Assignment 6
Objective: To conduct a frontal car crash analysis using RADIOSS and extract the forces experienced at the A-Pillar, shotgun, rails, and at bumper to rail interface.
Case Setup and Execution:
Unit check: Open 0000.rad file to check the units. It shows that the units used here are [ Kg, mm, ms ]. Thus the units followed here are and in the 300k model is [kg, mm, ms].
Interface Creation: Now we need to create the interface. The interface here used is TYPE 7 as it is a universal contact. Go to Solver > right-click and select Inter > select the card image as Type 7 > For slave and master nodes select all the 74 components > set the other values as mentioned in the image below.
Rigid Wall Setup: Rigid wall can be created in the model viewer panel. Right-click on the panel select the rigid wall option > ensure the geometry type to be INfinite plane, then in the engineering data set the base node (Xm, Ym, Zm) as 4600, -67, 500 > now set the normal as -1,0,0 as the plane is perpendicular to the x-axis and the opposed the motion of the frontal biw model. Set the slide as 2 (this is sliding with friction) also here I set the Dsearch as 1000.0 and the Coulomb friction must be 0.1 as asked in the question.
Initial velocity: The provided velocity is 35m/hr which is 15.646 mm/ms. Go to the solver browser > right click > create > under engine keywords select INIVEL > select the type as TRA (as the type of motion is translation) > ( as it is only in x direction) Set Vx = 15.646 > in Grnod_id select all the nodes.
Time step and run-time: In the solver, browser go to the engine keyword, under DT select DT/Noda > Select eng_dt_noda_file > change Tmin to 0.0005 as time step is given as 0.5 microseconds. Whereas to set the runtime, under the engine keywords select RUN > then in the eng_run file set Tstop to 80.0. For the frequency, I set it as 0.5 by editing the Anim/DT engine file.
Mass addition and Positioning of CG: To admass and change the center of gravity to match it with the full-scale model we use the HYPERCRASH application. To access hypermesh go to Applications> click hypercrash > set the units as KN, kg, mm & ms > then drag the edited frontal crash file. Then on the other hand import the 300k model but set the units as N, T, mm, s.
In the full-scale model go to the Mass tab and select balancing. A new tab opens which shows the entire mass of the full-scale body. The mass of the full-scale model is 1216.555 Kg with its Cg coordinates to be (X = 312.41 mm Y = 5.77mm). Now the mass in the frontal crash should be added in such a manner that the CG of the frontal crash BIW is approximately the same as the full-scale model at X and Y coordinates.
Now pull up the frontal crash model in the hypercrash window and double click on the Added Mass and then click create new. Selec the Type+0,1,2,3,... as necessary to position the CG closer to the full-scale model. I added masses using mostly type 1 card to position the CG.
The closest CG I could obtain was (311.85mm, 1.84mm). With the mass of the model to be 736.85 Kg.
Now when this is done go to the model in hypermesh and create sents for the nodes used to add mass. Then in the solver browser, go to ADMAS > right-click to create > then create the similar masses at the same position as in the HYPERCRASH window. This method is chosen as it is easier to view the change and add mass in the hypercrash window.
Model checker and penetration checker: To check for penetrations in the hypermesh window go-to tools > then click penetration check > under selections select all the type 7 contact group > then click run. No penetrations were observed in my model. If there are any penetrations then click click depenetrate or use the translate feature.
To check model go-to tools > model checker > Select RADIOSS block > then run it. Several errors and a warning will appear with a short description of it. Read the descriptions and performs actions accordingly to omit those errors. If there are any free nodes or an empty feature then we can delete it.
Sections & Accelerometer: Four sections have to be created to extract the forces experienced by those parts in that section throughout the crash process. To do so in the model browser we right-click > create > then select cross-section > select the parts that have to be included > then select the base nodes (we can use the provided node id here) and the N1, N2 direction. Section to be created is for shotgun, A-pillar, Rail, then rail to bumper interaction.
For the Accelerometer, in the model browser we right-click > create > select accelerometer > insert the node id.
Output blocks: In the model browser > right click on the output blocks > select create > then in entity id enter the type of entity for which the TH has to be extracted. Use this to create an output block for sections, nodes, and accelerometer.
Results and Discussions
Accelerometer:
X axis:
Y-axis:
Z-axis:
Resultant acceleration: Here we see that the initial acceleration is high and then decreases rapidly in the first 10ms. This is because a constant velocity is applied to all the parts of the front biw. So, at 0.0ms as the velocity suddenly increases the acceleration is at its peak. After that, the small changes in the acceleration is due to the crash it experiences against the rigid wall.
For the X-axis acceleration sudden retardation is observed which is because of the obstruction offered by the rigid wall.
Forces at sections:
Bumper to Rail: The Rail experiences a maximum total resultant force of 9.5 to 11kN from the bumper. In the beginning, the total force is small and reaches 6kN till 10 ms. Then it drops and increases to 11kN. The force then drops a little and then drops to 1.5kN. It is seen that it increases again. This shows that the force traveling is pulsating. Whereas we see the resultant normal force also changes similarly. Its maximum value is 7kN and drops to almost zero. The difference between both is only its magnitude.
Rail: When the resultant force at the previous section is low ( from appx 12-22ms ) it increases along the rail and the impact is high .i.e 25kN. Here the duration of the maximum force is short but the force experienced by the rail high.
Shotgun: The shotgun receives the maximum total resultant force among all the sections under observation which is just over 30kN. The Resultant normal force and the total resultant force is similar for most of the duration of the crash. It also has 2 maximum force peaks and for most of the crash duration, the force through the shotgun is low.
A-pillar: The forces are maximum at the starting and end of the simulation. The forces experience are pulsating forces with consistent rise and fall in the forces. The force, in the end, would have been even higher if the simulation was carried for a longer period as it stops as the A-pillar starts to undergo the deformation. It is obvious that the total resultant force at every time step is higher than the Resultant normal force and also that change for both the forces in the same pattern.
Conclusion: This plot shows the comparison of total resultant force of all the four sections. Here we notice that the shotgun rail experiences the maximum force and the A-pillar experienced the least resultant force.
The frontal crash was successfully conducted with a suitable contact interface for a velocity of 35mi/h.
Files Drive: https://drive.google.com/file/d/1yg76wT6_Qb1xh62zfIBc1jrIXf0a3kHn/view?usp=sharing