David Glenn Moore

Nondestructive inspection of bonded composite doublers for aircraft

One of the major thrusts established under the FAAs National Aging Aircraft Research Program is to foster new technologies associated with civil aircraft maintenance. Recent DOD and other government developments in the use of bonded composite doublers on metal structures has supported the need for research and validation of such doubler applications on US certificated airplanes. Composite doubler technology is rapidly maturing and shows promise of cost savings on aging aircraft. While there have been numerous studies and military aircraft installations of composite doublers, the technology has not been certified for use on commercial aircraft. Before the use of composite doublers can be accepted by the civil aviation industry, it is imperative that methods be developed which can quickly and reliably assess the integrity of the doubler. In this study, a specific composite application was chosen on an L-1011 aircraft in order to focus the tasks on application and operation issues. Primary among inspection requirements for these doublers is the identification of disbonds, between the composite laminate and aluminum parent material, and delaminations in the composite laminate. Surveillance of cracks or corrosion in the inspection (NDI) method can inspect for every flaw type, therefore it is important to be aware of available NDI techniques and to properly address their capabilities and limitations. This paper reports on a series of NDI tests which have been conducted on laboratory test structures and on a fuselage section cut from a retired L-1011 aircraft. Specific challenges, unique to bonded composite doubler applications, will be highlighted. In order to quickly integrate this technology into existing aircraft maintenance depots, the use of conventional NDI, ultrasonics, x-ray, and eddy current, is stressed. The application of these NDI technique to composite doublers and the results from test specimens, which were loaded to provide a changing flaw profile, are presented in this paper. The development of appropriate inspection calibration standards will also be discussed.

Experimental study of impulse resuspension with laser Doppler vibrometry.

Particle resuspension due to mechanical impulse was studied for spherical polymethylmethacrylate (pmma) particles ranging from 1.7 to 14.4 μm in diameter on titanium dioxide (TiO2) and silicon dioxide (SiO2) wafers. Dry powders were dispersed, electrostatically neutralized, and allowed to deposit under the influence of gravity. Contaminated surfaces were then mechanically excited with a 5 MHz piezoelectric transducer where surface accelerations (∼106 m/s2) and resuspension ratios were quantified with laser Doppler vibrometry (LDV) and digital microscopy, respectively. For TiO2, experiments were performed over a broad range of relative humidity (25 to 95%) to assess the effects of capillary condensation. Resuspension was a monotonically decreasing function of relative humidity. Existing theories were used to separate data into two adhesion regimes based on capillary bridge formation: van der Waals (vdW) and capillary dominated adhesion. For relative humidity above 60%, resuspension forces were nondimensionalized by the theoretical capillary force. Resuspension data for all particle sizes and relative humidity were described by a single sigmoid function dependent on the dimensionless resuspension force. Below 60% relative humidity, resuspension forces were nondimensionalized by the vdW force calculated with Johnson–Kendall–Roberts adhesion theory. The experimental work of adhesion (pmma-TiO2) was optimized such that the dimensionless resuspension curves, for capillary and vdW forces, had equivalent dimensionless resuspension forces at 50% resuspension. The calculated value, 0.047 J/m2, was within the range of values expected from other published works. Resuspension was not observed for particles on SiO2 substrates. This result was attributed to electrostatic surface charge patches where particle charge and surface resistivities were measured to analyze the relative influence of electrostatic adhesion forces. Copyright 2012 American Association for Aerosol Research

Non-destructive inspection approach using ultrasound to identify the material state for amorphous and semi-crystalline materials

At present, there are many methods to identify the temperature and phase of a material using invasive techniques. However, most current methods require physical contact or implicit methods utilizing light reflectance of the specimen. This work presents a nondestructive inspection method using ultrasonic wave technology that circumvents these disadvantages to identify phase change regions and infer the temperature state of a material. In the present study an experiment is performed to monitor the time of flight within a wax as it undergoes melting and the subsequent cooling. Results presented in this work show a clear relationship between a material’s speed of sound and its temperature. The phase change transition of the material is clear from the time of flight results, and in the case of the investigated material, this change in the material state occurs over a range of temperatures. The range of temperatures over which the wax material melts is readily identified by speed of sound represented as a function of material temperature. The melt temperature, obtained acoustically, is validated using Differential Scanning Calorimetry (DSC), which uses shifts in heat flow rates to identify phase transition temperature ranges. The investigated ultrasonic NDE method has direct applications in many industries, including oil and gas, food and beverage, and polymer composites, in addition to many implications for future capabilities of nondestructive inspection of multi-phase materials.At present, there are many methods to identify the temperature and phase of a material using invasive techniques. However, most current methods require physical contact or implicit methods utilizing light reflectance of the specimen. This work presents a nondestructive inspection method using ultrasonic wave technology that circumvents these disadvantages to identify phase change regions and infer the temperature state of a material. In the present study an experiment is performed to monitor the time of flight within a wax as it undergoes melting and the subsequent cooling. Results presented in this work show a clear relationship between a material’s speed of sound and its temperature. The phase change transition of the material is clear from the time of flight results, and in the case of the investigated material, this change in the material state occurs over a range of temperatures. The range of temperatures over which the wax material melts is readily identified by speed of sound represented as a funct...

Comparison of ultrasonic wave speed measurements on wax at elevated temperatures to numerical method predictions

Ultrasonic stress wave amplitude and time-of-flight values may change as a media is heated. The measurement of relatively small variations in velocity and material attenuation can detect and quantify significant variations within a material’s microstructure, such as a change in phase from solid to liquid. This paper discusses the experimental setup, ultrasonic wave speed tracking methods and signal analysis algorithms that are used in this study to document the changes within highly attenuative wax material as it is either being heated or cooled from 25°C to 90°C. The experimental set-up utilizes ultrasonic probes in a through-transmission configuration. The ultrasonic waveforms are recorded and analyzed during long duration thermal experiments. To complement the ultrasonic data, a Discontinuous-Galerkin Model (DGM) was also created, which uses unstructured meshes to determine how waves travel in this media and how the sound interacts with the prescribed boundary conditions. This numerical method solves p...

Application of Temporal Moments and Other Signal Processing Algorithms to Analysis of Ultrasonic Signals Through Melting Wax.

Ultrasonic analysis is being explored as a way to capture events during melting of highly dispersive wax. Typical events include temperature changes in the material, phase transition of the material, surface flows and reformations, and void filling as the material melts. Melt tests are performed with wax to evaluate the usefulness of different signal processing algorithms in capturing event data. Several algorithm paths are being pursued. The first looks at changes in the velocity of the signal through the material. This is only appropriate when the changes from one ultrasonic signal to the next can be represented by a linear relationship, which is not always the case. The second tracks changes in the frequency content of the signal. The third algorithm tracks changes in the temporal moments of a signal over a full test. This method does not require that the changes in the signal be represented by a linear relationship, but attaching changes in the temporal moments to physical events can be difficult. Thi...