Project Leader: C.M. Fortunko
M.A. Hamstad, E.S. Boltz, J.D. McColskey,M.J. Anderson, V.K. Tewary

MSEL Program Polymer-Matrix Composites	MRD Focus Technology Ultrasonic Characterization
Strategic Thrust Advanced Materials	Character of Research Automotive

Technical Description

Experimental techniques are under development for characterizing the microstructures of advanced composite materials. Microstructure includes orientation, shape, distribution, and concentration of reinforcement phase in a matrix material. Wideband ultrasonics and acoustic emission methods are under development for both long-fiber and short-fiber composites, which are extensively used by the automotive industry. The acoustic emission work is principally aimed at studies of uniformity or lack or uniformity of microdamage during stressing. The wideband ultrasonic studies are aimed at development of quantitative methods for determining the elastic properties and relating them to the microstructure.

Technical Objectives

1. Evaluate the practicality of using noncontact, air-coupled ultrasonics for stiffness determination in composite plate geometries used in aerospace and automotive and other applications.

2. Develop wideband acoustic emission techniques to identify, locate, and characterize microdamage in short-fiber polymer composites used in automotive applications. Demonstrate that such sensors will be useful to control quality in automotive and other industrial applications.

3. Develop laboratory and in-line ultrasonic measurement methods and instrumentation for determining the stiffness moduli and fiber-orientation distributions in short-fiber reinforced composite materials. Validate the methods using metallographic and micro-mechanical modeling techniques.

FY95 Accomplishments

Completed evaluation of air-coupled ultrasonic systems for determination of the stiffness moduli of composite plates. Transferred the key elements of the technology to a CRADA partner (XXsys/Composite Retrofit Corporation).

Completed and evaluated an infrared Michelson interferometer for wideband ultrasonic measurements in composite materials. The interferometer was needed to obtain high-fidelity ultrasonic waveforms in composite materials. The interferometer is also used to characterize conventional piezoelectric contact transducers, which are used in nondestructive evaluation of composites.

Used the infrared interferometer to optimize the performance of wideband acoustic emission transducers specifically intended for studies of microdamage in composites and validate the main features of Green's theory of elastic-wave propagation for plate geometries.

Developed a quiet four-point-bend fixture and demonstrated the feasibility of using wideband acoustic emission transducers to locate and characterize microdamage states in short-fiber reinforced composites. Showed that fiber-orientation distributions obtained from ultrasonic measurements of elastic-wave velocities are consistent with those obtained by classical metallographic methods and from inversion of acoustic resonance spectroscopy (ARS) measurements. Thus, the feasibility of using ultrasonic methods to determine elastic moduli was demonstrated.

FY95 Outputs

1. M.J. Anderson, P.R. Martin, and C.M. Fortunko, Resonant Transmission of a Three Dimensional Sound Beam through a Solid Plate in Air: Theory and Measurement, J. Acoust. Soc. Am. 98(5), Pt. 1, Nov. 1995, pp. 2628-2638.

2. M.J. Anderson, P.R. Martin, and C.M. Fortunko, Gas-Coupled Ultrasonic Measurement of Elastic Stiffness Moduli of Polymer Composite Plates, in Proc. 1994 Ultrasonics Symp., B.R. McAvoy ed. (IEEE, New York, 1995) pp. 1255-1260.

3. V.K. Tewary, M. Mahapatra, and C.M. Fortunko, Greens Function for Anisotropic Half-Space Solids in Frequency Space and Calculation of Mechanical Admittance, J. Acoust. Soc. Am., accepted for publication.

4. V.K. Tewary and C.M. Fortunko, Theory of Elastic Waves in Three-Dimensional Anisotropic Plates, J. Acoust. Soc. Am., accepted for publication.

5. V.K. Tewary and C.M. Fortunko, Surface Waves in Three-Dimensional Half-Space Tetragonal Solids, J. Acoust. Soc. Am., submitted for publication.6. V.K. Tewary and C.M. Fortunko, Lattice Correction to Mechanical Admittance of Solids, J. Acoust. Soc. Am., submitted for publication.

7. W.A. Grandia and C.M. Fortunko, NDE Applications of Air Ultrasonic Transducers, in Proc. 1995 Ultrasonics Symp., B.R. McAvoy ed. (IEEE, New York, 1995), in press.

8. H. Ledbetter, C. Fortunko, and P. Heyliger, Off-Diagonal Elastic Constants in Fiber-Reinforced Composites, in Proc. 10th Internat. Conf. on Composite Materials, Vol. IV (Woodhead, Cambridge, England, 1995) pp. 19-24.

Industrial Interactions:

Collaborated closely with industrial consortia: Automotive Composite Structures: Development of High-Volume Manufacturing and Low-Cost Manufacturing Processes and Design/Sensor Technologies for Seismic Upgrading of Bridge Columns. Both consortia received partial support from the NIST Advanced Technology Program. In collaboration with a small instrument maker and material inspection company specializing in testing of advanced materials (Quality Material Inspection), prepared and presented an invited paper entitled: NDE Applications of Air-Coupled Transducers. The paper was presented at the 1995 IEEE Ultrasonics Symposium in Seattle, WA.

Organized the 1996 Gordon Research Conference on NDE. The theme of the conference is: Microstructure Evolution, Characterization, and Property Relationships. The invited papers at the conference will reflect current trends in industry, academia, and national laboratories. There will also be foreign participation.