DEVELOPMENT AND TESTING OF A 56-IN-DIA JOINTED GLASS PRESSURE HULL,
  JOURNAL OF ENGINEERING FOR INDUSTRY, August, 1970, by D.W. Murphy, 20 pages.

During development of a spherical glass pressure hull up of two hemispheres joined with a metallic joint ring, a problem of bearing edge cracking was encountered. A joint was developed through a series of model tests which placed the bearing edge in radial compression, thus eliminating the cracking. This joint was used to assemble a 56-in. spherical glass pressure hull which was proof-tested to 1610 psi (3650 ft) and cycled 100 times at 1000 psi (2250 fl). Three minor spalls occurred on the proof cycle. This spalling is attributed to either adhesion of the epoxy support material to the glass or support of surface irregularities by the epoxy. Testing was stopped at 100 cycles due to a failure in the epoxy seat-containing material. The joint concept appears workable to 4000 psi if the proper materials are used for the seat-containing material.