Shell theories, six small accurately machined high-yield steel models were 
fabricated. To facilitate fabrication and subsequent instrumentation and 
thereby save time and funds, the models were designed and machined as 
hemispherical heads bounded by externally ring-stiffened reinforced cyl- 
inders in lieu of the actual spheres. The cylinder of each separate model 
was so deSigned as to Simulate at the boundary the action of the remaining 
half of the sphere, i.e., membrane deflection and no rotation. The measured 
uniform strain-gage readings and collapse pressures are consistent with 
similar work being performed on spherical shells and suggest an adherence 
of the test results to the ideal boundary design. 
Five of the models were designed to fail after the inception of 
yielding (inelastic buckling), and the remaining model was designed to 
fail well below the yield point within the elastic range (elastic buckling). 
The test resullits of these six near-perfect machined models, all of which 
failed within their proper ranges of elasticity, are presented in this 
report and compared with theory. 
A nondimensional plot of experimental results is also presented 
and discussed. The plot is presented for the purpose of providing a simple 
method of structural design for similar accurately machined thin spherical 
shells with similar stress-Strain patterns. The results of a similar plot 
currently being developed at the Model Basin from work performed on larger 
Segmentally welded high-strength steel hemispherical shells are also dis- 
cussed. 
DESCRIPTION OF MODELS 
Six hemispherical models bounded by external ring-stiffened cylinders 
were machined from high-strength, special-treatment steel (STS). Models 
6, 4A, 4A Revised, 1CR, and 1CR Revised are approximately 7 in. in diameter 
and possess respective measured spherical shell thickness to nominal radius 
ratios (h/R) of 0.007, 0.017, 0.018, 0.035, and 0.036. Model 7A is 
approximately 4 in. in diameter and possesses an h/R equal to 0.003. 
Structural dimensions including the average compressive yield strengths as 
individually measured from eight representative sample coupons taken from 
the stock material of each model are presented in Table 1 together with a 
generalized sketch of the models. Typical stress-strain curves for the STS 
