2. Tests of a machined model (OV-5), incorporating a redesign 

 of the sandwich configuration, resulted in a collapse strength 13 percent 

 higher than the minimum specified. The critical mode of failure for the 

 redesign is the same as that for the original design. It is a mode which 

 is greatly influenced by the shape of the stress -strain curve of the mate- 

 rial in the structure. 



3. Before any final conclusions can be drawn concerning the ade- 

 quacy of the suggested redesign, it will be necessary to test larger scale 

 fabricated models with built-in residual stresses and out-of-roundness 

 to simulate the effects due to rolling and welding of plating as expected 

 in the fabrication of the prototype. 



ACKNOWLEDGMENTS 



The authors are indebted to Mr. William E. Ball, Jr., who, prior 

 to leaving the Model Basin, served as project manager of this program. 

 He conducted the pertinent strength calculations and worked out the neces- 

 sary details for the construction and instrumentation of Models OV-1 and 

 OV-2. They are also indebted to Mr. John G. Pulos for his suggestions 

 and advice. 



34 



