Mats Lecture 11-12

Question 1

What is the formula for stress?

Answer 1

(Applied Force)/Area Supporting Force

Question 2

What is the formula for strain?

Answer 2

(amount object stretches)/length of object

Question 3

What is normal stress and normal strain?

Answer 3

-when an applied force, F is acting normal (perpendicular) to the area A
-Can be tensile or compressive

Question 4

What is the definition of Elastic Strain?

Answer 4

fully recoverable strain resulting from an applied stress

Question 5

What is Shear Stress and Shear Strain?

Answer 5

-When an applied force is acting parallel to the area

Question 6

What is Hydrostatic Stress and Dilation?

Answer 6

-When there is a uniform pressure, P applied in all directions to a body of initial volume V

Question 7

What happens to a material when it is stretched elastically in one direction?

Answer 7

-The material will contract in the transverse directions in order to maintain a constant volume
-This is measured by Poisson’s ratio

Question 8

List the methods used to measure mechanical properties

Answer 8

-Tensile test
-Shear test
-Flexural test

Question 9

What does the tensile test measure?

Answer 9

-The resistance of a material to a static or slowly applied force

Question 10

Define what strain rate is

Answer 10

-The rate at which strain develops in a material

Question 11

Define elastic deformation

Answer 11

-When a material deforms during loading, but returns to its original shape when load is released

Question 12

What is elastic modulus also known as?

Answer 12

-Young Modulus

Question 13

What does the elastic modulus measure?

Answer 13

-Measures a material’s resistance to elastic deformation

Question 14

What is the formula for elastic modulus?

Answer 14

(stress)/strain

Question 15

List examples of materials with high elastic modulus

Answer 15

-Metals
-Steel
-Titanium
-Nickel
-Diamonds

Question 16

List examples of materials with low elastic modulus

Answer 16

-Rubber
-Polymers
-Nylon

Question 17

Define what plastic deformation is

Answer 17

-When a material deforms during loading and undergoes permanent shape change (it does not return to its original shape upon unloading)

Question 18

Define yield stress

Answer 18

-The stress at which a material yields is called yield stress (or strength)

Question 19

List examples of materials with high yield stress

Answer 19

-Metals
-Steel
-titanium
-nickel
-diamond

Question 20

List examples of materials with low yield stress

Answer 20

-Rubber
-Polymers
-Nylon

Question 21

What happens when a material is deformed enough?

Answer 21

it fails (breaks)

Question 22

What is the definition of Ultimate Tensile Strength?

Answer 22

-The maximum stress after which the material starts to fail

Question 23

What is the definition of Ductility?

Answer 23

-Ability of a material to deform plastically

Question 24

What is the definition of Toughness?

Answer 24

-The energy absorbed by a material before it breaks

Question 25

What is toughness graphically?

Answer 25

-The area under the stress-strain curve

Question 26

What is the definition of fracture toughness? What symbol is it denoted by?

Answer 26

-The resistance of materials to cracking and fracture
-KIC

Question 27

What are materials with high KIC called?

Answer 27

Ductile

Question 27

What are materials with low KIC called?

Answer 27

-Brittle