49 CFR § 572.7 - Neck.
(a) The neck consists of the assembly shown as number SA 150 M020 in Figure 1 and conforms to each of the drawings subtended by number SA 150 M020.
(b) When the neck is tested with the head in accordance with paragraph (c) of this section, the head shall rotate in reference to the pendulum's longitudinal centerline a total of 68° ±5° about its center of gravity, rotating to the extent specified in the following table at each indicated point in time, measured from impact, with a chordal displacement measured at its center of gravity that is within the limits specified. The chordal displacement at time T is defined as the straight line distance between (1) the position relative to the pendulum arm of the head center of gravity at time zero, and (2) the position relative to the pendulum arm of the head center of gravity at time T as illustrated by Figure 3. The peak resultant acceleration recorded at the location of the accelerometers mounted in the head form in accordance with § 572.11(b) shall not exceed 26g. The pendulum shall not reverse direction until the head's center of gravity returns to the original zero time position relative to the pendulum arm.
| Rotation (degrees) | Time (ms) ±(2 + .08T) | Chordal Displacement (inches ±0.5) |
|---|---|---|
| 0 | 0 | 0.0 |
| 30 | 30 | 2.6 |
| 60 | 46 | 4.8 |
| Maximum | 60 | 5.5 |
| 60 | 75 | 4.8 |
| 30 | 95 | 2.6 |
| 0 | 112 | 0.0 |
(c) Test procedure: (1) Mount the head and neck on a rigid pendulum as specified in Figure 4, so that the head's midsagittal plane is vertical and coincides with the plane of motion of the pendulum's longitudinal centerline. Mount the neck directly to the pendulum as shown in Figure 4.
(2) Release the pendulum and allow it to fall freely from a height such that the velocity at impact is 23.5 ±2.0 feet per second (fps), measured at the center of the accelerometer specified in Figure 4.
(3) Decelerate the pendulum to a stop with an acceleration-time pulse described as follows:
(i) Establish 5g and 20g levels on the a-t curve.
(ii) Establish t1 at the point where the rising a-t curve first crosses the 5g level, t2 at the point where the rising a-t curve first crosses the 20g level, t2 at the point where the decaying a-t curve last crosses the 20g level, and t4 at the point where the decaying a-t curve first crosses the 5g level.
(iii) t2–t1 shall be not more than 3 milliseconds.
(iv) t3–t2 shall be not less than 25 milliseconds and not more than 30 milliseconds.
(v) t4–t3 shall be not more than 10 milliseconds.
(vi) The average deceleration between t2 and t3 shall be not less than 20g and not more than 24g.
(4) Allow the neck to flex without impact of the head or neck with any object other than the pendulum arm.