Radial displacement behavior along the length of the cylinder is 

 shown in Figures B-23 through B-25. The effect of the simple-support 

 is vividly shown in Figures B-23 and B-25. The compliance of the 

 actual ring stiffener in the experimental tests can be observed in Fig- 

 ure B-25 where approximately 0.02 inch (0.5 mm) of radial movement 

 occurred. 



For the free-support cylinder (Figure B-24), the difference 

 betvireen experimental and analytical behavior appears great. However, 

 this same difference is shown in Figure B-21, where the comparison 

 appears better. Experimentally, the free-support end-condition using a 

 rubber gasket modeled the ideal free- support quite well. 



FINDINGS 



1. Analytically, using the finite element program NONSAP-A with 

 an advanced constitutive material model, the behavior of the cylinder 

 specimens was predicted with good accuracy. The implosion pressures 

 were predicted 7% lower than actual when a stress criterion controlled 

 failure. It was found experimentally that specimens of L/D of 2.35 

 had an implosion strength 41% greater than specimens of infinite length 

 (long cylinders); analytically, the increase in strength was predicted as 

 53%. 



2. Out-of- roundness was an important parameter in implosion 

 strength and radial displacement behavior. Analytically, the effect of 

 out-of-roundness was to reduce the implosion strength of perfect cylin- 

 ders by 16% to 46% depending on t/D ratio and end-support condition. 

 The ultimate radial displacement for the free- support experimental 

 specimens of t/D = 0.037 was 0.508 inch (13 mm), which was 6.4 times 

 the displacement for a perfect cylinder. The need to model out-of- 

 roundness to obtain accurate analytical predictions was found important. 



79 



