Ignacio Perez

Modeling of Pulsed Thermography in Anisotropic Media

As active thermography continues to gain acceptance as an NDE tool for both inservice and manufacturing applications, the need for robust physical models of the process increases. Although the sophistication of both analytical and numerical modeling efforts has increased considerably [1–3], development of a 3-dimensional model for anisotropic media is still a formidable task.

PRELIMINARY MIXTURE DESIGN PROCEDURE FOR RECYCLED ASPHALT MATERIALS

This paper summarizes the findings of a study to evaluate the strength, fatigue, and elastic characteristics of recycled asphalt pavement materials and to develop a preliminary mixture design procedure. Mixtures with different types and amounts of additives for three recycling projects in Texas were evaluated. The primary method of evaluation was the static and repeated-load indirect tension test. Estimates of tensile strength, resilient elastic characteristics, and fatigue characteristics were obtained. A preliminary mixture design procedure was formulated which was based on the results of this study and standard tests on the mixture and extracted asphalt and a review of pertinent literature and past experience. The objective of this preliminary design procedure is to allow engineers to begin routinely to design mixtures involving recycled, deteriorated asphalt cements. Preliminary findings indicate that recycled asphalt mixtures can be treated through the addition of asphalt or reclaiming agents to produce a material which exhibits satisfactory engineering properties as measured by laboratory tests on both laboratory-prepared specimens and field cores. A preliminary mixture procedure which can be used to design recycled mixtures is presented. Future work will lead to modifications of this procedure. However, at present it is felt that the procedure is practical and capable of being used routinely. (Author)

Bragg Grating Corrosion Sensor

Historically, corrosion has not been included in the calculation of the life expectancy of aircraft. It is well known how stress-corrosion cracking and corrosion fatigue can significantly reduce the life expectancy of structures. Therefore, it can be correctly assumed that some aircraft flying near their expected life might actually be flying well beyond their “safe life”. Furthermore, due to DoD present tight budget requirements, its is expected that some defense aircraft might not be retired at their original expected life but will be reconditioned to fly beyond that time. All of these considerations indicate that early detection, quantification and prevention of corrosion is of critical importance for military aircraft. This is particularly true for Navy aircraft which fly in the most corrosive environment of all services.

Thermographic modeling of water entrapment

A common problem found in advanced structural materials is water entrapment. This problem is a major cause of material degradation. In metals it can lead to corrosion and in composites it adds unnecessary weight to the structure and can lead to material degradation especially after freezing and thawing. Thermography has been investigated as a means of detection water entrapment in metallic structures. A simple model has been derived that accurately describes the thermal response of these structures to short heat pulses. In this paper results on Aluminum panels with various amounts of water entrapment will be presented. Sensitivity relations will be derived and validated.

Flash infrared thermography for nondestructive testing (NDT) I/E of naval aircraft

In this effort we have used thermographic techniques to inspect several structures of interest to naval aviation, with the purpose of determining the effectiveness of these techniques in finding flaws/defects. The structures/materials used in this study included metals with metallic and nonmetallic coatings, graphite/epoxy bonded assemblies, ceramic matrix composites, and a boron/epoxy panel. The results that were obtained indicate that IR thermography works well identifying disbonds in coatings and bonded assemblies, quantifying porosity in ceramic matrix composite materials, identifying delaminations, and identifying large amounts of material loss (> 10%). It was not reliable for identifying small amounts of material loss (< 10%), however, efforts are continuing to improve our detection limits and reduce false indications.

A New Technique to Produce Josephson Junctions Based on Controlled Crack Growth Techniques

The ability to introduce microcracks by placing multiple microindentations in pre-defined locations in a single crystal substrate opens the possibility for the use of microindentation techniques for electronic device fabrication. It is the objective of this study to demonstrate the possibility of fabricating a superconducting Josephson junction (JJ) by using microindentation cracking techniques. Other potential areas where microindentation techniques can be applied for device fabrication are RF microcircuitry and fiber optics. Once a microindentation is produced, with its associated crack pattern, a means of growing the cracks is required. In this study we present three methods of crack growth, a bending moment method, a thermal stressing method and a crack tip to tip bridging method. Results of these methods applied to single crystal MgO and LaAlO 3 are discussed.