ANSYS -Material Models Part A

Material Behavior Under Dynamic Loading

In general, materials have a complex response to dynamic loading

The following phenomena may need to be modelled

– Non-linear pressure response

– Strain hardening

– Strain rate hardening

– Thermal softening

– Compaction (porous materials)

– Orthotropic behavior (e.g. composites)

– Crushing damage (e.g. ceramics, glass, geological materials, concrete)

– Chemical energy deposition (e.g. explosives)

– Tensile failure

– Phase changes (solid-liquid-gas)

No single material model incorporates all of these effects

Engineering Data offers a selection of models from which you can choose based on the material(s) present in your simulation

Modeling Provided By Engineering Data

Material Deformation

Material deformation can be split into two independent parts

– Volumetric Response - changes in volume (pressure)

Equation of state (EOS)

– Deviatoric Response - changes in shape

Strength model

Also, it is often necessary to specify a Failure model as materials can only sustain limited amount of stress / deformation before they break / crack / cavitate (fluids).

Principal Stresses

A stress state in 3D can be described by a tensor with six stress components

– Components depend on the orientation of the coordinate system used.

The stress tensor itself is a physical quantity

– Independent of the coordinate system used

When the coordinate system is chosen to coincide with the eigenvectors of the stress tensor, the stress tensor is represented by a diagonal matrix

The principal stresses may be combined to form the first, second and third stress invariants, respectively.

Because of its simplicity, working and thinking in the principal coordinate system is often used in the formulation of material models.

Elastic Response

For linear elasticity, stresses are given by Hooke’s law :

where λ and G are the Lame constants (G is also known as the Shear Modulus)

The principal stresses can be decomposed into a hydrostatic and a deviatoric component :

where P is the pressure and si are the stress deviators

Then :

Non-linear Response

Many applications involve stresses considerably beyond the elastic limit and so require more complex material models

Models Available for Explicit Dynamics

http://www.cadfamily.com/html/Article/ANSYS%20-Material%20Models%20Part%20A_817_1.htm

http://www.cadfamily.com/html/Article/ANSYS%20-Material%20Models%20Part%20A_817_2.htm

http://www.cadfamily.com/html/Article/ANSYS%20-Material%20Models%20Part%20A_817_3.htm

http://www.cadfamily.com/html/Article/ANSYS%20-Material%20Models%20Part%20A_817_4.htm

ANSYS -Material Models Part B

http://www.cadfamily.com/HTML/Article/ANSYS%20-Material%20Models%20Part%20B_818.htm