What it shows:
A metal under stress will not fracture straight away, but will deform plastically due to the dislocation of crystal boundaries; this is called creep.
How it works:
Here we use lead as the test sample because there is significant creep compared to other metals. The lead is loaded (see fig.1) to a value that is just below the breaking stress of the sample. When creep occurs, the lead is drawn thinner at its weakest point (called 'necking', see fig.2) until its reduced cross-sectional area causes the sample to exceed its breaking...
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