This document discusses factors that influence machine design, including the type and nature of loads, motion of parts, material selection, size and shape of parts, lubrication, operational features, use of standard parts, safety, workshop facilities, number of components, cost, and assembly. It covers types of loads such as steady, live, and impact loads. Key considerations for design include withstanding stresses from various loads, selecting suitable materials, ensuring parts can perform intended motions, facilitating assembly, and optimizing for cost, safety, and other practical factors. Fatigue from cyclic or fluctuating loads is also addressed.

1. STEADY STRESSES AND
VARIABLE STRESSES IN
MACHINE MEMBERS
UNIT-1

2. Design process
Design is a series of activities to gather all the
information necessary to realize the designer’s idea as
a real product.
Designer’s
Idea
Real
Product
Design Process

7. DESIGN PROCESS

8. DESIGN PROCESS

9. DESIGN PROCESS

10. OPTIMUM DESIGN

11. GENERAL CONSIDERATIONS IN DESIGNING A
MACHINE COMPONENT
(FACTORS INFLUENCING MACHINE DESIGN)
1. Type of load and stresses caused by the load:
– Steady or static or dead load: Whose magnitude and direction will not
change with respect to time.
– Live or variable or dynamic load: Whose magnitude and direction
change time to time.
– Impact load: This is suddenly applied with some velocity
2. Motion of the parts:
(1) Rectilinear motion.(reciprocating)
(2) Curvilinear motion. (rotary)
(3) Constant speed.
(4) Constant or variable acceleration

12. 3. Selection of materials:
The selection of material for a part depends upon the forces that are
acting on that part and stresses developed on that part.
4. Form and size of the parts:
Based upon the stresses acting on the part, the size and form shape
(appearance) of a component is to be designed
The size is inversely proportional to material strength if the load is
kept constant.
5. Lubrication:
There is always a lot of heat is dissipated between movable parts

13. 6. Operational features:
-the start button, controlling levers, stop button should be designed
based upon the convenient handling of the operator.
7.Use of standard parts
– using the existing standard parts like bolts, nuts, washers, Gears and
pulleys etc Reduces the cost of a machine and also it simplifies the
manufacturing process
8. Safety of operation
– Some machines are dangerous to operate at maximum speed. It is
necessary that a designer should always provide safety devices for
the safety of the operator

14. 9. Work shop facilities:
The designer has to always design the part based upon his
employer’s work shop facilities available to him
10. Number of components to be manufactured:
If the number of components to be manufactured are less, using the
standard shapes and sizes (or) he can go for a new product (design) of the
part for more part production.
11. Cost of construction
Use of standard parts and using the manufacturing process available
to him can reduce the cost of construction
12. Assembling
Based upon the local conditions at errection of the machine, the
designer should design the different components of a machine.

15. SELECTION OF MATERIAL BASED ON MECHANICAL
PROPERTIES

16. STANDARDIZATION IN DESIGN
• For easy identification of materials
• further improvement of machine elements
• easy replacement of worn-out parts
• quick and easy manufacturing

17. PREFERRED NUMBERS

18. Arithmetic Progression

19. Geometric Progression

20. Geometric Progression

21. .

22. LIMITS , FITS AND TOLERANCE

23. Terms Used

24. Terms Used

25. Terms Used

26. Terms Used

27. Terms
Used

28. Terms
Used

29. Unilateral – Bilateral Tolerances

30. Hole Base & Shaft Base System

31. Hole Base System

32. Shaft Base System

33. FITS

34. Introduction
FITS

35. TYPES - FITS
Clearance Fit

36. Types Of Clearance Fit

37. INTERFERENCE FIT

38. TRANSITION FITS

39. Features of types of fits

40. tolerance grades Usage

41. Basic Hole and Basic Shaft
Letter H
Letter h

42. Calculation of Tolerance Grades

43. .

45. .

46. 38.73mm + (10.92861/ 1000)
= 38.73 + 0.01092861
= 38.7409 mm

47. .

50. HOLE

51. SHAFT

53. .

58. .

62. Notch Sensitivity (q)

63. Fatigue stress Concentration Factor
(Kf)

64. Relation Kt , q and Kf

65. Design for variable loading
Static Stress
Varying Stress

66. Cyclic loads produce cyclic stress which can lead to mechanical fatigue
failure:
Mechanical Fatigue = The progressive and localized structural damage
that occurs when a material is subjected to cyclic loading. The cyclic
stress is well below tensile, Su and yield, Sy , strengths!

67. Varying Stress -Types
1. Completely Reversed or Cyclic Stresses
2. Fluctuating Stresses
3. Repeated Stresses
4. Alternating Stresses

68. 1.Completely Reversed or Cyclic Stresses

69. 2. Fluctuating Stresses

70. 3. Repeated Stresses

71. 4. Alternating Stresses

73. FATIGUE CRACK

74. • Fatigue limit, endurance limit, and fatigue
strength are all expressions used to describe a
property of materials.

76. Endurance
• Endurance strength is the stress level that a
material can survive for a given number of load
cycles.
• Endurance limit is the stress level that a
material can survive for an infinite number of
load cycles.
• Estimate for Wrought Steel:
Endurance Strength = 0.50(Su)
• Most nonferrous metals (aluminum) do not
have an endurance limit.

78. Factors affecting endurance limit
1. Load Factor (KL)
2. Surface Finish Factor (KSF)
3. Size Factor (KSZ)
4. Reliability Factor (KR)
5. Miscellaneous Factors (K)

85. S-N Curve
• S of S-N curve stands for "Stress". That means repeatitive load.
• N stands for "Number of cycles to failure".
S describes a vertical axis and N describes a cross axis. Those make a
graph below.