INlRODUCTION Composite materials increasingly playa major role in industrial applications. To utilize a composite appropriately, its physical properties and mechanical behavior must be understood; ultrasonics is a common means of obtaining such information. For most conventional materials, ultrasonic measurements are relatively straightforward. Since the elastic properties of such materials are independent of direction, a single plate specimen and pulse-echo methods can be used [1, 2] . This

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... figuration is of limited usefulness for composites, however, because their anisotropic nature means that the elastic properties vary as a function of propagation direction. The obvious solution of preparing and measuring multiple plate specimens with different orientations can be slow and expensive, and may provide incomplete information. Therefore, a fresh approach is needed. In this paper, we describe techniques that enable ultrasonic measurements for virtually any propagation direction in an anisotropic material. The experiments use hemispherical test samples in conjunction with a versatile mechanical fixture. By connecting the apparatus to a commercial acquisition system possessing automated scanning capabilities, waveforms may be obtained over a wide range of propagation directions. The data are then analyzed to determine the velocity, attenuation, or other information as a function of direction. Experimental results for a composite are presented in order to illustrate the technique's capabilities and highlight specific information that may be gained. MEASUREMENT TECHNIQUES Mechanical Test Fixture A suitable apparatus for accurate measurement of three-dimensional ultrasonic properties must meet several requirements. These requirements include: (a) the capability to