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ATL Mechanical Engineering Principles
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Terms in this set (48)
What does SI stand for?
International System of Units
What are the seven base units used in SI?
Meter (m) - Length
Kilogram (kg) - Mass
Second (s) - Time
Ampere (A) - Electric current
Kelvin (K) - Thermodynamic temperature
Mole (mol) - Amount of substance
Candela (cd) - luminous intensity
How is the expansion of material when heated calculated?
Length or diameter x coefficient of material x change in temperature (cº)
Describe 'Elesticity'
The ability to return back to it's original shape
What is tensile force?
Where force pulls or stretches the material
What is compressive force?
Where force push and compress the material
What is shear force?
Where force is at a right angle to the cross-sectional area of the material
Describe 'strain'
The ratio of deformation to an original dimension
Strain = extension/original length
Describe 'Ductility'
The property that allows material to deform under a load
High ductility allows material be drawn into wire or tube
What does FoS stand for and what does it mean?
Factor of Safety
Term to describe the structural capacity of something beyond the expected/actual load it is put under
How much stronger something is than it needs to be under intended circumstances
What does MoS stand for and what does it mean?
Margin of Safety
Term to describe the ratio of the strength of the structure to the requirements
Has two definitions
1. Measure of capacity like FoS
2. Measure of satisfying design criteria
Repeated loading can cause what problems?
Fatigue stress
Brittle cracks
Brittle fracture
When measuring angles, what is a positive angle?
Angle read anticlockwise from 0º
When measuring angles, what is a negative angle?
Angle read clockwise from 0º
Describe the term 'equilibrium'
When opposing forces are equal to each other
What does CoF stand for and what does it mean?
Co-efficient of Friction
The ratio of friction between two bodies, and the force pressing them together
Concerning work and energy, 1 Joule (J) = ?
1 Newton/metre
Describe the formula for calculating efficiency in terms of energy input and output
Efficiency % = Energy output J /energy input J
OR
Energy input J = energy output J /efficiency %
OR
Energy output J = energy input J x efficiency %
What is a proper fraction?
A fraction where the numerator and denominator are both positive
What is an improper fraction?
A fraction where the numerator is a higher number than the denominator
How is the area of a cylinder calculated?
Radius x radius x Pi (3.142)
How is the volume of a cylinder calculated?
Area x height
How is the volume of a pyramid calculated?
⅓ area of base x height
How is the volume of a cone calculated?
⅓ area of base (Radius x radius x Pi) x height
What are the three types of crystalline metallic structures?
Body Centre Cubic - Strong metals
Face Centre Cubic - Ductile metals
Hexagonal Close-Packed - Brittle metals
What is a dendrite?
Branch-like crystalline structure
Describe annealing of steel
Heat treatment to soften the metal
Heat to approx 40ºc above upper critical point
Upper critical point is 724ºc in low carbon steel
Cool slowly
Produces a finer grain after re-crystalisation
Describe normalising of steel
Heat treatment to return the metal to it's normal state
Heat to approx 40ºc above upper critical point
Upper critical point is 724ºc in low carbon steel
Air-Cool normally
Often used to restore metal after forging or cold working
Describe hardening of steel
Heat treatment to harden the metal
Heat to approx 40ºc above upper critical point
Upper critical point is 724ºc in low carbon steel
Cool rapidly be quenching
Water quenching results in harder more brittle state
Oil quenching slightly reduces hardness but also cracking
Describe tempering of steel
Heat treatment to toughen hardened steel
Heat to below critical point
Upper critical point is 724ºc in low carbon steel
Cool rapidly be quenching
Different temper temperatures are used for different results
What would the Faint-yellow - 176 °C temper be used for?
Engravers, razors, scrapers
What would the Light-straw - 205 °C temper be used for?
Rock drills, reamers, metal-cutting saws
What would the Dark-straw - 226 °C temper be used for?
Scribers, planer blades
What would the Brown - 260 °C temper be used for?
Taps, dies, drill bits, hammers, cold chisels
What would the Purple - 282 °C temper be used for?
Surgical tools, punches, stone carving tools
What would the Dark blue - 310 °C temper be used for?
Screwdrivers, wrenches
What would the Light blue - 337 °C temper be used for?
Springs, wood-cutting saws
What would the Grey-blue - 371 °C and higher temper be used for?
Structural steel
What is stronger - Face centre cubic or body centre cubic?
Body centre cubic (Ferrite)
At what temperature does steel become plastic?
Above 700ºc
What is 'yield point'
The point at which a material becomes permanently deformed
Describe the Brinell test
Used to test the hardness of a material
Hardened 10mm steel ball is pressed into the material
Hardness is assessed by measuring the indent
Describe the Vickers test
Used to test the hardness of a material
Diamond pyramid is pressed into the material
Hardness is assessed by measuring the indent
Most accurate method
Describe the Rockwell test
Used to test the hardness of a material
Small steel ball or diamond pyramid is pressed twice into the material
First press is light, the second heavy and prolonged
Hardness is assessed by measuring the increase in depth between the two loads
Describe the Shore test
Used to test the hardness of a material
Diamond tipped hammer is pressed dropped onto the material
The rebound is measured to assess the hardness of material
Easily transported for on site use
negligible damage to material
What is a polymer made up of?
A chain of monomers
What is vyniloop?
A recycling process for plastics
Separates PVC from other materials
What are the 5 methods of heat generation that are used in welding?
Thermo-chemical (oxygen and fuel gas)
Electric arc (MIG, TIG, MMA)
Electric Resistance (resistance welding)
Mechanical processes (friction, ultrasonic)
Endothermic reaction (thermit)
Radiation of heat and light (laser, electron beam)
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