Documentation:FIB book/problems/HIC problem

A company is developing a new-generation of helmets for bicycle riding. They are testing their devices with a dummy head. To examine the helmet's response to head impact, they did a helmet drop test and wanted to use the Head Injury Criterion (HIC) to evaluate its safety performance. The drop was done only on the X-Z plane. So only accelerations on the X-Z plane were recorded. You could download the raw data here: File:Bike Helmet Drop Test Acceleration Data.xlsx

Notes: Head Injury Criterion (HIC) is calculated as follows: $HIC=\max _{t_{1},t_{2}}\left({\frac {1}{t_{2}-t_{1}}}\int _{t_{1}}^{t_{2}}a(t)dt)\right)^{2.5}(t_{2}-t_{1})$
where a_r is resultant linear head acceleration in g, and t₁ and t₂ are in seconds. 

You can use MATLAB to import the Excel sheet data and process it. Please include the MATLAB code (or other source code if you choose to use other software for data analyzing), relevant formulas and calculations, etc. with your submission.

Question 1 Plot the resultant linear acceleration

Plot the resultant linear acceleration vs. time. Identify the peak resultant linear acceleration.

SOLUTION (expand to show)
Plot: Figure 1. Resultant linear accelerations for bike helmet test data The peak resultant linear acceleration is 80.7370 g.

Question 2 Plot the HIC values using 5 ms, 15 ms and 36 ms window

Plot HIC values using 5 ms, 10 ms, and 15 ms time window vs. time in one figure. Identify the maximum HIC values from each time window. Determine the HIC15 value based on the results of these three time windows.

SOLUTION (expand to show)
Plot: Figure 2. HIC values using 5, 10 and 15 ms windows The maximum HIC value is 177.0352 using a 5 ms window, is 271.2855 using a 10 ms window, is 147.6691 using a 15 ms window. Therefore, based on these three results, HIC15 corresponds to the highest among them, which is 271.2855.

Question 3 Discuss why checking different time intervals for HIC15

Explain why we need to check different time intervals, 5 ms and 10 ms in this assignment, for getting HIC15.

SOLUTION (expand to show)
HIC15 is defined as the maximum HIC value over a time interval of 15 ms or LESS. Therefore, we need to check shorter time intervals to see if they can produce even higher impacts or not.

Question 4 Name one major strength and one major limitation of using HIC

Name one major strength and one major limitation of using HIC to estimate the severity of head injuries.

SOLUTION (expand to show)
Strengths: HIC considers the head impact over a time duration, which is more realistic compared to only considering the maximum acceleration impact value. Limits: One of the biggest concerns of using HIC is that it solely uses linear acceleration measurements to compute its value, lacking a consideration on other vital factors such as rotational acceleration, location/area of the impact, etc.

References

Special thanks to Emily Blevin for kindly providing the raw acceleration data.