Lecture 5

JT ME 443/643: Material Models

ME 443/643

Design Techniques in

Mechanical Engineering

Instructor:

Dr. Jagadeep Thota

Lecture 5:

Altair: Material Model & Units


Material Types

All the finite element (FE) materials can be broadly

classified into the following types:

– Isotropic

The characteristics of the material remain same along any axis

or plane

Example: All metals and alloys

– Orthotropic

This material has mechanical properties that are different along

three mutually perpendicular directions

Example: Any composite material (fiber-glass, kevlar-epoxy,

etc), wood (assumed), etc.

– Anisotropic

The material properties are different along any axis or plane

Example: Concrete, sand, wood, foam, composite materials, etc


Radioss

Radioss is the processor or solver available in

HyperWorks software

Can process linear (bulk format) and non-linear

material models (block format)

We will for now limit our study to linear analysis

(bulk format) in Radioss

Radioss (bulk format) has a total of 7 material

models:

– Isotropic: MAT1 & MAT4

– Orthotropic: MAT5 & MAT8 (2D elements only)

– Anisotropic: MAT2 (2D only) & MAT9 (3D elements only)

– Fluid: MAT10


MAT1

Defines the material properties for linear, temperature-independent,

isotropic materials • For a simple linear structural

non-temperature analysis only

E, NU & RHO need to be

defined

• For thermal stresses A and

TREF are defined

• When conducting vibrational analysis, there

might be a need to define GE

• GE = 2*(critical damping coefficient)

• This material model can be used to define a

composite material by assuming the properties

of the material are predominant in only one

direction.

• In such a case, the stress limits ST, SC & SS

need to be defined for failure analysis


MAT4

This material card is needed for heat transfer problems like

conduction and convection

• This card can be used in

combination with either MAT1,

MAT2, MAT8 or MAT9 card for

conducting a combined

structural-heat transfer problem


MAT5

Defines the thermal material properties for orthotropic (and also can

be used for anisotropic) materials


MAT8

Defines the material properties for linear temperature-independent

orthotropic material for two-dimensional elements


MAT2


anisotropic materials for two-dimensional elements


MAT9


anisotropic materials for solid elements


Creating Radioss Material Cards

in HyperMesh


Opening Radioss in HyperMesh

(1) (2)

(3)


Geometry Creation

Create a square of 2 units length


Meshing Mesh the square geometry with 2D elements

We will go in detail regarding meshing in the next class

(1)

(2)


Meshing


Meshing

Try the by window and by collector options too when practicing


Meshing


Meshing

When your FE model is ready to be solved, all the lines, nodes, surfaces (and any

unwanted components) created for meshing need to be deleted

Do not delete the nodes formed when the mesh was created

Hence, to make our life easy, we tell HyperMesh to delete the surface automatically

when it has created the mesh

(1)

(2)


Meshing

(1)

(2)

(3)

(4)


Meshing


When deleting the geometry objects like lines and nodes, it is a good practice to hide

the elements so that you do not delete the element nodes by mistake.

Deleting the Geometry

(2)

(1)

Click on this icon to

hide/show the elements

of the auto1 component


Deleting Geometry Line


Deleting Geometry Lines

(1)

(2)


Deleting Geometry Nodes

(1)

(2)


Deleting Geometry Nodes


Unhide the Mesh


Material Collector


Create MAT1

(1) (2)

(3)


Create MAT1

(1) (2)


Enter the Properties for MAT1 Card

(1)

(2) (3)

(4)


Creating MAT1


Assigning MAT Collector to Component

The created material collector needs to be assigned to the intended component (auto1)


Assigning Material to Component

(1)

(2)


Assigning Material to Component


Units

Like most of the FE software, there is no option to choose a

particular unit system in HyperMesh

It is left to the user to maintain consistency in the units

Length, mass and time are the basic units

– Based on these the units of other quantities should be maintained

consistent

Example: A FE model created with the following basic units

– Length = mm, Mass = kg, Time = s

– The derived quantities should be having units as shown below to

maintain consistency

Force = mass x acceleration = kg x mm/s2 = N/1000 = mN

Pressure/Stress = Force/Area = N/mm2 = 1x106 Pa = MPa

Density = Mass/Volume = kg/mm3


Consistent Units

Mass Length Time Force Stress Energy

kg m s N Pa J

kg mm s mN MPa mJ

kg mm ms kN GPa kN-mm

Slug ft s lbf psf lbf-ft

lbf-s2/in in s lbf psi Ibf-in

ton mm s N MPa N-mm

1 slug = 32.18 kg

1 kg/m3 = 0.9112 slug/ft3

1 N = 0.2248 lbf

1 ft = 0.3048 m


Ending Remarks

Practice creating components and assigning

material models to them

In a FE model make sure the units are

consistent

– Inconsistency in the units is the number one reason

for new FEA users to get incorrect results

Next Class

– Look at common types of elements

– Create 1D, 2D and 3D elements using HyperMesh

– HW 1 is due

Lecture 5

Documents

Transcript of Lecture 5