Parametric Study on a Frontal Car Crash Setup
Parametric Study of a Frontal Crash Setup
Objective: To carry out a parametric analysis of a frontal crash setup and determine the effect of varrying the thickness of the model on Equivalent Stress and Deformation.
Geometry: The model consists of a wall of thickness... and a car body (just the outline of the sheet metal).
Symmetry Definition: The entire setup mentioned above represents just hald the model. The analysis is carried out on a half model to reduce computation time. To get results for the full model, two symmetry regions are defined about which the results of the half model are duplicated.
Material Definition: The wall is assigned " Structural Steel" as the working material, the properties of which are:
|
Particulars |
Magnitude |
Unit |
|
Density |
7.85E-06 |
Kg/mm3 |
|
Young’s Modulus |
2.00E+05 |
MPa |
|
Shear Modulus |
76923 |
MPa |
|
Bulk Modulus |
166670 |
MPa |
|
Poisson’s Ratio |
0.3 |
|
|
Yield Strength |
250 |
MPa |
|
Ultimate Strength |
460 |
MPa |
To observe the non-linear behaviour of the crash, the car body is assigned "Stainless Steel NL" as the working material:
|
Particulars |
Magnitude |
Unit |
|
Density |
7.75E-06 |
Kg/mm3 |
|
Young’s Modulus |
1.93E+05 |
MPa |
|
Shear Modulus |
73664 |
MPa |
|
Bulk Modulus |
169300 |
MPa |
|
Poisson’s Ratio |
0.31 |
|
|
Yield Strength |
210 |
MPa |
|
Tangent Modulus |
1800 |
MPa |
Body Interactions: The interaction between the wall and the body is set to formulate as "Penalty" with the contact detection algorithm being set to "Trajectory". The surface interaction between the colliding parts is assumed to be frictionless.
Meshing: The wall is meshed using Tetrahedrons and by Patch Confirming Method. The rear surfaces of the car are provided with an element size of 175mm. The rest of the car is meshed by the default quad element size of 56mm.
Analysis Settings: The simulation is set to run for 1ms and for a maximum of 1E+07 cycles. The energy error is capped to 0.1 or 10% of the reference cycle energy.
Boundary Conditions: For this setup, the rear surfaces of the car are provided a fixed support and the wall is provided a displacement of 500mm in the Z-direction.
Parameter Definition: Instead of running separate simulations to get the results, a parametric approach is resorted to. The thickness of the car body is set as the input parameter. For the output parameter, the Total Deformation and Equivalent Stress are set as the output parameters. Sample parameter settings are shown below.
The three cases for the simulation are:
Case1: Car body thickness of 0.3mm.
Case2: Car body thickness of 0.5mm.
Case3: Car body thickness of 1.0mm.
Results:
The project interface page appears as below, with a parameter set option. Double clicking that option opens up the results to the simulations.
The results page from the parameter set page appears as below:
The results obtained have been tabulated below:
|
SR No |
Particular |
Case1 (0.3mm) |
Case2 (0.5mm) |
Case3 (1.0mm) |
|
1. |
Total Deformation (mm) |
1042.3 |
1038.2 |
1026.9 |
|
2. |
Equivalent Stress (MPa) |
11390 |
11305 |
11143 |
|
3. |
Equivalent Stress on car body (MPa) |
3909.4 |
3038.1 |
3250 |
1) Total Deformation: The location of maximum deformation is the same in all cases with the maximum deformation being where the thickness is minimum.
Case1
Case2
Case3
The green, blue and red lines indicate the respective maximum, average and minimum deformation in the model.
2) Equivalent Stress: This value gives the stress in the overall model. The region of maximum Von-Mises Stress is computed on the rear end of the wall with the highest stress being recorded in Case1.
Case1
Case2
Case3
The green, blue and red lines indicate the respective maximum, average and minimum Equivalent Stress in the model.
3) Equivalent Stress on the car body: The car body experiences the highest Von-Mises stress when the thickness of the shell is the least. The location of the maximum stress, in all the cases, can be observed to be at one of the elements in the deformed front part.
Case1
Case2
Case3
The green, blue and red lines indicate the respective maximum, average and minimum Equivalent Stress in the car body alone.
Inference:
The simulations terminate succesfully when updated and with the energy errors being within the prescribed limit of 10% of reference cycle energy.
Energy conservation curve for 0.3mm thickness
Energy conservation curve for 0.5mm thickness
Energy conservation curve for 1.0mm thickness
From the results obtained, the following can be deduced:
- With increase in thickness of the car body, the number of cycles and hence the time taken to solve the mathematical model also increases.
Solver Output for 0.3mm Solver Output for 0.5mm
Solver Output for 1.0mm
- With increasing thickness, the Total Deformation in the model keeps decreasing as the impact energy generated from the collision does not suffice to produce enough deformation and gets stored more as internal energy in the car body.
- On account of the lowest thickness of the car body, Case1 exhibits the highest strains and consequently equivalent stress.