Theories of Failure (Continued) — Lesson 2

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

01:14 - Explanation of the concept of stress reaching a critical level leading to material failure.
15:33 - Discussion on the concept of strain energy density and its role in material failure.
22:59 - Explanation of the maximum distortion energy density criterion or von Mises criterion.
28:12 - Comparison of the five criteria for material failure.
35:12 - Explanation of the failure of a chalk piece under tension and torsion using the maximum principal stress criterion.
43:12 - Explanation of the failure of an aluminum specimen in a tensile test using the maximum shear stress criterion.
48:45 - Application of the various criteria in estimating the rivet diameter in a riveted joint.

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.