Neck assembly and test procedure.

§ 572.73 Neck assembly and test procedure. (a) Neck assembly. The neck consists of the assembly designated as SA 106C 020 on drawing SA 106C 001, sheet 2, and conforms to each drawing listed on SA 106C 001, sheet 9. (b) Neck assembly impact response requirements. When the head-neck assembly (SA 106C 010 and SA 106C 020) is tested according to the test procedure in § 572.73(c), the head: (1) Shall rotate, while translating in the direction of the pendulum preimpact flight, in reference to the pendulum's longitudinal center line a total of 78 degrees ±6 degrees about the head's center of gravity; and (2) Shall rotate to the extent specified in Table B at each indicated point in time, measured from time of impact, with the chordal displacement measured at the head's center of gravity. (i) Chordal displacement at time “T” is defined as the straight line distance between the position relative to the pendulum arm of the head's center of gravity at time “zero;” and the position relative to the pendulum arm of the head's center of gravity at time T as illustrated by Figure 3 in § 572.11. (ii) The peak resultant acceleration recorded at the location of the accelerometers mounted in the headform according to § 572.77(b) shall not exceed 30g. Table B Rotation (degrees) Time (ms) ±(2 + .08T) Chordal displacement (inches) ±0.8 0 0 0 30 26 2.7 60 44 4.3 Maximum 68 5.8 60 101 4.4 30 121 2.4 0 140 0 (3) 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. (c) Neck test procedure. The test procedure for the neck is as follows: (1) Mount the head and neck assembly on a rigid pendulum as specified in § 572.21, Figure 15, so that the head's midsagittal plane is vertical and coincides with the plane of motion of the pendulum's longitudinal center line. Attach the neck directly to the pendulum as shown in § 572.21, Figure 15. (2) Release the pendulum and allow it to fall freely from a height such that the velocity at impact is 17.00 ±1.0 fps, measured at the center of the accelerometer specified in § 572.21, Figure 15. (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 t 1 at the point where the rising a-t curve first crosses the 5g level; t 2 at the point where the rising a-t curve first crosses the 20g level; t 3 at the point where the decaying a-t curve last crosses the 20g level; and t 4 at the point where the decaying a-t curve first crosses the 5g level. (iii) t 2 −t 1 shall not be more than 3 milliseconds. (iv) t 3 −t 2 shall not be more than 22 milliseconds, and not less than 19 milliseconds. (v) t 4 −t 3 shall not be more than 6 milliseconds. (vi) The average deceleration between t 2 and t 3 shall not be more than 26g, or less than 22g. (4) Allow the neck to flex without the head or neck contacting any object other than the pendulum arm. (5) Allow at least 60 minutes between successive tests. [56 FR 57836, Nov. 14, 1991, as amended at 57 FR 4086, Feb. 3, 1992]