Common Material Properties

These material properties are common to all types of materials.

Fracture Toughness Properties

These properties set material properties that determine the fracture toughness of the material and control various aspects of crack propagation.

XML Notes

There are some material properties that are common to all material types. These properties are only used in NairnMPM and are not allowed in NairnFEA. Some of these properties only work for selected materials (refer to each material for possible details). The common properties are

<rho>1.5</rho>

The material density (in g/cm³) (can be used in NairnFEA files, but it is ignored).

<Cp>1.5</Cp> or <Cv>1.5</Cv>

The material's heat capacity (in J/(kg-K)). It is used when doing <a href="thermal.html">conduction calculations and/or coupled mechanical energy</a> and by some material constitutitive laws. Both Cp and Cv set the same (and only) heat capacity used in the MPM calculations. MPM is a strain-drive method, which implies the heat capacity should be interpreted as the constant-volume heat capacity.

<a name="csat"></a><csat>0.5</csat>

The material's saturation concentration entered as a weight fraction. Only used when doing diffusion calculations.

<Propagate criterion='1' direction='0' traction='1'/>
<AltPropagate criterion='7' direction='4' traction='1'/>

These properties let each material have a different primary and secondary propagation criterion and/or directions than the ones defined in the <a href="mpmheader.html">MPM Header</a>. Set these criterion as described for the <a href="mpmheader.html#propagate">Propagate</a> and <a href="mpmheader.html#altpropagate">AltPropagate</a> commands in the <a href="mpmheader.html">MPM Header</a>. To activate propagation:

1. The <a href="mpmheader.html">MPM Header</a> must have a <a href="mpmheader.html#propagate">Propagate</a> command.
2. The <a href="mpmheader.html">MPM Header</a> can optionally have an <a href="mpmheader.html#altpropagate">AltPropagate</a> command.
3. Any material can override the default primary and/or secondary criteria by using a Propagate and/or AltPropagate command within its material defintion. Even if the <a href="mpmheader.html">MPM Header</a> does not have an <a href="mpmheader.html#altpropagate">AltPropagate</a> command, a material can add a secondary criterion with its own AltPropagate command.

<KIc>2.3</KIc>

Critical mode I stress intensity factor (in MPa m^1/2). Only used when there is crack propagation with <a href="mpmheader.html#cracks">criteria</a> 1, 4, or 5.

<KIexp>2.3</KIexp>

Exponent p in the elliptical criteria for crack growth. Only used for crack propagation with <a href="mpmheader.html#cracks">criterion</a> 5.

<KIIc>1.2</KIIc>

Critical mode II stress intensity factor (in MPa m^1.2). Only used when there is crack propagation with <a href="mpmheader.html#cracks">criterion</a> 5.

<KIIexp>2.3</KIIexp>

Exponent q in the elliptical criteria for crack growth. Only used for crack propagation with <a href="mpmheader.html#cracks">criterion</a> 5.

<JIc>2.3</JIc>

Critical mode I energy release rate (in J/m²). Only used when there is crack propagation with <a href="mpmheader.html#cracks">criteria</a> 2, 3, or 7. For criterion 2, it is only used if the initTime is not being used. Also used by <a href="#traction">traction-law</a> materials.

<JIIc>1.2</JIIc>

Critical mode II energy release rate (in J/m²). Currently only used by <a href="#traction">traction-law</a> materials.

<nmix>2</nmix>

A parameter used in some mixed-mode failure laws (e.g., to implement failure when (G_I/J_Ic)^nmix + (G_II/J_IIc)^nmix = 1 in <a href="#traction">TriangularTraction</a> cohesive law).

<initTime>3</initTime>

Time (in ms) to start crack growht. Only used when there is crack propagation with <a href="mpmheader.html#cracks">criteria</a> 2. For criterion 2, initTime takes precidence of a JIc property.

<speed>5</speed>

Define the constant crack speed (in m/sec). This speed, however, is only active when there is crack propagation with <a href="mpmheader.html#cracks">criterion</a> 2.

<maxLength>20</maxLength>

Define the maximum length of the crack (in mm). The crack growth will stop when this length is reached. This limit, however, is only active when there is crack propagation with <a href="mpmheader.html#cracks">criterion</a> 2.

<gamma>.5</gamma>

Only used when there is crack propagation with <a href="mpmheader.html#cracks">criterion</a> 3. Still in development and not meant for general use.

<p>.5</p>

Only used when there is crack propagation with <a href="mpmheader.html#cracks">criterion</a> 3. Still in development and not meant for general use.

<gain>10e5</gain>

Only used when there is crack propagation with <a href="mpmheader.html#cracks">criterion</a> 3. Still in development and not meant for general use.

<xGrow>20</xGrow> and <yGrow>0</yGrow>

These properties (one or both with default 0) specify a unit vector for a constant crack growth direction. They only apply for crack propagation with <a href="mpmheader.html#cracks">criterion</a> 2 and then only when that criterion selects the default propagation direction. The result is constant crack growth direction regardless of stress state or crack tip orientation. Any input vector will be normalized to a unit vector. If constant crack growth directions with a <a href="cracks.html">fixed crack</a> are located precisely on grid lines, it is possible for the crack algorithm to not recognize the crack plane. It is better to move such a crack sligthly off grid lines.

<delIc>0.1</delIc> and <delIIc>0.1</delIIc>

Critical crack opening displacement. Only used when there is crack propagation by <a href="mpmheader.html#cracks">criterion</a> 6. Also used by <a href="#traction">traction-law</a> materials.

<a name="artificialvisc"></a><ArtificialVisc/>, <avA1>.2</avA1>, and <avA2>2.0</avA2>

This first empty tag turns artificial visocsity on, which adds a pressure, Q, related to velocity gradient on the particle, but only when it is compressing. The equation is

Q = Δx*|D_kk|*(A1*C + A2*Δx*|D_kk|)

where Δx is the cell size of the mesh, |D_kk| is the relative volume change rate, C is the bulk wave speed in the material, and A1 and A2 are adjustable constants, which are entered using the above <avA1> and <avA2> commands. The defaults are off, A1=0.2, and A2=2.0. It is common, but not required, to choose A2 = 10*A1.
    The artificial viscosity property is supported in some materials (as documented under each material). If you use these commands in a material that does not support, an error will result.

<a name="friction"></a><Friction mat='2'>0.3</Friction>

This command within a material definition allows multimaterial mode to have different contact laws between different pairs of materials. Set the contact law as explained for <a href="mpmheader.html#friction">Friction command</a> in the <a href="mpmheader.html#cracks">Cracks section of the MPM header</a> except that a setting less than -10 means to assume materials are always in contact and revert to single material mode. The mat attribute defines contact mechanics between this material and the one listed (self contact is ignored). Alternatively, the other material can be specified by name using a matname attribute as explained <a href="definematl.html#usemats">here</a>. If a node has more than two materials, the contact law used will be one between each material and the other material with the most volume.
    You only need to set friction on one of the materials in a pair. If you set both, the setting for the second material will override the one from the first material.

<color red='0.1' green='0.5' blue='0.3' alpha='1.0/>

Sets the color of the material with red, green, blue, and alpha values between 0.0 and 1.0. The color may be used by post-analysis software, but it has no affect on the calculations.