Dynamic Characteristics of Parallel Linkage Pendulums 760374
Many impact tests use some type of pendulum. For example, the compliance test of Federal Motor Vehicle Safety Standard No. 215, the bumper standard of automobiles, is usually conducted by using a parallel linkage pendulum. Since the center of percussion as well as the equivalent impacting mass of the test device are mentioned in the standard, some dynamic characteristics of the pendulum need to be examined.
It is found that for a parallel linkage pendulum: (1) There exists no center of percussion regardless where the impact line is on the impacting block; but nevertheless, the summation of horizontal reaction forces in the top supporting hinges reduces drastically when the mass ratio of the impact block and the total masses of the supporting linkages is greater than one. (2) There does exist an optimum impact point to eliminate the rotational effect of the vertical reactions. The impactor would have a translational motion at the instant of impact even if it is suspended by cables when an impact is through this point. The location of this impact point is dependent upon the mass ratio of the impact block and the linkages as well as the distance from the mass center of the impactor to the level of the hinge points on the block. (3) The equivalent impacting mass of the device is equal to the sum of the block mass plus one third of the total linkage mass and it is independent of the impact location on the block.