CompositesWorld
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43 CompositesWorld.com NEWS N E W S N S N E W S E N W S W SHM Update as tools to monitor structural and in-fight certifcation tests, and the frst applications for monitoring structures in service are now fying on commercial and military aircraft (see Table 2, p. 47). As a sign of this impetus and a possible tipping point, seven of Te Boeing Co.'s (Chicago, IL, US) 737 narrowbody aircraft operated by Delta Air Lines (Atlanta, GA, US) have been outftted with Comparative Vacuum Monitoring (CVM) sensors for crack detection (see "Structural health monitoring: Te toolbox," p. 47) in a program that aims to obtain approval for SHM as an alterna- tive inspection method by 2016. Part of a broader SHM initiative at the Airworthiness Assurance Nondestructive Inspection Vali- dation Center (AANC) operated by Sandia National Labs (Albu- querque, NM, US) for the US Federal Aviation Admin. (FAA, Wash- ington, DC, US), its goal is to schedule maintenance based on the actual condition of each aircraft's structures rather than on fxed time periods based on the average performance of an entire feet. Tis could save millions of dollars in revenue currently lost due to lengthy but often unnecessary manual inspections and aircraft downtime. At Airbus Operations Germany (Bremen), Dr. Clemens Bock- enheimer, SHM leader and head of A350 composites, surface and standardization, reports that local SHM — limited-area moni- toring close to sensors — has moved away from R&D; and is now ready for qualifcation per specifc aircraft application. Although reliability assessment for global SHM monitoring (systems that simultaneously monitor the health of an entire aircraft) is still in development, Airbus is proceeding with local SHM technology- readiness requirements. In fact, Airbus drafted the requirements section of ARP-6461 and is preparing the Validation & Verifcation (V&V;) Center within Airbus Materials, Process & Testing (MP&T;) as its single entry point for SHM technology, with sister Airbus Group company, Testia GmbH (Bremen, Germany), named as the center's operator. Testia will help coordinate testing and other requirements with SHM technology companies, OEMs, parts manufacturers and aircraft operators, to minimize matu- ration time and cost. "Tis is a new and fresh approach that is just now being communicated to the industry," says Testia CEO Holger Speckmann. Looking mainly at the two most mature systems — CVM and an acousto-ultrasonics (AU) technology called SMART Layers — CW here walks through SHM's entry into service and the potential it ofers for future composite aerostructures. SHM already in service SHM has become a standard tool used in aircraft certifcation to monitor structures during ultimate load and fatigue tests. Sensors installed across components and complete aircraft structures eliminate the need to stop the test for manual inspection of selected areas. For example, acoustic emission (AE) sensors from Physical Acoustics Corp. (PAC, Princeton Junction, NJ, US) were used to monitor Boeing's full-scale fatigue testing of the carbon fber reinforced plastic (CFRP) horizontal stabilizer on its 777 widebody aircraft. Also used during the structure's ultimate load and destruction tests, the AE systems supplied the data used in those cases to identify and evaluate subcritical damage propaga- tion and to help defne the part failure sequence. Similarly, the Airbus (Toulouse, France) A380 full-scale fatigue test, performed by IABG (Dresden, Germany), simulated 47,500 fights over 26 months of cyclic loading and used a variety of SHM sensors, including CVM, eddy-current foil sensors (ETFS), acoustic emission (AE), and crack wires (each is defned in "Te toolbox," p. 47). Installed throughout the fuselage and wings, these SHM systems provided detailed information about the initiation of cracks in the plane's aluminum structure, CFRP center wingbox and glass fber aluminum (GLARE) fuselage sections. Te Airbus A350 and Bombardier's (Montréal, QC, Canada) Learjet 85 also used SHM during structure certifcation and/or SHM: Alternative to manual inspection? CVM sensors (see inset, for example) are fying on Delta Air Lines 737 aircraft like this one (left) as part of a program aimed to approve structural health monitoring as an alternative inspection technique to manual disassembly and visual inspection for commercial aircraft by 2016. Source (main image) | Sandia / Photo | Randy Montoya. Source (inset) | Structural Monitoring Systems