values of Young's modulus.
Answer
Steel about 200 GPa, aluminium about 70 GPa, timber 10 to 15 GPa, polymers 1 to 3 GPa.
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Topic 7.2 hub
Structural systems applied
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