Influence of body vibration on deceleration under the slap down drop test

In drop tests, especially under slap down drop test that lid side is suffered the secondary impact, the deceleration is generally higher than that of the horizontal drop test.Reason for the higher deceleration is explained as follows.- Increase of the potential energy due to drop condition (height of the center of gravity under slap down drop test is higher than that of horizontal drop test)- Increase of rotational speed of the package by rebounding of primary impact sideHowever, in some drop tests, high deceleration value is observed, which cannot be explained by these factors.In this study, analysis of 9m slap down drop test with a package model is performed, and factors of the deceleration observed under the slap down drop test is considered.1/3 scale model of a type B package with a mass of 100 metric tonnes and analysis of the 9m slap down drop test using the 1/3 scale model was selected for this study.- Time history of deceleration, which is obtained directly from the package model, would be similar to the actual drop test result. In addition, the deceleration due to the overall behaviour of the package also can be calculated from reaction force of the target floor. By comparison of these values, the fact is observed that the deceleration on the package model includes some vibration.- Such significant vibration is shown just after the impacts at each end of the package. By result of eigenvalue analysis for the 1/3 scale model, it is demonstrated that the vibration is caused by oval deformation of the body due to the impact.Therefore, the high deceleration value with high frequency includes some influence of the vibration, which is caused by the oval deformation.For the evaluation of the deceleration of drop test, the component of the vibration should be separated since this vibration does not affect to overall behaviour of the package. However, the frequency of this vibration is sometimes close to the cut-off frequency, which is suggested in SSG-26 for a package with a mass of 100 metric tonnes. So, the cut-off frequency should be carefully considered to separate an influence of such vibration.