Unit 1 definitions Flashcards
(Stress strain graph) Limit of proportionality:
Up to this point stress is proportional to strain / obeys Hooke’s law / Force proportional to extension
Elastic Limit:
Point after which there would be some permanent/plastic deformation would occur
Yield point:
Point at which plastic deformation begins / point at which material shows a larger increase in strain for a smaller increase in stress
Tensile strength/Maximum tensile stress:
Greatest stress before fracturing
Ultimate Tensile Stress:
Stress at fracture
Young’s Modulus:
Gradient of stress/strain graph in linear region
Stress-Strain Graph
Limit of proportionality: Up to this point stress is proportional to strain / obeys Hooke’s law / Force proportional to extension (A)
Elastic Limit: Point after which there would be some permanent/plastic deformation would occur (B)
Yield point: Point at which plastic deformation begins / point at which material shows a larger increase in strain for a smaller increase in stress (C)
Tensile strength/Maximum tensile stress: Greatest stress before fracturing (D)
Ultimate Tensile Stress: Stress at fracture (E)
Hooke’s Law:
The force is proportional to extension i.e. the graph passes through the origin and is straight.
Compressive/tensile strain:
Compressive is a decrease in extension/negative extension. Tensile is an increase in extension/positive extension
Plastic deformation:
Doesn’t return to original shape/length OR stays stretched OR permanently deformed … when force/stress removed
Elastic deformation:
Returns to original shape/length when force/stress removed
Ductile:
Undergoes large permanent/plastic deformation under tension OR can be easily drawn into wires
N.B. All ductile materials are malleable but not necessarily the other way round
Malleable:
Undergoes large permanent/plastic deformation under compression OR can be easily hammered into shape/rolled into sheets
N.B. All ductile materials are malleable but not necessarily the other way round
Brittle:
Breaks with no/little plastic deformation. Absorbs little energy before fracture. Shatters when subject to impact / sudden force
Tough:
Able to absorb lots of energy without failure/in the plastic region OR can withstand impact forces/shocks
Stiff:
Gradient of stress/strain graph is high OR large stress for a small deformation /strain OR Large Young modulus
Strong:
Large/high breaking stress
Hard:
Resists surface indentation/scratching
Laminar flow:
No abrupt change in velocity/direction speed of flow OR flows in layers/ streamlines with no mixing/in parallel OR velocity at a point is constant
Turbulent flow:
Mixing of layers OR contains eddies/vortices OR abrupt/random changes in speed or direction
Draw a diagram showing laminar and turbulent flow around an object
e.g. air aound a chimney stack or water around a bridge support
Vector:
A quantity with magnitude and direction
Scalar:
A quantity with magnitude only
Centre of Mass:
Point where all of the weight (can be assumed to) act OR the point around which the net moment is zero
