mechanical testing
DESCRIPTION
Mechanical Testing. Here’s what we’re going to learn about!. Forces Newton’s 2nd Stress Strain Young’s Modulus. s. e. Force. A force is a push or a pull A Force is represented in diagrams by an arrow SI unit of force is Newton (N) N = . 5 N. 10 N. kg m. 20 N. s 2. - PowerPoint PPT PresentationTRANSCRIPT
Mechanical Testing
Here’s what we’re going to learn about!
•Forces•Newton’s 2nd
•Stress•Strain•Young’s Modulus
s
e
Force
• A force is a push or a pull
•A Force is represented in diagrams by an arrow
•SI unit of force is Newton (N)
N = kg m
s2
5 N 10 N
20 N
Newton’s 2nd Law of Motion
F = ma
Force = (mass)(acceleration)
Units
F: N = kg m/s2
m: kg
a: acceleration (due to gravity)Symbol: a or g
Value: 9.81 m/s2
Newton’s 2nd Law of Motion
F = ma
Force = (mass)(acceleration)
Weight = (mass)(acceleration)
W = mga = g = 9.81 m/s2
Only on Earth!
Newton 2 can describe weight:
Example: Use Newton 2 to calculate your mass
F = maW= mg 1 lb = 4.45 N
150 lb1 lb
4.45 N = 668 N
m= W/g
m= 668 N / 9.81 m/s2
m= 68 kg
Formulas
Convert your weight in lb to SI unit of Newtons
Rearrange the equation to solve for mass
Plug and chug
This is a conversion factor
Example: Use Newton 2 to calculate your weight on Mars!
a = g = 3.71 m/s2
On Mars
F = maW= mg
Formulasm = 68 kg
W= mg
W= (68 kg)(3.71 m/s2)W= 252 N
1 lb = 4.45 N
252N 1 lb4.45 N
= 57 lb
Hey
Hi
Question:
We just saw that my mass on Earth is 68 kg.
What is my mass on Mars?
Answer: 68 kg-my mass will not change.
My weight changes because acceleration changes on mars
Stress
Stress =ForceArea
s =FA
Stress
Stress =ForceArea
s =FA
12 N
1 m
3 m
Example
Stress
Stress =ForceArea
s =FA
12 N
1 m
3 mF = 12 N
Example
Stress
Stress =ForceArea
s =FA
12 N
1 m
3 mF = 12 N
Example
A= (1m)(3m) = 3m2
We want the area that isperpendicular to the force
Stress
Stress =ForceArea
s =FA
12 N
1 m
3 mF = 12 N
Example
A= (1m)(3m) = 3m2
s =FA
=12 N3m2
= 4 N/m2
= 4 Pascals= 4 Pa
You try one!
s =FA
F =
A=
s =FA
=
3.14 N
Diameter = 2 m
Strain
Strain =Lf - Li
Li
e =Lf - Li
Li
Li
initial
Strain
Li
Lf
Force
Strain =Lf - Li
Li
e =Lf - Li
Li
initial
final
Strain
Li
Lf
Force
Lf - LiStrain =Lf - Li
Li
e =Lf - Li
Li
initial
final
Example
10 N
10 NLf =
e =Lf - Li
Li
Li =
e =
initial
final
1 mm
5 mm
Now put it together
What if we make a plot of stress vs. strain?
s
e
Young’s Modulus
Stress vs. StrainThe slope of the stress-strain curve is a material property of stiffness
We call this parameter Young’s Modulus
s
e
Young’s Modulus
Stress vs. StrainThe higher the slope, the stiffer the material
s
e
Material 1
Material 2
Material 3
Material 3 is the stiffest
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Lab activity!
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