MMET 207 EXAM QUESTIONS WITH
COMPLETE ANSWERS
Stress - Answer--A force distributed over an area or object
-Stress = F/Ao
-Units: (lb/in2) or (psi or ksi) or (N/m2)
Strain - Answer--Percentage size change of a material in a particular direction when
subjected to a force in that direction
-Strain (Es) = Lf - Lo / Lo
-Units: none or (in/in) or (m/m)
Ultimate tensile strength - Answer-The maximum stress that can be applied to a
material before it breaks
Elastic limit/Yield Point - Answer-point where a material goes from elastic to plastic; last
point on linear part of graph
Break point - Answer-End of plastic behavior; where a material breaks
What is 0.2% offset yield (Engineering yield strength) - Answer-the stress at which a
material exhibits a specified deviation from proportionality of stress/strain. Also, it hard
to determine precisely so yield point is considered at an offset strain of 0.2%
How to find 0.2% offset yield - Answer-determining .002 strain and traveling parallel to
modulus of elasticity
Modulus of Elasticity
(What is it?, formula, where on stress/strain curve, tell about the material?) - Answer--A
measure of rigidity ( or stiffness)
- Slope of linear line
- delta stress/ delta strain (Es)
- tells a material's stiffness
Modulus of Elasticity of Steel - Answer-E(steel) = 30x10^6 psi
Standard gauge for tensile specimens - Answer-2 inches
Elastic Behavior - Answer-returns to original shape
Plastic Behavior - Answer-Does not return to original shape... permanent deformation
Necking - Answer-Tensile deformation where relatively large amounts of strain localize
disproportionately in a small region of the material (post UTS an about to break)
, Impact testing (what for) - Answer-Tests toughness; measures a materials ability to with
stand a shock load
- Temperature also has a huge impact on it
Impact Testing (how) - Answer-Take a material that is NOTCHED, whack it with
pendulum or hammer; Charpy Vee or Izod
Charpy Impact Testing - Answer-- Has a notch in it and is facing away from impact
- Done more often, easier, faster
Izod Impact Testing - Answer-Notch not in center
Nil Ductility Temp - Answer-the temp at which the toughness of a material drops below
the DBTT
DBTT - Answer-Ductile to Brittle Transition Temperature
Fatigue Strength - Answer-The highest stress that a material can withstand for a given
number of cycles without breaking
Fatigue Strength Test - Answer-Continuously loading (bending back and forth) a
material at given stress levels until it breaks
Endurance Strength - Answer-Where the material levels out
Endurance Limit - Answer-The point where you can bend a metal back and forth infinite
times and it never breaks
Creep Strength - Answer-elongation that is caused when a load is added over a period
of time
Creep Testing - Answer-Used to rate the resistance of a material to plastic deformation
under a sustained load and temp; a load is put on a material and when load is taken off,
did it retain elasticity
- EX: Fan blade in container
Factors involved in material selection - Answer-Chemical, Mechanical, and Physical
properties
Melting Point - Answer-The temperature at which a solid becomes a liquid
Specific Heat - Answer-The amount of energy required to raise the temperature of 1
gram of a substance by 1 degree celcius
COMPLETE ANSWERS
Stress - Answer--A force distributed over an area or object
-Stress = F/Ao
-Units: (lb/in2) or (psi or ksi) or (N/m2)
Strain - Answer--Percentage size change of a material in a particular direction when
subjected to a force in that direction
-Strain (Es) = Lf - Lo / Lo
-Units: none or (in/in) or (m/m)
Ultimate tensile strength - Answer-The maximum stress that can be applied to a
material before it breaks
Elastic limit/Yield Point - Answer-point where a material goes from elastic to plastic; last
point on linear part of graph
Break point - Answer-End of plastic behavior; where a material breaks
What is 0.2% offset yield (Engineering yield strength) - Answer-the stress at which a
material exhibits a specified deviation from proportionality of stress/strain. Also, it hard
to determine precisely so yield point is considered at an offset strain of 0.2%
How to find 0.2% offset yield - Answer-determining .002 strain and traveling parallel to
modulus of elasticity
Modulus of Elasticity
(What is it?, formula, where on stress/strain curve, tell about the material?) - Answer--A
measure of rigidity ( or stiffness)
- Slope of linear line
- delta stress/ delta strain (Es)
- tells a material's stiffness
Modulus of Elasticity of Steel - Answer-E(steel) = 30x10^6 psi
Standard gauge for tensile specimens - Answer-2 inches
Elastic Behavior - Answer-returns to original shape
Plastic Behavior - Answer-Does not return to original shape... permanent deformation
Necking - Answer-Tensile deformation where relatively large amounts of strain localize
disproportionately in a small region of the material (post UTS an about to break)
, Impact testing (what for) - Answer-Tests toughness; measures a materials ability to with
stand a shock load
- Temperature also has a huge impact on it
Impact Testing (how) - Answer-Take a material that is NOTCHED, whack it with
pendulum or hammer; Charpy Vee or Izod
Charpy Impact Testing - Answer-- Has a notch in it and is facing away from impact
- Done more often, easier, faster
Izod Impact Testing - Answer-Notch not in center
Nil Ductility Temp - Answer-the temp at which the toughness of a material drops below
the DBTT
DBTT - Answer-Ductile to Brittle Transition Temperature
Fatigue Strength - Answer-The highest stress that a material can withstand for a given
number of cycles without breaking
Fatigue Strength Test - Answer-Continuously loading (bending back and forth) a
material at given stress levels until it breaks
Endurance Strength - Answer-Where the material levels out
Endurance Limit - Answer-The point where you can bend a metal back and forth infinite
times and it never breaks
Creep Strength - Answer-elongation that is caused when a load is added over a period
of time
Creep Testing - Answer-Used to rate the resistance of a material to plastic deformation
under a sustained load and temp; a load is put on a material and when load is taken off,
did it retain elasticity
- EX: Fan blade in container
Factors involved in material selection - Answer-Chemical, Mechanical, and Physical
properties
Melting Point - Answer-The temperature at which a solid becomes a liquid
Specific Heat - Answer-The amount of energy required to raise the temperature of 1
gram of a substance by 1 degree celcius
