Introduction to Abaqus Kelvin Voigt Viscoelastic Model
A viscoelastic material acts like both a solid and a fluid under stress. Imagine a material that can stretch like a rubber band (elasticity) but also slowly oozes over time like honey (viscosity). That’s the essence of a viscoelastic material. They exhibit a time-dependent response, deforming gradually under constant stress and sometimes taking time to return to their original shape even after the stress is removed. This unique behavior makes them valuable in various applications, from shock absorption in athletic shoes to dampening vibrations in buildings.
The Voigt model, also known as the Kelvin-Voigt model, is a mechanical model used to describe viscoelastic behavior. It consists of a spring and a damper arranged in parallel. In this model (Abaqus kelvin voigt viscoelastic), the observable variable is the total strain, and its associated variable is the stress. In this model, we divide the stress into an ‘elastic’ part and an ‘anelastic’ part. The model defines the reversible power and the dissipated power in a material. The linear isotropic theory for this model uses the same thermodynamic potential as for linear isotropic elasticity.
Applications
Here are some applications of the Kelvin-Voigt model:
- This model is effective for predicting creep, the tendency of a material to deform slowly under constant stress. For instance, we can use it to analyze the deflection of a polymer beam over time under a sustained load.
- The Kelvin-Voigt model can be used in simulations to study the response of materials to impacts. This is helpful in designing shock absorbing materials or protective packaging.
- Engineers can use the Kelvin-Voigt model to determine the viscoelastic properties of materials like foams, rubbers, and some biological tissues. This data is crucial for designing components that will perform well under specific conditions.
- We can apply the model to analyze the viscoelastic behavior of tissues like ligaments, tendons, and cartilage. This can aid in understanding how these tissues respond to stress and potential injury mechanisms.
It’s important to note that the Abaqus Kelvin Voigt viscoelastic model has limitations. While it excels at capturing creep behavior, it doesn’t perfectly describe stress relaxation (stress decreasing over time), observed in many viscoelastic materials. In such cases, other models or modifications to the Kelvin-Voigt model might be necessary.
In this tutorial we will discuss the implementation of Kelvin-Voigt model in Abaqus CAE.
Workshop
Today, finite element software has made it easy to implement the Kelvin-Voigt model for various problems. Among these software options, Abaqus is a powerful tool that allows us to define desired material properties via its subroutines, even if they are not provided in its prebuilt material library. This simplifies the implementation of the Voigt viscoelastic model. To do so, we can define the material model in UMAT and VUMAT subroutines. The standard solver uses the UMAT subroutine, while the explicit solver uses the VUMAT subroutine.
Implementation of Kelvin Voigt model Abaqus using UMAT and VUMAT Subroutines
UMAT and VUMAT subroutines, while powerful tools, present challenges in their use. This is because they must be written in Fortran, requiring comprehensive knowledge of the language. Understanding that you might face difficulties doing this yourself, we have made it easy for you in this tutorial. It includes a guide on reviewing the formulation of this model first. Then, it provides a step-by-step guide on writing the UMAT and VUMAT subroutines based on your solver, covering both the standard and explicit Abaqus solvers (kelvin voigt model Abaqus).
The results
In this tutorial, we focus on presenting the formulation and writing the subroutine. To demonstrate its functionality, we used the subroutine to capture damage in a problem. However, the results extracted in the model are general, such as stress and displacement, which are often required for engineering problems. You can use the subroutine for your desired models and extract the results you need without significant difficulty or challenge. We hope this tutorial will be helpful for you in applying the Kelvin-Voigt model to your desired applications.
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