Theories of Failure (Continued) and Their Applications, Griffith Theory of Brittle Fracture — Lesson 3

This lesson covers the application of failure criteria in the design of machine components. It delves into the concept of strain energy and surface energy, and how these energies interact during the propagation of a crack in a material. The lesson also discusses the Griffith theory or energy balance theory, which is used to assess the safety of components with defects. It further explains how to calculate the critical load that will trigger the extension of a crack in a material with a specific surface energy capacity. The lesson concludes with an explanation of how to experimentally measure the fracture toughness of a material. For instance, if a component made of mild steel is subjected to sub-zero temperatures, it may behave like a brittle material.

Video Highlights

01:14 - Explanation of the example of a shaft made up of a ductile material.
05:51 - Explanation of the maximum shear stress criterion
09:41 - Introduction to the distortion energy density criterion.
17:53 - Discussion on the theory of brittle failure.
24:16 - Explanation of the Griffith theory or energy balance theory.
34:52 - Discussion on how to assess the safety of a component with defects.
43:26 - Explanation of how to calculate the critical load capacity of a component with a known crack dimension .
45:27 - Discussion on the concept of damage tolerance design .

Key Takeaways

- The Griffith theory or energy balance theory is used to assess the safety of components with defects.
- The critical load that will trigger the extension of a crack in a material can be calculated using the Griffith theory.
- The strain energy of a body gets converted into surface energy during the crack propagation process.
- The critical stress or load capacity of a component can be determined using the fracture toughness of the material.
- The fracture toughness of a material can be measured experimentally.