MECHANICAL PROP. & TESTING

Question 1

Engineering STRESS?

Answer 1

Eng. Stress= F/Ao [N/m^2]

Question 2

Engineering STRAIN?

Answer 2

Eng. Strain= change in length/ original length

Question 3

Explain the TENSILE TEST

Answer 3

Apply a tensile force/load slowly to a sample until fracture occurs.

Question 4

Is the ELASTIC deformation reversible?

Answer 4

Yes

Question 5

How do you find Young’s Modulus(E)?

Answer 5

Slope of Elastic Region of Stress vs Strain curve

Question 6

What information does E give us?

Answer 6

The Stiffness of a material.

Question 7

Give exemple of materials with HIGH E VALUE (very stiff)

Answer 7

Ceramics (300GPa) & Steel (207GPa)

Question 8

True or False plastic has a medium E value

Answer 8

False (3GPa not stiff)

Question 9

Stiffness depends directly on ______ and therefore

on ______ .

Answer 9

The Temperature + The bonds of the atoms

Question 10

Hooke’s Law?

Answer 10

Stress=E*Strain

Question 11

Explain PLASTIC deformation.

Answer 11

When bonds have broken and reformed with different atoms.

Question 12

Yielding is when ____ changes from _____ to _____.

Answer 12

Deformation + Elastic + Plastic

Question 13

What do we define as the maximum stress an object can take before permanent deformation?

Answer 13

Yield Strength

Question 14

What happens at tensile strength of a POLYMER?

Answer 14

When polymer backbone chains are aligned and about to break.

Question 15

Once TS is reached deformation becomes more ____.

Answer 15

Localized

Question 16

True or False: In Alloys, TS happens right when we have passed the elastic region of a stress vs strain curve.

Answer 16

False, it’s with CERAMICS

Question 17

Define Ductility.

Answer 17

Amount of plastic deformation before fracture

Question 18

When we have little to no deformation we say that the material is _____.

Answer 18

Brittle

Question 19

When we have some plastic deformation we say that the material is _____.

Answer 19

Ductile

Question 20

What does a material require to be TOUGH?

Answer 20

Strength and Ductility

Question 21

What is defined as the ability to absorb energy before fracture?

Answer 21

Toughness

Question 22

How can we find the toughness of a material in the Stress vs Strain curve?

Answer 22

Area under the curve

Question 23

What is Resilience?

Answer 23

The ability to absorbs energy on elastic loading and release on unloading.

Question 24

When describing PLASTIC deformation, use ____ and ____.

Answer 24

True stress + True strain

Question 25

True or false: True stress is ALWAYS higher than engineering stress.

Answer 25

True

Question 26

If yielding has occurred and the load is released, the material recovers _______ only.

Answer 26

ELASTIC STRAIN

Question 27

True or False: PLASTIC deformation has both elastic and plastic strain components.

Answer 27

True

Question 28

Explain the phenomena of elastic strain recovery and strain hardening.

Answer 28

The elastic region is higher when we reload after unloading for the first time.

Question 29

The _____ the indent, the harder the material.

Answer 29

Smaller

Question 30

What is N?

Answer 30

Factor of Safety