A. V. Clark

Texture monitoring in aluminium alloys: a comparison of ultrasonic and neutron diffraction measurement

Abstract Theories have been developed by several authors to calculate velocities of bulk, guided and surface waves in polycrystalline aggregates of cubic metals. These theories can be used to predict the effect of texture on ultrasonic velocity in rolled aluminium and steel sheet, provided that the effects of dislocations, second-phase particles, inclusions, etc. can be ignored. The theories predict that ultrasonic velocities will will be influenced by three orientation distribution coefficients (ODCs). The ODCs are quantitative measures of the texture in the material; in general, more than three ODC are required to completely characterize texture. Neutron diffraction pole figures can also be used to obtain the ODCs. Neutron diffraction measurements of ODC can be compared against ultrasonic values to obtain an independent check on the validity of the ultrasonic theories. In this work, the texture of thin sheets of a commercial grade aluminium alloy was measured with both ultrasonics and neutron diffraction. Several ultrasonic techniques were employed, using bulk, guided and surface waves. Both piezoelectric and electromagnetic-acoustic transducers (EMATs) were used. Quantitative measurements of texture made with different ultrasonic techniques were in good agreement. These ultrasonic measurements also agreed with neutron diffraction measurements, indicating that the dominant features of the effect of texture on wave propagation have been modelled with sufficient accuracy. The extension of the ultrasonic technique to on-line (production) monitoring of texture is considered. In particular, it appears that EMATs are the transducer of choice for on-line texture measurement of rolled sheet, since they are non-contacting.

Characterization of residual stress and texture in cast steel railroad wheels

Residual stress and texture were characterized in the rim of a cast steel railroad wheel, using both an electromagnetic-acoustic transducer (EMAT) and a piezoelectric transducer. Orthogonally polarized shear-horizontal waves were propagated through the thickness of the rim, and arrival times measured (in pulse-echo) with a precision of about 0.00001. The difference in arrival times (birefringence) is related to the difference of principal stresses and also to texture. The wheel had been sawcut in a previous experiment; the residual stress had been relieved at the sawcut. The birefringence was measured at the sawcut and subtracted from the birefringence measured at stressed regions. This allowed the authors to map out variations in stress around the circumference of the wheel. the circumference of the wheel. Stresses measured with the agreed to within 10 MPa.

Effect of Liftoff on Accuracy of Phase Velocity Measurements Made With Electromagnetic-Acoustic Transducers

Electromagnetic-acoustic transducers (EMATs) work on transduction principles which allow them to operate with a clearance (liftoff) between them and a conducting specimen. They have the potential for on-line ultrasonic measurements of rapidly moving materials.Liftoff causes changes in the effective inductance and resistance of the EMAT. Consequently, it causes a phase shift in the output voltage of a receiving EMAT. This can cause errors when the EMAT is used for velocity measurements.In this paper, we develop a model for the effect of liftoff. The model gives good agreement with measured liftoff-induced arrival time changes. The model can be extended to the case of an EMAT used with a voltage stepup transformer.The maximum signal is obtained for EMATs operating at resonance; however, the maximum sensitivity to liftoff also occurs then. Thus, a tradeoff must be made between optimum signal and suppressing liftoff artifacts. Our model, and experimental results, can be used to make these tradeoffs.

Ultrasonic Measurement of Formability in Thin Ferritic Steel Sheet

The formability of rolled sheet metal is strongly influenced by the texture of the polycrystalline metal. For steel sheet, it is desirable to have high drawability to make automobile body parts, etc. In addition, material homogeneity is desired; that is, material cut from different parts of a rolled sheet should have the same plastic deformation when subjected to deep drawing.

Ultrasonic Measurement of Sheet Steel Texture and Formability: Comparison with Neutron Diffraction and Mechanical Measurements

AbstractUltrasonic measurements were made on a set of thin steel sheets, using the lowest-order shear horizontal mode (SH0-mode) and lowest-order symmetric Lambwave mode (S0-mode). The velocities of these modes were measured as a function of angle relative to the sheet rolling direction. From the data reduction it is, in theory, possible to (1) partially characterize the texture of the sheet, and (2) predict the plastic strain ratio (r-value). The plate texture can be completely characterized by quantities known as orientation distribution coefficients (ODCs). The lowest-order ODCs can be obtained from our measurements; these were compared with ODCs measured by neutron diffraction, with good agreement for the dominant ODC. The r-value is a commonly used measure of sheet formability. It is typically measured mechanically with uniaxial tension specimens subjected to large plastic strain. Therefore, the r-value test is destructive and time consuming. We found a good correlation between S0-mode velocity measurements andn

The Use of Ultrasonics for Texture Monitoring in Aluminum Alloys

bar r

Ultrasonic Methods of Texture Monitoring for Characterization of Formability of Rolled Aluminum Sheet

n, the average in-plane r-value. Consequently, the use of noncontacting electromagnetic-acoustic transducers (EMATs) may offer an online nondestructive measurement of sheet formability.

Crystallographic Texture in Rolled Aluminum Plates: Neutron Pole Figure Measurements

The study of the applications of the acoustoelastic effect, i.e. the stress-dependence of the propagation velocity of ultrasonic waves in deformed elastic media, has undergone considerable progress in recent years.1 Techniques for the determination of applied and residual stresses have been proposed both for bulk2–5 and for surface6–9 ultrasonic waves. However, for the practical application of these techniques to fabricated materials, the difficulty of separating the often competing effects of stress and texture remains a vexing problem.