Common Material Properties
These material properties are common to all types of materials used in MPM simulations.
Basic Properties
These are basic material properties.
| Property | Description | Units | Default |
|---|---|---|---|
| rho | The material's density | g/cm3 | 1 |
| csat | The saturation concentration potential as a weight friction from 0 to 1. it is only used when doing diffusion calculations. | none | 1 |
| Cv | The constant-volume heat capacity. It is used when doing conduction calculations and/or coupled mechanical energy and by some material constitutitive laws. You do not need to enter a constant pressure heat capacity (which is need in conductivity equations) because material models calculates it from Cv and thermodynamic relations for the difference between Cp and Cv | J/(kg-K | 1 |
Fracture Toughness Properties
These properties set material properties that determine the fracture toughness of the material and control various aspects of crack propagation.
| Property | Description | Units | Default |
|---|---|---|---|
| JIc | Critical energy release rate fracture toughness for mode I. It is only used for crack propagation by criteria 2, 3, or 7. For criterion 2, it is only used if initTime is not specified. It is also used to set toughness of traction law materials. | J/m2 | none |
| JIIc | Critical energy release rate fracture toughness for mode II. It is currently only used to set toughness of traction law materials. | J/m2 | none |
| KIc | Critical mode I stress intensity factor. It is only used for crack propagation by criteria 1, 4, or 5. | MPa m1/2 | none |
| KIIc | Critical mode II stress intensity factor. It is only used for crack propagation by criteria 1, 4, or 5. | MPa m1/2 | none |
| KIexp | Exponent p in the elliptical criteria for crack growth. It is only used for crack propagation by criterion 5. | none | 2 |
| KIIexp | Exponent q in the elliptical criteria for crack growth. It is only used for crack propagation by criterion 5. | none | 2 |
| delIc | Critical crack opening displacement for mode I. Only used for crack propagation by criterion 6. It is also used by traction-law materials. | mm | none |
| delIIc | Critical crack opening displacement for mode II. Only used for crack propagation by criterion 6. It is also used by traction-law materials. | mm | none |
| initTime | The time when crack propagation starts. It is only used for crack propagation by criterion 2. For criterion 2, when initTime is specified, takes precedence over the JIc property. | ms | none |
| speed | The crack speed in steady state crack propagation. This speed, however, is only active for crack propagation by criterion 2. (also used in criterion 3 as an initial crack speed, but that criterion is not meant for general use) | m/sec | 1 |
| maxLength | The maximum crack length for steady state crack propagation. The simulation will stop soon after crack reaches the input length. This length, however, is only active for crack propagation by criterion 2. | mm | none |
| nmix | An exponent used in mixed-modes failure of some traction laws. | none | 1 |
| gamma | Crack surface energy. It is only used for crack propagation by criterion 3, which is in development and not meant for general use. | J/m2 | none |
| p | Irreversible energy term in energy balance crack growth and probably should be between 0 and 1. It is only used for crack propagation by criterion 3, which is in development and not meant for general use. | none | 1 |
| gain | Gain used in feedback loop to maintain energy balance during crack growth. It is only used for crack propagation by criterion 3, which is in development and not meant for general use. | 1e5 | 1 |
Crack Propagation Properties
The setting of crack propagation properties are done differently for scripted and XML files. For scripted commands, you can set the following material properties:
| Property | Description | Units | Default |
|---|---|---|---|
| criterion | To set a custom crack propagation criterion. You can use any propagation option. Setting this property in a material overrides the default propagation criterion setting. This command is for scripted files only; see below to set criterion in XML files. | none | none |
| direction | To set a custom crack propagation direction. You can use any direction option. Setting this property in a material overrides the default propagation direction setting. This command is for scripted files only; see below to set traction in XML files. | none | none |
| traction | To set a custom traction law to create for crack propagation in this material. A traction law set in a material overrides the default traction law. The traction law can be set by material ID (if the traction law has already been defined) or by number (if it is not defined yet). This command is for scripted files only; see below to set criterion in XML files. | none | none |
| altcriterion | Same as "criterion" property above except that it applies to the alternate propagation criterion for the material | none | none |
| altdirection | Same as "direction" property above except that it applies to the alternate propagation criterion for the material | none | none |
| alttraction | Same as "traction" property above except that it applies to the alternate propagation criterion for the material | none | none |
| xGrow | This property along with yGrow (if on one given the other is set to 0) specify a unit vector for a constant crack growth direction. t is only used for crack propagation by criterion 2 and then only if that criterion is using its default propagation direction. The result is a constant crack growth direction regardless of stress state or crack tip orientation. Any input vector will be normalized to a unit vector. If a constant crack growth direction with a fixed crack is located precisely on grid lines, it is possible the crack algorithm will not recognize the crack plane. Is it better to move such a crack slightly off grid lines. | none | none |
| yGrow | Crack growth direction - see xGrow above. | none | none |
| constantTip | Set to 0 or 1. The default of 0 means the crack tip will track the material around the crack tip. Changing it to 1 means crack tips with this material will always use this material even if the crack propagates into another material. The default 0 allows modeling crack growth in composites with fracture properties changing as cracks move between materials. Using 1 allows modeling multiple cracks in the same material having different fracture propertie by using the following steps:
|
none | 0 |
Propagation Properties in XML Files
In XML files, the criterion, direction, and traction properties (and the analogous alternate propagation properties) are set differently. To set crack propagation criteria, you use instead
<Propagate criterion='(critNum)' direction='(dirNum)' traction='(traction)'/> <AltPropagate criterion='(critNum)' direction='(dirNum)' traction='(traction)'/>
where the settings are the same as defined in the default crack propagation commands (or the alternate propagation command), but the XML element is now used within a <Material> definition instead of within the <Cracks> element in the <MPMHeader>.
Contact Properties
These properties can set custom friction and interface properties between two specific materials. If these properties are not used, material-to-material contact and interface will use the global friction and interface propertties.
| Property | Description | Units | Default |
|---|---|---|---|
| Friction | A Friction property within a material definition can define custom frictional properties for multimaterial mode MPM contact between the current material and another material. This property takes two parameters; the first is the same as for the standard Friction command and the second gives the other material. | none | none |
| Interface | An Interface property within a material definition can define custom imperfect interface parameters properties for multimaterial mode MPM contact between the current material and another material. | none | none |
In scripted files, the other material is specified by its material ID, which means the Friction and Interface properties must be used in the secondly-defined materials (such that material ID for the first material is available). In XML files, the second material is defined by number (or by name) using a mat or matname attribute.
Script Notes
The following material properties are common to all types of materials, although not used by all materials. These properties are only used in MPM analyses.
CporCvfor heat capacity (in J/(kg-K)). Heat capacity is used when doing <a href="conduction.html">conduction calculations and/or coupled mechancial energy</a> adn by some material models. BothCpandCvset 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="artificialvisc"></a>
ArtificialVisccan beonoroffto turn artificial viscosity on. When it is on, it adds a pressure, Q, related to velocity gradient on the particle, but only when it is compressing. The equation isQ = Δx*|Dkk|*(A1*C + A2*Δx*|Dkk|)
where Δx is the cell size of the mesh, |Dkk| 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
avA1andavA2properties. The defaults are artificial viscosity 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. avA1andavA2to set the coefficients when artficial viscosity is on.color 0.1,0.5,0.2,1.0: Sets the color of the material with the four arguments being red, green, blue, and alpha values between 0.0 and 1.0. A single argument can be used instead to set gray level between 0.0 and 1.0 (with alpha=1.0). Three arguments set red, green, and blue with alpha=1.0. The color is used in <a href="../movieplots.html">material point method plots</a> of <a href="../quantities.html">material type</a>. If no color is provided, a color will be picked from the current spectrum using the material number.
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
- <a name="csat"></a><csat>0.5</csat>
- The material's saturation concentration entered as a weight fraction. Only used when doing diffusion calculations.
- <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*|Dkk|*(A1*C + A2*Δx*|Dkk|)
where Δx is the cell size of the mesh, |Dkk| 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
matattribute defines contact mechanics between this material and the one listed (self contact is ignored). Alternatively, the other material can be specified by name using amatnameattribute 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.