CompositesWorld
Issue link: https://cw.epubxp.com/i/546021
AUGUST 2015 44 CompositesWorld FEATURE / STRUCTURAL HEALTH and proper maintenance actions before the plane resumes service. Integrating impact damage detection into the tail's structural design has enabled weight savings because ground contact is no longer a damage case for which the tail must be overbuilt to sustain continued service. Instead, it is detected and dealt with immediately. Another example is the Life-Time Monitoring System (LTMS), an optional installation on Airbus A400M aircraft, which uses strain gages to measure and record aircraft structural loads, including overloads, hard landings and total cycles accumulated. Tese data enable operators to better track aircraft use and associ- ated fatigue for more efcient maintenance planning. Local frst, then global "Confdence in local SHM applications for selected technologies, for example CVM and eddy current, is no longer an issue," says Bockenheimer. Numerous demonstrator installations and dura- bility tests for a wide array of SHM systems have been completed over the past two decades (see "Side Story," at left). However, Bockenheimer cautions that local SHM applica- tions are very diferent from global SHM systems. "Local is more restricted, monitoring under and close to the sensor, similar to conventional NDT, so how to prove it is more clear. For example, we proved Probability of Detection (POD) for CVM in 1995." How to prove detection capability for global monitoring and how the whole system communicates across the fuselage and with other systems is still in development. Te industry is gaining confdence, however, as it continues to accrue successful fight history with local SHM systems. "Te need now is for standardization in the process for quali- fcation and implementation in specifc aircraft applications," Bockenheimer asserts. He notes that Airbus has been working with AISC-SHM and other industry groups for more than a decade to build a robust certifcation path. "Aircraft engines have used condition monitoring systems for years," says Andrew Chilcott, director, Structural Monitoring Systems (SMS, Nedlands, Australia; Century City, CA, US and Ashford, UK). Bockenheimer agrees, citing Built-In Test Equip- ment (BITE) in avionics and Health and Usage Monitoring Systems (HUMS) in helicopters as additional examples of this trend to integrate condition monitoring into the overall aircraft systems architecture. He adds, "SHM will become one more core element in this architecture, enabling manufacturers to design and qualify systems that will reduce the time and cost of scheduled and unscheduled maintenance and increase aircraft availability." Alternative aircraft inspection method Tis is exactly the aim of the program at Delta Air Lines led by the AANC and its operator, Sandia Labs. "Te program to achieve certifcation of SHM for routine use on commercial aircraft began several years ago," says Sandia senior technical fellow, Dennis Roach. Te application is an aluminum ftting in the Boeing 737NG aluminum center wingbox, for which an airworthiness directive had been issued, mandating visual and eddy-current SIDE STORY Current momentum in local structural health monitoring (SHM) development can be credited, in part, to developmental efort on the part of the system developers that follow. CVM system demonstrations in both metal and composites applica- tions by Structural Monitoring Systems (SMS, Nedlands, Australia; Century City, CA, US and Ashford, UK) include installations fying on military fxed-wing aircraft and rotorcraft as well as commercial airliners in service, most notably for Delta Air Lines (see main article). The last readings from those systems — mounted to metal structures — were taken a couple of years ago, making that nearly a decade of in-fight service, and that data was subsequently shared with the US Federal Aviation Admin. (FAA, Washington, DC, US). Brazilian aircraft manufacturer Embraer (Embraer-Empresa Brasileira de Aeronautica S.A., São José dos Campos) also has E-190 regional jet aircraft ftted with CVM and SMART Layer systems fying for several commercial airline customers, as it prepares to introduce a scheduled structural health monitoring (S-SHM) system that involves the installation of fatigue and corrosion sensors in hard-to-access areas of the aluminum airframe around the aft doors. Meanwhile, Acellent Technologies (Sunnyvale, CA, US), the US Army Research Laboratory (ARL, Adelphi, MD) and the Aero-Flight Dynamics Directorate (AFDD, Mofett Field, CA, US) have been fight-testing Acellent's SMART Layers on H-60 Blackhawk helicopter metal structures for 5 years to validate their integration and long-term operation and survivability on rotorcraft. Acellent also has completed Small Business Innovation Research (SBIR) projects with the US Navy for SHM systems on composites, which are supported by H-60 manufacturer, Sikorsky (Stratford, CT, US), for future implementation on the more composites-intensive CH-53K. Other large-scale tests include those completed by the Tokyo, Japan-based "heavies" — Fuji Heavy Industries, Kawasaki Heavy Industries and Mitsubishi Heavy Industries — as part of the Japanese SHM Technologies for Aircraft Composite (JASTAC) structures program. In 2013, Airbus (Toulouse, France) extended this program to a second phase — which also includes the Japanese Aerospace Exploration Agency (JAXA, Tokyo) — targeted to deploy Phase I optical fber- based SHM technologies into aircraft, extending through what Airbus terms Generation 3 in its SHM Roadmap (see Fig. 1, p. 45). Decades of SHM demonstrations build confdence in local SHM fight testing, as do various SHM protosystems — early develop- ments/smart structure forerunners that sense and communicate data about structures — fying on Airbus, Boeing and military aircraft today (Table 2, on p. 47). One example, developed for the Airbus A340-500/600 family of long-haul aircraft, is the tail strike indication (TSI) system now also deployed on the Airbus A380. Te TSI uses two sensors, each with two crack-wire lines for redundancy in sensing if the fuselage tail contacts the ground during take-of. If the conductive/resis- tive wires along the tail are disrupted, a cockpit indicator alerts the crew. A crewmember, then, can trigger procedures for inspection