key term - Fracture

Definition

A fracture is the breaking or cracking of a hard object, such as bone, under stress. In the context of elasticity and stress-strain relationships, a fracture occurs when the material is subjected to forces that exceed its ultimate strength, causing it to break apart.

5 Must Know Facts For Your Next Test

1. Fracture is the final stage of a material's response to stress, occurring when the applied stress exceeds the material's ultimate strength.
2. The type of fracture (e.g., brittle, ductile) depends on the material's atomic structure and its ability to undergo plastic deformation before breaking.
3. Stress concentration points, such as cracks or notches, can significantly increase the likelihood of fracture in a material.
4. The fracture toughness of a material, which measures its resistance to crack propagation, is an important factor in determining its susceptibility to fracture.
5. Fracture can be prevented or delayed through proper material selection, design, and the use of stress-relieving techniques.

Review Questions

• Explain the relationship between stress, strain, and fracture in the context of elasticity.
  • As a material is subjected to increasing stress, it initially undergoes elastic deformation, where the material stores energy and can return to its original shape when the stress is removed. However, if the stress continues to increase and exceeds the material's ultimate strength, the material will experience fracture, where the atomic bonds break, and the material permanently separates into two or more pieces. The point at which fracture occurs depends on the material's stress-strain characteristics and its ability to undergo plastic deformation before reaching its ultimate strength.
• Describe how the concept of stress concentration can influence the likelihood of fracture in a material.
  • Stress concentration refers to the localized increase in stress at specific points or features within a material, such as cracks, notches, or geometric irregularities. These stress concentration points act as sites of weakness, where the applied stress is significantly higher than the average stress in the surrounding material. This increased stress can lead to the initiation and propagation of cracks, ultimately resulting in fracture at stress levels lower than the material's ultimate strength. Understanding and mitigating stress concentration is crucial in the design and engineering of structures and components to prevent premature fracture.
• Evaluate the importance of fracture toughness in determining a material's resistance to fracture.
  • Fracture toughness is a material property that measures a material's ability to resist the propagation of cracks or flaws, which can ultimately lead to fracture. Materials with high fracture toughness are more resistant to crack growth and can withstand higher stresses before fracturing, making them more suitable for applications where failure due to fracture is a concern. The fracture toughness of a material is influenced by its atomic structure, microstructure, and the presence of defects or impurities. Selecting materials with appropriate fracture toughness is essential in engineering design to ensure the safety and reliability of structures and components, especially in critical applications where the consequences of fracture can be severe.

Related terms

Stress:

The force applied per unit area on a material, causing internal resistance and deformation.

Strain:

The deformation or change in shape and size of a material in response to an applied stress.

Ultimate Strength: The maximum stress a material can withstand before it breaks or fractures.