Creep

Definition

Creep is the slow, time-dependent deformation of a material under constant stress, typically occurring at elevated temperatures or over extended periods. This phenomenon is crucial for understanding how materials behave under load over time, especially in structures that experience long-term service conditions. Creep can lead to failure if not properly accounted for, impacting design considerations and material selection in engineering applications.

5 Must Know Facts For Your Next Test

1. Creep occurs primarily at high temperatures where materials can deform more easily, often seen in metals and polymers.
2. The creep rate is influenced by factors such as temperature, stress level, and the material's microstructure.
3. Creep can be divided into three stages: primary (decreasing rate), secondary (steady state), and tertiary (accelerating rate leading to failure).
4. Engineering designs must consider creep to prevent long-term deformation that can affect structural integrity.
5. Materials like superalloys are specifically designed to resist creep in high-temperature applications such as jet engines.

Review Questions

• How does temperature influence the creep behavior of materials under constant stress?
  • Temperature has a significant effect on creep because higher temperatures increase atomic mobility within a material, allowing it to deform more easily under load. As a result, materials typically exhibit higher creep rates at elevated temperatures. For instance, metals may show increased creep when subjected to temperatures approaching their melting point, necessitating careful consideration during material selection and design for high-temperature applications.
• Discuss the three stages of creep and their implications for engineering design.
  • Creep consists of three stages: primary, secondary, and tertiary. In the primary stage, the creep rate decreases over time as the material begins to accommodate the applied stress. During the secondary stage, the creep rate reaches a steady state, which can be critical for long-term applications. Finally, in the tertiary stage, the creep rate accelerates leading to failure. Understanding these stages is essential for engineers to predict and mitigate potential deformations in structures over their lifespan.
• Evaluate the importance of accounting for creep in materials selection and engineering design processes in high-temperature environments.
  • In high-temperature environments, failing to account for creep can lead to catastrophic failures in structures and components. Materials must be selected based on their ability to withstand long-term stresses without significant deformation. For example, superalloys are often chosen for turbine blades due to their superior creep resistance. Evaluating creep behavior helps engineers ensure reliability and safety in critical applications, ultimately influencing the longevity and performance of engineered systems.

Related terms

viscoelasticity: A property of materials that exhibit both viscous and elastic characteristics when undergoing deformation.

strain rate: The rate at which deformation occurs in a material, often influencing its response to applied loads.

relaxation: The reduction of stress in a material over time when it is subjected to constant strain.