Yield stress

Definition

Yield stress is the minimum stress required to initiate flow in a material, specifically in non-Newtonian fluids. It represents a threshold that must be exceeded for the fluid to start deforming or flowing under applied stress. This concept is critical in understanding how different fluids respond to forces and is key to classifying non-Newtonian fluids, modeling their behavior, and analyzing their flow characteristics.

5 Must Know Facts For Your Next Test

1. Yield stress is essential for understanding the behavior of materials like slurries, paints, and pastes, which do not flow until a specific stress is applied.
2. Bingham plastics are a prime example of fluids with yield stress, requiring an initial force before they begin to flow.
3. The yield stress can be influenced by factors such as temperature, particle concentration, and shear rate in a fluid.
4. Understanding yield stress is crucial for applications in industries such as food processing, cosmetics, and construction where material flow needs to be controlled.
5. It plays a significant role in predicting how non-Newtonian fluids will behave during mixing, pumping, and storage.

Review Questions

• How does yield stress affect the classification of non-Newtonian fluids?
  • Yield stress is a fundamental parameter that helps categorize non-Newtonian fluids into distinct groups. For example, Bingham plastics require a specific yield stress to begin flowing, distinguishing them from other non-Newtonian fluids that may not have this threshold. This classification is essential for predicting fluid behavior under different conditions and for selecting appropriate models to describe their flow characteristics.
• Discuss how yield stress influences the flow behavior of non-Newtonian fluids in practical applications.
  • In practical applications, yield stress significantly impacts how non-Newtonian fluids are handled and processed. For instance, in food processing or paint application, knowing the yield stress allows engineers to determine the necessary pressure or force required for these materials to flow. This understanding is crucial for optimizing equipment design, ensuring efficient mixing and pumping operations while preventing blockages and ensuring product quality.
• Evaluate the implications of yield stress on the development of rheological models for non-Newtonian fluids.
  • Evaluating yield stress is vital for developing accurate rheological models that predict the flow behavior of non-Newtonian fluids. These models must incorporate yield stress to accurately represent how these materials behave under varying shear rates and stresses. By considering yield stress in these models, engineers can better simulate real-world conditions, leading to improved designs and processes across various industries such as pharmaceuticals and construction. The implications extend beyond theoretical understanding, influencing practical outcomes in material performance and processing efficiency.

Related terms

Bingham Plastic: A type of non-Newtonian fluid that behaves like a solid until a certain yield stress is exceeded, after which it flows like a viscous liquid.

Viscoelasticity: The property of materials that exhibit both viscous and elastic behavior when undergoing deformation, affecting how they respond to stress.

Thixotropy: A time-dependent shear thinning property of certain fluids where viscosity decreases under constant shear stress over time.