User defined MPC
I am using an MPC subroutine (ABAQUS Standard) that will allow me to release nodes along the line of symmetry which also happens to be my defined crack-path when the strain at that point crosses a critical value. This is to simulate crack propagation using the Critical Plastic Strain Fracture Mechanics Model (CPFSM) / Rice-Tracey model.
I am having trouble in defining the MPC in my *.inp file as I am unaware of as to how to define the nodes upon which I intend to impose the MPC. The manual instructs one to type the individual nodes following the command line:
*MPC, USER, MODE=DOF
I would be glad if anyone could tell me how am I supposed to define the nodes in the line following the above command line. Also, if anybody has done something similiar to what I have done, I would be glad if you could send me a specimen *.inp and MPC subroutine.
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Guidance needed on user defined MPC
To be more specific, I have written an USDFLD subroutine defining my damage parameter which I will then be using within the MPC. If the multi-axial plastic strain value at the crack-tip crosses this damage value, the MPC is instructs all DOF of the node to be released. I am sure this is on par with what many other people do in order to simulate crack propagation.
Also, note that I am 'not' using Cohesive elements at all which rules out me using a separation law. This is my attempt to incorporate the Rice-Tracey model for crack propagation.
Is it the way I have framed
Is it the way I have framed the question that makes my query go unanswered? I strongly believe in the forum's know-how and expertise pool. I am sure this is not a very difficult question for many here who often use MPCs for their analysis in Abaqus.
I require a little guidance on as to how the nodes are referenced within the MPC. I have written the logic behind my node release,ie., if damage crossed 1 ahead of the crack-tip, all DOFs in the node should be released. Assume that my crack-path is defined along the line of symmetry (U2=0) and are numbered from 100 through 200. I just want to know as to how the IEL card is used within the MPC to refer to these nodes and as to how these nodes are externally defined in the *.inp file. I am persisting on this query as I am unable to get convincing information in the manuals, especially on execution of user MPC.
I would be very grateful if I am simply shown a path on accomplishing this or some reference material that I could go through. This is a bottleneck for the completion of a lot of work that has gone into realising CPFSM / Rice-Tracey model in an FE simulation of crack propagation in a simple DCB test.