What is a hardening function? What does it represent?

In summary, plastic deformation and hardening functions are used to measure the strain of a material under stress. The linear and kinematic functions are commonly used, but the choice depends on the material and can be found in literature or through experimentation. In the specific case of choosing a hardening function for Earth's heated crust, an elastic perfectly plastic model may be suitable, but further considerations need to be taken into account depending on the surface conditions.
  • #1
PinkGeologist
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So, I was introduced tangentially to plastic deformation and hardening functions. I see we have three basic function ... and the linear and kinematic seem to be the most common defaults ... I see it is a measure of the strain of a material under stress.

But how would you know which version to use for some material? Is it some tabled value like thermal conductivity or specific heat?

For instance, I need to choose a "hardening function" for Earth's heated crust as it undergoes the pressure of an inflating magma reservoir. I cannot find such a function in the literature so how would I go about choosing some reasonable function?

As an added note, this has to be applied in COMSOL multiphysics software which requires a "Isotropic tangent modulus" and a "kinematic tangent modulus" ... I cannot find ANY value for those parameters. I'm not even sure WHAT they are. Are these parts of the hardening function to describe the curvature of the line?

Since mechanics and materials is not the mainstay of what I do, this is all new to me.

Thanks for any help!
 
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  • #3
Without knowing the details of the COMSOL models, I would pick an elastic perfectly plastic model. Since they are using tangent moduli, setting them equal to zero would probably do this. This means that after the material yields, the shear stress will remain constant. This will require 2 elastic constants and a yield strength which should be findable. Depending on whether you are near the surface, to improve the results i would either take into account the pressure/temperature sensitivity or the fracture behavior next if needed.
 

What is a hardening function?

A hardening function is a mathematical function that represents the relationship between stress and strain in a material when it is subjected to repeated loading and unloading cycles. It describes how a material becomes stronger and more resistant to deformation as it is subjected to repeated stresses over time.

What does it represent?

A hardening function represents the hardening behavior of a material, which is the ability of a material to become stronger and more resistant to deformation as it is subjected to repeated stresses. It describes the change in material properties, such as yield strength and ductility, as the material is subjected to repeated loading and unloading cycles.

What factors affect the shape of a hardening function?

The shape of a hardening function can be influenced by various factors, including the type of material, its microstructure, the rate of loading, and the temperature. Different materials and loading conditions can result in different hardening behaviors, leading to variations in the shape of the hardening function.

How is a hardening function measured or determined?

A hardening function is typically determined through experimental testing, such as tensile or compression tests, where the material is subjected to repeated loading and unloading cycles. The resulting stress-strain curves are then used to calculate the hardening function, which can be further validated using mathematical models.

Why is understanding hardening functions important?

Understanding hardening functions is crucial in many fields of science and engineering, such as materials science, mechanical engineering, and structural engineering. It allows us to predict and control the behavior of materials under repeated loading, which is essential for designing safe and durable structures and components.

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