I am trying to model a Micropipette Aspiration experiment, which is in fact creeping of a portion of a hyperelastic thin wall spherical membrane into a rigid pipette as a result of applying negative pressure (suction) through the pipette.
I obtained the equibiaxial data from my experiments and accordingly defined the test data in the Material properties section in ABAQUS. The problem is although in reality (experiment), there is up to 50 % nominal areal strain (in the portion of sphere which is sucked into the pipette), my FE model in abaqus/standard (quasi-static solution) would be aborted after experiencing 7% areal strain with unknown errors and warnings such as
I have used almost all possible hyperelastic models in my FE analysis (to find which is the best fit) but they didn’t work out and they all got aborted in the same point of running. Also, I have tried different contact conditions and considering different steps of solution but they didn’t work for me so far.
Does anybody think that I should write any subroutine (UMAT,…) to sort this problem out? If yes, which one? Given that I am new in using ABAQUS, I would be grateful if anybody could kindly send me any file/tutorial in this regard or point me to the correct direction.
For your further consideration, I have also attached a figure of the experiment I am trying to simulate.
Any guide or suggestion would be much appreciated.
Many thanks in advance.
Navid
Hi Marat.
Many thanks for your comment. The problem with Explicit is I do not have the density. I have also tried different density values, but they have the same problem with different errors. I have already refined the mesh near the contact area and high deformed area, but no success.
I always receive these warnings with Standard solution before the job abortion:
***WARNING: THE AVERAGE FORCE USED TO ENFORCE CONTACT CONSTRAINTS AT NODE
LIPOSOME-SOLID-1.1 IS 347.492E+03 TIMES LARGER THAN THE AVERAGE
ON THE OTHER ELEMENTS IN THE MODEL.
AVERAGE MOMENT 1.783E-13 TIME AVG. MOMENT 1.000E-02
ALL MOMENT RESIDUALS ARE ZERO
LARGEST INCREMENT OF ROTATION -3.475E-46 AT NODE 1 DOF 6
INSTANCE: PART-4-1
LARGEST CORRECTION TO ROTATION -2.264E-49 AT NODE 1 DOF 4
INSTANCE: PART-4-1
THERE IS ZERO MOMENT EVERYWHERE
***WARNING: THERE IS ZERO MOMENT EVERYWHERE IN THE MODEL BASED ON THE DEFAULT
CRITERION. PLEASE CHECK THE VALUE OF THE AVERAGE MOMENT DURING THE
CURRENT ITERATION TO VERIFY THAT THE MOMENT IS SMALL ENOUGH TO BE
TREATED AS ZERO. IF NOT, PLEASE USE THE SOLUTION CONTROLS TO RESET
THE CRITERION FOR ZERO MOMENT.
Thanks again.
Navid
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