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

Objective: Calculation of engineering stress, strain, true stres, strain and the stretch ratio for an hyperelastic material for different element formations (1,-1,2,-2)

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Given problem conditions:

1. Block of 10mmx10mmx10mm with 10 elements to be created

2. Ogdon material to be used

3.. Tensile test

4. Upto stretch ratio 5 and uniaxial behaviour is to be simulated

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Steps followed to solve the problem:

Step 1: Load the Ogdon_Material.key file. Following figure shows the material properties contained in the Ogdon_Material.key file. The material is hyperelastic.

Step 2: Geometry creation --> A cube of 10mm x 10mm x 10mm is created and meshed into 10 equal elements in X, Y and Z directions.

Step 3: Section and element form --> According to the conditions specified in the problem, sections with ELEFORM 1, -1 , 2 and -2 are created for each simulation.

Step 4: SPC Constraint

Once face of the cube is constrained in X direction. Create Entity - SPC

Step 5: Middle Nodes Constraint

Miidle nodes are constrained for uniform compression

Step 6: Define load curve

Load curve is defined as hown in the figure. Since the direction is negative X, the values are in negative. A scaling factor can also be used with positive values.

Step 7: Boundary Prescribed motion

Step 8: Database extent binary STRFLG=1. Databse extent binary file is requested with STRFLG=1

Step 9: Implicit command--> SInce it is a implicit simulation, we create implicit_auto, implicit_general and implicit_solver cards as shown in following figures.

Solution: Finally after verifying all the cards, the input keyword is solved.

Results :

e_true = ln (1+e_eng)

e_eng = exp(e_true)-1

s_true=s_eng(1+e_eng)

ELEFORM 1 RESULTS

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ELEFORM -1

ELEFORM -2

ELEFORM 2

Conclusions:

The plot of engineering stress Vs stretch ratio is nearly same for all the ELEFORM formations.