ABSTRACT 
Six structural models, consisting of hemispherical 
Shells bounded by ring-stiffened cylinders designed to 
provide ideal boundary conditions, were hydrostatically 
pressure-tested to collapse. The models were accurately 
machined from high-strength steel (STS) and were designed to 
investigate both elastic and inelastic huckling modes of 
collapse. The resuits of the tests are compared with theory, 
and the collapse pressures agree within + 7 percent of those 
computed by the TMB empirical buckling equation. 
A nondimensional plot of experimental results is 
presented for the models tested. Based on the plot, a 
simple design method is given for similar accurately machined 
thin spherical shells. 
INTRODUCTION 
In the past decade, increasing emphasis has been placed on the use 
of spherical shells in pressure vessels. Their use encompasses a wide 
range of applications for confinement of internal pressure, and there is an 
accelerating trend for external pressure applications in the field of deep 
underwater research. 
Because most of the materials used in deep~Sea underwater vehicles 
exhibit strain-hardening properties, which may deviate widely from the 
perfectly plastic (plateau) stress-strain pattern, there is a great need 
for wider understanding of the nature of inelastic buckling. However, 
greater knowledge of elastic buckling must also be emphasized in view of 
the growing interest in new tough materials such as glass and ceramics 
which have such extremely high compressive strengths that practical struc- 
tural designs for pressure vessels prevent inception of yielding at even 
the greatest of ocean denehees A historical background of the elastic and 
inelastic theories which apply to spherical shells subjected to external 
pressure has been extensively summarized in Reference 2. 
To evaluate the validity of the hydrostatic collapse pressures 
predicted by the buckling formulas developed from the various spherical 
Re reranees are listed on Page 20. 
