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Materials spec (Be able to draw and interpret tensile or compressive…
Materials spec
Be able to draw and interpret tensile or compressive stress-strain graphs, and understand the term breaking stress
Yield point = The material starts to stretch without any extra load
Plastic deformation takes place without an increased load
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Ultimate tensile stress and the breaking stress both depend on the conditions, for example, the temperature
The gradient of the straight section of a stress-strain graph is equal the the Young modulus of the material (stress/strain)
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Understand that Stokes's law applies only to small spherical objects moving at low speeds with laminar flow (or in the absence of turbulent flow) and that viscosity is temperature dependent
When an object moves through a fluid, there is friction between the object and the fluid - viscous drag
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Viscosity is temperature-dependent, liquids get less viscous with temperature but gases get more viscous with temperature
Laminar flow = Flow pattern where all the parts of the fluid are flowing in the same direction and the layers in the fluid do not mix. This usually occurs when the object s#is moving slowly (or the fluid is flowing slowly)
Turbulent flow = The layers of the fluid mix. This usually occurs when the object is moving quickly (or the fluid is flowing quickly)
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Understand the terms limit of proportionality, elastic limit, yield point, elastic deformation and plastic deformation and be able to apply them to force-extension and force-compression graphs (can be applied to stress-strain graphs too)
Limit of proportionality = The point beyond which the material no longer obeys Hooke's law
The straight section of a force-extension graph is the region in which the material obeys Hooke's law
The limit of proportionality is the point where the straight line starts to curve
Elastic limit = The point beyond which the material will be permanently stretched
When the force is removed, the material will have changed shape
Elastic deformation = The material returns to its original shape once the forces are removed
When the material is put under tension, the atoms of the material are pulled apart from one another
Atoms move slightly relative to their equilibrium positions, without changing position in the material
Once the load is removed, the atoms return to their equilibrium distance apart
Plastic deformation = The material is permanently stretched
Some atoms in the material move position relative to one another
When the load is removed, the atoms don't return to their original positions
When a material is stretched beyond its elastic limit and an unloading line is drawn on a force-extension graph, the area between the loading line and unloading line is the work done by the force to deform the wire
The unloading line is also parallel to the loading line
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