Chapter 6 Mechanical Properties

Question 1

Describe Elastic Deformation

Answer 1

• Elastic deformation is the region where a material is deformed but can still go back to its original condition (no visible deformation)
• Can be described via Hookes’s Law

Question 2

Describe Plastic Deformation

Answer 2

Permanent and non-reversible distortion of a material beyond the elastic region

Question 3

Enumerate Elastic Properties

Answer 3

Elastic Properties can be summarized into the following material constant:
• Elastic Modulus (E) : Resistance to being deformed elastically
• Shear modulus (G): Measure of rigidity
• Bulk modulus (K): Resistance to compression
• Poisson’s Ratio (v): Ratio of Deformation at radial and anti-axis

Question 4

Enumerate Plastic Properties

Answer 4

• Yield strength: point at which material starts to “ Yield” (Deform)
• Tensile strength: maximum stress on an engineering stress-strain curve
• Ductility: a measure of the degree of plastic deformation sustained at fracture. Can be expressed as %EL or %RA
• Toughness: Energy to break a unit volume of material. Area under the engineering stress-strain curve
• Resilience: Capacity of a material to absorb energy when it is deformed elastically and recover this energy upon unloading.

Question 5

What is design factor?

Answer 5

Precautionary measure to ensure safe working range by avoiding the condition that will cause material Fracture Failure

Question 6

What is Elastic Modulus (E)

Answer 6

It is an Elastic Property that measures the materials’ stiffness or resistance to being deformed elastically

Question 7

What is Bulk Modulus (K)

Answer 7

It is an Elastic Property that measures the materials’ stiffness or resistance to compression

Question 8

What is Shear Modulus (G)

Answer 8

It is an Elastic Property that measures the materials’ resistance to shear or materials’ rigidity

Question 9

What is Toughness?

Answer 9

• It is a Plastic Property that measures the energy to break a unit volume of material.
• Area under the engineering stress-strain curve

Question 10

What is Ductility?

Answer 10

It is a Plastic Property that measures the degree of plastic deformation sustained at fracture. Can be expressed as %EL or %RA

Question 11

Differentiate Yield Strength versus Tensile Strength

Answer 11

• Yield strength: point at which material starts to “ Yield” (Deform)
• Tensile strength: maximum stress on an engineering stress-strain curve

Question 12

Define Hardness

Answer 12

Resistance to permanently indenting the surface.

Question 13

What is the criteria if you would like to have low deformation?

Answer 13

To minimize deformation, select a material with a

large elastic modulus (E or G).