What Is Theories of Failure - Theories of Elastic Failure - Strength of Materials

TL;DR

This video discusses four theories of failure in materials - Orowan's theory, Woods theory, Cottrill and Hull theory, and Mott theory - which explain the formation of cracks and subsequent fatigue failure.

Transcript

Hello friends here in this video we will see what are the Theories of Failure let us get started the Theories of failure in total there are four theories of failure and they are the first one is called as Orowan's theory second it is called as woods theory third it is called as cottrell and hull theory and the fourth one is called as Mott theory so... Read More

Key Insights

• 🚩 Orowan's theory states that weak regions within a material and metallurgical inclusions can lead to crack formation and fatigue failure when the material is loaded beyond the plastic region.
• 🔑 Woods theory suggests that slip movements due to fatigue can result in the formation of notches or extrusions in a material, leading to crack propagation and fatigue failure.
• 💡 Cottrell and Hull theory involves edge dislocations in two different directions, leading to the formation of intrusions or extrusions in a material. Cracks will start propagating from these regions, causing fatigue failure.
• 🌟 Mott theory states that screw dislocations can remove a column of material from a component, leaving behind cavities. Cracks will begin propagating from these cavities, resulting in fatigue failure.
• 🔧 These theories help to understand how cracks are formed and how fatigue failure occurs in materials subjected to plastic deformation and continuous loading.
• 📚 Understanding the theories of failure is crucial for designing materials and structures that can withstand fatigue and avoid catastrophic failures.
• 🔬 Research based on these theories can lead to the development of materials with enhanced fatigue resistance and improved structural durability.
• 💡 The study of failure theories provides valuable insights into the mechanics of fatigue and helps in devising preventive measures to avoid failures in various industries.

Questions & Answers

Q: What are the main factors that contribute to crack formation according to Orowan's theory?

Orowan's theory states that weak regions with metallurgical inclusions and loading the material beyond its plastic region are the main factors that contribute to crack formation. These weak regions provide favorable conditions for slip, while the inclusions act as sites for crack initiation. When the material is stressed beyond its plastic limit, cracks form and lead to subsequent fracture.

Q: How does Woods theory explain crack propagation in materials?

According to Woods theory, slip movements caused by fatigue can result in the formation of notches or extrusions within the material. These irregularities in the material's surface serve as starting points for crack propagation. When cracks initiate from these weak regions, they can propagate further under cyclic loading, leading to fatigue failure.

Q: What is the key concept behind Cottrill and Hull theory?

Cottrill and Hull theory involves the concept of edge dislocation in two different directions. The theory suggests that these dislocations can cause the formation of intrusions and extrusions within the material. Cracks then initiate from these intrusions and extrusions due to the stress concentration caused by the change in the material's area, ultimately resulting in fatigue failure.

Q: How does Mott theory explain the occurrence of fatigue failure?

Mott theory explains that screw dislocations in a material can remove a column of material, leaving behind cavities or empty spaces. When the material is subjected to external loads, cracks initiate from these cavities and propagate, leading to fatigue failure. The presence of these cavities creates stress concentration areas, making them susceptible to crack formation.

Summary & Key Takeaways

• Orowan's theory proposes that weak regions with metallurgical inclusions in a material lead to the formation of cracks when the material is stressed beyond its plastic region.

• Woods theory states that slip movements due to fatigue can result in the formation of notches or extrusions within the material, which become starting points for crack propagation.

• Cottrill and Hull theory suggests that edge dislocations in different directions create intrusions and extrusions in the material, leading to crack formation when stressed.

• Mott theory explains that screw dislocations can remove a column of material, leaving cavities that initiate crack propagation and eventual fatigue failure.