DYNAMICS OF PACKAGE CUSHIONING 



369 



lbs. Substituting these values in (1.6.1) and (1.6.2), we find ^o = 255 and 

 r = 108. Then 



AW2hr 4 X 22.5 X 36 X 108 



B = 



ka 



(255)' 



l/t" - / 



2 X 36 X 255 



22.5 



= 5.4, 



= 28.6. 



Entering Fig. 1.5.2 with B = 5.4 we find Gm/Go = 1.9. Hence 



G^ = 28.6 X 1.9 = 55 



This is close enough to the 50g rating of the tube to call the cushioning 

 safe insofar as maximum acceleration is concerned. 



0.2 0.4 0.6 08 1.0 12 1.4 1.6 1.8 2.0 



Fig. 1.6.1 — Experimental load-displacement curve for a corrugated cardboard spring pad 



and excelsior cushion. 



The maximum displacement, obtained by entering Fig. 1.5.1 with B = 

 5.4 and finding dmldn = 0.75. Then dm = 0.75 X 2h/Go = 1.95 inches. 

 Hence, the package is much larger than necessary since approximately 8 

 inches of cushioning thickness is supplied to accommodate 2 inches of 

 displacement. 



1.7 The Tension-Spring Package (Class B) 

 The tension spring package is useful when the allowable Gm is so small 

 and height of drop so great that a large displacement (say dm > several 

 inches) is required. The decision as to whether or not a tension spring 

 package is indicated may be made on the basis of a preliminary estimate 

 of displacement based on the linear case. Suppose the height of drop is 

 to be 60 inches and the allowable acceleration for the packaged item is 



