Stachiw 



model. When the rigidity of the penetration insert was considerably 

 lower than the rigidity of concrete (0.5 x 10^ psi for polyvinyl 

 chloride versus 3.65 x 10" for concrete) the sphere equipped with 

 such inserts (Sphere No. 17) imploded at a significantly lower 

 pressure than the sphere without penetrations (Table 4). 



Table 4. Implosion Pressures of Concrete Spheres With Solid 

 Penetration Inserts. 



* Strength of concrete was determined by subjecting 3x6 inch test 

 cylinders of the same mix and age as the associated concrete 

 sphere to compression testing in an uniaxial test machine. The 

 compressive strength shown is the average of 18 test cylinders 

 loaded to destruction at 2100 psi/minute rate. 



THE EFFECT OF PENETRATION INSERT RIGIDITY ON STRAINS AND 

 STRESSES IN THE SPHERE - The strains at the small penetrations in 

 the concrete were not significantly different from strains measured 

 at locations in the sphere away from penetrations. The strains at 

 the large penetrations in the concrete, however, were significantly 

 higher than strains measured at locations in the sphere away from 

 penetrations only in the sphere No. 17 containing plastic inserts 

 in the penetrations. The strains measured there one half of an inch 

 away from the edge of the penetration with a plastic insert were 

 approximately 40 percent higher than the strains in the same sphere 

 not in close proximity to the penetrations. When the strains on the 



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