Mechanical Engineering Quiz

Mechanics and Strength of Materials

• Center of percussion: The point where the resultant of all the forces on the body does not pass through the center of gravity.
• Mechanics: Deals with the effects of forces in causing or preventing motion.
• Center of rotation and center of gravity: Statics deals with bodies in equilibrium, while dynamics deals with bodies not in equilibrium.
• Motion: A progressive change of position of a body.
• Velocity: The rate of change in position.
• Acceleration: When the velocity is variable and constantly increasing.
• Retard motion: When the motion is decreasing.
• Newton's Law of Motion:
  • First law: Every body continues in a state of rest or uniform motion until it is compelled by a force to change its state.
  • Second law: Change of motion is proportional to the force applied and takes place along the straight line in which the force acts.
  • Third law: To every action, there is always an equal reaction.

Forces and Energy

• Force: A push or pull.
• Work: The product of force times distance.
• Power: The product of force times the distance divided by time.
• Horsepower: A unit of power used in engineering work.
• Torque: A measure of a tendency of the force to rotate the body upon which it acts.
• Mechanical energy: Includes kinetic energy and potential energy.
• Kinetic energy: The energy of motion.
• Potential energy: The energy of position or stored energy.
• Elastic potential energy: Energy possessed by a spring that has been compressed or extended.

Rotation and Oscillation

• Simple pendulum: A pendulum similar to a compound pendulum except that the mass of the body is concentrated at a single point.
• Conical pendulum: A pendulum similar to a compound pendulum except that the weight suspended by the cord moves at a uniform speed around the circumference of a circle.
• Torsional pendulum: A pendulum that consists of a disk fixed to a slender rod, the other end of which is fastened to a fixed frame.

Strength of Materials

• Strength: The ability of a material to withstand loads without breaking down.
• Shear strength: The ability of a material to withstand forces that cause it to deform by shear.
• Compressive strength: The ability of a material to resist being crushed.
• Bending strength: The ability of a material to resist forces that cause it to bend or deflect.

Shafts and Axles

• Shaft: A rotating member that is used to transmit power.
• Axle: A stationary member carrying rotating wheels or pulleys.
• Machine shaft: A shaft that is an integral part of a machine.
• Line shaft: A transmission shaft driven by a prime mover.
• Counter shaft: A transmission shaft intermediate between the line shaft and the driven machine.
• Spindles: Short axles and shafts.

Flywheels and Rivets

• Flywheel: A wheel that is used to equalize the energy exerted and the work done.
• Rivet: A mechanical fastener used to join two or more plates together.
• Rivet joints: Lap-joint and butt-joint.
• Rivet holes: Usually made 1/16 inch larger in diameter than the nominal diameter of the rivet.

Screws and Threads

• Thread definitions:
  • Actual size: A measure size.
  • Allowance: The prescribed difference between the design size and the basic size.
  • Black crest thread: A thread whose crest displays an unfinished cast, rolled, or forged surface.
• Taping and thread cutting: Methods of tapping include hand tapping and machine tapping.
• Hand taps: Taper taps, plug taps, and bottoming taps.

Cams and Followers

• Cams: May be divided into two classes: uniform motion cams and accelerated motion cams.
• Follower: The moving part that is in contact with the cam.
• Undercutting: Cannot occur at the concave portion of the cam profile.

Bearings

• Properties of bearing materials:
  • Fatigue resistance: The ability of the bearing lining material to withstand repeated applications of stress and strain.
  • Embeddability: The ability of the bearing lining material to absorb or embed within itself any of the larger dirt particles.
  • Compatibility or anti-scoring: The ability of the shaft and bearing to "get along" with each other.
  • Conformability: The ability of the material to creep or flow slightly under load.
• Types of bearings: Rubber bearings, ball bearings, cylindrical roller bearings, and spherical roller bearings.

Couplings

• Flexible coupling: Used to connect two shafts that are not in line with each other.
• Universal coupling: A coupling that connects two shafts the axis of which are not in line with each other.
• Friction clutch: A clutch that transmits motion from the driving to the driven member by friction between the engaging surfaces.
• Positive clutch: A clutch that connects the driving and driven members by engagement of interlocking teeth or projecting lugs.### Belts and Pulleys
• Three principal types of leather belting produced are: oak tanned, mineral tanned, and combination oak tanned and mineral retanned.
• Oak tanned is for general applications but should not be used where the drive is to operate at an ambient temperature above 120°F.
• Mineral tanned is used for high-speed small-diameter pulley applications and is also suitable for high-speed motor drives.
• Combination oak tanned and mineral retanned is made of a ply of oak-tanned leather with a ply of mineral retanned leather.
• Rubber belts are used in places exposed to the weather or the action of steam, as they do not absorb moisture or stretch as readily as leather belts.
• Standard belt lengths are in increments of 1 1/2 inches.
• Wood pulleys are not much lighter than cast iron pulleys but are superior as transmitters of power.

Heat Treatment Terms

• Aging is a change in a metal by which its structure recovers from an unstable or metastable condition that has been produced by quenching or cold working.
• Annealing is a heating and slow cooling of a solid metal, usually done to soften it.
• Critical range is the same as transformation range.
• Drawing is often used to mean tempering.
• Hardening is the heating of certain steels above the transformation range and the quenching, for the purpose of increasing the hardness.
• Malleabilizing is an annealing process whereby combined carbon in white cast iron is transformed wholly or in part to temper carbon.
• Normalizing is the heating of an iron-base alloy to some 100°F above the transformation range with subsequent cooling to below that range in still air at room temperature.
• Spheroidizing is any heating and cooling of steel that produces a rounded or globular form of carbide.
• Stress relieving is the heating of a metal body to a suitable temperature and holding it at that temperature for a suitable time for the purpose of reducing internal stress.
• Tempering is a reheating of hardened or normalized steel to a temperature below the transformation range, followed by any desired rate of cooling.
• Transformation range for ferrous metals is the temperature interval during which austenite is formed during heating.

Roller Chains

• Roller chains are made up of two links: roller links and pin links alternately spaced throughout the length of the chain.
• Types of sprockets: plain plate (type A), with a hub on one side only (type B), and with a hub on both sides (type C).
• Types of lubrication in roller chains: manual or drip lubrication (type A), bath or disc lubrication (type B), and oil stream lubrication (type C).
• The efficiency of silent chain is 99%.
• Side guide chain has guide links which straddle the sprocket sides to control the chain laterally.
• Center guide chain has guide links that run within a circumferential groove or grooves for lateral control.

Alloy Steels

• Low alloy structural steels were developed for structural uses where light weight is important, such as in the transportation industry.
• Low-carbon alloy steels (0.10-0.25%C) are used chiefly for carburizing.
• Medium carbon alloy steels (0.25-0.50%C) are usually quenched and tempered to hardness between 250 and 400 Brinell.
• High-carbon alloy steels (0.50-0.70%C or more) are heat-treated to hardness between 375 and 500 Brinell, for use as springs, wear-resisting parts.
• Alloying elements have various functions, such as de-oxidizing, hardenability, improving machinability, and increasing toughness and strength.

Typical Heat Treatment for Various Types of Steel

• Commercial annealing involves heating to 1500°F, cooling in mica, and eliminating scale by packing in charcoal.
• Commercial normalizing involves heating to 1425°F and cooling in air.
• Carburizing of low carbon steel involves heating in cyanide at 1500°F to 1560°F, quenching in brine, and reheating to 1425°F.
• Heat treatment for various types of steel, such as SAE 1075 spring steel, SAE 1095 tool steel, SAE 3150 die steel, and SAE 5132 steel, involves different temperatures and quenching methods.

Hardenability

• Hardenability is the capacity of steel to through-harden when cooled from above its transformation range.
• Types of hardening include carburizing, which involves adding carbon to the surface of steel by exposing it to hot carbonaceous solids, liquids, or gases above transformation temperature, quenching, and usually tempering at 300-450°F for the purpose of relieving stresses.