Week-6 Calculate the Stretch Ratio by comparing the ELFORM (-2,-1,1,2) with Ogden_Material Model.

Aim: To perform the simulation using ELFORM = 1, 2, -1, -2 and calculate the stretch ratio.

OBJECTIVE:

1) To Create a block of 10mmx10mmx10mm dimension with 10 elements for each direction and use the material card attached (Ogden_Material.k).

2) Use appropriate boundary conditions to simulate uniaxial tensile behavior for the model.

3) Compare the results of the simulation with ELFORM = 1, 2, -1, -2 by plotting Engineering Stress vs Stretch Ratio up to stretch ratio 5.

4) To use a proper solver (Implicit/Explicit).

Procedure:

1) The given LS-Dyna keyword file is opened in LS-PrePost using the option File->Open->LS-Dyna Keyword File. The imported keyword file consists of only the Ogden material card as shown in the image given below.

2) The FE model of a solid block of 10mmx10mmx10mm dimension with 10 elements for each direction is created using the Shape Mesher under the mesh tab as shown in the image given below.

Section Creation:

3) The section properties of the FE model created is assigned as a solid element with different ELFORM such as,

Case (1). ELFORM = 1, constant stress solid element.

Case (2). ELFORM = -1, Fully integrated S/R solid intended for elements with poor aspect ratio, efficient formulation.

Case (3). ELFORM = 2, Fully integrated S/R solid

Case (4). ELFORM = -2, Fully integrated S/R solid intended for elements with poor aspect ratio, accurate formulation.

The section definition for each case is shown in the images given below.

Material:

4) The material card given in the below image is already provided in the keyword file, the unit system followed is gm-mm-ms and it is assigned to the solid block part.

Assigning Material and Section to Part:

5) The material and section properties are assigned to the solid part as shown in the image given below.

Boundary Conditions:

6) To perform the uniaxial tensile test on the specimen, the nodes of one of the faces are fixed along the X-axis.

7) Then we fix the vertical middle nodes along Z- direction fixed in Y-direction.

8) Then we fix the horizontal Middle nodes along Y-direction fixed in Z-direction.

9) The Nodes in the moving face are selected for applying load.

10) The minimum load to be applied on the moving surface to attain a stretch ratio of 5, is calculated by using the following relation,

True strain = ln (1+Engg.strain)δl=40mm,">

Stretch Ratio = 1+Engg.strain

5 = 1+ ( delta L / L )

delta L = 40 mm

Hence, the minimum value of 40mm is taken to define the load curve.

11) The node-set and load curve ID's are assigned to the prescribed motion set so the selected nodes move along the X-direction.

Control Cards:

12) CONTROL_IMPLICIT_AUTO card as shown in the below image is used for automatic time step control during implicit analysis. Input value for Automatic time step control flag = IAUTO = 1.

13) CONTROL_IMPLICIT_GENERAL card as shown in the below image is used to activate implicit analysis and define associated control parameters. This keyword is required for all implicit analyses.

The input value for IMFLAG=Implicit/Explicit switching flag = 1 (implicit analysis)

DT0=Initial time step size for implicit analysis = 0.01.

14) CONTROL_IMPLICIT_SOLUTION card as shown in the below image is used to specify whether a linear or nonlinear solution is desired. The default values are set as it is in the card.

15) The control termination function as shown in the below image is enabled to specify the end time of the simulation. The termination time is set for 1 ms.

Database:

16) The time step value of 0.01 ms is given for the BINARY_D3PLOT as shown in the below image and the DATABASE_ASCII option for GLSAT and ELOUT.

17) The DATABASE_EXTENT_BINARY card with STRFLG =1, as shown in the below image is used to compute the elastic strain in the model.

Model Check:

18) The keyword file created is checked for errors using the option keyword manager>model check as shown in the below image.

19) The keyword file is saved using the ‘.k’ extension and is made to run in the solver by getting normal termination messages for different cases of ELFORM.

Results and Discussion:

Case (1). ELFORM = 1, constant stress solid element.

Case (2). ELFORM = -1, Fully integrated S/R solid intended for elements with poor aspect ratio, efficient formulation.

Case (3). ELFORM = 2, Fully integrated S/R solid.

Case (4). ELFORM = -2, Fully integrated S/R solid intended for elements with poor aspect ratio, accurate formulation.

CONCLUSION:

The case setup was done as per the objective and the corresponding output requests are obtained. Implicit solver is used for the simulation because the effect of strain rates are minimal.

The value of stretch ratio is calculated for various element formulations.