Week-7 Head Impact

fObjecive:

To Create a Head Impact simulation using the child head sample and the car hood model.

1. Create a sample crash test using the sphere.

2. Rotate the Child head model using the define card.

3. Create the head impact test using Child head model with the help of Rigidwall.

4. Include the hood model using the include key card.

5. Create the same head impact test by using the hood model.

Theory:

The HIC criterion associates different likelihoods of head injury to different ranges of
values of the HIC number.
What Happens to the Car During a Car Crash?
• The car itself experiences a very large negative acceleration (tens of times larger
than = 9.8 m/s2 due to the almost sudden stop.
• The absolute (positive) value of this negative acceleration is often referred to as
the deceleration of the car.
• The impact lasts for only a fraction of a second (typical values of 100 to 250
milliseconds or so). The forces acting on the car during that time are very high
and destructive.
What Happens to the Driver (and Passengers) During a Car Crash?
• Various parts of the body will move inside the car and impact the inside of the car
at various points.
• The head, in particular, may also experience very large and short-lived
accelerations resulting from impacting the steering wheel, the windshield, the
side window, head rest.
• These impacts also last for only fractions of a second but can result in serious or
deadly head injuries.
How is the HIC Number Determined?
• In a car safety crash test, inert manufactured bodies (sophisticated
mannequins) known as anthropomorphic test devices, or simply as
dummies are placed in the driver’s and/or passenger’s seat(s).

• To find the HIC number for a particular type of car in a particular
type of crash, the head of the dummy is loaded (equipped) with
devices called accelerometers used to measure and record the large
acceleration experienced by the head during that particular crash.

• The discrete set of acceleration values recorded as a function of time
provides the primary data for calculating a HIC number for the car
and test in discussion.

 Current accident analysis shows that the head of
the pedestrian impacts most frequently into or around
the windscreen since cars in recent have a short hood.
Therefore, the injury risks to the head in contact with
various locations of the car including the windscreen
and its frame were examined on the basis of headform
impact tests.

The HIC is high from contact with the cowl,
lower windscreen frame or A pillar, and it is low with
increasing distance from these structural elements. In
the windscreen center, the HIC is less than 500.

The headform impact test results were compared
between earlier and current car models. The HICs in the
bonnet top area are similar in either type car except for
the car built especially for pedestrian safety. However,
on the A pillar, the HICs are much greater for current
cars.

Procedure:

Step 1. First we need to import the sphere model and need to create a sample crash test using the rigidwall.

Step 2. Create the rigidwall using the planar and two node option and apply it.

Step 3. Create a velocity card using the intial option and apply it.

Step 4. Create a contact card using the automatic single surface card and select the sphere as a slave part id.

Step 5. Now we created the sample crash test with the sphere model and now we have to create with the head model same as above.

Step 6. First we need to import the child head form and then we need to rotate the head model.

Step 7. To rotate the head form first go to the define transorm key card and select the rotate option and give the value of 50 deg and insert it.

Step 8. Now we have to include this key card into include transformation card and add the main file.

Step 9. Now we rotated the head, to create a complete head impact test we need to create a rigidwall and the intial velocity, here intial velocities are split into two because head has rotated and it has two components of velocities (7.13&8.51).

Step 10. Now save the file into seperate folder and add the database cards like ascii, extent binary card for output results and control card for termination.

Step 11. Now we created the head impact test with the rigidwall and now wwe have to create same with the hood model. 

Step 12. Create a material id card and section id card for the hood model. Save the file seperately.

Step13. Now open the head rotated keyword file, here we need to include the hood model into this keyword file. To include go to the include card and select the hood keyword file and insert it. Now save the entire file.

Step 14. Now open the hood with head keyword file seperately. Here we need to create a contact and card and bounmdary card.

Step 15. To create contact card go to automatic sutface to surface card and select the slave part id as a head and master part id as a hood and accept it.

Step 16. To create boundary go to include and select the spc boundary and restrict all rotation movements in all directions and accep the card.

Results & Discussion:

Thus we solve the three keyword file using the Ls Manager and we need to extract the stress and strain plots for the tests, to get the results we need to open d3plot of the three keyword files.

1. Go to the repective saved files of three tests and select the file path as d3plot and open three tests in different tabs.

2. After opening the files select the stress contour option and see the values of stress for all three simulations.

As we can see the simulation of both the tests of stress contours, the stress acted on the head is high and less distributed due to the sample rigidwall, where in the hood and head impact test we can see more stress distribution in the hood model and head impact is less when compared to the above head and rigidwall test.

3. Now we have to get the strain contours for head impact with the rigidwall and head impact with the hood.

 4. Now we need to extract the stress and strain plots for the head and rigidall impact test.

First we are going to compare the stress plots of the head and rigidwall impact test ang head and hood impact test.

5. Here we can see that head and rigidwall test has the breaking at 4.5ms due to the  impact and where in hood impact test stress is not reaking the head and it becomes zero because stress is absorbed by the hood in this casae.

Here we are going to compare the strain plots

Here we can see that strain of the head and rigidwall impact test has the less strain and becomes zero when the head starts to break due to the impact, where in the hood and head impact test the strain goes to the negative after the impact this is because human tissue has the negative poisoins i.e, it has neagtive lateral strain so the output we got is in negative.

6. Now we have to plot the hic values for the both the test, to get the lots go to the ASCII option and select the nodout and load the file of nodout and plot the hic and resultant acceleration.

As we comparing the head acceleration of the head impact with the rigidwall and head impact with the hood we extracted the two type head injury criterion i.e, hic15 and hic36 aqnd we can see from the plots that both has same the graph for both the tests and we can see that for the rigidwall impact test has approximately 1 gm/s2 where in the hood impact test it less than 1gm/s2.

Conclusion:

Thus we have created complete three type of simulations for head impact test and get the outputs for the test using the Ls-dyna aand Ls manager. For the first test we just ran sample simulation for sphere which impacts the rigidwall and we find out the stress values for the test. In second test we use the dummy head form and ran the test which impacts the same rigidwall but here we get different stress values and strain and also we find the hic values for the test. For the third test we have done same procedure as the second test but we used the hood for the impact test and find out the stress and strain values of the test and also find the head acceleration and sees the head will break or not in this head is not broken.