this type of analysis was highly dependent on actual coefficients and the nominal load transmitted through  the diaphragm. To address that part of the issue, development tests were performed to determine the actual loads needed to remove the wedge as pressure was varied. The development tests were performed with materials that had higher than as-designed couples to drive the coefficient of friction to the  highest possible. The valve was to be all Inconel 718. The development test was performed with an Inconel 718 wedge and an aluminum body. These tests showed that the 350-lbf (1560 N) maximum design point was twice the highest value recorded. Twenty tests were run and none had loads greater than 185 lbf (823 N), with pressure ranging from as little as 100 psig (600 kPa) to over 3500 psig (24,000  kPa). With a requirement for 100% force margin, the spring load required was set at 700 lbf (3000 N).    An unforeseen issue was found during testing. We showed that the analysis of the disk, assuming a thin  membrane, was predicting failure at much lower pressures than those found. Using a disc diameter of 0.25 in (6.4 mm) and thickness of 0.002 to 0.003 inch (0.051 to 0.076 mm), a Roark’s pure membrane  analysis indicated that rupture would occur at around 50 psig (344 kPa) to 150 psig (1,000 kPa). Testing  showed this to be a variable from 300 (2,000 kPa) to 900 psig (6,200 kPa). Review of the actual failure  and analysis from the MSFC analysis branch showed that the actual failure mechanism is a combination of shear, bending, and membrane type failures. An empirical method was developed to match the test data to the analysis, and it was determined that disk area needed to increase as thickness could not be  consistently controlled to less than 0.002 inch (0.051 mm). This drove the disk size to a 0.75-inch (0.02m) diameter.  Figure 4 shows some of the development test articles and a graph of the load results. Visually, the test  revealed that the rupture disk stayed intact, fractured cleanly along the “petals”, and opened fully to  achieve the required flow area. Flow testing of this design will be performed to prove the flow is  acceptable. This was to be accomplished following final assembly or the completed design later in the development effort. Flow testing was never an objective of this development. Additional development testing showed this to be satisfactory given that no test article failed to rupture at 250 psig (1,700 kPa) or less. So, this larger disk concept was incorporated into the valve.  To address the second concern, the fluid used to burst the development valves was collected and  sampled for particulate generation. This testing showed that there were no particles over the limit of 0.5 micron found. In fact, none were ever detected. This validated the burst disk design features of a circular cut 340 degrees around the edge of the opening and an “X” shape in the center to force the  ruptured dick to open like pedals when the disk failed. For each test, the development hardware disk  failure matched this configuration. The third issue was the spring-rate. MSFC built two trial springs (see Figure 5) and each was tested. Even though neither was heat treated, a minimum spring rate of 4000 lbf/in (700,000 N/m) was achieved. The actual loads are assumed to be 10% to 20% greater when heat treated. Even this lower number provided the ideal 800 lbf (3600 N) required at 0.200-in (5-mm) stroke for this design, and still yielded the  required 100% margin.   The results of these test showed that the spring/bellows system and the disk concept were valid, and the  design was completed. The only remaining concern was the flow consistency. This could only be  addressed with the final design and in a lot test program. Additional funding was requested and obtained later in the year. The results from that effort will be reported when available. The development testing resulted in similar failures for each test over the wide range of test pressures. The concern was mitigated with this qualitative data. Hard quantitative data is to be obtained later in Fiscal Year (FY) 14.    479