Plastic properties and Tensile testing I Flashcards
What is plastic deformation?
Permanent (irreversible) deformation
What is yield strength and what is it also known as?
Elastic limit:
Stress beyond which plastic deformation begins to
accumulate (permanent and irreversible component
Define work hardening
The increase in stress required to
continue deformation beyond the elastic limit
What is ultimate tensile strength
-The maximum stress on an engineering stress-strain curve
-Marks the onset of necking
Where does heterogeneous yield in steels occur?
Lueder’s bands
When does elastic recovery occur?
After plastic deformation
How can elastic recovery be approximated?
By calculating the slope of the elastic region.
When should elastic recovery be accounted for?
When designing plastically formed parts.
What is the onset of necking marked by?
The utilmate tensile strength
Why does necking occur?
Necking is caused by cavitation of pores (damage) in the material. It’s due to localized plastic deformation
What is the neck region characterized by?
Complex stress fields
What happens when pores combine during deformation?
Pores join together with increasing
deformation leading to localization of
deformation at the neck, and
reduction in load bearing area.
Define ductility.
The amount of deformation a material will tolerate
before failure.
Define toughness.
Toughness is a material property indicative of a material’s resistance to failure. It is measured as the energy absorbed by the material before fracture.
What does carbon composition affect when it comes to steels?
Strength, Ductility, and Toughness
How can ductility be expressed?
In terms of % elongation and
% reduction in area)
What is the conventional offset for the offset yield stress method?
0.002
What is the offset yield stress method used for?
To determine the yield strength of a material and compare it to other materials.
What does the point of yielding represent for metals experiencing a gradual elastic-plastic transition?
It may be determined as the initial departure from linearity of the stress–strain curve.
What is the relationship between ductility, toughness, and resistance/tolerance to deformation?
More ductility = more deformation the material can withstand = more toughness.
Describe the mechanical properties of low-carbon steel?
The low carbon steel has the lowest yield strength, hardness, and ultimate tensile strength but the highest ductility (least brittle).
What does brittle mean?
Low ductility
What is the relationship between carbon composition in steel and its yield strength, ultimate tensile strength, hardness, ductility, and brittleness?
More carbon = higher yield and ultimate tensile strength = more hardness = lower ductility = more brittle
Describe high carbon steel in terms of its yield strength, ultimate tensile strength, ductility, hardness, and brittleness.
High carbon steel has the highest yield strength, hardness, and ultimate tensile strength but the lowest ductility and is the most brittle.
Describe low carbon steel in terms of its yield strength, ultimate tensile strength, ductility, hardness, and brittleness.
The low carbon steel has the lowest yield strength, hardness, and ultimate tensile strength but the highest ductility (least brittle).
How can toughness be determined graphically?
By calculating the area under the stress-strain curve up to the point of fracture.
Which type of carbon steel has the most toughness and why?
Medium carbon steel because the steel is a trade-off between ductility and strength.
What is the cause of deformation being localized along Lueder’s bands?
It’s due to the pinning of dislocations by interstital atoms (here, carbon).
What happens after the gauge region is deformed?
After the gauge region is Leuder deformed,
global plastic deformation continues.
What is the limit for approximating true stress?
Up to the point of necking.
