Objectives

This course will help the student think about design of various mechanical components from the viewpoint of size, assembly, deformation, strength, various modes of failure, statistics, and environmental issues.

Course content

Dimensions and assembly, deformations and compliance, unexpected deformations, material failure, fatigue, extremely long-serving components, unexpected failure modes, statistical aspects, and environmental aspects.

Total number of lectures: 28

Lecturewise breakup

1. Discussion of ways in which a machine element may fail: 1 Lecture

• Shape, dimensions, or assembly 

• Deformations too large or small, component too compliant or not compliant enough

• Unexpected deformations (buckling)

• Plastic yielding or brittle fracture, leading to quick failure

• Fatigue (cyclic loading below yield and below buckling, ~1,000 to ~1,000,000 cycles)

• Extremely long-life goals not being met (more than 1,000,000 cycles)

• Other (becomes loose, jams or locks, has too much friction, vibrates, makes a noise)

2. Shape, dimensions, assembly: 4 Lectures

• Part drawing, subassembly drawing, production drawing, assembly drawing

• Different types of fits, geometric and dimensional tolerances

• LAB 1 Drawing, assembly, dimensions

3. Deformations too large or small, component too compliant or not compliant enough: 4 Lectures

• Helical compression springs for sizing and compliance

• Approximate deformation analysis of other components by hand; discussion of role of FEA

• How much should a bolt be tightened?

• LAB 2 Design of springs and bolts

• LAB 3 Approximate deformation analysis and comparison with supplied FEA results

4. Unexpected deformations (buckling): 2 Lectures

• Euler buckling (purely elastic), role of plasticity in buckling of shorter columns

• Sensitivity to imperfections. Presentation on other buckling problems (no calculations)

• LAB 4 Buckling problems

5. Plastic yielding or brittle fracture, leading to quick failure: 3 Lectures

• Ductile materials and brittle materials, stress concentration

• Design of bolted joints under tension and shear. Welded joints

• Local yielding that is contained. Yielding that cannot be contained. Limit load estimates

• LAB 5 Application of failure theories to any of the above

6. Fatigue. Design for fatigue: 5 Lectures

• What is fatigue? S-N curves. Nonzero mean loads. Fluctuating loads

• Physical phenomena. Localized yielding, hardening, crack initiation and growth

• Low cycle versus high cycle, strain versus stress controlled

• Role of flaws and microstructure.

• Empirical formulas. Various factors in design books

• Design example: fatigue in helical springs

• Fatigue under combined loading: simplest approaches

• Ideas of factor of safety in fatigue design

• LAB 6 Fatigue design 1

• LAB 7 Combined design problem involving previous lab topics

7. Extremely long-life goals: 5 Lectures

• Example 1: rolling element bearings

• How many cycles is typical?

• Types of bearings

• Sizing and life estimates from bearing catalogues

• Empirical correction factors

• Example 2: gearing

• Involute gear profile geometric parameters

• Elementary formulas for stress and fatigue

• Introduction to AGMA approach for design of spur and helical gears

• LAB 8 Involving bearings and gears

8. Other failure modes : 2 Lectures

• High levels of vibration. Removal of resonances, tuned vibration absorbers, dampers

• Whirling of shafts. Simple formulas

• LAB 9 Something from dynamics and vibrations as above

9. Accelerated testing and elementary statistical assessment: 1 Lecture

• LAB 10 Analysis of given data from an accelerated testing program

10. Design for a circular economy: 1 Lecture.

• Additional lab slots (11-14) may be used for supplementary lectures or for a project

Recommended books

1. Machine Component Design, RC Juvinall and KM Marshek

2. Shigley’s Mechanical Engineering Design, RG Budynas and JK Nisbett

Proposing instructors: Dr. A. Chatterjee, Dr. Shakti Gupta, Dr. A. Mimani