Comparison of Crash Box Analysis using different shell thickness
Comparison of Crash Box Analysis using different shell thickness
Objective: The aim of this project is to analyse the crash analysis of box with different shell thickness and compare the different parameters as follows
- Cross sectional forces at the mid plane.
- Acceleration of a node at the midplane.
- Maximum directional stress and strain along the longitudinal axis.
- Energy plots mentioned and
- Comparing acceleration and stress/strain plots for the 1.2/1.5 shell thickness box.
All the above scenarios are to be carried out by following the given instructions which include
- Creating a *RIGIDWALL_PLANAR.
- Considering the steel as the box material.
- Assigning an Initial velocity of 50kmph = 13.888 mm/ms.
- Following a (g,mm,ms) unit system
Procedure:
Material Creation: As mentioned above the material is 'Steel' and the units to be considered must be in (g,mm,ms) unit system.
| SNo | Parameter | Value | Units |
| 1 | Density | 7.85e-3 | g/mm3 |
| 2 | Young's Modulus | 2.1e+5 | g/(mm*ms2) |
| 3 | Poisson's Ration | 0.3 | Constant |
| 4 | Yield Strength | 350 | MPa |
A MAT_PIECEWISE_LINEAR_PLASTICITY 24 has been taken and the parameter values in the table have been assigned with a MID of 1
Section creation: Two models have to be created with 1.2 and 1.5 mm thickness with a SecID as 1
Part Assignment: The Material and the section keyword have to be assigned to the part. Assign the material and the section with the MID and SECID.
Rigidwall creation: A *RIGIDWALL_PLANAR keyword has been created on where the box impacts. The Rigid wall was positioned 15mm away from the crashbox.
Initial Velocity: A velocity of 13.888 mm/ms has been imputed in the negative X-axis to all the nodes of the Box.
Contact creation: In case of Impact/crash scenarios where the box crashes into the rigidwall the box buckles and self contact itself. It is recommended that AUTOMATIC_SINGLE_SURFACE has to be considered for creating a contact between RIGIDWALL and BOX. To obtain the contact forces from the contact and to write the RCFORC file a CONTACT_FORCE_TRANSDUCER_PENALTY must be defined.
Control Creation: It is important that at what time the Simulation must end for this a CONTROL_TERMINATION keyword has to be created and CONTROL_ENERGY for the Hourglass and Sliding Interface energies to be generated. The Hourglass energy is present because of the ELFORM is set to 2 in the SECTION_SHELL which is Belytschko-Tsay and the Sliding interface energy comes into picture as there is contact between RIGIDWALL and BOX.
DATABASE CREATION
Cross section Creation: One of the required outputs is Cross sectional force at the middle of the crashbox for this a DATABASE_CROSS_SECTION_SET has to be created and set of nodes and a set of element set are also has to be created and assigned a Node Set ID and Shell Set ID to their respective to the DATABASE_CROSS_SECTION_SET
The acceleration at the middle node has to be plotted, for this DATABASE_HISTORY_NODE has be created and the DATABASE_D3PLOT with 0.1ms DT for the time interval between output.
Finally
ASCII_option : ELOUT,GLSTAT,MATSUM,NODOUT,RCFORC,RWFORC,SECFORC and SLEOUT have been created.
RESULTS:
Simulation of the crashbox for 1.2 mm shell thickness.
Simulation of the crashbox for 1.5mm shell thickness.
CROSS-SECTION FOR AT THE MIDPLANE:
The Mid plane section resultant forces for the 1.2mm and 1.5mm shell thickness are 19KN and 20.1KN at the instant of impact and then at the last frame they are 6.56 KN and 5.96KN respectively
ACCELERATION OF NODE AT MID PLANE:
The Mid plane section acceleration for the 1.2mm and 1.5mm shell thickness at the node 6407 are 1.24e+3 and 1.09e+3 mm/s2 respectively at the instant of impact and then at the last frame they are 623 and 219 mm/s2 respectively.
DIRECTIONAL STRESS:
Stresses along X-axis:
The X-stresses at the 1.2mm and 1.5mm thick shell have no much difference between them. The values being 2.907e+2 and 2.925e+2 MPa respectively.
Stresses along Y-axis:
The Y-stresses at the 1.2mm and 1.5mm thick shell have no much difference between them. The values being 2.695e+2 and 2.413e+2 MPa repectively.
STRAIN:
Strain along X-axis :
The strain in the X-axis for the 1.2mm and 1.5mm shell thickness 8.726e-6 and 7.798e-6 respectively.which is negligible.
Strain along Y-axis :
The strain in the Y-axis for the 1.2mm and 1.5mm shell thickness 8.901e-6 and 7.098e-6 respectively.which is negligible.
Contact Energy:
The Resultant Contact forces on both slave and master are zero for both the shell thickness.
Energy plots:
For 1.2mm shell thickness:
| Sno | Energy | Value at Impact 1.2ms | Value at End 5ms |
| 1 | Total Energy | 1.08e+5 J | 1.08e+5 J |
| 2 | Kinetic Energy | 8.80e+4 J | 8.68e+4 |
| 3 | Internal Energy | 1.94e+4 J | 1.73e+4 J |
| 4 | Hourglass Energy | 188 J | 3.45e+3 |
| 5 | Sliding Energy | 0 J | 0 J |
For 1.5mm shell thickness:
| Sno | Energy | Value at Impact 1.2ms | Value at End 5ms |
| 1 | Total Energy | 1.35e+5 J | 1.35e+5 J |
| 2 | Kinetic Energy | 1.11e+5 J | 1.09e+5 J |
| 3 | Internal Energy | 2.37e+4 J | 2.17e+4 J |
| 4 | Hourglass Energy | 244 J | 3.57e+3 |
| 5 | Sliding Energy | 0 J | 0 J |
Comparing Acceleration and Stress/strain for 1.2mm and 1.5mm shell thickness at the time of impact:
| SNo | Parameter | 1.2mm thickness | 1.5mm thickness |
| 1 | Stress | 2.907e+2 MPa | 2.925e+2 MPa |
| 2 | Acceleration at node 6407 | 1.24e+3 mm/s2 | 1.09e+3 mm/s2 |
Conclusion:
- There is no much between the the stress between the two thicknesses but when one has to be opted then the 1.5mm shell thickness is 0.018e+2 MPa.
- The values cannot completely be true because there are uneven peaks and valleys in the almost all the plots that has been put in the report.
- The Stress values are very below the yield stress 350MPa.
- The acceleration is for the 1.2mm thickness is slightly higher than the other.
- Since, the simulation satisfied the first case i.e., crashes onto the rigidwall and rebounds completely, there is no significant deformation that can be observed as the interation between the box and the rigidwall is only 0.1-0.2ms so strain is negligible and the contact force for the slave and master is zero.
- The Residual Strain is taken because the box is having some initial kinetic energy and hits the rigidwall. So, it can be assumed through 'SHOT PEENING' the box gets compressed at the impact time where some residual stress forms which indicates that there is residual stress which is very much less 'Micro units' negligible.
Comparison of Crash Box Analysis using different shell thickness
Objective: The aim of this project is to analyse the crash analysis of box with different shell thickness and compare the different parameters as follows
- Cross sectional forces at the mid plane.
- Acceleration of a node at the midplane.
- Maximum directional stress and strain along the longitudinal axis.
- Energy plots mentioned and
- Comparing acceleration and stress/strain plots for the 1.2/1.5 shell thickness box.
All the above scenarios are to be carried out by following the given instructions which include
- Creating a *RIGIDWALL_PLANAR.
- Considering the steel as the box material.
- Assigning an Initial velocity of 50kmph = 13.888 mm/ms.
- Following a (g,mm,ms) unit system
Procedure:
Material Creation: As mentioned above the material is 'Steel' and the units to be considered must be in (g,mm,ms) unit system.
| SNo | Parameter | Value | Units |
| 1 | Density | 7.85e-3 | g/mm3 |
| 2 | Young's Modulus | 2.1e+5 | g/(mm*ms2) |
| 3 | Poisson's Ration | 0.3 | Constant |
| 4 | Yield Strength | 350 | MPa |
A MAT_PIECEWISE_LINEAR_PLASTICITY 24 has been taken and the parameter values in the table have been assigned with a MID of 1
Section creation: Two models have to be created with 1.2 and 1.5 mm thickness with a SecID as 1
Part Assignment: The Material and the section keyword have to be assigned to the part. Assign the material and the section with the MID and SECID.
Comparison of Crash Box Analysis using different shell thickness
Objective: The aim of this project is to analyse the crash analysis of box with different shell thickness and compare the different parameters as follows
- Cross sectional forces at the mid plane.
- Acceleration of a node at the midplane.
- Maximum directional stress and strain along the longitudinal axis.
- Energy plots mentioned and
- Comparing acceleration and stress/strain plots for the 1.2/1.5 shell thickness box.
All the above scenarios are to be carried out by following the given instructions which include
- Creating a *RIGIDWALL_PLANAR.
- Considering the steel as the box material.
- Assigning an Initial velocity of 50kmph = 13.888 mm/ms.
- Following a (g,mm,ms) unit system
Procedure:
Material Creation: As mentioned above the material is 'Steel' and the units to be considered must be in (g,mm,ms) unit system.
| SNo | Parameter | Value | Units |
| 1 | Density | 7.85e-3 | g/mm3 |
| 2 | Young's Modulus | 2.1e+5 | g/(mm*ms2) |
| 3 | Poisson's Ration | 0.3 | Constant |
| 4 | Yield Strength | 350 | MPa |
A MAT_PIECEWISE_LINEAR_PLASTICITY 24 has been taken and the parameter values in the table have been assigned with a MID of 1
Section creation: Two models have to be created with 1.2 and 1.5 mm thickness with a SecID as 1
Part Assignment: The Material and the section keyword have to be assigned to the part. Assign the material and the section with the MID and SECID.