Fig 1.
(a) FE head models of different ages, including the 1.5YO, 3YO, and 6YO showing continuous growth model accounting for the sutures in the head. Side view of the upgraded 18YO head model to highlight the corrected occipital shape after upgrading. (b) Isometric view of the head model illustrated with the baseline head model of a 6YO.
Table 1.
Summary of material properties used in the head model.
Fig 2.
Mesh morphing pipeline to “correct” the PIPER software generated flat-headed 18YO, obtaining an upgraded 18YO head model.
Table 2.
CORA score comparison between analysis for relative skull-brain motion.
Table 3.
CORA scores between experimental and simulation results for helmet validation drop test.
Fig 3.
The baseline Helmet-A (upper row) and B (lower row) fit on the 3YO head and scaled helmets model are fitted to 1.5, 6, and 18YO with factors as indicated. The factors are calculated as head circumference between different ages divided by that of the 3YO (49.8, 51.2, 54.3, and 59.6 cm for the 1.5, 3, 6, and 18YO respectively).
Fig 4.
Age dependence of maximum res.lin.accel (left column) and max. skull stress (right column) for all linear impacts (row 1: flat anvil; row 2: kerbstone anvil; row 3: kerbstone-rotated anvil).
Error bars are plotted together with the average values between different impacts plotted as gray lines. The back line in the first row is the fitted curve with coefficients indicated.
Fig 5.
Age dependence of (a) max.res.ang.vel & (b) max.res.ang.acc (b) and (c) maximum brain strain.
Fig 6.
Age-dependence maximum v-M stress in the skull (a,b) and of brain strain (c) with Helmet-A. A sagittal plane of brain strain (1.5, 6, and 18YO oblique front) and skull stress (1.5 and 6YO linear side and linear rear) captured when peak value occurs (illustration with Helmet-A).
Fig 7.
Correlation between max.res.lin.accel and skull stress for Helmet-A with each circle representing one age (column 1) at one impact location; Bar plot of ratio calculated as max.res.lin.accel (g)/max.skull stress (MPa) for each age and all 4 linear impact locations including crown, front, rear, and side (column 2).
Each circle on column 1 corresponds to one bar on the right bar plot, e.g. as indicated for the 1.5YO and 18YO front impact (blue color). The factor indicated in each bar plot is defined as mean ratio of the 4 impacts for the 1.5YO divided by the corresponding value for the 18YO. For example, for a linear flat anvil (row 1), the mean ratio for the 1.5YO is 0.206 and the mean ratio for the 18YO is 0.116, resulting in a value of 1.77 representing the difference between 1.5YO and 18YO. Similarly, the factor for linear kerbstone and kerbstone rotated are calculated as 1.67 and 1.57 respectively. The same analysis is done for Helmet-B resulting in 1.66, 1.66, and 1.57.
Fig 8.
Correlation between max.res.ang.vel and brain strain.
The relatively constant relation between brain strain and rotational velocity suggests a similar pass/fail criteria of rotational velocity for child helmets as adults.