DYNAMICS OF PACKAGE CUSHIONING 



355 



Essentially, a package consists of 



1. Elements of the packaged article which are susceptible to mechanical 

 damage. 



2a. The packaged article as a whole. 



2b. A cushioning medium (excelsior, cardboard spring pads, metal springs, 

 etc.) 



3. An outer container (cardboard carton, wood packing case, etc.) 

 The four major components are illustrated schematically in Fig. 0.2.1. 

 The system is further ideahzed by "lumping the parameters"; for example, 

 the outer container is considered as a single mass, the cushioning is con- 

 sidered as a massless spring with friction losses. The result of this idealiza- 

 tion is to lose some of the fine detail of the real distributed system such as 

 wave propagation through the cushioning and higher modes of vibration in 



o- 



2a 



■2b 



Fig. 0.2.1 — Schematic representation of a package. 

 1. Element of packaged article 

 2a. Packaged article as a whole 

 2b. Cushioning 

 3. Outer container 



the package structure and in the packaged article. Some consideration of 

 these details is given in Part W. 



The idealized system is illustrated in Fig. 0.2.2. The major components 

 of the system are as follows: 



1. A structural element of the packaged item is represented by a mass 

 (wi) supported by a linear massless spring with or without velocity 

 damping. The mass nti is assumed to be small in comparison with 

 the mass of the whole packaged item. 

 2a. The whole packaged item is represented by a mass m-^. 

 2b. The cushioning is represented by a spring which may have a linear 

 or non-linear load-displacement characteristic and which dissipates 

 energy through velocity damping or dry friction. Permanent de- 

 formation of the cushioning is not considered, that is, in a repetition 

 of the drop test it is assumed that the package has the same properties 

 as before the first test. A properly designed package will have essen- 



