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Ultrasonic method of nondestructive evaluation of fiber reinforced composite structures has sensitivity to detect small distributed inadequacies such as microvoids and microfractures which effect strength and continuity of composite.
The apparent attenuation which would result if certain damage states (transverse cracks and delaminations) are introduced into a graphite/epoxy laminate through which an ultrasonic wave passes is investigated. Experimental data for two different laminates are presented which shows changes in the apparent attenuation of about one db. These changes generally occur at loads which correspond to the range predicted for the formation of the damage. The predicted changes in the attenuation for several simple and common damage states are well within the range of experimental values.
The principles underlying the design and use of magnetostrictive ultrasonic probes is illustrated by oscillograms and sketches. Attention is given to such concepts as magnetostrictive transduction, broadband pulse shaping, guided wave propagation, wave impedance, reflection, transmission, and attenuation coefficients, coupling methods, and impulse-induced resonance. A number of applications of such probes are discussed including the measurement of elastic moduli, temperature, and acoustic emission and resonance studies.
Calibrated method for ultrasonic C-scanning is based on direct correlation of gray-scale response to electronic signal used. In procedure, optical density of reference recording is measured to generate curve of reflective intensity versus transmission.
Ultrasonic transmission technique, using reflector plate, indicates resistance to corona formation. Technique is useful as tool for mapping specific panels to permit selecting best areas of laminate for circuit board use. Procedure is relatively safe, fast, inexpensive, and uses commercially-available equipment.
Extensometer using ultrasonic pulse reflections to measure elongations in tightened belts and studs is much more accurate than conventional torque wrenches in application of specified preload to bolts and other threaded fasteners.
Photoconductive acoustoelectric transducer (AET) functions as phase-insensitive ultrasonic transducer. Device is easy to use and requires no additional noisy components such as light or thermal source.
A CW ultrasonic device is described for measuring frequency shifts of the peak of a mechanical resonance in a body. One application of the device is measuring the strain in a bolt, and other applications such as measuring the thickness of a body, measuring the depth of a flaw in a body, measuring the elongation of a body, and measuring changes in velocity of sound in a body. The body is connected, by means of a CW transducer, to electrical circuit means including a narrow band RF amplifier to form a closed loop feedback marginal oscillator that frequency locks the device to the peak of a mechanical resonance in the body. When the frequency of this peak changes, because of a physical change in the body, the frequency of the oscillator changes. The device includes an automatic frequency resonant peak tracker that produces a voltage that is related to a change in frequency of the oscillator. This voltage is applied to the RF amplifier to change the center of its frequency band to include the frequency of the peak and is a measure of the frequency shift.
Details of the method used to measure the stress wave factor are described. Frequency spectra of the stress waves are analyzed in order to clarify the nature of the wave phenomena involved. The stress wave factor was measured with simple contact probes requiring only one-side access to a part. This is beneficial in nondestructive evaluations because the waves can run parallel to fiber directions and thus measure material properties in directions assumed by actual loads. The technique can be applied where conventional through transmission techniques are impractical or where more quantitative data are required. The stress wave factor was measured for a series of graphite/polyimide composite panels, and results obtained are compared with through transmission immersion ultrasonic scans.
An ultrasonic-acoustic technique was used to indicate the strength variations of tensile specimens of a graphite-epoxy composite. A stress wave factor was determined and its value was found to depend on variations of the fiber-resin bonding as well as fiber orientation. The fiber orientations studied were 0 deg (longitudinal), 10 deg (off-axis), 90 deg (transverse), 0 deg + or - 45 deg/0 deg symmetrical, and + or - 45 deg] symmetrical. The stress wave factor can indicate variations of the tensile and shear strengths of composite materials. The stress wave factor was also found to be sensitive to strength variations associated with microporosity and differences in fiber-resin ratio.
The principles of operation employed in the focusing of a sound field are considered, taking into account the use of solid and liquid coupling media. The focusing limits for a given transducer are investigated. As a diffraction phenomenon, focusing is a function of the system dimensions, the frequency, and the sound velocity. The frequency and the material used for the lenses are in most cases determined in accordance with considerations regarding sound propagation. Changes in the focus are therefore effected mainly by the selection of transducer and lens dimensions. The functions of the focusing factor for a normal immersion probe and a direct contact angle probe are represented in graphs. The deviation of the appropriate parametric values for an ultrasonic probe is illustrated with the aid of examples.
The on-shuttle antenna pattern of the MSBLS receiver, and the azimuth and elevation beamwidths were simulated by their corresponding ultrasonic transducer beams. The scanning rate for the azimuth and elevation beams was 1.75 degrees/second. The results were adjusted for full-scale maximum sinusoidal scan rates of 691 and 377 deg/sec for AZ and EL respectively. The rain drops were simulated by air bubbles, with a similar size distribution, in water. The rain volume was created along a part of the propagation path, and not on the runway, because it was found difficult to avoid an accumulation of bubbles on the runway surface and surroundings simulated by the model surface. Multipath fading from the ground, and its possible degrading effect on the orbiter received beam shape and the associated landing guidance parameters is discussed.
A method for simultaneous reproduction of images, requiring different amounts of time to reproduce, on a cathode ray tube (CRT) screen is disclosed. Ultrasonic sectional views and electrocardiogram curves are simultaneously reproduced on the CRT screen by producing the images on different areas of a screen with two phosphors having different persistence times and luminous colors, within the times required for the appearance of the images. In front of the area on which is produced the image requiring the shorter time is a color filter which is permeable to the color of the phosphor with the shorter persistence time by which absorbs the color of the other phosphor.
The theory of a phase insensitive receiver based on acousto-electric effect is presented along with experimental characteristics of a CdS acousto-electric converter (AEC). Since the AEC is nearly phase insensitive, it is ideal for measurements in inhomogeneous materials and/or materials with irregular flatness and parallelism. Through transmission ultrasonic C-scan data of phantom flaws demonstrates a significant improvement in flaw characterization with an AEC over that of a conventional transducer. In addition, measurements with conventional transducers in anisotropically stressed metal samples are shown to lead to grossly inaccurate results due to phase sensitivity. Various other measurements are presented with data contrasting conventional transducers with an AEC in specific NDE applications.
An ultrasonic-acoustic technique was used to indicate the strength variations of tensile specimens of a graphite-epoxy composite. A 'stress wave factor' was determined and its value was found to depend on variations of the fiber-resin bonding as well as fiber orientation. The fiber orientations studied were 0 deg (longitudinal), 10 deg (off-axis), 90 deg (transverse), (0 deg/+ or - 45 deg/0) symmetrical, and (+ or - 45 deg) symmetrical. The stress wave factor can indicate variations of the tensile and shear strengths of composite materials. The stress wave factor was also found to be sensitive to strength variations associated with microporosity and differences in fiber-resin ratio.
The theory of a phase insensitive receiver based on acousto-electric effect is presented along with experimental characteristics of a CdS acousto-electric converter (AEC). Since the AEC is nearly phase insensitive, it is ideal for measurements in inhomogeneous materials and/or materials with irregular flatness and parallelism. Through transmission ultrasonic C-scan data of phantom flaws demonstrates a significant improvement in flaw characterization with an AEC over that of a conventional transducer. In addition, measurements with conventional transducers in anisotropically stressed metal samples are shown to lead to grossly inaccurate results due to phase sensitivity. Various other measurements are presented with data contrasting conventional transducers with an AEC in specific NDE applications.
Remote inspection technique uses reflectance of ultrasonic waves from machined steps in root area of electron beam welds to indicate sound or faulty welds.
System utilizing natural ringing frequency of electronic circuit coupled to wideband transducer is used to determine frequency dependence of ultrasonic properties of tissue. With procedure frequency data can be obtained rapidly and inexpensively.