loading. Subsequently, the sustained pressure for specimen 4-2 was 

 lowered to 80% of predicted short-term strength, while specimen 4-3 was 

 subjected to 70%. 



Specimen 4-2 was accidently imploded after 44 hours of load expo- 

 sure during modification of the electronic pump control equipment; no 

 record of the actual implosion pressure was obtained. The implosion 

 value listed in Table B-4 was based on a calculated estimate of the 

 pressure increase in the vessel for a known duration of pump opera- 

 tion . Data were available on the exact time of operation of the pump 

 before implosion occurred. The estimated implosion pressure is pro- 

 bably within a 5% error limit. 



Specimen 4-3 withstood a pressure load of 450 psi (3.1 MPa) for 

 168 hours without incident. The pressure was then reduced to zero 

 where it remained for 16 hours before the specimen was subjected to 

 85% of short-term strength. The pressure level was sustained for 2.5 

 hours without any signs of major structural distress, then the pressure 

 level was raised to 95% where implosion occurred after 3 minutes . 



Radial Displacement Behavior 



Radial displacement terms are defined diagrammatically in Figure 

 B-17. The deflectometer instrumentation method measured radial dis- 

 placement from initial to deflected shape, w. Membrane radial displace- 

 ments, w , were determined from the w data. The following method 

 was used. The reader should picture radial displacement data being 

 displayed on oscillograph paper as a potentiometer moves around the 

 circumference of a cylinder. A straight line would mean a perfect 

 circle. The specimens were not perfect; therefore, the line moved 

 upward (for inward displacement) and downward (for outward displace- 

 ment) . The wavy line on the oscillograph paper is a chart of out-of- 

 roundness data. The wavy line can be digitized (i.e., each point along 

 the line can be given a magnitude value). The average of these values 

 is plotted as a straight line and represents the membrane curve. The 

 average defines the size or radius of the membrane circle. 



63 



