CompositesWorld
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45 CompositesWorld.com NEWS N E W S N S N E W S E N W S W SHM Update inspection for crack detection at periodic intervals. "All aircraft are designed according to damage-tolerance principles," says Roach. "Te FAA and OEM directives are thus based on how long and what loads it takes to make cracks form and grow." For the wingbox fttings, inspection is time-consuming, necessitating removal of seats and foor panels. Roach stresses that none of the normal maintenance is changed until the SHM method is certifed: "Delta is doing both the traditional inspections as well as the SHM." Te ultimate goal is to have sensors mounted in place so that mechanics can plug in from a convenient location to acquire the required data without the time and cost of disassembly and manual inspection. Tis also reduces potential damage to struc- ture during access and risk of human error during inspection. "We have seven aircraft fying with 10 sensors on each aircraft," says Roach. Te program is using SMS' CVM sensors, shape-custom- ized and adhered to wingbox fttings. Tese detect crack initiation and growth by monitoring the slightest pressure change between 0.64-mm channels or "galleries" laser etched into a Tefon pad. Sensors are applied using a self-stick adhesive. Roach says some surface preparation is required to achieve a very tight seal, but on a fairly smooth surface that can be approached directly, "a single CVM sensor can be applied in 10-15 minutes." Vacuum tubes are then routed to a testing socket and attached using snap- clip connectors like those used in landline telephones. During the mandated inspections, a handheld scanning unit is plugged into these testing sockets to interrogate the sensors and give a clear pass or fail indication. According to Roach, system interrogation for the 737 aircraft is performed every three months, typically while the aircraft is at a terminal gate overnight. Te aim is to work with Boeing through the latter part of 2015 to compile collected data and present it to the FAA. "We hope that Delta is able to use SHM as an alternative inspection technique in 2016," says Roach. Tis is just one part of a much larger SHM efort at Sandia, which includes testing of many other types of SHM systems as well as laboratory performance testing as a statistical basis for valida- tion. Standardizing this validation process also is a key objective. "One of our tasks in this program at Delta is to see how well it fts vs. the ARP-6461 guidelines," says Roach. "Tere must be some level of standardization in how SHM is integrated into the airline maintenance operations, including training of the maintenance personnel and cradle-to-grave issues, such as continued airwor- thiness of the SHM system." Paving the path for composites Many in the industry hope the Delta program will serve as a blueprint for SHM implementation on other commercial aircraft. "Once you have one system approved, it should be easier to get another approved," says Amrita Kumar, executive VP of business at Acellent Technologies (Sunnyvale, CA, US). "I am hoping we will get a composites SHM application approved within the next 2-3 years." SMS CEO Toby Chandler sees the Delta program as key in devel- oping recognition of SHM as a commercial technology. "We have clearly established that CVM is an efective tool, and regulatory bodies are close to allowing it as an inspection regime," adds Trevor Lynch-Staunton, project manager at SMS' manufac- turing partner, Anodyne Electronics Manufacturing Corp. (AEM, Kelowna, BC, Canada). "But this is just the tiniest tip of the iceberg," says Chilcott, "particularly with composites, where the understanding of damage is still young and developing. Tis type of capability with compos- ites will allow reducing weight in the doors and vertical tails, for example, because you will develop an understanding of where and how the damage initiates and its progression. We don't have a good way to do that right now." Condition-based maintenance "With the growing number of older aircraft in service, the business case for SHM retroft applications is gaining more and more momentum," explains Bockenheimer in the article "Structural health monitoring: A real-time on-board 'stethoscope' for condi- tion based maintenance," published in the August 2014 issue of Airbus' Flight Airworthiness Support Technology (FAST #54) magazine. "Such an application is typically Generation 1 and aimed at known structure hotspots," he adds. Tese hotspots are defned during an aircraft's certifcation testing and with continuous monitoring following entry into FIG. 1: Antidote to overdesign In the Airbus Roadmap for SHM development, the Generation 1 CBM systems for "hot spot" monitoring (e.g., Delta Air Lines' wingbox ftting program) will be followed by Generation 2 applications, now in development, which enable less conservative, lighter weight designs. Source | Airbus Generation 3 — Fully Integrated Sensor During Manufacture • Manufacturing and assembly quality control • CBM • Weight-saving and damage-tolerance optimized designs • Smart structures Generation 2 — In-service Monitoring for Component Performance • CBM • Weight saving (less conservative design) via improved understanding of damage and reliable, repeatable monitoring Generation 1 — In-service "Hot Spot" Monitoring • Alternative inspection method • Improved aircraft availability via optimized scheduled & unscheduled maintenance • Condition based maintenance (CBM) Generation 0 — Structural and Flight Testing Monitoring • Reduced testing time and cost • Improved engineering design & analysis In Development In Development ✔ ✔