Gabriel V. Garcia

LASER ULTRASONIC MONITORING OF CERAMIC SINTERING

Noncontacting laser‐ultrasonic measurements of the sintering of ceramics in real‐time are described. Lasers are used for both generation and detection of ultrasonic waves propagating through the material. A pulsed laser generates the ultrasonic wave from thermoelastic absorption at the material surface. Detection is accomplished by a confocal Fabry–Perot interferometer, which is insensitive to the speckle nature of the scattered light from the sample surface and can obtain measurements from samples with rough or diffusely reflecting surfaces. The densification of the ceramic sample is determined by changes in the bulk longitudinal wave velocity and the sample shrinkage.

Damage Detection using ARMA Model Coefficients

The objective of this paper is to perform damage detection utilizing the coefficients obtained from an ARMA model. The Damage Index Method has been proven to be one of the better modal based damage detection methods currently in use. One major drawback to this method is the need to determine mode shapes from the frequency response function (FRF) data. Extracting mode shapes from FRF data can be extremely time consuming and the result at times can be highly dependent on the users knowledge and the application of the software package being utilized to extract the modal parameters. In an attempt to minimize user interaction in the damage detection process and to eliminate the need to determine modal parameters, we will develop a method which is capable of providing damage detection results from accelerometer time histories. This will be accomplished by utilizing the parameters of an ARMA model as damage indicators. Expressions for classification is attempted for a simply supported beam which contains damage of various degrees at several locations. The damage detection result will then be compared to the damage detection results obtained by the Damage Index Method.

Process Monitoring Using Optical Ultrasonic Wave Detection

Certain microstructural features of materials, such as grain size in metals, porosity in ceramics, and structural phase compositions, are important for determining mechanical properties. Many of these microstructural features have been characterized by ultrasonic wave propagation measurements, such as wave velocity and attenuation. Real-time monitoring of ultrasonic wave propagation during the processing stage would be valuable for following the evolution of these features. This paper describes the application of laser ultrasonic techniques to the monitoring of ceramic sintering. Prior to this work, ultrasonic wave measurements of the sintering of ceramics have been made only through direct contact with the material with a buffer rod [1,2]. Recently, several advances have been made using lasers for both generation and detection of ultrasonic waves in a totally noncontacting manner for material microstructure evaluation [3–5]. Application of laser ultrasonic techniques now opens the possibility for real-time monitoring of materials in very hostile environments as are encountered during processing [6].

Application and evaluation of classification algorithms to a finite element model of a three-dimensional truss structure for nondestructive damage detection

The objective of this paper is to apply and evaluate the relative performance of classification algorithms for nondestructive damage detection (NDD). The classification algorithm are obtained form various forms of Bayes Rule. An established theory of damage localization, which yields information on the location of the damage directly form changes in mode shapes, is selected. Next, the application of classification is performed to the existing theory of damage localization. Expressions for the classification algorithms using the damage indicator functions from the damage localization theory are generated. Criteria for the evaluation of the proposed classification algorithms are then generated. Using the classification algorithms, damage localization is attempted in a numerical model of a 3D truss structure which contains simulated damage at various locations. Finally, the accuracy and reliability of the classification algorithms is evaluated using the established criteria.

Effect of damage size and location on the stiffness of a rectangular beam

Current analytical damage detection schemes for Euler-Bernoulli beams are based on the modal parameters generated from a one dimensional finite element model. However, since damage has been limited to an effective loss in bending stiffness at the damage location, the interpretation of the damage has not been addressed in any great detail. The objective of this paper is to investigate the effects of damage size and location in a beam on the apparent damage inflicted on adjacent locations.

Combining damage detection methods to improve probability of detection

The objective of this work is to improve the probability of detecting damage and reduce the probability of false positives by combining damage detection methods. Most vibration-based NDD methods are derived from expressions relating the modal properties (i.e., mode shapes and frequencies) and/or the physical properties (i.e., stiffness or flexibility) of an undamaged structure to the modal properties of a damaged structure. These methods utilize some form of a damage indicator to identify the existence and location of damage in a structure. The basic assumption is that the modal and physical properties of the undamaged and damaged structure will differ. Thus, by measuring and comparing the modal properties of the damaged and undamaged structure one can infer whether or not damage exists and in some cases the location of the damage. In this work, we present a methodology to combine the results of the different NDD methods using the techniques of pattern recognition. To accomplish this task, we begin with a review of pattern recognition. Next, we develop a methodology to combine the results of the different NDD methods. To investigate the applicability of the combined approach we perform damage detection on a beam using two damage detection methods (Damage Index Method and a method that utilizes the parameters of an ARMA model as damage indicators) separately and then combined using the developed methodology. Finally, a comparison of the probability of detection and the probability of a false positive is made between the combined approach and the NDD methods applied separately.

Comparison of damage detection results utilizing an ARMA model and an FRF model to extract the modal parameters

The objective of this paper is to make a comparison of the damage detection results obtained from an analysis of the modal parameters extracted from a time domain model and a frequency domain model. In this paper, an autoregressive moving average (ARMA) model and a FRF model will be utilized to extract the modal parameters of a beam. Expressions for the modal parameters using the ARMA model are developed. Next, an established theory of damage localization, which yields information on the location of the damage directly from changes in mode shapes, is selected. Expressions for classification algorithms using the damage indicator functions from the damage localization theory are then generated. Using the classification algorithms, damage localization is attempted for a pinned-pinned beam which contains damage of various degrees. Finally, the modal parameters and damage detection results obtained from the two methods are compared.

Integration of ESPI and structural analysis to determine the impact of structural defects

The identification of a defect and the ability to determine its impact on the structure provides the information needed to determine the resulting integrity of the structure. Electronic Speckle Pattern Interferometry (ESPI) is used to help find defects. One shortcoming of ESPI is the inability to determine the impact of the defect on the overall structural integrity. Displacement and strain data from ESPI measurements can be used to determine the parameters of a structure, thus providing a quantifiable means of determining the structural integrity. Parameter estimation techniques provide the means to bring ESPI data and structural models together. An example of the integration of parameter estimation and ESPI displacement output on a fixed-free supported beam will be discussed in this paper.

Incorporation of a FADOF to an ESPI system

Electronic Speckle Pattern Interferometry (ESPI) has been used for many years in nondestructive testing applications in laboratories. Field applications of ESPI systems have been limited by the need to restrict the amount of light, sunlight and other sources, during operation. Interference filters and other techniques have been tried to increase the applicability of ESPI systems in daylight environments. Each of these attempts have been moderately successful. The FADOF (Faraday Anomalous Dispersion Optical Filter) is a revolutionary filter that improves throughput, field-of-view, and the signal-to-noise ratio of the laser signal returning from the test object. This paper describes the basics of a FADOF and how the filter can be incorporated into an ESPI system.