How to define my

material data? This guide starts from basic knowledge

of material properties. Then it introduces

different material types based on

physical property and linearity, and

especially how to assign materials in

midas NFX

TABLE OF CONTENTS:

Reminder about material properties..1

Types of Material.....3

Linear Material.......5

Elasto-plastic material.......6

Hyper-elastic material9

Assign material to FEA model10

Stress and strain are linked together by stress-strain curve.

And stress-strain curve of each material is usually obtained

by experimental tests (tension test).

Stress-strain curve can be separated to several stages which

correspond to different states of the material:

When strain is small, elastic deformation occurs and linear

material model is used.

When the strain is large enough, plastic deformation will

occur and a nonlinear material model will have to be

considered.

Reminder about material properties

// Page 1

1

Strain ()

Stress ()

Ultimate Stress (u)

Yield Stress (y)

Fracture

Elastic Region

Plastic Region

Slope of Elastic Region

(Modulus of Elasticity, )

E

Example of Stress-Strain Curve

In the linear region, the stress-strain relation (Hooks law) can be simplified into:

// Page 2

s=Ee (: stress, E: modulus of elasticity, : strain)

Modulus of Elasticity (Youngs Modulus)

1) Description of an objects tendency to be deformed elastically when a force is apply to it.

2) It is equal to the slope of the stress-strain curve within the

elasticity region

Poissons Ratio

The relative ratio of the change in length of an object in the

direction to which force is applied to the change in length in the

other two directions

Modulus of Elasticity

Poissons Ratio

Types of Material

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2 Materials can be divided into linear and nonlinear material.

Linear Material models are suitable for any analysis in which

small strains are considered and deformation remains in the

elastic region.

Nonlinear Material models (Elasto-plastic, Hyper-elastic) provide

more complex material models for analysis in which model is

submitted to plastic deformation.

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For isotropic material, properties are identical in all directions. This is the most commonly used model. Isotropic Material can be chosen as linear, elasto-plastic, hyper-elastic materials or temperature-dependant.

For anisotropic material, properties are directionally dependant, as opposed to isotropic material.

Orthotropic material is a specific case of anisotropic material which has two or three mutually orthogonal twofold axes of rotation symmetry so that its mechanical properties are different along each axis. (ex: wood, crystal)

For CFD analysis, special CFD materials for fluid or solid have to be used.

Rigid material is a special type of material which is used to simulate parts with a very high stiffness (almost rigid). Rigid material can save calculation time during the analysis. When using rigid materials, boundary conditions must be assign to only one node of the part.

Linear material

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3 For linear structural analysis, only 2 constants are required:

elastic modulus and the Poisson's ratio. If gravity is present,

mass density have to be defined as well.

Thermal constants are required for thermal transfer analysis and

thermal expansion coefficient is required for thermal stress

analysis.

The value of the tension will be used for the calculation of the

factor of safety.

Material damping factor will be used for linear dynamic analysis.

Elasto-plastic material

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4 For elasto-plastic nonlinear material model, basic structural

constants have to be defined along with material stress-strain

curve.

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Stress-strain data can be defined either by defining the full stress-

strain curve, either by defining the plastic hardening function.

In the first row, stress and strain are

null.

In the second row, elastic strain and

yield stress are entered.

In the third row, strain and plastic

stress are entered

In the first line, enter 0 for the strain

and yield stress.

In the second line, enter the plastic

strain and plastic stress.

* Value of the strain should be

calculated correctly form the yield

point, which is the starting point of the

curve.

Stress-strain curve

Plastic hardening function

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Stress-strain curve is defined as a function. The data can be

directly imported from MS Excell into midas NFX.

Hyper-elastic material

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5 Hyper-elastic materials can be considered as nonlinear elastic

materials. It is usually used for rubber materials.

Hyper-elastic materials can be loaded and submitted to a

deformation of 500% and recover their original shape after

unloading.

As a nonlinear material, nonlinear analysis have to be used, but

principle of superposition can still be used as for linear analysis.

Different ways to assign material to FEA model

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6 In NFX Designer mode, you can assign materials by using direct

drag & drop or right click menu selection.

Assign Materials by Drag & Drop

Select the part and right click to assign material

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In midas NFX Analyst mode, materials are linked with

properties, so the user doesnt need to assign the material to the CAD model directly.

Now you are ready to add your own materials to your midas NFX model

Please contact us if you have any question

during your trial:

Email: Info@MidasUser.com

Telephone: +82-31-789-4040