James M. Nelson

One Sided Radiographic Inspection Using Backscatter Imaging

Radiographic inspection, where access is limited to one side of the part, can be performed by the use of backscatter imaging techniques. Compton scattering is the primary source of the backscattered signal strength with some contribution from x-ray fluorescence. A variety of approaches have been used in both medicine and industry to create the images [1–25]. The flying spot technique which uses a collimated beam of x-rays, and a large area detector has been used in the work reported here. The backscatter imaging is particular useful in the inspection of low-density, composite materials.

Data fusion for process monitoring and NDE

The quality of a final product is assured by a combination of process control measurements during manufacturing and acceptable final inspections. These activities are often performed independently and the information from various measurement method and production steps is rarely shared. For advanced structures, that require a high level of assurance, a data fusion approach using both process data and NDE measurements is proposed to improve interpretation by utilizing all available information in a systematic manner. NDE and process data fusion can occur in may forms, some relatively simple and some very complex. As the complexity and performance requirements of a product increase the need for data fusion can justify the additional cost of implementation. Typically, a data fusion workstation is used. The data fusion workstation accepts information in a variety of forms, providing a platform to interpret the data in combination or simplified presentation modes. The interpretation of data is improved by knowledge obtained from both in-process monitoring and multiple inspection measurements, leading to reduced risk of failure.

Novel methods for aircraft corrosion monitoring

Monitoring aging aircraft for hidden corrosion is a significant problem for both military and civilian aircraft. Under a Wright Laboratory sponsored program, Boeing Defense & Space Group is investigating three novel methods for detecting and monitoring hidden corrosion: (1) atmospheric neutron radiography, (2) 14 MeV neutron activation analysis and (3) fiber optic corrosion sensors. Atmospheric neutron radiography utilizes the presence of neutrons in the upper atmosphere as a source for interrogation of the aircraft structure. Passive track-etch neutron detectors, which have been previously placed on the aircraft, are evaluated during maintenance checks to assess the presence of corrosion. Neutrons generated by an accelerator are used via activation analysis to assess the presence of distinctive elements in corrosion products, particularly oxygen. By using fast (14 MeV) neutrons for the activation, portable, high intensity sources can be employed for field testing of aircraft. The third novel method uses fiber optics as part of a smart structure technology for corrosion detection and monitoring. Fiber optic corrosion sensors are placed in the aircraft at locations known to be susceptible to corrosion. Periodic monitoring of the sensors is used to alert maintenance personnel to the presence and degree of corrosion at specific locations on the aircraft. During the atmospheric neutron experimentation, we identified a fourth method referred to as secondary emission radiography (SER). This paper discusses the development of these methods.

NDT Data Fusion in the Aerospace Industry

The process of integrating data from diverse process measurements and nondestructive observations of a known object into a consistent description of the condition of the object is an important function of aerospace manufacturing review board and failure investigations. NDE data fusion methods commonly used in aerospace applications include procedures and software to co-register, collocate, and combine multiple NDT data sets into useful, condensed forms, often as a key input to critical contracting, delivery, deployment, and or production decisions. While co-registration and collocation of data at the instrument or sensor level is a potentially useful implementation of NDT data fusion processes, it is often impractical for these types of aerospace decision processes. This is because the primary aerospace applications for NDT data fusion typically involve historical data, remote process steps, the use of extremely large and complex testing facilities, and both national security and proprietary issues. Consequently, the emphasis of NDT data fusion method development has been toward development of post-process NDT data fusion systems and methods where workstation based co-registration and collocation of diverse sets of NDT, engineering, and process data sets is the key technical functionality.