Assignment 4 Compare and analyse material models and failure models
Objective:
To compare 7 material cases and analyse the models for rupture
Case setup and execution:
The models are imported into Hypermesh and properties of the model are changed according to the question and analysed
Case 1: Run as it is
Case 2: Change Ifail_sh=1, Dadv=1, Ixfem=1 in /FAIL/Hohnson
Case 3: Delete /FAIL/JOHNSON
Case 4: Delete eps_max value
Case 5: Convert material model to Law 1 Elastic with same E, nu and density value
Case 6: Convert card to Law 36 Plas_tab with recommended properties
Case 7: Open Law27_0000.rad file. Change shell properties to recommended and run
Result and Conclusion:
Question 1: Calculated at the end of simulation
|
Run |
Total no. of cycles |
Energy error |
Mass error |
Simulation time |
|
Law 2 epsmax failure |
49480 |
0.2% |
0 |
119.99s |
|
Law 2 epsmax crack |
49397 |
4% |
0 |
99.81s |
|
Law 2 no fail |
49405 |
0.8% |
0 |
119.37s |
|
Law 2 |
48737 |
3% |
0 |
117.64s |
|
Law 1 Elastic |
47969 |
0.3% |
0 |
114.99s |
|
Law 36 Plas tab |
53162 |
-1.2% |
0 |
130.70s |
|
Law 27 Plas Brit |
49356 |
1.1% |
0 |
119.11s |
Since we used QEPH shell formulation, there is no or negligible hourglass energy which is evident from the energy error from all the 7 cases. All the cases have mass error = 0 and energy error less than 5% which is acceptable
Questions 2. and 5.
Case1: Elements are deleted once the plastic strain on one integration point reaches 15.1% of total plastic strain (obtained from material properties) or once the value D is greater than 1 whichever is lower.
Case2: Since ixfem=1, Ifail_sh=1, Dadv=1, Elements start to crack if
- element has no failed neighbors and D > 1, then in this case, new crack initialization in element.
- element has failed neighbors and D > Dadv, then in this case, crack advanced and Dadv is used for crack advancement. Dadv will be used if existing crack arrives to a boundary of an element.
Element deleted, if a second crack arrives to the same element.
Case3: Elements are deleted once the plastic strain on one integration point reaches 15.1% of total plastic strain (obtained from material properties)
Case4: no element deletion. Since eps_max value is deleted, it assumes the default eps_max value of 10E30 which is very large and elements will fail or gets deleted only when plastic strain on one integration point reaches 15.1% of 10E30. But the plastic strain is well within the value so there is no element deletion
Case5: There is no rupture of failure model associated with this Elastic case. So, no element deletion and stress raises to a comparatively higher value
Case6: Elements are deleted once the plastic strain on one integration point reaches 15.1% of total plastic strain (obtained from material properties)
Case7: This law allows the modeling of material damage and brittle failure in two principal directions (1 and 2). Elements get deleted when the strain reaches Ef1 or ef2.
Question 3
Kinetic energy doesn’t increase since only the ball is having velocity and the plate is being hit by it. The internal energy increases till rupture. Once the element gets deleted some energy gets lost which is evident from the drop(wavy portion) in Internal energy. Based on the point of rupture or failure model, the rate of change of internal energy changes.
Question 4:
Case 2 with Johnson Cook material and Failure Johnson model closely represents the on-field scenario with crack initiation and propagation