I am trying to solve a structural problem but solution doesn’t converge or some elements become distorted. Basically, a flat ended indenter punches a very soft material. I am using a Neo-Hookean hyperelastic model. <\/p>\n
Since there are too many variables to change in the indenter to get a converged solution, I am testing the basis of the problem with a very simplified model. This second model is a cylinder of Neo-Hookean hyperelastic material in which radius and height are equals. The model takes advantage of its axial symmetry to solve faster.<\/p>\n
The lower circular base of the cylinder is fixed (Uy=0) and the upper circular base can be loaded in two alternative ways: either by displacing downwards the upper circular base; or by applying a pressure on it. <\/p>\n
When I set the model in “displace mode”, I can obtain easily a solution even compressing the cylinder an 80% of its height. For this displacement, the Y-component of stress allows to calculate the weight necessary to obtain the same displacement (1.637 Kg).<\/p>\n
However, when I set the model in “weight mode” and load the upper tap with 1.637 Kg, solver terminates by “error in element formulation” or “unconverged solution”. I only get to compress the material a 28%.<\/p>\n
The question is… WHY? Both problems (displace mode and weight mode) are the same in terms of element and material capacities, but the second fails. I think that my original and complex problem to which I referred to in the first paragraph fails because of the same reason that this simplified model. <\/p>\n
Thanks in advance!<\/p>\n
The code is:<\/p>\n
FINISH
\/CLEAR,START
\/PREP7<\/p>\n
!*****CONTROL PANEL: HERE YOU CAN CHANGE MODEL PARAMETERS.<\/p>\n
!Geometry parameters:
Height=0.01 !Cylinder Height (m)
Radius=Height !Cylinder Radius (m)
NEle=10 !Number of elements at each lines of the model.<\/p>\n
!Material model
EX01=30000 !Young Modulus (this data is used later only to assess the equivalent Neo-Hookean model parameters)
PRXY01=0.49 !Poisson’s Ratio<\/p>\n
!Load Parameters
ByWeight=1 !If 1, a uniform weight is applied on the upper cylinder tap. If 0, a downward displacement is applied.
Weight=1.637 !Weight in Kg.
Displac=-0.8 !If negative, downward displacement divided by cylinder Height.<\/p>\n
!Time Control
Time_sim=1 !Simulation Time. Loads are ramped along the simulation time. <\/p>\n
!*****END OF THE CONTROL PANEL<\/p>\n
!MATERIAL SECTION<\/p>\n
nhmu01=EX01\/2\/(1+PRXY01) !This is the “mu” parameter of the Neo-Hookean model
nhK01=EX01\/3\/(1-2*PRXY01) !This is the “k” parameter of the Neo-Hookean model, Bulk modulus
nhd01=2\/nhK01 !This is the “d” parameter of the Neo-Hookean model<\/p>\n
TB,HYPE,1,1,2,NEO
TBTEMP,0
TBDATA,,nhmu01,nhd01,,,, <\/p>\n
!***ELEMENT DEFINITION<\/p>\n
ET,1,PLANE183
!*
KEYOPT,1,1,0 !Cuadrilateral element shape
KEYOPT,1,3,1 !Axisymmetric element behavior
KEYOPT,1,6,0 !Pure displacement for element formulation.<\/p>\n
!****MODEL CONSTRUCTION<\/p>\n
BLC4,0,0,Radius,Height,<\/p>\n
!****MODEL MESHING<\/p>\n
MSHAPE,0,2D
MSHKEY,1
MAT,1<\/p>\n
LESIZE,1,,,NEle,,,,
LESIZE,2,,,NEle,,,,
LESIZE,3,,,NEle,,,,
LESIZE,4,,,NEle,,,,
AMESH,1,,<\/p>\n
!SETTING THE MECHANICAL CONSTRICTIONS
DL,1,,UY,0
DL,4,,UX,0<\/p>\n
FINISH
\/SOLU<\/p>\n
ANTYPE,STATIC !Static Analysis.
NLGEOM, ON !Large Deformation<\/p>\n
OUTRES,ALL,ALL, !all data to inspect the solution<\/p>\n
*IF,ByWeight,EQ,1,THEN
SFL,3,PRES,9.8*Weight\/(3.1415*Radius**2),
*ELSE
DL,3,,UY,Displac*Height
*ENDIF<\/p>\n
TIME,Time_Sim
AUTOTS,1
DELTIM,Time_Sim\/1000,,1
KBC,0
SOLVE<\/p>\n","protected":false},"template":"","class_list":["post-251371","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t