The goals of this modified drop tower test are to more closely represent on-field impacts of the American football helmet system to promote enhanced safety standards and to develop enhanced headgear for concussion prevention. This method can help answer key questions in the field of biomedical engineering, such as, the on-field response of protective headgear and how to better prevent sports related concussions. The main advantage of this technique is that it offers a more robust helmet safety test while it uses the current NOCSAE standard twin-wire test device.
This test uses an NOCSAE twin-wire drop carriage assembly. First, verify that all components of the assembly are securely attached. Then, attach a large sized NOCSAE headform to the drop carriage assembly.
Adjust the headform collar in the desired position and tighten it down with the lock ring. Then, secure the attached, the Triaxial Accelerometer to the center of the accelerometer plate, which is located at the headform center of gravity. Use the provided Allen head screws.
To complete the setup, configure the Data Acquisition System and enter the sensor information for the accelerometers. Prepare to conduct the baseline helmet impact tests with baseline safeguards, in contrast to the NOCSAE standard. To calibrate the headform, first secure the attached a three inch calibration MEP pad to the Anvil using an Allen wrench.
Next, adjust the impact orientation. First, remove the taper lock bolt from the headform rotator assembly, which may require using a vice and punch. Now, orient the headform bolt holes to the desired position and securely refasten the taper lock bolt.
To rotate the headform, loosen the headform threaded lock ring. Finally, adjust the specific point of impact. Loosen the two base plate Anvil bolts and slide the Anvil into position.
Then, re-tighten the bolts and double check that all the refastened connections are secure. To begin the calibration, lift the drop carriage assembly to the height of the release system, center the release system to its attachment point on the drop carriage assembly and turn on the electro magnetic release system. Now, raise the drop carriage assembly to get the desired impact velocity.
Due to variation and friction of different systems, the required height needs to be determined empirically. Before conducting the test, make sure the data acquisition system will start when the release system is triggered. Now, simultaneously trip both toggles on the release system power box to drop the carriage assembly.
Next, calculate and record the resulting SI value. The desired value is within two percent of 1200 SI.Continue by repeating the calibration for all three required impact locations. For the test, exchange the MEP pad used for calibration with the MEP test pad.
Then, select the impact location and velocity for testing. The impacts must be conducted from the lowest drop velocity to the highest. Also, conduct ambient temperature impacts before conditioned impacts.
Next, properly adjust the headform orientation and Anvil position for the desired impact location as before. Now, fit the test helmet to the test form according to the helmet's fitting instructions and the NOCSAE procedures. Then, secure the helmet's chin strap to the headform.
Proper fit of the helmet on the headform is critical. And since some of the face mask attachment systems vary, some face masks may have to be attached after the helmet is fit on to the headform. Sometimes, a little talcum powder can help make the fit.
Next, attach the mechanical release system to the drop carriage assembly. Raise the carriage to the required height, and conduct the test, just like during calibration. Then, compare the recorded results to the pass/fail criteria.
After all the tests are completed, perform a systems check and compare the post test check to the pre test check to ensure a variation of seven percent or less. SI values were determined for various helmets with and without the faceguard using three consecutive impacts within 90 seconds of each other. While the mean value was well below the NOCSAE 1200 SI threshold, each helmet displayed a unique location dependent response when the faceguard was attached.
A least squares regression by analysis of variance was used for the P value calculations. Significant differences were found with helmets with and without faceguards. Specifically, the Xenith X2 helmet with and without faceguard, at 4.88 meters per second, was very different in the acceleration time history profile at each measured access.
The overall results were strongly dependent on impact location and velocity. Once mastered, this technique can be done in two hours if it's performed properly. While attempting this procedure, it is important to remember not to induce additional variation by ensuring that the mechanical test assembly is properly and securely maintained.
After its development, this technique offers and effective solution. It allows the ability to better assess current and future football helmet systems. After watching this video, you should have a good understanding on how to perform modified NOCSEA impact tests on American football helmets by inclusion of the faceguard.
These procedures include twin-wire drop test device set up helmet preparation, calibration, and helmet impact testing routines. Don't forget that droop-tower testing can be dangerous and safeguards should be used to avoid accidental triggering of the drop-tower test device.
