MEEN 223 Final Review

Interstitial defects weaken the material by creating localized stresses.

False

Polymers are typically poor electrical and thermal conductors.

True

Crystalline materials have short-range order but lack long-range order.

False

Aluminum is more ductile than aluminum oxide.

True

Experimentally measured strengths of metals are lower than theoretically predicted due to defects.

True

Reducing the grain size of a metal typically decreases its strength.

False

A material with high melting temperature has a large coefficient of thermal expansion.

False

Polycrystalline materials are effectively isotropic due to random grain orientation.

True

In a screw dislocation the Burgers vector is parallel to the dislocation line.

True

Vacancies increase entropy and exist in metals at room temperature.

True

Vacancies facilitate diffusion.

True

Dislocations are a key mechanism for plastic deformation in metals.

True

Slip directions are usually those with the longest distance between like atoms.

False

Dislocations play an important role in the deformation of polymers.

False

BCC metals have lower strength but higher ductility than FCC metals.

False

The rate of diffusion depends strongly on concentration gradient and temperature.

True

Metals are typically harder and stronger than polymers.

True

Interstitial atoms typically require more activation energy than substitutional atoms.

False

Cutting temperature is a result of cutting force alone.

False

Specific cutting energy means the energy to remove a unit volume of material.

True

Machining can be performed automatically on a CNC machine.

True

Metal forming prefers brittle materials (less ductility).

False

Springback in sheet metal forming is due to the recovery of elastic deformation.

True

Forging must be done in a heated environment.

False

Metal forming processes can often change the strength of the raw material.

True

Casting creates uniform microstructures throughout the part.

False

Die casting usually creates a better surface finish than sand casting.

True

Risers in casting are used to compensate for shrinkage.

True

Casting must be done above the melting temperature of a metal.

True

As compared to fusion welding solid state welding produces a lot more heat.

False

Joining is a labor-intensive manufacturing process and cannot be automated.

False

Generally no polymer can function properly above 250°C.

True

All thermoset plastics can be recycled.

False

Polymer is produced from monomers through a mechanism called "crystallization."

False

Additive manufacturing is limited to polymers and metals.

False

Fused deposition modeling (FDM) can handle both thermoplastics and thermoset.

False

3D printing produces parts with tighter tolerance and higher dimensional accuracy than machining.

False

Die casting uses an expendable mold.

False

Sand casting is the most common casting method by total weight.

True

Ultrasonic welding can be readily automated.

True

Spot welding is primarily used to join thick components.

False

In arc welding a shielding gas is often used to prevent oxidation of molten metals.

True

In linear friction welding the heat-affected zone often has lower strength than the parent material.

True

Cutting forces are larger for a larger feed and larger depth of cut.

True

An end mill is preferred over a face mill to flatten large surfaces quickly.

False

Metal forming at high temperatures requires less force and power than cold forming.

True

Stamping is a relatively slow process.

False

Casting is only viable for small parts.

False

Die casting uses an expendable mold.

False

Sand casting is the most common casting method by total weight.

True

Ultrasonic welding is used to join very thin materials including fabrics.

True

Spot welding can be automated but not used for very thick parts.

True

In linear friction welding the heat-affected zone often has lower strength than the parent material.

True

Many polymers are amorphous unlike metals.

True

Thermoplastic polymers are more recyclable than thermosets.

True

Thermo-formed polymer products usually have better quality than injection-molded ones.

False

Steps of FDM include light scanning and cross-linking.

False

Material Jetting involves depositing droplets followed by curing with a light source.

True

In Directed Energy Deposition metal powders are ejected and melted by a laser.

True

Additive manufacturing is best suited for high-volume production.

False

Vat photopolymerization uses metal powders and lasers to form molten droplets.

False

Thermosets typically have higher strengths than thermoplastics.

True

Thermo-forming is usually cheaper than injection molding especially at low volume.

True

Polymers can be amorphous, crystalline or both.

True

Compression molding is mainly used to make plastic bottles.

False

A Vacancy is produced when an atom/ion is missing from its normal site in the crystal structure.

True

Substitutional defects in a metal ditrort the surrounding lattice, therby decreasing the strength.

False

Increasing the grain size typically strengthens a metal.

False

Diamond and graphite are both made of carbon and thus have quite similar properties.

False

Aluminum has a larger yield strength than aluminum oxide

False

Materials with strong bonds typically have large coefficients of thermal expansion.

False

Polyurethane is often used for ball bearings in bicycle wheels due to its high strangth and hardness.

False

Most additive manufacturing processes are high throughput

False

Thermoforming is a high throughput technique to produce polymer parts.

True

Turned surfaces are typically smmother if a faster feed is used.

False

The temperature produced during cutting increases with increasing cuttingspeed and increasing cutting force.

True

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