Assignment 7

Crash Test Simulation for the Side part of the Car.

Aim:

To perform crash test simulation for the side region of the car and to observe the impacts formed in various regions of the car with the help of graphs.

Abstract:

The given car model has a very basic shape as required for performing the crash simulation and for observing the deformation on the side region of the car. The required conditions are to be set for preparing the car for the simulation process. The errors and penetrations are to be checked and rectified before simulation. After the simulation process, the deformations formed are to be checked by plotting the graphs for the required cross-sections.

Methodology:

1. Import the starter file for opening the component.
2. Check the units set of measurements and change them as required.
3. Set the group type as required and set the standard values for defining the material type of the car.
4. Create a centre of gravity for the model as required for simulation.
5. Check for any kind of errors and penetrations on the component and fix the errors.
6. Create cross sections and skew points so that the impacts can be noted and plotted for the graphs.
7. Start the simulation process.
8. Check the animation of the simulation and plot the graphs for observation after completion of the simulation process.

Introduction:

Crash simulation is a process where crash tests are done for any type of components to observe and determine which type of material or the production process is to be done for manufacturing. For the production of vehicles the simulations are done in such a way that in case of an accident, most of the impacts are absorbed by the vehicle to keep the passengers safe inside. For the following simulation, the car model shown below is to be simulated as per the required safety conditions.

Fig 1: Given car overview. Fig 2: side view.

Fig 3: Top view. Fig 4: front view.

Procedure:

1. Check the units of the component in the begin card file in the tab bar. Change the units as required. The required units are

(i) Input mass unit = kg

(ii) Input length unit = mm

(iii) Input time unit = ms.

Fig 5: Begin card

2. A group card is to be created for defining the material property and the standard values are to be mentioned in the group card. The created group card is set to /TYPE7.

Interface/TYPE7 is a multi-usage impact interface, modelling contact between a master surface and a group of slave nodes. It is also possible to consider heat transfer and heat friction. The values for the card are mentioned per the standard values shown below.

Fig 6: Group card type 7

3. Penetrations and intersections should not be present in the model. To check the penetrations, select the penetration check option in the tools option, select the group which has been created for the simulation and run the check process. If no penetrations the software shows as ‘0 collisions found’. If penetrations found the mesh is to be adjusted manually.

Fig 7: Selection of penetration check Fig 8: Penetration check card

Fig 9: Group selection Fig 10: Group selection window.

Fig 11: completed penetration check

4. Make sure that the rigid connections for the components are connected properly. If needed connect the components in required regions.

5. The simulation is to be done on the side part of the cars i.e., the testing the deformation of the door panel and the pillars of the car. To perform the simulation a rigid pillar is created at the side of the car as shown in the fig. The positioning distance is to be mentioned as per the position of the component. The friction for the rigid wall is set as 0.1, the Dsearch value is set to 1000 and the diameter of the pillar is 254mm.

Fig 12: Rigid pillar card Fig 13: Created rigid pillar.

Fig 14: Rigid pillar top view. Fig 15: Rigid pillar side view.

6. Mass, as well as the centre of gravity (COG), is to be created for the component. As per the given conditions, the mass of the component is to be set as 700 kg. To provide mass as well as COG the mass is to be distributed throughout the nodes in the component until the required mass and position of COG is achieved.

(i) First create an ‘ADMAS’ file in the solver deck tab. Create a new mass file. Open the file and set the file type as ‘0: Mass is added to each node of the node group.

(ii) Right-click on the gmd_ID and create the gmd_ID file. This is to be done twice because a duplicate file will be created for the first time and for the second time a set file will be created in the model tab.

Fig 16: ADMAS card

(iii) The mass for each node is set as 0.15 kg. Select the node option in the Entity_ID option and select the nodes through the component until the desired mass and COG position is achieved.

Fig 17: Selection of nodes for adding mass and positioning COG.

(iv) To check the mass and COG details, select the mass details option in the tools menu. Click on mass, cog and inertia option and go to COG option. The mass and COG details are as shown below.

Fig 18:Selection of mass and COG details

Fig 19: Mass and COG details.

(v) To view the exact position of the COG, take the values COG position and enter those values for creating the node viewing COG.

Fig 20: Plotting node to view COG

7. Initial velocity is to be created for the model so that to represent the car crashing with that particular velocity. To provide the initial velocity create a ‘INIVEL’ card in the solver tab. As per the given condition the velocity is to be given as 35mph i.e., 15.6 mm/ms. Select the created file and mention the velocity. As the side of the car is facing in the y-axis, mention the velocity in the y phase. Set the remaining options in the file as shown below.

Fig 21: Creating INIVEL card Fig 22: INIVEL card

Fig 23: Created initial velocity.

8. Check the model for any errors and fix the errors. To check the errors, select the model check option in the tools menu. Select as ‘Radioss Block’ in the model checker. The model checker tab is created in the tab area. Right-click on the errors file and select the run option. The software will check if there are any errors. If any errors the software will show the errors in the tab area. The errors are to be fixed manually.

Fig 24: Selection of model checker Fig 25: Running for errors detection.

Fig 26: Results of error detection.

9. Few errors are to be checked and rectified in the hypercrash software. The errors are solved in the hyper crash software and are to be exported back to the HyperWorks software.

10. Cross-sections are to be created for the mentioned areas as per the conditions.

(i)To create cross-sections, create a ‘SECT’ file in the solver tab.

(ii) Considering both the lower rails of the model. Make sure that the region to be cross-sectioned should have quad elements throughout that particular row.

(iii) Select the nodes N1, N2, N3 in an ‘L’ shape to that to represent the x, y, z axis for the cross-sections. The selected nodes will be mentioned in the card as a node ID.

(iv) Select the gmod_ID on the component i.e., select the three rows of nodes throughout which the N1, N2, N3 are created.

(or)

Create a ‘FRAME’ file in the solver tab and mention the frame_ID in the SECT card instead of mentioning the gmod_ID.

(v) Mention the ‘delta T’ and ‘alpha’ values as 0.1 and 1.67 respectively.

Where delta T = time step for saving data

Alpha = coefficient for filtering the time step.

(vi) Shell elements are to be selected at the region where the 3 rows of nodes are being selected before (or) covering the created frame region. Right-click and create two grshell_IDs. Select the entity_IDs in the grshell_IDs. Click on elements are select the elements.

Fig 27: Selection of entity IDs

(vii) Set the Iframe type to 12 i.e., the COG of the section.

Fig 28: Cross-section card for the rail

Create another cross-section for the rail beside.

Fig 29: Cross sections created.

11. Intrusions are to be created near the fuel tank rail, B pillar and hinge pillar to calculate the movement of the nodes after the impact. Select a node for each mentioned areas above and mark them as their node IDs. Create a skew file in the solver tab, create a skew parallel to the selected nodes. In the SKEW file select the node to be targeted to track the impact. Create another skew parallel to a different node.

Fig 30: Creating intrusions at the required regions.

Fig 31: Intrusion at the hinge component.

12. Create another intrusion on the door panel by creating random skew on a node and select the same node as the nodal ID to calculate the relative velocity at the door panel.

Fig 32: Intrusion at the door panel.

13. Create the output blocks in the model tab for the cross-sections and skews. The files are to be mentioned for each output block files in the entity IDs as shown below.

14. Set the Tfreq from 0.5 to 0.1 ms.

15. Set the Tstop in the engine run file as 80ms.

16. The model is to be prepared for the simulation process.

17. Create a new file for the simulation files and set the direction for saving the simulation files in Radioss. Set the necessary options as shown below and start the simulation process. The process may take 2 hours to complete the simulation.

After the completion of the simulation process, the simulation animation and the graphs are to be observed. Both are viewed in hyperview and hyper graph respectively.

Errors faced:

Few errors are to be fixed manually by the user. Some of those errors.

Unsupported Cards:

When a model is imported from another software to the HyperWorks software, few non-supported files occur which are written to the unsupported cards panel. Unsupported cards are stored as text and pointers are not considered.

Fig 33: Location of the unsupported card.

This error will not be found while running error detection. The user should delete the file from the cards file in the model tab. Otherwise, the simulation will fail to show as ‘error 54’.

Fig 34: Error 54 formation.

Empty files:

Few errors are not found in the HyperWorks error checker, but the simulation won’t run showing errors containing empty files. These errors are found in the hypercrash software. Run the model checker operation to detect empty file errors. The volume which is mentioned besides the file name shows ‘0’ if the file is empty. The empty files can be deleted from the hypercrash software.

Fig 35: Empty files formation. Fig 36: Error detection in the hypercrash.

Fig 37: empty files detection in hypercrash software

These empty files are formed while creating gr_nodes and gr_shell elements twice, where one file is for creating a duplicate file.

Hyper view:

Set the hyper mesh software mode to hyper view to start the animation. The animation files and the graph files will be saved in the newly created folder. Import the animation H3D file to the hyper view control panel and click on apply. The animation will start while playing the simulation.

Fig 38: Selecting a hyper view option.

Fig 39: hyper view control panel.

Hyper graph:

The created cross-sections, accelerometers are to be plotted in the graph for observation. To check the graph set the hyper view mode to hypergraph model. Import the graph file (T01) to the hypergraph control panel. Select the properties to be analyzed in the graph as mentioned in the assignment.

Fig 40: Hypergraph control panel.

Observation:

The simulated animations and the graphs are as shown below.

Fig 41: Car crash to the poll animation picture top view.

Fig 42:Car crash test overview.

The graphs for the above model are as shown below.

Fig 43: Energy graph

1. The energy graph is plotted as shown in fig 42. The initial velocity is increasing approximately from 9ms whereas the kinetic energy was constant and decreases where the initial energy increases. This deviation is formed because the deformation started at 9ms.

2. The Hourglass and contact energies are almost constant at total energy zero kg*mm2.

3. The total energy is constant at 90000 kg*mm2.

Cross Sections:

Fig 44: Cross-section 1 Fig 45: Cross-Section 2

The cross-sections 1 and 2 shown are for the rails 1 and 2 respectively. The component has no stress formation up to 9ms of time. When the car experiences the impact, a sudden change in stress is formed on the rails. The highest impact is experienced by rail 1. The rail 1 has the highest stress formation at 23ms with stress near to 7kN/mm2 and the rail 2 experiences at 34 ms of time with the highest stress of 3.5 kN/mm2.

Intrusions:

Intrusions are plotted as mentioned in the above procedure. The distance is to be measured for the node and the skew after the impact. So the distance is to be measured between the node and the skew before the impact. The measured distances between each node and skew as shown below.

intrusion 1 = 1305.361mm , node = 125388

intrusion 2 = 1330.703mm, node = 123543

intrusion 3 = 1313.306mm, node = 83

The graphs are plotted as shown below.

Fig 46: Intrusion 1 Fig 47: intrusion 2

Fig 48: Intrusion 3

The graphs are plotted as per the resultant displacement for finding out the distance between the nodes and skews after the impact.

For intrusions 1 and 2 the distance between the nodes and the skews are reduced nearly 350mm after the impact. This is because the rigid pillar was directly in contact at the place where the nodes are being placed. At intrusion 3 the nodes the distance between the node and the skew is nearly 900mm as per the graphs plotted.

Intrusion 4 is used for finding out the impact caused on the door so that to find a way to reduce the impact on the passenger. So resultant velocity is to be plotted to find out the impact on the door panel.

Fig 4: Intrusion 4

As per the graph, the velocity is reduced after the impact after crossing 10ms of time. The remaining impact is not more than 8kgf of force.

To reduce the stresses occurring at the fuel tank region, the shape of the component is to be improved such that maintaining some gap between the fuel tank and the rail near by and the material which is to be choosed for manufacturing should be strong enough to sustain the impact.

Result:

Thus simulating the given car model as per the given conditions and plotting the energies caused during the impact and observation of the cross-sections are completed as required.

Learning outcomes:

• Learned to set the group card conditions.
• Learned to create cross-sections in the required regions.
• Learned to check the errors and penetrations in the model.
• Learned to simulate the given model.
• Learned to plot the graphs and observe the impacts formed.