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Madaras, E. I.

Publications and source records attributed to Madaras, E. I..

8 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Lamb wave characterization of the effects of long-term thermal-mechanical aging on composite stiffness

Lamb waves offer a promising method of evaluating damage in composite materials. The Lamb wave velocity is directly related to the material parameters, so an effective tool exists to monitor damage in composites by measuring the velocity of these waves. The Lamb Wave Imager (LWI) uses a pulse/receive technique that excites an antisymmetric Lamb mode and measures the time-of-flight over a wide frequency range. Given the material density and plate thickness, the bending and out-of-plane shear stiffnesses are calculated from a reconstruction of the dispersion curve. In this study, the time-of-flight as well as the elastic stiffnesses D11, D22, A44, and A55 for composite samples which have undergone combined thermal and mechanical aging are obtained. The samples examined include a baseline specimen with 0 cycles, specimens which have been aged 2350 and 3530 cycles at high strain levels, and one specimen aged 3530 cycles at low strain levels.

Aircraft↗
NASA NTRS1999

Pulse Compression Techniques for Laser Generated Ultrasound

Laser generated ultrasound for nondestructive evaluation has an optical power density limit due to rapid high heating that causes material damage. This damage threshold limits the generated ultrasound amplitude, which impacts nondestructive evaluation inspection capability. To increase ultrasound signal levels and improve the ultrasound signal-to-noise ratio without exceeding laser power limitations, it is possible to use pulse compression techniques. The approach illustrated here uses a 150mW laser-diode modulated with a pseudo-random sequence and signal correlation. Results demonstrate the successful generation of ultrasonic bulk waves in aluminum and graphite-epoxy composite materials using a modulated low-power laser diode and illustrate ultrasound bandwidth control.

Anastasi, R. F.↗
NASA NTRS1992

Structural analysis of an NDE-inspected carbon-carbon component

In this research, it is demonstrated that the integration of nondestructive evaluation with the finite element method (a quantitative NDE/FEM approach) can be used for analysis and behavior prediction of advanced materials, such as fiber composites, after processing and during in-service testing. First, stress, strain, and energy data were calculated by the finite element method for square plates with a 10 percent difference in the material properties between specified segments, i.e., between the center and the outside section or between two halves of the plate. This demonstrated the efficiency of the method in predicting variations in the structural behavior based on small material property differences. Then, finite element analyses and actual axial compression tests were performed on a Space Shuttle brake stator made from woven carbon-carbon composites. The material properties used in the numerical modeling of the stator were previously characterized at a large number of points on the component by quantitative NDE-procedures, i.e., ultrasonics and radiography. The results from the experimental compressive loading tests were used to verify the NDE/FEM results. Good agreement was found for most parameters.

Striz, A. G.↗
NASA NTRS1991

The use of ultrasonic property measurements as the basis for finite element analysis of composite materials

In this work, the use of ultrasonic property measurements as the basis for finite element analysis of full scale composite components is presented. The approach utilizes multiple velocity measurements at oblique angles of incidence and quantitative analysis of radiographic images for the local determination of each of the nine orthotropic moduli in a woven carbon-carbon composite. These values were then used as input into a finite element code (NASTRAN) to analyze the response of the material to load: here, diametric compression. The predicted response was then compared with strain gage results at several locations to validate the approach.

Madaras, E. I.↗
NASA NTRS1991

Ultrasonic modulus determination in composite media

A nondestructive test procedure for determining the elastic properties of anisotropic media is presented. The technique is based on transit time measurements for multiple angles of incidence and a numerical solution of the resulting coupled nonlinear equations for modulus determination. Methods for compensating for energy flux deviation from the wave normal and the resulting differences group and phase velocity are devised.

Kline, R. A.↗
NASA NTRS1987

A nondestructive technique for predicting the strength remaining in filament wound composites subjected to low-level impact

A model for predicting the fracture strength of homogeneous materials is proposed. Impacted FWC samples were evaluated using ultrasonic testing and an X-ray dye penetration method. The ability of the model to measure fracture strength was also examined. The relation between attenuation and velocity measurements is studied. It is observed that the X-ray method is not useful for predicting fracture strength because the dye could not penetrate the matrix. It is noted that fracture strength predictions derived from the fracture mechanical model and the ultrasonic measurements correlate well with actual measured fracture strengths.

Madaras, E. I.↗