Difference between revisions of "Traction Laws"
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MPM implements [[Defining Cracks|explicit cracks]] by defining a series or massless particles that define the crack path. The method is called the CRAMP algorithm.<ref name='CRAMP'>J. A. Nairn, "Material Point Method Calculations with Explicit Cracks," <i>Computer Modeling in Engineering & Sciences</i>, <b>4</b>, 649-664 (2003). ([http://www.cof.orst.edu/cof/wse/faculty/Nairn/papers/MPMCracks.pdf See PDF])</ref> The CRAMP algorithm takes care of the crack geometry and can handle [[Friction#Friction on Explicit Cracks|crack-surface contact]] or [[Imperfect Interfaces#Imperfect Interfaces on Explicit Cracks|imperfect interface]] contact. In addition, MPM can implement traction laws on the crack surfaces by assigning a traction laws to one or more crack particles along the crack. The traction laws can be assigned when [[Defining Cracks|creating the crack]] or during [[Crack Propagation Commands|crack propagation]] (''i.e''., new crack surfaces can be dynamically create traction laws). | MPM implements [[Defining Cracks|explicit cracks]] by defining a series or massless particles that define the crack path. The method is called the CRAMP algorithm.<ref name='CRAMP'>J. A. Nairn, "Material Point Method Calculations with Explicit Cracks," <i>Computer Modeling in Engineering & Sciences</i>, <b>4</b>, 649-664 (2003). ([http://www.cof.orst.edu/cof/wse/faculty/Nairn/papers/MPMCracks.pdf See PDF])</ref> The CRAMP algorithm takes care of the crack geometry and can handle [[Friction#Friction on Explicit Cracks|crack-surface contact]] or [[Imperfect Interfaces#Imperfect Interfaces on Explicit Cracks|imperfect interface]] contact. In addition, MPM can implement traction laws on the crack surfaces by assigning a traction laws to one or more crack particles along the crack. The traction laws can be assigned when [[Defining Cracks|creating the crack]] or during [[Crack Propagation Commands|crack propagation]] (''i.e''., new crack surfaces can be dynamically create traction laws). | ||
Traction laws have several uses. The most common is to implement cohesive zones where the traction laws will naturally debond if the critical opening displacements are reached. When | Traction laws have several uses. The most common is to implement cohesive zones where the traction laws will naturally debond if the critical opening displacements are reached. When they are modeling cohesive zones, the visualization tools can plot total crack length or debonded crack length (which is length with no traction laws). Their difference is the length of crack surface with traction law materials still bonded. The tools can also plot the opening and shear displacements at the actual crack tip or the transtion from debonded crack into the traction zone. | ||
This section explains the possible traction laws. See the [[Defining Cracks|crack creation]] and [[Crack Propagation Commands|crack propagation commands]] for how to use traction laws on cracks. | This section explains the possible traction laws. See the [[Defining Cracks|crack creation]] and [[Crack Propagation Commands|crack propagation commands]] for how to use traction laws on cracks. | ||
Revision as of 18:10, 6 January 2014
Traction laws can be placed on crack surfaces to model cohesive zones.
Introduction
MPM implements explicit cracks by defining a series or massless particles that define the crack path. The method is called the CRAMP algorithm.[1] The CRAMP algorithm takes care of the crack geometry and can handle crack-surface contact or imperfect interface contact. In addition, MPM can implement traction laws on the crack surfaces by assigning a traction laws to one or more crack particles along the crack. The traction laws can be assigned when creating the crack or during crack propagation (i.e., new crack surfaces can be dynamically create traction laws).
Traction laws have several uses. The most common is to implement cohesive zones where the traction laws will naturally debond if the critical opening displacements are reached. When they are modeling cohesive zones, the visualization tools can plot total crack length or debonded crack length (which is length with no traction laws). Their difference is the length of crack surface with traction law materials still bonded. The tools can also plot the opening and shear displacements at the actual crack tip or the transtion from debonded crack into the traction zone.
This section explains the possible traction laws. See the crack creation and crack propagation commands for how to use traction laws on cracks.
The use of traction laws on MPM cracks is described in Nairn (2009)[2] and used in Bardenhagen et al. (2011)[3] and Matsumoto and Nairn (2012).[4]
Define a Traction
You create traction law materials using a Material command block. Within that block all traction properties are set using property commands. Refer to each traction law type to learn about its possible properties.
For normal opening, traction laws only apply traction when a cracked is opened. The crack contact mechanics handles the case where the crack surfaces are in contact. For shear opening, the traction law applies forces in both directions. To avoid conflict between contact and tractions, the crack surface contact must use frictionless sliding. In fact any crack with traction laws will automatically convert to a frictionless crack regardless of settings you use for the crack's contact condition. Besides creating cracks with traction laws, you can also assign traction laws to new crack surfaces that are created when a crack propagates. The propagation traction law can be assigned globally or specifically for a given material type. Since a crack that starts with no traction laws, but creates them when it propagates, will not automatically convert to a frictionless crack, you should be sure that all such cracks are setup to use frictionless crack contact.
In addition, for planar 2D calculations you must specify the crack thickness using a Thickness command.
Traction Law Materials
References
- ↑ J. A. Nairn, "Material Point Method Calculations with Explicit Cracks," Computer Modeling in Engineering & Sciences, 4, 649-664 (2003). (See PDF)
- ↑ J. A. Nairn, "Analytical and Numerical Modeling of R Curves for Cracks with Bridging Zones" Int. J. Fracture, 155, 167-181 (2009). (See PDF)
- ↑ S. G. Bardenhagen, J.A. Nairn, and H. Lu, "Simulation of dynamic fracture with the Material Point Method using a mixed J-integral and cohesive law approach," Int. J. Fracture, 170, 49-66.
- ↑ J.A. Nairn, "Fracture Toughness of Wood and Wood Composites During Crack Propagation," Wood and Fiber Science, 44, 121-133 (2012).