1. STEM
Stress Strain

2. Key Terms Stress Strain Forces Shear Torsion Load Beam
Modulus of rigidity
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

3. Lesson Objective
SWBAT show how stress and strain apply to mechanical failure or
everyday objects like scissors
By summarizing the information given in this weeks lecture
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

4. You will be successful if…
Make a checklist of the following items and check yourself off during the lesson.
You can explain how scissors cut.
You can mathematically describe how a piece of metal fails
You can explain Space X’s latest rocket failure of a strut
Is there anything you can add, or would take away in order to help you meet our lesson objective this week
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

5. Introduction- Monday Stress and strain Torsion
Introduction to stress and strain, stress strain diagram
Elasticity and plasticity and Hooke’s law
Shear Stress and Shear strain
Load and stress limit
Axial force and deflection of body
Torsion
Introduction, round bar torsion, non-uniform torsion.
Relation between Young’s Modulus E,  and G
Power transmission on round bar
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

6. Diving in Shear Force and bending moment Bending Stress
Introduction, types of beam and load
Shear force and bending moment
Relation between load, shear force and bending moment
Bending Stress
Introduction, Simple bending theory
Area of 2nd moment, parallel axis theorem
Deflection of composite beam
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

7. Non Simetric Bending Shear Stress in beam Deflection of Beam
Introduction, non-simetric bending
Product of 2nd moment area, determination of stress
Shear Stress in beam
Introduction, Stream of shear force
Shear stress and shear strain in edge beam
Deflection of Beam
Introduction
Equation of elastic curve, slope equation and integral deflection
Statically indeterminate Beams and shaft
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

8. Fun video or picture describing subject
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

9. DIRECT STRESS When a force is applied to an elastic body, the body deforms. The way in which the body deforms depends upon the type of force applied to it.
Compression force makes the body shorter.
A tensile force makes the body longer
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

10. Connections to past
Your whole life you’ve been using scissors to cut, and have hole punched papers. How can this relate to stress or strain?
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

11. Connections to future
Have you ever seen a car wreck where a car was split in half?
How can measuring stress or strain help you stay safe in the future?
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

12. Heavy Tensile and compressive forces are called DIRECT FORCES
Stress is the force per unit area upon which it acts.
Note: Most of engineering fields used kPa, MPa, GPa.
….. Unit is Pascal (Pa) or
( Symbol – Sigma)
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

13. DIRECT STRAIN ,
In each case, a force F produces a deformation x. In engineering, we usually change this force into stress and the deformation into strain and we define these as follows:
Strain is the deformation per unit of the original length.
The symbol
called EPSILON
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

14. Direct Strain cont.
Strain has no unit’s since it is a ratio of length to length. Most engineering materials do not stretch very mush before they become damages, so strain values are very small figures. It is quite normal to change small numbers in to the exponent for 10-6( micro strain).
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

15. Objective Review-Monday
What was our objective?
Discussion- Put todays objective in your own words and talk to your partner about it. I’ll call on 3 people at random. What did you and your partner come up with? Does anyone have something different.
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

16. Criteria for success- Mon
Are you meeting our criteria for success?
How? (notes here on peardeck)
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

17. MODULUS OF ELASTICITY (E)
Elastic materials always spring back into shape when released. They also obey HOOKE’s LAW.
This is the law of spring which states that deformation is directly proportional to the force. F/x = stiffness = kN/m
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

18. If F and x is refer to the direct stress and strain , then
The stiffness is different for the different material and different sizes of the material. We may eliminate the size by using stress and strain instead of force and deformation:
If F and x is refer to the direct stress and strain , then
and
hence
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

19. The stiffness is now in terms of stress and strain only and this constant is called the MODULUS of ELASTICITY (E)
A graph of stress against strain will be straight line with gradient of E. The units of E are the same as the unit of stress.
ULTIMATE TENSILE STRESS
If a material is stretched until it breaks, the tensile stress has reached the absolute limit and this stress level is called the ultimate tensile stress.
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

20. STRESS STRAIN DIAGRAM

21. Rate yourself
How well do you feel you’ve met the objective according to the Ouchi rubric grading scale. 1 2 3 4
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

22. Objective review-Mo Why is our objective relevant outside of Ouchi HS?
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

23. Criteria for success
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

24. Objective Review- Wed
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

25. Criteria for success- Review
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

26. Popcorn
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

27. Fun vid or sample vid
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

28. STRESS STRAIN DIAGRAM Elastic behaviour
The curve is straight line trough out most of the region
Stress is proportional with strain
Material to be linearly elastic
Proportional limit
The upper limit to linear line
The material still respond elastically
The curve tend to bend and flatten out
Elastic limit
Upon reaching this point, if load is remove, the specimen still return to original shape

29. STRESS STRAIN DIAGRAM Yielding
A Slight increase in stress above the elastic limit will result in breakdown of the material and cause it to deform permanently.
This behaviour is called yielding
The stress that cause = YIELD POINT
Plastic deformation
Once yield point is reached, the specimen will elongate (Strain) without any increase in load
Material in this state = perfectly plastic

30. STRESS STRAIN DIAGRAM STRAIN HARDENING NECKING
When yielding has ended, further load applied, resulting in a curve that rises continuously
Become flat when reached ULTIMATE STRESS
The rise in the curve = STRAIN HARDENING
While specimen is elongating, its cross sectional will decrease
The decrease is fairly uniform
NECKING
At the ultimate stress, the cross sectional area begins its localised region of specimen
it is caused by slip planes formed within material
Actual strain produced by shear strain
As a result, “neck” tend to form
Smaller area can only carry lesser load, hence curve donward
Specimen break at FRACTURE STRESS

31. SHEAR STRESS
Shear force is a force applied sideways on the material (transversely loaded).
When a pair of shears cut a material
When a material is punched
When a beam has a transverse load

32. Shear stress is the force per unit area carrying the load
Shear stress is the force per unit area carrying the load. This means the cross sectional area of the material being cut, the beam and pin.
Shear stress,
and symbol is called Tau
The sign convention for shear force and stress is based on how it shears the materials as shown below.

33. Objective Review Thursday
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

34. Criteria for success Thurs
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

35. SHEAR STRAIN
The force causes the material to deform as shown. The shear strain is defined as the ratio of the distance deformed to the height
. Since this is a very small angle , we can say that :
Shear strain
( symbol called Gamma)

36. The gradient of the graph is constant so
MODULUS OF RIGIDITY (G)
If we conduct an experiment and measure x for various values of F, we would find that if the material is elastic, it behave like spring and so long as we do not damage the material by using too big force, the graph of F and x is straight line as shown.
The gradient of the graph is constant so
and this is the spring stiffness of the block in N/m.
If we divide F by area A and x by the height L, the relationship is still a constant and we get

37. If we divide F by area A and x by the height L, the relationship is still a constant and we get
Where
then
This constant will have a special value for each elastic material and is called the Modulus of Rigidity (G).

38. ULTIMATE SHEAR STRESS
If a material is sheared beyond a certain limit and it becomes permanently distorted and does not spring all the way back to its original shape, the elastic limit has been exceeded.
If the material stressed to the limit so that it parts into two, the ultimate limit has been reached.
The ultimate shear stress has symbol and this value is used to calculate the force needed by shears and punches.

39. Connections to past Learning
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

40. Connections to future learning
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

47. Criteria for success? Rate yourself 1-4
1-What are we doing?
2- I got 1 of them
3- I got all of them
4- I understand them and can apply them to other subjects
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

48. Supplementary example
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

49. Example cont.
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors

50. Copy link to peardeck!
Pear deck
Objective: SWBAT show how stress and strain apply to mechanical failure or everyday objects like scissors