What is the Difference Between Plastic and Pseudoplastic Flow

The key difference between plastic and pseudoplastic flow is that plastic flow describes the flowing behavior of a material after the application of stress, whereas pseudoplastic flow exhibits the behavior of both Newtonian flow and plastic flow.

Plastic flow is a chemical phenomenon that describes the flowing behavior of a material after applying stress which reaches a critical value. Pseudoplastic flow exhibits the behavior of both Newtonian flow and plastic flow. Newtonian flow of fluids describe the property of the viscous stress that arises from the fluid’s flow at every point that is linearly correlated to the local strain rate.

1. Overview and Key Difference
2. What is Plastic Flow
3. What is Pseudoplastic Flow
4. Plastic vs Pseudoplastic Flow in Tabular Form
5. Summary – Plastic vs Pseudoplastic Flow

What is Plastic Flow?

Plastic flow is a chemical phenomenon that describes the flowing behavior of a material after applying stress which reaches a critical value. It is also known as plastic deformation. It is the permanent distortion that occurs if we subject a material to tensile, compressive, bending, or torsion stresses, which tend to exceed its yield strength. It can also cause the material to elongate, compress, buckle, bend, or sometimes twist.

Plastic vs Pseudoplastic Flow in Tabular Form

Figure 01: Plastic Flow

Plastic flow can occur in many metal-forming processes such as rolling, pressing, forging, etc. Moreover, we can find this in some geological processes. We can describe the plastic flow using the flow plasticity theory.

Flow plasticity theory is a solid mechanics theory that is useful in describing the plastic behavior of a material. Moreover, the theory of flow plasticity can be characterized by an assumption; there is a flow rule we can use to determine the amount of plastic deformation that happens in the material. Typically, in a flow plasticity theory, we assume that the total strain in the body can undergo decomposition additively into a plastic part and an elastic part. Among them, the elastic part can undergo computing from a linear elastic or hyperelastic constitutive model.

What is Pseudoplastic Flow?

Pseudoplastic flow exhibits the behavior of both Newtonian flow and plastic flow. In the process of pseudoplastic flow, the liquid tends to flow as plastic at high shear rates. However, it does not have a yield point, and therefore, it will always flow under the shear stress similar to a Newtonian liquid.

A common example of pseudoplastic behavior is blood. Furthermore, a dilatant fluid containing sand in water is another common example of pseudoplastic flow. Besides, when the viscosity decreases when the shear stress increases, we call it pseudoplastic fluid.

Plastic and Pseudoplastic Flow - Side by Side Comparison

Figure 02: Pseudoplastic Behavior in a Diagram

Generally, pseudoplastic flow occurs in contrast to Bingham fluid. Pseudoplastic fluids can increase viscosity as a force is applied. For example, cornstarch mixed in water behaves like pure water when there is no other force applied.

What is the Difference Between Plastic and Pseudoplastic Flow?

Plastic flow is a chemical phenomenon that describes the flowing behavior of a material after applying stress which reaches a critical value. Pseudoplastic flow exhibits the behavior of both Newtonian flow and plastic flow. The key difference between plastic and pseudoplastic flow is that plastic flow describes the flowing behavior of a material after application of stress, whereas pseudoplastic flow exhibits the behavior of both Newtonian flow and plastic flow. Bending a piece of metal or pounding it into a new shape is an example of plastic flow, whereas blood, sand in water, honey, etc. are examples of pseudoplastic flow.

Below is a summary of the difference between plastic and pseudoplastic flow in tabular form for side by side comparison.

Summary – Plastic vs Pseudoplastic Flow

Plastic and pseudoplastic behavior are two rheological processes regarding different materials. The key difference between plastic and pseudoplastic flow is that plastic flow describes the flowing behavior of a material after application of stress, whereas pseudoplastic flow exhibits the behavior of both Newtonian flow and plastic flow.

Reference:

1. “Plastic Deformation.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Biegeanimation 2D” By Borowski~commonswiki assumed – No machine-readable source provided. Own work assumed (based on copyright claims). (Public Domain) via Commons Wikimedia
2. “Shear rate vs. Shear stress” By Chucklingcanuck – Wikimedia Commons (CC BY-SA 3.0) via Commons Wikimedia