AFRL examines technology used to test B-2 aft deck performance

  • Published
  • By Jack Coate and Pete Meltzer, Jr.
  • AFRL Materials & Manufacturing Directorate
WRIGHT-PATTERSON AIR FORCE BASE, Ohio --  Engineers at the Air Force Research Laboratory, working with the 780th Test Squadron Aerospace Survivability and Safety Flight here, have identified an effective method for measuring deformation in the aft deck of the B-2 bomber using a series of special engine tests conducted last year at the base's Aerospace Vehicle Survivability Facility. 

The aft deck structure is located behind the exhaust nozzles on the upper surface of the aircraft and is subjected to repeated thermal and vibro-acoustic stresses sufficient to cause premature fatigue cracking. Measuring deformation is an effective way of validating computer models of the aft deck's mechanical response to these stresses. 

The aft deck project demonstrated the reliability of the proposed deformation measuring system, ARAMIS 3D Image Correlation technology, developed by the German company GOM Optical Measuring Techniques, using live ground engine test runs and a test specimen. These tests also validated the findings obtained from previous laboratory tests and experiments, and most importantly, confirmed that ARAMIS technology can work in the field. 

ARAMIS is designed to inspect complex materials and geometries for deformation and strain during loading. The system offers a non-contact and material independent determination of deformation and strain using three-dimensional video correlation methods and high-resolution digital cameras. 

The object under load is viewed by one or more high-resolution digital cameras. A clearly visible random or regular structure (showing a good contrast) that has been applied to the object's surface is deformed along with the object. The cameras record the deformation under different load conditions and the results--3D-displacement, tangential strain and the component's contour--are evaluated using digital image processing. 

The AFRL Materials and Manufacturing Directorate Systems Support Division Materials Test and Evaluation Team and 780th TS/OL-AC worked together to design and set-up the engine test runs to examine the performance of the ARAMIS system. The AFRL team configured the thermal imaging cameras and mounting structures; provided data acquisition systems and contracted technical support to Trilion Quality Systems, the U.S. vendor for ARAMIS; and handled heavy equipment requirements. They also supplied and installed test instrumentation, such as microphones and accelerometers, required to conduct the test runs. 

The 780th TS/OL-AC successfully executed the ARAMIS Engine Exhaust Building Block Test in the approved detailed test plan. The goal was to run the engine up to as close to maximum power as possible while maintaining safety and continue to run the engine to ensure the exhaust temperature reached a stabilized condition. ARAMIS and thermal cameras/thermocouples provided and configured by the AFRL team recorded the rise data. Three engine runs were conducted to gauge the repeatability of the test, with time set aside between the runs for inspections, adjustments and maintenance. 

Northrop Grumman's B-2 Spirit stealth bomber brings massive firepower to bear, in a short time, anywhere on the globe. Its "stealth" characteristics give it the unique ability to penetrate an enemy's most sophisticated defenses and threaten its most valued, and heavily defended, targets. Ensuring its operational readiness is paramount to its critical role in the United States Air Force's concept of "Global Power, Global Reach." 

Accurate assessment of the aft deck's integrity is and will continue to be a high priority because of mission readiness factors. In the mean time, modification and repair kits have been fielded to keep the B-2 flying until redesigned production decks can be delivered.