Nondestructive Evaluation Characterization Research Articles

Optimization of NDE Characterization Parameters for a RF-SQUID Based System Using FEM Analysis

We have investigated the dependence of the optimal non destructive evaluation (NDE) characterization on different excitation parameters in an eddy current SQUID NDE system for samples with known flaw depths. The considered parameters in our study include the configuration of the excitation-coil and its current frequency. The system is based on a high-TC YBCO gradiometer RF-SQUID sensor with a flux noise level below 100 muPhi0/radicHz at 100 Hz in an unshielded environment, while being shielded against external RF EMI (electromagnetic interference). According to experimental results and the associated numerical analysis using finite element (FEM) simulations, we have derived the optimized parameters for the maximum sensitivity of the system. The optimized parameters are found using a new model for excitation coil and eddy current anomalies caused by the flaws. Very good agreement between experimental and numerical approaches confirmed our model and the resultant implemented optimization method.

NDE Characterization and Mechanical Behavior in Ceramic Matrix Composites

Several nondestructive evaluation (NDE) techniques, including ultrasonic C-scan, X-ray computed tomography (CT), and infrared (IR) thermography, were employed on ceramic matrix composites (CMCs) to illustrate defect information that might effect mechanical behavior and to analyze structural performance of CMCs. Prior to tensile testing, through C-scan and CT analyses results, the qualitative relationship between the relative ultrasonic transmitted amplitude and porosity based on CT was exhibited. An IR camera was used for in-situ monitoring of progressive damages and to determine temperature changes during tensile testing. Moreover, scanning-electron microscopy characterization was used to perform microstructural failure analyses. This paper describes the use of nondestructive evaluation (NDE) techniques to facilitate the understanding of tension behavior of CMCs.

Nondestructive Evaluation and Characterization of Microfibers Modified Textile Carbon-Phenolic and Carbon-Carbon Composites

Short carbon microfibers have been added to carbon-phenolic fabric composites of plain, eight-harness satin (8HS) and stretch broken 8HS weave architectures. The resulting composites have been studied for their interlaminar mechanical properties as well as process related material evolution mechanisms that result in carbon-carbon (C-C) composites. Dry coupling ultrasonic A-scan velocity measurements, immersion type ultrasonic C-scan technique, acousto-ultrasonic (AU) stress wave factor measurements and vibration damping ratio based nondestructive evaluation-characterization (NDE-C) test parameters were studied in relation to the carbon-phenolic and C-C composites. Interlaminar shear strength (ILSS) tests were conducted along with acoustic emission (AE) monitoring. From the various NDE techniques accompanied by mechanical tests and processing stages, the dependence of fabric weave architectures with short microfibers has been established.

Nondestructive Characterization/ Evaluation of Functional Sandwich and Hybrid Carbon-Carbon Composites

Carbon/carbon (C/C) composites were developed on a conceptual basis with a goal of developing low cost functional composites. The current approach in chooing a precursor material system deviates from conventional C/C systems in that nonwoven carbon mat reinforcement is used in conjunction with continuous fabric. C/C composite systems considered in this study are classified into two categories; hybrid and sandwich. These composites were fabricated from continuous woven carbon fabric in plain, eight harness satin (8HS) and stretch broken weave architectures along with nonwoven carbon mat reinforcement. In sandwich composites, the nonwoven mat is sandwiched between continuous fabric reinforcement; while in hybrid composites, the nonwoven mat is alternated with continuous reinforcement. Ultrasonic and vibration based nondestructive evaluation/characterization (NDE/C) was conducted at three processing stages, namely; as-cured, after first carbonization and after first densification. Ultrasonic velocity measurements in the in-plane and through-the-thickness directions were found to be influenced by the evolving material microstructure and fabric architecture. Vibration damping of sandwich and hybrid composites was found to be an order of magnitude higher than conventional woven C/C composites. Acoustic emission (AE) signatures from the two composite systems were correlated to matrix cracking, fiber filament and bundle fracture, onset and occurrence of delamination and failure of the nonwoven layer(s). With regard to processing, the incorporation of nonwoven carbon mat in conjunction with continuous reinforcement enabled rapid infiltration during densification stage of sandwich and hybrid C/C composites.