PKG 221 END OF COURSE UPDATED QUESTIONS AND
ANSWERS GRADED A+
✔✔Percent neckdown formula - ✔✔[(Change in width @ YP) / (Original width)] x 100
YP or X, BP, etc...
✔✔Definition of Tensile strength - ✔✔Highest point on curve. Could be at break point or
at yield point. "Ultimate strength" of material, measures max carrying capability.
✔✔Definition of Modulus of elasticity (MoE) - ✔✔Stiffness of material, higher MoE=
stiffer material.
✔✔What is the difference between true stress and engineering stress? - ✔✔True stress
uses the actual CSA simultaneously when doing tensile test.
(True stress is always > engineering stress)
✔✔Does air have weight? - ✔✔Yes
✔✔What is atmospheric pressure? - ✔✔The weight of a column of air from sea level to
the top of the atmosphere.
✔✔What is sea level pressure? - ✔✔1 atm or 14.7 psi
✔✔What can change altitude pressure? - ✔✔weather (hurricanes) and altitude
✔✔What is two ways of measuring atmospheric pressure? - ✔✔Manometer & Bourdon
tube
✔✔What happens to a water bottle when filled up with the air on the top of a mountain,
closed and brought back down to sea level? - ✔✔The bottle crushes down because the
pressure outside is larger than the pressure inside.
✔✔Definition of Axial stress - ✔✔the stress that is in the direction of the axis of a
cylinder
✔✔Definition of Hoop stress - ✔✔the stress that is around a cylinder
✔✔What is the normal pressure for Lansing Michigan? - ✔✔about 14.2 psi
✔✔What is the normal pressure for colorado? - ✔✔about 9.04 psi
✔✔What is an example of the pressure being greater inside the package than outside?
- ✔✔carbonated pop & aerosols
, ✔✔What is an example of the pressure being greater outside the package than inside?
- ✔✔Vacuum packed pouch
✔✔Definition of compression strength - ✔✔The force required to overcome the gas
pressure
✔✔Formula for pressurized can compression strength - ✔✔(Empty can CS) + [(gas
pressure) x (area of top)]
✔✔When do stress concentrations usually occur? - ✔✔when the material is brittle or in
tension
✔✔What are some voids in materials that act as stress risers?
Which is the most concerning?
The stress at the edge of the void is ____times the stress in the rest of the material. -
✔✔pits, scratches, cracks
Scratches
3
✔✔What are factors that influence stress? - ✔✔Direction: Machine direction may be
higher, and Cross direction may be in between normal plot
Temperature: Higher temp, lower curve
Rate: Faster= higher curve
✔✔Definition of creep - ✔✔Deflection under constant load, over time
✔✔When is the stress most aggressive during the creep? - ✔✔Near the Break Point
✔✔What type of materials creep? - ✔✔Ductile
✔✔Stresses below EL = Creep? - ✔✔rarely occurs, no matter how long.
✔✔Definition of viscoplasticity - ✔✔Deformation (stretch) under load is rate dependent
(how fast is the force applied)
Having a mixture of properties, viscous and elastic, so they are sensitive or dependent
of application or test rate.
✔✔Formula for Percent Stress Retention - ✔✔(Final Stress / Initial Stress) x 100%
✔✔Definition of Relaxation - ✔✔Hold the deformation constant and look at force over
time.
ANSWERS GRADED A+
✔✔Percent neckdown formula - ✔✔[(Change in width @ YP) / (Original width)] x 100
YP or X, BP, etc...
✔✔Definition of Tensile strength - ✔✔Highest point on curve. Could be at break point or
at yield point. "Ultimate strength" of material, measures max carrying capability.
✔✔Definition of Modulus of elasticity (MoE) - ✔✔Stiffness of material, higher MoE=
stiffer material.
✔✔What is the difference between true stress and engineering stress? - ✔✔True stress
uses the actual CSA simultaneously when doing tensile test.
(True stress is always > engineering stress)
✔✔Does air have weight? - ✔✔Yes
✔✔What is atmospheric pressure? - ✔✔The weight of a column of air from sea level to
the top of the atmosphere.
✔✔What is sea level pressure? - ✔✔1 atm or 14.7 psi
✔✔What can change altitude pressure? - ✔✔weather (hurricanes) and altitude
✔✔What is two ways of measuring atmospheric pressure? - ✔✔Manometer & Bourdon
tube
✔✔What happens to a water bottle when filled up with the air on the top of a mountain,
closed and brought back down to sea level? - ✔✔The bottle crushes down because the
pressure outside is larger than the pressure inside.
✔✔Definition of Axial stress - ✔✔the stress that is in the direction of the axis of a
cylinder
✔✔Definition of Hoop stress - ✔✔the stress that is around a cylinder
✔✔What is the normal pressure for Lansing Michigan? - ✔✔about 14.2 psi
✔✔What is the normal pressure for colorado? - ✔✔about 9.04 psi
✔✔What is an example of the pressure being greater inside the package than outside?
- ✔✔carbonated pop & aerosols
, ✔✔What is an example of the pressure being greater outside the package than inside?
- ✔✔Vacuum packed pouch
✔✔Definition of compression strength - ✔✔The force required to overcome the gas
pressure
✔✔Formula for pressurized can compression strength - ✔✔(Empty can CS) + [(gas
pressure) x (area of top)]
✔✔When do stress concentrations usually occur? - ✔✔when the material is brittle or in
tension
✔✔What are some voids in materials that act as stress risers?
Which is the most concerning?
The stress at the edge of the void is ____times the stress in the rest of the material. -
✔✔pits, scratches, cracks
Scratches
3
✔✔What are factors that influence stress? - ✔✔Direction: Machine direction may be
higher, and Cross direction may be in between normal plot
Temperature: Higher temp, lower curve
Rate: Faster= higher curve
✔✔Definition of creep - ✔✔Deflection under constant load, over time
✔✔When is the stress most aggressive during the creep? - ✔✔Near the Break Point
✔✔What type of materials creep? - ✔✔Ductile
✔✔Stresses below EL = Creep? - ✔✔rarely occurs, no matter how long.
✔✔Definition of viscoplasticity - ✔✔Deformation (stretch) under load is rate dependent
(how fast is the force applied)
Having a mixture of properties, viscous and elastic, so they are sensitive or dependent
of application or test rate.
✔✔Formula for Percent Stress Retention - ✔✔(Final Stress / Initial Stress) x 100%
✔✔Definition of Relaxation - ✔✔Hold the deformation constant and look at force over
time.
