Wednesday  |  Salon 7  |  04:40 PM–05:00 PM

#15955, DIC Replacement of Draw Wire Sensors for Vulcan Centaur Component Structural Testing

Digital image correlation (DIC) systems are normally used with full-field random patterning, to determine displacements and strains at thousands or sometimes tens of thousands of closely spaced data points. However, some applications do not require such a rich data set, and much insight can be gained from a relatively low number of readings, measuring only displacements. Modal analysis is one increasingly common example, for which 50-100 locations is often sufficient to extract an operating deflection shape. For trajectory tracking, a best-fit plane using 3-5 points enables measuring roll, pitch, yaw, velocity and acceleration.

This presentation is an overview of the use of DIC to replace draw wires to measure displacements for structural testing of the payload launch adapter, interstage adapter and booster of the Vulcan Centaur rocket. During this test program, a total of 24 DIC systems were used simultaneously on two test rigs at NASA Marshall in Huntsville AL, and 10 additional ones were used for booster structural qualification tests at the Dynetics test stand on the United Launch Alliance campus in Decatur, AL. Real-time displacement data was channelized, streamed to the control room, and combined with hundreds of channels of standard instrumentation such as strain gauges. For the first test, the equivalent of 72 draw wires was obtained using 8 DIC systems. For later tests, hundreds of optical gauges were being monitored and recorded.

A newly developed function dubbed Total ReCal enabled push-button recalibration of each sensor from the control room, with no physical action required, and was essential for the use of so many DIC systems in a long-term test setup to be practical. To achieve the desired accuracy levels of 1-2 mils (~25-50 microns), stability of the sensors relative to ground was critical. This was verified by a separate stability test of equal duration to each load case, typically 45-60 minutes, immediately before or after each one.

Tim Schmidt   Trilion Quality Systems
Jose Samaniego   Trilion Quality Systems
Rusty Littleton   NASA Marshall Spaceflight Center
Shelby Balch   Jacobs Space Exploration Group
Jacob Chancery   Jacobs Space Exploration Group
Alan Patterson   Russell Management Group, LLC