9702 · 6.1
Stress and strain flashcards
Revision flashcards for Cambridge 9702 Stress and strain (syllabus 6.1). Flip, recall, then mark a real past-paper question.
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What is **deformation**?
Any change in an object's shape or size caused by applied forces.
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Define **tensile** and **compressive** forces.
Tensile forces stretch an object, while compressive forces push it inwards, reducing its length.
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What is **stress ($\\sigma$)**?
Force applied per unit cross-sectional area (\\sigma = F/A), measured in Pascals (Pa).
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What is **strain ($\\epsilon$)**?
The ratio of extension to original length (\\epsilon = \\Delta L / L_0), a dimensionless quantity.
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State **Hooke's Law**.
The extension of an elastic object is directly proportional to the applied force, up to the limit of proportionality, provided temperature is constant.
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What is the **spring constant ($k$)**?
A measure of an object's stiffness, representing the force needed per unit extension. Its unit is N m$^{-1}$.
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How is **elastic potential energy (EPE)** calculated for linear deformation?
It's the area under a force-extension graph, or EPE = \\frac{1}{2}F\\Delta L or EPE = \\frac{1}{2}k(\\Delta L)^2.
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Define **Young Modulus (E)**.
The ratio of stress to strain (E = \\sigma / \\epsilon), a material's inherent stiffness, measured in Pascals (Pa).
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What is the key difference between **elastic** and **plastic deformation**?
Elastic deformation is reversible (object returns to original shape), while plastic deformation is permanent (object does not fully return).
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Describe **ductile materials**.
Materials that undergo significant plastic deformation before fracturing, e.g., copper.
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What is the **limit of proportionality**?
The point on a force-extension or stress-strain graph where Hooke's Law no longer applies.
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What does the gradient of a **stress-strain graph** represent in its linear region?
The Young Modulus (E) of the material.
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What is the **elastic limit**?
The maximum stress or force that can be applied to an object without causing permanent (plastic) deformation. If the force is removed, the object will return to its original shape.
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What is the **ultimate tensile strength (UTS)**?
The maximum stress a material can withstand while being stretched before it starts to neck down and weaken. It is the highest point on the engineering stress-strain curve.
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Describe **brittle materials**.
Materials that fracture with little or no plastic deformation, often suddenly. They typically have a high Young Modulus. Examples include glass and ceramics.
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What does the area between the loading and unloading curves on a force-extension graph represent?
The work done to permanently deform the material, which is dissipated as thermal energy (heat). This only occurs when the material is stretched beyond its elastic limit.