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# Materials

In the materials section, you can define multiple materials and assign volumes to them. To do so, click on the ‘+’ button next to Materials.

Afterward, a library of materials appear. Select one material from the list. The specific material parameters to be defined depending on the analysis type of the simulation.

If the material that you wish to use is not on the list, it’s possible to input custom properties by editing each parameter.

## Solid Materials

For solid mechanics analysis, every volume that belongs to the simulation domain has to be assigned to exactly one material. For example, in the case of a solid mechanics simulation, you have to choose a material law that describes the relationship between the strains and the consequent stresses. Please be aware that the material behavior can be linear or nonlinear (e.g. plastic material) and therefore may affect the numerical effort of the calculation. Solid material properties and behavior are defined by a thermal solid model.

Find below the solid material models available on SimScale:

### Linear elastic

Linear elastic material deforms elastically throughout the analysis, which means that it will return back to its initial state upon unloading, irrespective of the deformation.

### Elasto-plastic

Elasto-plastic material model describes an elastic behavior until the onset of plasticity after which the solid material undergoes irreversible deformation when subjected to loading.

### Hyperelastic

Hyperelastic materials are a special class of materials that tend to respond elastically when they are subjected to very large strains. They show both nonlinear material behavior as well as large shape changes.

### Creep

Creep is the inelastic, irreversible deformation of structures over a long period of time. It is a life-limiting factor and depends on stress, strain, temperature, and time.

### Damping

Damping, in dynamic simulations, means energy dissipation out of the system. It can be used to remove unphysical oscillations of the system or to mimic effects such as internal friction of the material.

## Fluid Materials

All incompressible analysis types require the material density (a constant) to be specified by the user. For compressible simulations, the density is solved as part of the equation of state and does not need to be provided in the material definition. Fluid material properties and behavior are defined by the thermophysical fluid model.

Assigning vacuum as the material medium

Yes! You heard it right! In SimScale it is possible to create a vacuum medium by changing the conductivity of air. Follow the steps:

• Select Air from the material library.
• Since fluid conductivity is defined as $$\frac {Density\ (\rho) \times Kinematic\ viscosity\ (\nu) \times Specific\ heat\ (C_p)}{Prandtl\ number (Pr)}$$ adjust the values such that conductivity is in the order of 1e-11.
• In case temperature boundary condition is involved make sure that it is set to a fixed value.
• ### Viscosity Model

For analysis types that do not include energy/heat, the fluid materials are categorized based on the viscosity model of the fluid. The models generally relate the behavior of viscosity to the strain rate of the fluid. The 2 fundamental types of viscosity models that define any fluid material are as follows:

Newtonian Model

In a Newtonian fluid model, the local stresses due to the viscous forces in the fluid change linearly with the local strain rate. Here, viscosity is then the constant of proportionality. The implemented Newtonian model assumes a constant kinematic viscosity $$ν$$: $$ν=(μ/ρ)$$ which is specified by the user in units of $$m^2/s$$. Some ‘Liquids’ and ‘Gases’, for example, water and air, follow a ‘Newtonian model’ under standard conditions.

Non-Newtonian Model

In a non-Newtonian fluid model, the local shear stress and the local shear rate of the fluid are not related linearly. Here, a constant of proportionality cannot be determined and so viscosity is a variable quantity. For these fluids, several non-Newtonian models exist that define the non-linear relation to determine the kinematic viscosity, ν (see link below for details). Some examples of non-Newtonian fluids include common substances like ketchup, custard, toothpaste, corn-starch suspensions, paint, blood, and shampoo.

Last updated: December 1st, 2020