Plastic properties and Tensile testing I

Question 1

What is plastic deformation?

Answer 1

Permanent (irreversible) deformation

Question 2

What is yield strength and what is it also known as?

Answer 2

Elastic limit:
Stress beyond which plastic deformation begins to
accumulate (permanent and irreversible component

Question 3

Define work hardening

Answer 3

The increase in stress required to
continue deformation beyond the elastic limit

Question 4

What is ultimate tensile strength

Answer 4

-The maximum stress on an engineering stress-strain curve

-Marks the onset of necking

Question 5

Where does heterogeneous yield in steels occur?

Answer 5

Lueder’s bands

Question 6

When does elastic recovery occur?

Answer 6

After plastic deformation

Question 7

How can elastic recovery be approximated?

Answer 7

By calculating the slope of the elastic region.

Question 8

When should elastic recovery be accounted for?

Answer 8

When designing plastically formed parts.

Question 9

What is the onset of necking marked by?

Answer 9

The utilmate tensile strength

Question 10

Why does necking occur?

Answer 10

Necking is caused by cavitation of pores (damage) in the material. It’s due to localized plastic deformation

Question 11

What is the neck region characterized by?

Answer 11

Complex stress fields

Question 12

What happens when pores combine during deformation?

Answer 12

Pores join together with increasing
deformation leading to localization of
deformation at the neck, and
reduction in load bearing area.

Question 13

Define ductility.

Answer 13

The amount of deformation a material will tolerate
before failure.

Question 14

Define toughness.

Answer 14

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.

Question 14

What does carbon composition affect when it comes to steels?

Answer 14

Strength, Ductility, and Toughness

Question 14

How can ductility be expressed?

Answer 14

In terms of % elongation and
% reduction in area)

Question 15

What is the conventional offset for the offset yield stress method?

Answer 15

0.002

Question 16

What is the offset yield stress method used for?

Answer 16

To determine the yield strength of a material and compare it to other materials.

Question 17

What does the point of yielding represent for metals experiencing a gradual elastic-plastic transition?

Answer 17

It may be determined as the initial departure from linearity of the stress–strain curve.

Question 18

What is the relationship between ductility, toughness, and resistance/tolerance to deformation?

Answer 18

More ductility = more deformation the material can withstand = more toughness.

Question 19

Describe the mechanical properties of low-carbon steel?

Answer 19

The low carbon steel has the lowest yield strength, hardness, and ultimate tensile strength but the highest ductility (least brittle).

Question 20

What does brittle mean?

Answer 20

Low ductility

Question 21

What is the relationship between carbon composition in steel and its yield strength, ultimate tensile strength, hardness, ductility, and brittleness?

Answer 21

More carbon = higher yield and ultimate tensile strength = more hardness = lower ductility = more brittle

Question 22

Describe high carbon steel in terms of its yield strength, ultimate tensile strength, ductility, hardness, and brittleness.

Answer 22

High carbon steel has the highest yield strength, hardness, and ultimate tensile strength but the lowest ductility and is the most brittle.

Question 23

Describe low carbon steel in terms of its yield strength, ultimate tensile strength, ductility, hardness, and brittleness.

Answer 23

The low carbon steel has the lowest yield strength, hardness, and ultimate tensile strength but the highest ductility (least brittle).

Question 24

How can toughness be determined graphically?

Answer 24

By calculating the area under the stress-strain curve up to the point of fracture.

Question 25

Which type of carbon steel has the most toughness and why?

Answer 25

Medium carbon steel because the steel is a trade-off between ductility and strength.

Question 26

What is the cause of deformation being localized along Lueder’s bands?

Answer 26

It’s due to the pinning of dislocations by interstital atoms (here, carbon).

Question 27

What happens after the gauge region is deformed?

Answer 27

After the gauge region is Leuder deformed,
global plastic deformation continues.

Question 28

What is the limit for approximating true stress?

Answer 28

Up to the point of necking.