M. Kropf

NONDESTRUCTIVE INSPECTION OF A COMPOSITE MATERIAL SAMPLE USING A LASER ULTRASONICS SYSTEM WITH A BEAM HOMOGENIZER

A laser ultrasonics system was used to detect impact damage in samples of composite material used in the Brazilian aeronautics industry. The ultrasonic generation was accomplished with a high power Nd:YAG laser at 1064 nm and the detector was a Mach‐Zehnder interferometer. The Nd:YAG laser was configured so as not to cause damage to the sample and a beam homogenizer was used to distribute the laser energy homogeneously over the optical spot cross section.

Transmission Matching for Joining Two Acoustical Waveguides

Acoustical waveguides have valuable applications in nondestructive measurements. Magnetostrictive materials, such as Remendur, have received significant attention as waveguide materials because of their ultrasonic wave generation and reception properties. However, it may not be practical to use a magnetostrictive material in certain cases because of high material costs or insufficient material properties. It has therefore been conceived to join a small length of Remendur to steel or Molybdenum. Both finite element analyses and experimental verifications have been performed to evaluate joining two thin rods with a reinforcement sleeve. Results show than a properly designed sleeve improves wave transmission at the interface. Additional finite element modes have been used to consider joining a thin rod with a plate.

Low attenuation waveguide for leaky surface waves

A surface wave on a liquid/solid interface is well-known to radiate acoustic energy into the liquid and is therefore rapidly attenuated. In this work, we have been able to show by experiments and calculations that the proximity of another surface (layer 1 to layer 3 and layer 3 to layer 1) sustains the surface wave through long distances for layers of both plates and concentric tubes. In addition, even when the surface wave is reflected from a distant edge, the returning wave is sustained in the multi-layer system and can be easily detected. This is apparently one of the first observations of leaky surface waves traveling over large distances, in this case over a thousand wavelengths. The effect is modeled on the basis of a cooperative phenomenon between two interfaces separated by a water layer. The effect represents a valuable result in the wave propagation of acoustic surface waves and opens the door to many applications.

Remote High Temperature Thermometry Using Ultrasonic Guided Waves in Thin Wires

An ultrasonic technique to accurately and remotely measure high temperatures has been developed. Using long, thin (∼2 mm) refractory metal wires as ultrasonic wave guides, changes in time‐of‐flight between fixed reflectors are monitored while the temperature of the wire changes. Several physical phenomena contribute to the change in the time of flight as the temperature of the wire increases. The wire thermally expands causing both the physical distance between reflected signals to increase and the density of the wire to decrease. The velocity of sound decreases due to changes in Young’s Modulus and density. By relating these effects in terms of guided wave propagation to the precise time‐of‐flight measurement, temperature can be accurately measured from 20 to over 1000 degrees Celsius. Measurements have been made on wire waveguides of lengths greater than 20 meters. By using digitally automated signal processing to monitor the changes in time‐of‐flight, temperature measurements can be made continuously. ...

DISLOCATION DETECTION THROUGH HARMONIC GENERATION

A fundamental goal of ultrasonic nondestructive evaluation is to characterize material defects before failure. During material fatigue, dislocations tend to nucleate, becoming sources of stress concentration. Eventually, cracks start to form and lead to material failure. Recent research has indicated that nonlinear harmonic generation can be used to distinguish between materials of high and low dislocation densities. This research reports nonlinear harmonic generation measurements to distinguish between those areas of high and low dislocation densities in copper bars. The copper bars were subjected to flexural fatigue. Periodic scans were taken in order to track dislocation development during the fatigue life of the material. We show that this technique provides improved early detection for critical components of failure.

High Frequency Scanning Acoustic Microscopy as Diagnostic Tool in Tissue Science

The objective of this paper is to demonstrate the feasibility of High Frequency Scanning Acoustic Microscopy (HF SAM) as a tool to characterize biological tissues. The HF SAM is shown to provide both imaging and quantitative stiffness measuring abilities. The plant cell wall is used as a test analog to study the influence on stiffness when one important structural component is removed from a complex polymer structure. In particular, the hypothesis of this work was that the biopolymer pectin may have a strong effect on the mechanical properties of primary plant cell walls. The technical approach was to use HF SAM to document the effect of pectinase enzyme treatment to remove pectin from onion primary cell wall. The novelty in this work was to demonstrate the capability of HF SAM in terms of a characteristic curve called the V(Z) signature. The results indicate a significant change in the V(Z) signature with time into the enzyme treatment. Thus the HF SAM method opens the door to a systematically nondestructive study of complex bio-polymer structures.

PROGRESS TOWARDS THE DEVELOPMENT OF AN AUTOMATED ULTRASONIC NONLINEAR MEASUREMENT SYSTEM

Ultrasonic nondestructive evaluation utilizing nonlinear acoustic measurements has been of increasing prevalence in modern research. Nonlinear measurements based on harmonic amplitude ratios, in the form of the B/A term, can be used to detect variations in higher order material properties. This study presents the efforts in establishing an automated setup and procedure to measure the nonlinear B/A parameter for a variety of materials. The setup utilizes through transmission, and digital signal analysis while carefully compensating for the transducers’ frequency response. Finally, results will be presented for the case of nonlinear wave propagation in fluids pertinent to chemical and biodiesel processing applications.

Ultrasonic magnetostrictive transducers for guided ultrasonic waves in thin wires

The magnetostrictive effect is used to generate ultrasonic waves for a variety of health monitoring applications. Given the ductile nature of many ferromagnetic materials and the common geometrical configuration of magnetic inductance coils, magnetostrictive generation of ultrasound is especially suitable for long cylindrical waveguides such as thin wires. Furthermore, utilizing ultrasonic guided wave modes in such waveguides provides a robust tool for remote inspection of materials or environments over long distances. Through the use of different guided wave modes, structural health monitoring sensors could be tailored to suit individual applications. Guided wave modes offer a choice in displacement profile allowing sensors to be designed to be either sensitive or impervious to surface effects. The dispersivity of the guided wave velocity can also be optimized for applications involving time-of-flight measurements. Despite the advantages afforded by guided wave analysis, current magnetostrictive transducers, consisting of coil of wire and a bias magnet, can not perform at the frequencies necessary to excite higher order guided wave modes. In order to advance the capability of magnetostrictive transducers for ultrasonic guided waves in wires, the design parameters of inductance coils are examined. Using a Laser Doppler Vibrometer, ultrasonic displacements are measured over a range of excitation frequencies for different coil configurations and parameters to determine the feasibility of developing a higher mode magnetostrictive transducer.

Investigation of magnetostrictive materials and transducers for the generation of ultrasonic waves

The magnetostrictive effect is commonly exploited to generate ultrasonic waves for many applications. A better understanding of the physical mechanism of magnetostriction in terms of material and transducer characteristics could expand its utilization to many new sensor applications. Maximizing the ustable frequency bandwidth for ultrasonic wave generation alone allows for various choices of modes that are individually suitable for different applications. Several different materials were analyzed and compared in terms of theoretically expected magnetostrictive efficiency. Frequency content of ultrasonic waves generated via magnetostriction was examined with reference to the geometry and configuration of a magnetic coil transducer. Static measurements were made and extended in an attempt to quantify magnetostriction in the dynamic sense. A survey of current applications and direction for future research is included.

Ultrasonic stair case array for NDE

In this paper we present the results on the design of a unique two-dimensional phased array with low channel applications for imaging defects on a metal surface. First, basic transducer calculations will be shown. Followed by the results of important phased array variables, such as focusing, and angle beam sweeping ability, The final design will be given. Next the computer simulation results will be discussed. These results will indicate the performance of the actual array. The second half of the paper will be devoted to a discussion on the phased array testing results with a demonstration phased array.