Q.Describe the behaviour of a wire under gradually increasing load.
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Start your 14-day free trial to unlock the full solution →The stress-strain graph of a wire under gradually increasing load shows a linear elastic region, followed by yielding, plastic deformation up to ultimate strength, and finally fracture.
When a wire is subjected to a gradually increasing stretching load, its behaviour is best described using a stress-strain curve, plotting stress (load/area) on the y-axis against strain (extension/original length) on the x-axis. The wire passes through distinct stages:
1. Proportional limit (region OA): For small loads, stress is directly proportional to strain — the wire obeys Hooke's Law. The graph is a straight line through the origin, and Young's modulus is the slope of this line. If the load is removed here, the wire returns exactly to its original length (perfectly elastic).
2. Elastic limit (point A to B): Beyond the proportional limit, the stress-strain relation is no longer linear, but the wire is still elastic — i.e., it still returns to its original length if the load is removed, up to the elastic limit (point B).
3. Yield point (point B onwards): Beyond the elastic limit, the wire starts to undergo plastic deformation — a small increase in stress produces a disproportionately large increase in strain, and the deformation becomes permanent; the wire will NOT return to its original length even if the load is removed.
4. Ultimate tensile strength (peak of the curve): As loading continues, stress increases (though more slowly) until it reaches a maximum value called the ultimate tensile strength — the maximum stress the wire can withstand.
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