Which of the following causes the apparent stress to rapidly decrease in a stress-strain diagram?
- A.Necking
- B.Resonance
- C.Glass transition
- D.Hysteresis
Correct answer
Explanation
The correct answer is A, necking. Once a ductile specimen passes its ultimate tensile strength, the deformation stops being uniform and concentrates in one short length, which draws out into a narrow waist. The apparent stress is worked out by dividing the load by the original area of cross section, and since the real area at the waist has shrunk sharply, the load that the specimen can carry falls and the curve turns downward until fracture. Option B is wrong because resonance belongs to vibrating systems driven at their natural frequency and has no place in a static tensile test. Option C is wrong because the glass transition is the temperature at which an amorphous polymer changes from a brittle glassy state to a rubbery one, a thermal effect rather than a feature of this curve. Option D is wrong because hysteresis describes the gap between the loading and unloading curves of a material such as rubber.
Read the full article: Elasticity, Stress, Strain and Hooke's Law: Exam Notes
Practice Questions
View allHooke's law states that within the elastic limit
- A.Stress is directly proportional to strain
- B.Stress is inversely proportional to strain
- C.Strain is independent of stress
- D.Stress is proportional to the square of the strain
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Hooke found that so long as a body is not strained beyond its elastic limit, the restoring force per unit area rises in step with the fractional deformation, and the constant ratio of the two is called the modulus of elasticity.
Read the full explanation →The SI unit of stress is the
- A.Newton
- B.Joule
- C.Pascal
- D.Watt
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Stress is the restoring force divided by the area over which it acts, so its unit is the newton per square metre, and that combination is given the special name pascal, the same unit used for pressure.
Read the full explanation →Strain is a quantity that has
- A.The unit newton per square metre
- B.No unit and no dimensions
- C.The unit metre
- D.The same unit as energy
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Strain is defined as the change in a dimension divided by the original value of the same dimension, a length divided by a length or a volume divided by a volume, so the units cancel and only a pure number survives.
Read the full explanation →The ratio of longitudinal stress to longitudinal strain within the elastic limit is called
- A.Bulk modulus
- B.Modulus of rigidity
- C.Young's modulus
- D.Poisson's ratio
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It governs the stretching or compression of a wire or rod along its length and is obtained by dividing the force per unit area of cross section by the fractional change in length.
Read the full explanation →The reciprocal of the bulk modulus of a material is known as its
- A.Compressibility
- B.Rigidity
- C.Ductility
- D.Tenacity
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The bulk modulus measures how strongly a substance resists a change in volume under uniform pressure, so its reciprocal measures how readily the volume yields, and that quantity is called compressibility.
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