Week-6 Calculate the Stretch Ratio by comparing the ELFORM (-2,-1,1,2) with Ogden_Material Model.
Objective: To simulate the tensile behaviour of a solid block with different element formations and compare the stretch ratio from each case.
step 1: solid block creation and section definition
The given keyword file, which contain ogden material definition is opened in LSDYNA. The default values of the hyerelastic material definition can be retained.
A FE model of a solid box is created using shape mesher option under element and mesh panel as show.
section definition
The section properties for the solid block are assigned as shown below the different element formulations, that need to be tested are ELFORM 1,2,-1 and -2.
Part definition
The material and the section are then assigned to the part ID of the solid block as shown below.
The definition with different ELFORMS are saved seperately in a keyword file and simulate indivitually to obtain the result
step 2: Boundary condition
SPC-X direction
The nodes of the box on the YZ plane are selected and their motion is constrained in the X-direction, since they should be fixed.
SPC-Z direction
The motion of the middle nodes in the Y-direction is constrained in the Z-direction, to avoid vertical displacement.
SPC-Y direction
The motion of the middle node in the Z-direction is constrained in the Y-direction, to avoid lateral displacement.
Prescribed motion
The nodes on the opposite side of the YZ plane are selected and a displacement is given to them according to the minimum load to be applied on the moving surface to achieve a stretch ratio of 5.
therefore, a minimum value of 50mm is taken to define the load curve.
the above shown load curve is assigned to the nodes using the appropriate LCID as shown below.
step-3: control cards
A control_implicit_auto card, with AUTO set to 1, is used for automatic time step adjustment.
A control_implicit_general card is used with IMFLAG=1 to specify that an implicit solving scheme need to be used. The initial time step value DTD is set to 0.01
A control_impact_solution card is used to specify whether a linear or a non linear solution is desired. this card is used with default parameters.
the simulation time is set as 1ms using the control_termination card.
step 4: data base cards
A data base_binary_D3 plot is defined with an output frequency DT of 0.01ms.
under DATA BASE_ASCll, GLSTAT and ELOUT are selectd with the same value of DT
A DATA BASE_EXTENT_BINARY card is used with STRFLG=1, in order to compute the elastic strain in the model.
The keyword file is checked for errors using the model checker and saved before starting the simulation.
Result:
The simulation is completed with the following message showing a NORMAL TERMINATION
X stress
The uniaxial stress plots of the 4 cases can be plotted as shown below the max stress in the X-direction can be visualized
The peak stress are as follows
ELFORM 1 -5.024MPA
ELFORM 2 -5.031MPA
ELFORM-1 -5.024MPA
ELFORM-2 -5.024MPA
The peak strain are as follows
ELFORM 1 -1.788
ELFORM 2 -1.789
ELFORM-1 -1.788
ELFORM-2 -1.789
ELFORM 1
ELFORM 2
ELFORM-1
ELFORM-2
Comparision: From the graph of Engineering stress vs stretch ratio, the max value at a stretch ratio of 5 is approximately 0.8MPA the values from the 4 cases are almost the same, due to the simplicity of the model considered.
Conclusion: Thus FE model of a solid block has been simulated for uniaxial loading with various element formulation and the result of engineering stress vs stretch ratio have been compared.