Lab 3. Tensile Test

Question 1

elastic deformation

Answer 1

it is temporary change in the shape of a material when a load is applied. the object returns to its original shape on’removal of the load

Question 2

plastic deformation

Answer 2

this type of deformation is is not reversible. in this case, the material retains the deformed shape even after the removal of the load

Question 3

ductile materials

Answer 3

ductile materials experience significant plastic deformation before fracture. plastics and aluminum

Question 4

brittle materials

Answer 4

brittle materials show littler or no plastic deformation before fracture. iron mild steel

Question 5

stress (normal)

Answer 5

stress is defined as force per unit area. this one of the most basic engineering quanitiesq

Question 6

shear stress

Answer 6

shear stress has the same units as normal stress (force/area) but represents a stress that acts parallel to the surface

Question 7

strain

Answer 7

strain is the change in length per unit length

e=deltaL/l0

Question 8

axial strain

Answer 8

axial strain is the change in length per unit length along the direction of loading

Question 9

lateral strain

Answer 9

lateral strain is the change in length per unit length along the perpendicular direction of loading

Question 10

poissons ratio

Answer 10

the ratio of lateral strain over axial strain

lateral strain/axial strainn

Question 11

poisson ratio for most metals fall between

Answer 11

.25-.35

Question 12

one of the most common mechanical stress-strain tests is performed in …

Answer 12

tension

Question 13

a test specimen of ______ cross section is prepared from the material to be tested

Answer 13

circular, square of rectangular

Question 14

Data obtained from the tensile test is ___ and ___

Answer 14

load and displacement

Question 15

data can be used to calculate

Answer 15

stress and strain

Question 16

parameters that can be calculated are

Answer 16

modulus of elasticity, yield strength, ultimate tensile strength, failure strain, reduction in area at fracture, true stress and true strain

Question 17

elastic deformation

Answer 17

deformation in which stress and strain are proportional

Question 18

Hook’s law

Answer 18

within elastic limit, the stress is proportional to the strain

Question 19

the constant of proportionality……

Answer 19

E is the modulous of elasticity or youngs modulus

Question 20

slope

Answer 20

the slope of the linear segment of the stress-strain curve corresponds to modulus of elasticity E

Question 21

yield strength- σy-

Answer 21

is the stress at which a material just starts to undergo permanent plastic deformation. elastic limit

Question 22

offset yield point-proof stress

Answer 22

is the most widely used strength measure of metals. a plastic strain of .02% is usually used to define the offset yield stress, although other value may be used depending on the material and application

Question 23

ultimate tensile strength

Answer 23

is the highest value of stress on the stress-strain curve

Question 24

decline in the stress beyond maxium may

Answer 24

indicate that the material is becoming weaker… not true because it is actually increasing in strength

Question 25

the reduction in stress is because

Answer 25

it does not account the rapidly decreasing cross sectional cross area in neck region. more meaningful to use true stress-true strain

Question 26

true stress

Answer 26

true stress-is defined as the load divided by the instanteous cross-sectional area over which deformation is occuring

Question 27

true strain

Answer 27

is the instantaneous strain