Theories of Failure — Lesson 1

This lesson covers the concept of theories of failures, which provide the conditions for the initiation of failure of a material at a point. It explains how different components of a machine, such as a shaft or a pressure vessel, can fail under different types of loads like axial force, bending moment, and torsion. The lesson also discusses how these theories help in determining the load or combination of loads that can cause failure of a component, which is crucial for design purposes. For instance, in designing a component, one would be interested in finding out the combination of axial load, bending moment, and torsion that will cause failure, so as to prevent such failure by keeping the load level below the critical state. The lesson also introduces different theories of failures, including the maximum principal stress theory, maximum shear stress theory, and maximum principal strain theory.

Video Highlights

02:44 - The role of theories of failure in determining load capacity and preventing failure
08:39 - Explanation of stress-strain diagram and critical load for failure.
10:21 - Discussion on the utility of theories of failure.
28:15 - Explanation of different theories of failure.
34:34 - Detailed explanation of maximum principal stress or ranking criterion.
41:17 - Detailed explanation of maximum shear stress or Tresca criterion.

Key Takeaways

- Theories of failures provide the conditions for the initiation of failure of a material at a point.
- Different components of a machine can fail under different types of loads.
- These theories help in determining the load or combination of loads that can cause failure of a component.
- Different theories of failures include the maximum principal stress theory, maximum shear stress theory, and maximum principal strain theory.