Fig 1.
Schematic representation of the 28-inch shock tube illustrating sensor notation and their distribution.
The distance between sensors and the membrane mounting port is indicated. The headform was mounted in three different locations: 1) T5 (denoted as “Inside”), 2) D7 (denoted as “End”) and 3) PP (denoted as “Outside”). Bottom panel presents the evolution of the shock wave profile as a function of sensor location for two nominal BOPs of approximately 70 kPa (T5, left) and 140 kPa (T5, right). The arrival times were adjusted for the clarity of presentation. Profiles for T5, D7 and PP locations are highlighted in color.
Fig 2.
The schematic representation of the headform pressure sensor distribution.
The PCB 102B06 sensors were used exclusively: the five medial sensors H1-H5 are mounted at 45 degrees intervals along the midline, while additional sensors are mounted on the circumference: H6, H7 on the right side, H8 and H9 in the eye cavities and H10 on the right side. The DTS 6DX PRO six-axis accelerometer is mounted inside of the headform in the center of gravity. Representative pressure profiles recorded by surface pressure sensors at nominal BOPs of 70 kPa (left, bottom) and 140 kPa (right, bottom) are presented.
Fig 3.
The incident shock wave velocities.
The shock wave velocities were calculated at different sensor locations at three discrete BOPs, 70, 140 and 210 kPa, used in this study. Shock wave velocities were averaged for twelve individual measurements, and average values were fitted using the linear function. For a diagram of sensor distribution and dimensions refer to Fig 1.
Fig 4.
Quantification of four characteristics of the incident shock wave.
The peak overpressure (A), impulse (B), rise time (C) and duration (D) for three nominal BOPs used in the experimental design are presented. The evolution of the peak overpressure and impulse values is expressed as a function of sensor distance from the membrane mounting port. The bar plots were used to illustrate the evolution of the rise time and duration as a function of sensor location and BOP. Asterisk indicates the statistical significance exists between respective groups shown in both plots.
Fig 5.
The quantification of four pressure wave characteristics for the headform exposed to at a nominal incident shock wave intensity of 70 kPa.
The quantification of peak overpressure (A), rise time (B), impulse (C) and duration (D) recorded for a nominal BOP of 70 kPa. The average values (n = 4) in bar plots were grouped into the four following categories concerning sensor location: incident, eyes (H8 and H9), midline (H1 to H5) and circumference (H6, H7, and H10). For the quantification of the data recorded at 140 and 210 kPa BOPs refer to Supporting information, S2–S5 Figs in the supporting information.
Fig 6.
The normalization of the four characteristics of the pressure waveform recorded by headform surface sensors.
The bar plots of the normalized peak overpressure (A), rise time (B), impulse (C) and duration (D) for surface pressure profiles recorded at various locations on the headform as a function of shock wave intensity (70 and 140 kPa) and headform location (inside, end and outside). The values for 210 kPa BOP are not included for clarity. The values in bar plots were grouped into the four following categories with respect to sensor location: incident, eyes (H8 and H9), midline (H1 to H5) and circumference (H6, H7 and H10).
Fig 7.
The amplification factors for the peak overpressure and rise time at three nominal shock wave intensities.
The plots demonstrating peak overpressure (A) and rise time amplification factors as a function of sensor location along the abscissa of the direction of the shock wave propagation. Normalized values for pressure sensors calculated for measurements performed at 70, 140 and 210 kPa BOPs are presented. Inset: the schematic illustrating the origin and sensor distances used in fits where fourth-degree polynomial functions were used. The H8 and H9 data were excluded from fitting procedure in both cases, while for the rise time the data for H4 sensor were also eliminated.
Fig 8.
Comparison of the linear acceleration of the headform tested in three different locations.
Linear acceleration (X and Z axis) signals for the headform exposed to a 140 kPa nominal intensity shock wave at different locations: A) inside, B) end, and C) outside of the shock tube. The arrival time of the H1 sensor was used as a reference. Quantification of the peak acceleration for the acceleration along the X-axis (D) and Z-axis (E) for three nominal shock wave intensities and three test locations. Asterisk indicates groups with statistical significance threshold p < 0.05.
Fig 9.
The effect of peak overpressure and impulse on the peak acceleration.
The semi-log plots of the peak acceleration as a function of the peak overpressure (left) and impulse (right) measured at the respective test locations. The experimental data points for the Z-axis were fitted using exponential growth function y = a·bx.