Bond Strength Measurements by Ultrasonic Spectroscopy

The goal of this project has been to discover techniques for predicting the strength of a metal-to-metal adhesive bond from nondestructive measurements on the completed structure. Both the cohesive strength of the adhesive material itself and the adhesive strength of the metal-to-adhesive interface must be determined separately. In previous phases of the program, it was demonstrated that the Fourier transform of the ultrasonic echo returned from a metal-adhesive-metal sandwich structure immersed in a water bath contained sufficient information to obtain a prediction of the cohesive strength of the joint. Furthermore, certain features of the Fourier transform were shifted by thin layers of different materials at the metal-to-adhesive interfaces so that detecting poor adhesion was also a possibility. During the current phase of the program, more reliable mechanical tests and more accurate measurement techniques were developed. As a result, measurements of the wave velocity in FM-400 adhesive joints subjected to different degrees of cure correlated with the cohesive shear strength of the joints. Quantitative measurements of the standing wave resonant frequencies in Chemlok 304 adhesive joints showed a correlation with the strength of adhesion at the metal-to-adhesive interface

High Frequency, Angle Beam EMATs for Weld Inspection

Accompanying the requirements for higher quality welds in structural parts, there is a growing demand for more rapid and automatic methods for their nondestructive inspection. Conventional X-ray methods are inherently slow and are difficult to automate. Furthermore, they often present a safety hazard that adds mass and bureaucracy to the application of the method. Ultrasonics, on the other hand, can be very rapid, is easily made automatic, and does not present any safety problems. Its main drawbacks are the requirement for a carefully aligned transducer, a plumbing system to supply liquid couplant, and an educated operator to maintain the alignment and coupling throughout the scan of the weld line. Since electromagnetic acoustic transducers (EMATs)1 eliminate the need for a couplant fluid, they would appear to offer a major improvement for weld inspection technology

Monitoring of Precipitation Hardening in an HSLA Steel Through EMAT Measurements of Magnetostriction

This work demonstrates a novel application of ultrasound: measurement of magnetostriction, the change of length of a ferromagnetic material that accompanies a change in magnetization. The technique involves measuring ultrasonic waves generated by an electromagnetic acoustic transducer (EMAT), and it offers an alternative method of measuring magnetostriction in cases where it would not be feasible to use strain gages (for example, on fragile, thin films)

A Compact EMAT Receiver for Ultrasonic Testing at Elevated Temperatures

For the past several years, the AISI and several national laboratories have cooperated on a program to develop ultrasonic transducers that can be used in steel mills at the highest temperatures encountered during the processing of the solid metal {1}. To date, pulsed laser light focused on the surface appears to make a satisfactory generator or transmitter for ultrasonic pulses while the EMAT or Electromagnetic Acoustic Transducer appears to hold the greatest promise for the receiver {2}. Both of these essentially noncontact devices can be made to withstand the very hot environmnent and they are not very sensitive to the quality of the surface

Effects of Two Energy Scales in Weakly Dimerized Antiferromagnetic Quantum Spin Chains

By means of thermal expansion and specific heat measurements on the high-pressure phase of (VO)$_2$P$_2$O$_7$, the effects of two energy scales of the weakly dimerized antiferromagnetic $S$ = 1/2 Heisenberg chain are explored. The low energy scale, given by the spin gap $\Delta$, is found to manifest itself in a pronounced thermal expansion anomaly. A quantitative analysis, employing T-DMRG calculations, shows that this feature originates from changes in the magnetic entropy with respect to $\Delta$, $\partial S^{m}/ \partial \Delta$. This term, inaccessible by specific heat, is visible only in the weak-dimerization limit where it reflects peculiarities of the excitation spectrum and its sensitivity to variations in $\Delta$.Comment: 4 pages, 4 figures now identical with finally published versio

Narrow-Band Hybrid Pulsed Laser/EMAT System for Non-Contact Ultrasonic Inspection Using Angled Shear Waves

Conventional ultrasonic testing (UT) using angled shear waves to locate and size potentially critical cracks and flaws in power generation and refinery equipment has become a widely utilized industrial tool. Because this technique uses piezoelectric transducers it requires intimate surface contact and fluid couplants. Therefore, conventional UT has the important drawback that it is difficult to use on surfaces at elevated temperature and, as a result, may require costly plant shut downs to implement. The development of non-contact techniques for angled shear wave UT would represent a significant improvement in the ability to test hot vessels and pipes

Numerical Comparison of Experimentally Measured Ultrasound through a Multilayered Specimen

The integrity of bonded structures is of paramount importance in the safe and reliable operation of aircraft equipment. Fuselages, helicopter rotor blades and nose cones are multilayered composite structures bonded together. The operational readiness and security of these units depend to a large extent on the integrity of the interfacial bonds. Adhesive and cohesive strength studies do not appear promising because failure is really dominated by defects and not by some average physical properties of the adhesive and the interface [1].</p

Electronic interactions in fullerene spheres

The electron-phonon and Coulomb interactions inC$_{60}$, and larger fullerene spheres are analyzed. The coupling between electrons and intramolecular vibrations give corrections $\sim 1 - 10$ meV to the electronic energies for C$_{60}$, and scales as $R^{-4}$ in larger molecules. The energies associated with electrostatic interactions are of order $\sim 1 - 4$ eV, in C$_{60}$ and scale as $R^{-1}$. Charged fullerenes show enhanced electron-phonon coupling, $\sim 10$ meV, which scales as $R^{-2}$. Finally, it is argued that non only C$_{60}^{-}$, but also C$_{60}^{--}$ are highly polarizable molecules. The polarizabilities scale as $R^3$ and $R^4$, respectively. The role of this large polarizability in mediating intermolecular interactions is also discussed.Comment: 12 pages. No figure

Detection and Measurement of Defects in Butt Welds

Sheet metal is produced in rolling mills in the form of coils of finite length. However, stamping and forming plants use these coils as a continuous stream of material to produce all the products we take for granted throughout society. Thus, the middle of this production chain must contain a “shock absorber” where the end of one coil is welded to the beginning of another. If this weld fails, expensive damage can result and productivity is definitely slowed down. Figure 1 shows this process in a schematic form and indicates that the welding is performed in between two clamps that hold the ends of the coils together while the weld is made. Special storage sections are included in the line so that the downstream flow of metal is not interrupted during the time in which the upstream flow is stopped for the weld. This welding machine not only forms the joint but knives clean off the weld bead on the top and bottom of the plate so that a smooth surface is presented to the downstream machines