Fritz Friedersdorf

Development of a wireless miniaturized smart sensor network for aircraft corrosion monitoring

Corrosion of aircraft and rotorcraft costs the US military billions of dollars annually, and is by far the largest single maintenance cost driver for Navy and Marine Corps airframes. The various forms of localized corrosion, such as pitting corrosion, crevice corrosion, exfoliation, and environment assisted cracking, are particularly destructive and frequently occur without any outward signs of damage. To maintain acceptable risk levels, costly schedule based inspection and maintenance practices are used. In order to move away from schedule based maintenance and enable condition based maintenance techniques, a miniature corrosion monitoring smart sensor network to support diagnostics and prognostics for aircraft health management is being developed. The development of an ultra-low power, wireless, embedded corrosion monitoring system based on the IEEE 1451.X open architecture for smart transducers will be discussed in this paper. This system, funded through a NAVAIR Phase II SBIR, is capable of monitoring, recording, and analyzing data from environmental and corrosivity sensors for the purpose of aircraft health management. This paper will present the use of a standard network architecture consisting of transducer interface modules (TIMs) and network capable application processors (NCAPs), allowing for ease of system integration and plug-and-play simplicity. The hardware and software designs, relying on ultra-low power components and embedded energy conservation algorithms, will be presented. This low-power approach to aircraft corrosion and health monitoring is ideal for integration with energy harvesting techniques, giving rise to a self-contained, self-sustaining sensor network. Finally, corrosion modeling and embedded algorithm development based on data fusion from both commercial off the shelf (COTS) and novel, developmental sensors will be discussed and shown to be powerful diagnostic and prognostic tools. 1 2

Diagnostics and prognostics for aircraft structures using a wireless corrosion monitoring network

Corrosion of aircraft and rotorcraft is one of the primary maintenance cost drivers for the US Military, costing billions of dollars annually, and is by far the largest single maintenance cost for Navy and Marine Corps airframes. Various forms of localized corrosion, such as pitting corrosion, crevice corrosion, exfoliation, and environment assisted cracking, are particularly destructive and can lead to significant structural integrity problems for aircraft. Widespread current practice employs costly schedule based inspection and maintenance to retain acceptable risk levels. To enable condition based maintenance techniques, Luna is developing a diagnostic and prognostic system based on an intelligent wireless corrosion monitoring network.

Wireless corrosion monitoring for evaluation of aircraft structural health

The military spends billions of dollars annually on inspection, identification, and repair of damage resulting from aircraft corrosion. The currently available methods for identifying aircraft corrosion damage involve expensive, labor intensive scheduled inspections, resulting in longer periods in depot, and reduction in aircraft availability. In order to increase aircraft safety, availability, and operational efficiency, an on-platform monitoring system capable of fusing data streams from an array of environmental and corrosivity sensors is needed to provide inspection-free indicators of the existence of corrosion as well as the level of corrosive severity in difficult to access aircraft locations. This paper will discuss the design, test, and validation of such a system utilizing a wireless, ultra-low power network of sensors.1 2

Deployment of a wireless corrosion monitoring system for aircraft applications

With its extremely negative effects on critical military assets, corrosion continues to be one of the top maintenance cost drivers for the Department of Defense. As of 2010, an estimated

Nonlinear ultrasonic measurements based on cross-correlation filtering techniques

22.9B was required to cover the costs associated with corrosion in the DoD annually. Proper management of corrosion on high value military assets such as aircraft can significantly reduce costs associated with maintenance, component removal, and aircraft availability. This paper will discuss the design, validation, and deployment of a wireless, flight qualified corrosion monitoring system as well as analysis of data collected during field trials.

Environmentally Assisted Cracking Measurements in Structural Aluminum Alloys Under Accelerated Test Conditions

Cyclic loading of mechanical components promotes the formation of dislocation dipoles in metals, which can serve as precursors to crack nucleation and ultimately lead to failure. In the laboratory setting, an acoustic nonlinearity parameter has been assessed as an effective indicator for characterizing the progression of fatigue damage precursors. However, the need to use monochromatic waves of medium-to-high acoustic energy has presented a constraint, making it problematic for use in field applications. This paper presents a potential approach for field measurement of acoustic nonlinearity by using general purpose ultrasonic pulser-receivers. Nonlinear ultrasonic measurements during fatigue testing were analyzed by the using contact and immersion pulse-through method. A novel cross-correlation filtering technique was developed to extract the fundamental and higher harmonic waves from the signals. As in the case of the classic harmonic generation, the nonlinearity parameters of the second and third harmon...

Identification of material damage precursors using nonlinear ultrasonics

Environmentally assisted cracking (EAC) of aluminum alloys in corrosive atmospheres is an important maintenance and safety issue for U.S. Department of Defense assets. EAC initiation and propagation of cracks is influenced by the complex interactions of load, environment, and alloy properties. Traditional environmental fracture testing conducted under immersion or constant humidity conditions may produce results that are different than measurements collected under thin electrolyte layers or droplets formed during atmospheric exposure. In addition, most standard methods do not provide instantaneous measures of crack velocity that can be used to identify specific environmental conditions that promote cracking. Improved assessment of EAC susceptibility and the conditions that promote cracking of aluminum alloys has been accomplished with an autonomous, in situ measurement system that can be used in accelerated corrosion test chambers and outdoor exposure sites. Continuous measurements of crack length through...

Flaw characterization through nonlinear ultrasonics and wavelet cross-correlation algorithms

The primary goal of this research effort is to develop nondestructive evaluation techniques capable of detecting material damage precursors mainly for turbine engine materials under low and high-cycle fatigue testing. The experimental results presented in this paper show a significant increase of the relative acoustic nonlinearity, βr, in aluminum and Ni-based superalloy fatigued specimens. While in agreement with the prior research, the main advantage of the current technique over the previous methods is that the ultrasonic beam may be focused to inspect the presence of damage precursors at localized stress concentrator site. For example, when the ultrasonic beam travelled through the root of the round-notched specimens, the acoustic nonlinearity exhibited an increase of approximately 450% as compared to the pristine specimens. This procedure will be further developed to detect damage precursors in propulsion components undergoing thermo-mechanically fatigue to quantify their remaining useful life.

Novel approach of wavelet analysis for nonlinear ultrasonic measurements and fatigue assessment of jet engine components

​Ultrasonic measurements have become increasingly important non-destructive techniques that characterize flaws found in various in-service industrial components. Hence, the prediction of remaining useful life based on fracture analysis depends on the accurate estimation of flaw size and orientation. However, amplitude ultrasonic measurements are not able to provide an estimate of the plastic zones that exist ahead of the crack tips. Estimating the size of the plastic zone is an advantage since some flaw may propagate faster than others. This paper presents a wavelet cross-correlation (WCC) algorithm that was applied to nonlinear analysis of ultrasonically guided waves. By using this algorithm, harmonics present in the waveforms were extracted and nonlinearity parameters were used to indicate both the tip of the cracks and size of the plastic zone. B-scans performed with the quadratic and cubic nonlinearities were sensitive to micro-damage​ ​specific​ ​to​ ​plastic​ ​zones.

Aircraft corrosion monitoring and data visualization techniques for condition based maintenance

Widespread damage in aging aircraft is becoming an increasing concern as both civil and military fleet operators are extending the service lifetime of their aircraft. Metallic components undergoing variable cyclic loadings eventually fatigue and form dislocations as precursors to ultimate failure. In order to characterize the progression of fatigue damage precursors (DP), the acoustic nonlinearity parameter is measured as the primary indicator. However, using proven standard ultrasonic technology for nonlinear measurements presents limitations for settings outside of the laboratory environment. This paper presents an approach for ultrasonic inspection through automated immersion scanning of hot section engine components where mature ultrasonic technology is used during periodic inspections. Nonlinear ultrasonic measurements were analyzed using wavelet analysis to extract multiple harmonics from the received signals. Measurements indicated strong correlations of nonlinearity coefficients and levels of fati...