**2.6 NDE/I/T technology**

The use of composites for high performance applications requires the ability to identify and ultimately eliminate structural defects that occur during manufacture, assembly, service, or maintenance. The entire field of nondestructive evaluation (NDE) has continued to develop and evolve in parallel to the growth of composite

**111**

**Figure 22.**

*Autoclaves. Source: Spirit, DLR.*

speed, high-performance inspection method.

*The Evolution of the Composite Fuselage: A Manufacturing Perspective*

structure applications. It is both an enabling technology and one that has been driven by the market and the need. NDE of composites is a mature technology and has been used successfully for many years, however, the composite structures of today and tomorrow have grown in both scale and complexity. New and improved nondestructive testing (NDT) methods and technologies are necessary to improve detection capabilities, meet growing inspection needs, and address future nondestructive inspection (NDI) requirements. NDT methods currently used in aerospace applications span a broad range of technologies, from the simple coin tap test to fully automated, computerized systems that can inspect very large parts (**Figures 23** and **24**). Many of the newer NDI methods are "wide-area" inspection techniques, which enable more uniform and rapid coverage of a test surface which can improve productivity and minimize human error. Technical advances in both computing power and commercially available, multi-axis robots and/or gantry systems, now facilitate a new generation of scanning machines. Many of these systems use multiple end effector tools yielding improvements in inspection quality and productivity.

Ultrasound is the current NDE method of choice to inspect large fiber reinforced airframe structures. Over the last 2 decades, ultrasound scanning machines using conventional techniques have been employed by all airframe OEMs and their top tier suppliers to perform these inspections. A limitation of ultrasonic inspection can be the requirement to use a couplant between probe and test part. VACRS (variable automatic couplant and recovery system) has helped changed the way very large area ultrasonic inspections are done [6]. The VACRS system uses a lightweight couplant and delivery/recovery system that makes it possible to conduct a C-scan with large ultrasonic arrays without the large water requirements. It works with Boeing's mobile automated scanner (MAUS®) and other scanning systems on the market. Shearography and thermography are relatively fast, non-contact methods that require no coupling or complex scanning equipment. Laser shearography was initially applied to aircraft structure in 1987 by Northrop Grumman on the B-2 bomber. Since that time, laser shearography has emerged as an advanced, high-

*DOI: http://dx.doi.org/10.5772/intechopen.82353*

**Figure 21.** *Tooling. Source: Boeing, Coast composites.*

*The Evolution of the Composite Fuselage: A Manufacturing Perspective DOI: http://dx.doi.org/10.5772/intechopen.82353*

**Figure 22.** *Autoclaves. Source: Spirit, DLR.*

*Aerospace Engineering*

**2.5 Large autoclaves**

breakdown mandrel (**Figure 21**).

service their large autoclaves (**Figure 22**).

**2.6 NDE/I/T technology**

The sector panel construction used on the A350 allows for the use of invar for all the fuselage tooling. This includes the IML controlled sector panels fabricated by Spirit for Section 15. The approach Spirit applied is very similar to the one used on the 787 with the exception of the use of sector panels instead of a one piece barrel

One enabling capability that supports the evolution of the current state-ofpractice for composite fuselage manufacturing is large autoclaves. There are many, many, many, many research and historical, ongoing and planned for the future, development efforts focused on OOA (or non-autoclave as it was called in the 1980s) materials and processes with the goal of eliminating that monument, the autoclave. The goal is noble (and not new) and the development efforts are making great progress and will, someday in the future, represent a significant (if not all) portion of the composite structure on commercial passenger aircraft—just not today. We already see components made from liquid molding processes being used in specific applications and families of parts and components on aircraft like the 787 and A350, just not the primary fuselage panels and stringers—yet. The maturity, forgiving nature, and low risk of baseline autoclave cured systems made it an easy decision for programs like the 787 and A350 to progress knowing that it was just time and money required to build autoclaves large enough to meet the needs of the program. No new technology needed, just scale and incorporation of improvements being realized by the autoclave industry, such as control systems and operational efficiencies. Spirit even built their own liquid nitrogen generating plant onsite to

The use of composites for high performance applications requires the ability to identify and ultimately eliminate structural defects that occur during manufacture, assembly, service, or maintenance. The entire field of nondestructive evaluation (NDE) has continued to develop and evolve in parallel to the growth of composite

**110**

**Figure 21.**

*Tooling. Source: Boeing, Coast composites.*

structure applications. It is both an enabling technology and one that has been driven by the market and the need. NDE of composites is a mature technology and has been used successfully for many years, however, the composite structures of today and tomorrow have grown in both scale and complexity. New and improved nondestructive testing (NDT) methods and technologies are necessary to improve detection capabilities, meet growing inspection needs, and address future nondestructive inspection (NDI) requirements. NDT methods currently used in aerospace applications span a broad range of technologies, from the simple coin tap test to fully automated, computerized systems that can inspect very large parts (**Figures 23** and **24**).

Many of the newer NDI methods are "wide-area" inspection techniques, which enable more uniform and rapid coverage of a test surface which can improve productivity and minimize human error. Technical advances in both computing power and commercially available, multi-axis robots and/or gantry systems, now facilitate a new generation of scanning machines. Many of these systems use multiple end effector tools yielding improvements in inspection quality and productivity.

Ultrasound is the current NDE method of choice to inspect large fiber reinforced airframe structures. Over the last 2 decades, ultrasound scanning machines using conventional techniques have been employed by all airframe OEMs and their top tier suppliers to perform these inspections. A limitation of ultrasonic inspection can be the requirement to use a couplant between probe and test part. VACRS (variable automatic couplant and recovery system) has helped changed the way very large area ultrasonic inspections are done [6]. The VACRS system uses a lightweight couplant and delivery/recovery system that makes it possible to conduct a C-scan with large ultrasonic arrays without the large water requirements. It works with Boeing's mobile automated scanner (MAUS®) and other scanning systems on the market.

Shearography and thermography are relatively fast, non-contact methods that require no coupling or complex scanning equipment. Laser shearography was initially applied to aircraft structure in 1987 by Northrop Grumman on the B-2 bomber. Since that time, laser shearography has emerged as an advanced, highspeed, high-performance inspection method.


#### **Figure 23.** *NDI methods [5].*

An enabler for more widespread use of bonded structure in commercial aircraft applications will be improvements in cost and capability related to quantification of real-time structural bond integrity. Adhesive bonds degrade slowly over time and are highly dependent on surface preparation. On older aircraft, the only gauge for bond integrity is age, environmental exposures and statistics — not the actual condition of bonds. The ability to detect weak adhesive bonds, before they disbond will lead to more integration of parts and reduced fastener count and a reduction in everything that is involved with creating holes in cured composite parts. Military air vehicle platforms are more aggressive in this pursuit and the "pay-for-performance" mindset, the lower production rates and the size, visibility, and objectives of the programs allow for more flexibility in bonded structure implementation. The commercial world is different and just like the widespread implementation of composite material on new aircraft, it will not happen unless there are compelling economic advantages and very low risk.
