these stresses is also shown in Reference 2. From the stresses obtained 



2 

 by use of this analysis, theoretical strains can be computed and com- 

 pared directly with observed data. 



To evaluate the theoretical analysis, four sandwich-type models 

 were fabricated from epoxy resin and tested under external hydrostatic 

 pressure. Strains were recorded at locations next to the webs and midway 

 between the two webs on both outside and inside shells. A longitudinal 

 strain distribution along a web spacing was also measured in one model. 

 This report presents the experimental strains and a comparison of observed 

 and theoretical values. 



DESCRIPTION OF MODELS 



Four models, designated SER-1, SER-2, SER-3, and SER-4, were 

 fabricated from epoxy resin. The composition of the epoxy resin was 50 

 percent Versamid 125 and 50 percent Epon 828. A sandwich-type con- 

 figuration for the models was constructed by joining a series of channel- 

 shaped rings together. These rings were individually formed by pouring 

 liquid resin into a mold, allowing the resin to harden at room temperature 

 for 24 hr, and then post curing the rings in an oven for 8 hr at a tem- 

 perature of 130 F. Each ring was then machined to the final required 

 dimensions. The dimensions of these rings are shown in Figure 1. 



Specimens were made to determine the material properties of the 

 epoxy resin. A Young's modulus of 328,000 psi and a Poisson's ratio of 

 0.4 were determined from separate tests using a compressometer, deflectom- 

 eter, and a Tuckerman optical strain gage. These values were used for 

 determining the theoretical strains presented in this report. 



The design of the four models was oriented to study the effects of 



shell lengths on stress distributions in the sandwich shells. The basic 



design of the shell thicknesses and the radii was fashioned after a 



3 

 geometry for a proposed deep-diving oceanographic hull structure. On 



each of the four models, the outside radius was 5.40 in., the inside 



radius was 4.11 in., the outside and inside shell thicknesses were 0.163 



in., and the web thickness was 0.138 in. Only the web spacing in the four 



models varied. The spacings (dimension L shown in Figure 1) were 0.75 in. 



for Model SER-1, 1.00 in. for Model SER-2, 1.25 in. for Model SER-3, and 



1.50 in. for Model SER-4. 



