Generate cracks by duplicating nodes

[tfc1992]

Dear Moose user,
I am learning the phase field modeling of fracture using moose. And I want to create a pre-crack by duplicating the nodes. how do I realize it in moose? any examples available? Many thanks.

[ngrilli]

Dear @tfc1992

I believe this must be done in gmsh.
You can create "Point" and "Line" and "Line Loop" manually in the .geo file
You don't need to duplicate nodes, just define two different "Line" along the same segment
and define "Line Loop" by adding the two "Line" one after the other.
In this way the nodes on the two "Line" will be independent.
I paste below and example of .geo file, but it's not for crack, you will need to modify it.
Hope this helps.

Best Regards,
Nicolò Grilli

//Points
Point(1) = {0, 0, 0, 10};
Point(2) = {100, 0, 0, 10};
Point(3) = {600, 0, 0, 10};
Point(4) = {700, 0, 0, 10};
Point(5) = {700, 500, 0, 10};
Point(6) = {500, 500, 0, 10};
Point(7) = {200, 500, 0, 10};
Point(8) = {0, 500, 0, 10};
Point(9) = {100, 200, 0, 10};
Point(10) = {200, 200, 0, 10};
Point(11) = {200, 300, 0, 10};
Point(12) = {500, 300, 0, 10};
Point(13) = {500, 200, 0, 10};
Point(14) = {600, 200, 0, 10};
Point(15) = {700, 200, 0, 10};
Point(16) = {0, 200, 0, 10};
Point(17) = {200, 0, 0, 10};
Point(18) = {500, 0, 0, 10};
Point(19) = {50, 0, 0, 10};
Point(20) = {50, 200, 0, 10};
Point(21) = {50, 500, 0, 10};

//Lines

Line(1) = {8, 21};
Line(2) = {21, 7};
Line(3) = {7, 6};
Line(4) = {6, 5};
Line(5) = {5, 15};
Line(6) = {15, 4};
Line(7) = {4, 3};
Line(8) = {3, 18};
Line(9) = {18, 17};
Line(10) = {17, 2};
Line(11) = {2, 19};
Line(12) = {19, 1};
Line(13) = {1, 16};
Line(14) = {16, 8};
Line(15) = {7, 11};
Line(16) = {11, 10};
Line(17) = {10, 9};
Line(18) = {9, 20};
Line(19) = {20, 16};
Line(20) = {6, 12};
Line(21) = {12, 13};
Line(22) = {13, 14};
Line(23) = {14, 15};
Line(24) = {3, 14};
Line(25) = {13, 18};
Line(26) = {2, 9};
Line(27) = {10, 17};
Line(28) = {11, 12};
Circle(29) = {9, 10, 11};
Circle(30) = {14, 13, 12};
Line(31) = {10, 13};
Line(32) = {19, 20};
Line(33) = {20, 21};

// Line Loops

Line Loop(101) = {1, -33, 19, 14};
Plane Surface(201) = {101};
Line Loop(102) = {2, 15, -29, 18, 33};
Plane Surface(202) = {102};
Line Loop(103) = {3, 20, -28, -15};
Plane Surface(203) = {103};
Line Loop(104) = {4, 5, -23, 30, -20};
Plane Surface(204) = {104};
Line Loop(105) = {16, 17, 29};
Plane Surface(205) = {105};
Line Loop(106) = {28, 21, -31, -16};
Plane Surface(206) = {106};
Line Loop(107) = {-30, -22, -21};
Plane Surface(207) = {107};
Line Loop(108) = {12, 13, -19, -32};
Plane Surface(208) = {108};
Line Loop(109) = {11, 32, -18, -26};
Plane Surface(209) = {109};
Line Loop(110) = {27, 10, 26, -17};
Plane Surface(210) = {110};
Line Loop(111) = {25, 9, -27, 31};
Plane Surface(211) = {111};
Line Loop(112) = {8, -25, 22, -24};
Plane Surface(212) = {112};
Line Loop(113) = {6, 7, 24, 23};
Plane Surface(213) = {113};

// Transfinite Line

Transfinite Line {7, 8, 10, 23, 22, 17, 16, 21, 29, 30} = 11 Using Progression 1;
Transfinite Line {6, 24, 25, 27, 26, 32, 13, 15, 20, 4} = 21 Using Progression 1;
Transfinite Line {9, 31, 28, 3, 5, 14, 33} = 31 Using Progression 1;
Transfinite Line {11, 12, 18, 19, 1} = 6 Using Progression 1;
Transfinite Line {2} = 16 Using Progression 1;

// Transfinite Surface

Transfinite Surface {201};
//Transfinite Surface {202};
Transfinite Surface {203};
//Transfinite Surface {204};
//Transfinite Surface {205};
Transfinite Surface {206};
//Transfinite Surface {207};
Transfinite Surface {208};
Transfinite Surface {209};
Transfinite Surface {210};
Transfinite Surface {211};
Transfinite Surface {212};
Transfinite Surface {213};

// Recombine Surface

Recombine Surface {201};
Recombine Surface {202};
Recombine Surface {203};
Recombine Surface {204};
Recombine Surface {205};
Recombine Surface {206};
Recombine Surface {207};
Recombine Surface {208};
Recombine Surface {209};
Recombine Surface {210};
Recombine Surface {211};
Recombine Surface {212};
Recombine Surface {213};

// Physical Line

Physical Line("top") = {1, 2, 3, 4};
Physical Line("right") = {5, 6};
Physical Line("bottom") = {7, 8, 9, 10, 11, 12};
Physical Line("left") = {13, 14};

// Physical Surface

Physical Surface("sylgard") = {201, 202, 203, 204, 208, 209, 213};
Physical Surface("hmx") = {205, 206, 207, 210, 211, 212};

[ngrilli]

Dear @tfc1992
You can definitely reproduce that result in figure 6 with MOOSE.
It seems the crack surfaces in that figure are not coincident, so you can built a domain where the crack has already an opening
and you model the initial crack tip as a semi-sphere, you will see stress concentration at the tip and then the phase field =1 region will appear.
Please let us know which results you see in your simulations and share input file, otherwise it is difficult to help
Best Regards,
Nicolò Grilli
National University of Singapore

[tfc1992]

Dear @ngrilli Thank you for your help. Inspired by the method you proposed, I just got it in gmsh. Here is the .geo file. However, I haven't developed the moose input file yet. Actually, I am a new moose user.

Point(1) = {0, 0, 0, 1.0};
//+
Point(2) = {0.5, 0, 0, 1.0};
//+
Point(3) = {1, 0, 0, 1.0};
//+
Point(4) = {1, 0.5, 0, 1.0};
//+
Point(5) = {1, 1, 0, 1.0};
//+
Point(6) = {0.5, 1, 0, 1.0};
//+
Point(7) = {0, 1, 0, 1.0};
//+
Point(8) = {0, 0.5, 0, 1.0};
//+
Point(9) = {0.5, 0.5, 0, 1.0};
//+
Point(10) = {-0, 0.5, 0, 1.0};
//+
Line(1)={1,2};
//+
Line(2) = {2, 3};
//+
Line(3) = {3, 4};
//+
Line(4) = {4, 5};
//+
Line(5) = {5, 6};
//+
Line(6) = {6, 7};
//+
Line(7) = {7, 8};
//+
Line(8) = {8, 9};
//+
Line(9) = {9, 10};
//+
Line(10) = {10, 1};
//+
Physical Curve("top") = {6, 5};
//+
Physical Curve("left") = {7, 10};
//+
Physical Curve("right") = {4, 3};
//+
Physical Curve("bottom") = {1, 2};
//+
Line(11) = {9, 6};
//+
Line(12) = {9, 4};
//+
Line(13) = {9, 2};
//+
Curve Loop(1) = {7, 8, 11, 6};
//+
Plane Surface(1) = {1};
//+
Curve Loop(2) = {5, -11, 12, 4};
//+
Plane Surface(2) = {2};
//+
Curve Loop(3) = {13, 2, 3, -12};
//+
Plane Surface(3) = {3};
//+
Curve Loop(4) = {9, 10, 1, -13};
//+
Plane Surface(4) = {4};
//+
Transfinite Curve {7, 11, 6, 8} = 100 Using Progression 1;
//+
Transfinite Curve {5, 11, 4, 12} =100 Using Progression 1;
//+
Transfinite Curve {3, 13, 12, 2} = 100 Using Progression 1;
//+
Transfinite Curve {9, 10, 13, 1} = 100 Using Progression 1;
//+
Transfinite Surface {1};
//+
Transfinite Surface {2};
//+
Transfinite Surface {3};
//+
Transfinite Surface {4};
//+
Recombine Surface {1};
//+
Recombine Surface {2};
//+
Recombine Surface {3};
//+
Recombine Surface {4};

[ngrilli]

Dear @tfc1992

There are lot of ready input file for phase field fracture here:
https://github.com/idaholab/moose/tree/next/modules/combined/test/tests/phase_field_fracture

You just need to import your mesh using the FileMeshGenerator object
and assign "physical surfaces" in gmsh to apply boundary conditions in MOOSE

Best Regards,
Nicolò Grilli
National University of Singapore

[tfc1992]

Dear @ngrilli Many thanks. I found it.

Best Regards,
Fucheng Tian

[RWTHLHK]

@tfc1992 Dear Fucheng, I also need the same mesh urgently. But it always reports an error when I import the mesh generated by your .geo file. It always says the boundary top can't be found... And I checked the mesh using peacock, the top, bottom, and so on are blocks not boundaries...

[dschwen]

An easy hack is to precrack along a boundary by constraining displacements only for part of the boundary (the remaining unconstrained part is the crack).

[tfc1992]

Dear @dschwen , Thanks for your response. I tried this, but it won't work if the crack is not located at the boundary.

[jiangwen84]

To prescribe an initial crack for phase-field fracture in MOOSE, you can

1. Use meshing software, such as gmsh and Cubit, to explicitly mesh the crack by either duplicating nodes or creating non-overlapping crack surfaces.
2. You can use damage variable itself to prescribe the crack, and use either history variable approach or variational inequality solver to enforce the irreversibility of your initial crack.
3. Use XFEM capability to cut your mesh and represent the crack. Add the following blocks into your input. XFEM doesn't work with mesh adaptivity though.

[XFEM]
qrule = volfrac
output_cut_plane = true
[]

[UserObjects]
[./line_seg_cut_uo]
type = LineSegmentCutUserObject
cut_data = '0.5 1.0 0.5 0.5' #cut_data = 'x0 y0 x1 y1' and segment defined by point(x0,y0) and point(x1 y1) #
time_start_cut = 0.0
time_end_cut = 0.0
[../]
[]

[tfc1992]

Dear @jiangwen84 Thanks for your good suggestion. Under the help of @ngrilli, I solved this problem in Gmsh. But, I will try the second method you provided.

Best Regards,
Fucheng Tian

[GregVernon]

@tfc1992,

@jiangwen84 provides several great methods. If you are interested in his first suggestion, please know that you can get a free copy of Coreform Cubit Learn for non-commercial use, or a free-trial of Coreform Cubit for commercial use. I recently helped a group from SDSU build a mesh for a geological fault - which is essentially a crack - by duplicating nodes as you've described. I'd be happy to assist you with this approach if you're interested.

Link: https://coreform.com/products/coreform-cubit/

Best regards,

Greg Vernon
Director of Product Management
Coreform LLC