Analytical ultrasonics for structural materials

The application of ultrasonic velocity and attenuation measurements to characterize the microstructure of structural materials is discussed. Velocity measurements in cast stainless steel are correlated with microstructural variations ranging from equiaxed (elastically isotropic) to columnar (elastically anisotropic) grain structure. The effect of the anisotropic grain structure on the deviation of ultrasonic waves in cast stainless steel is also reported. Field-implementable techniques for distinguishing equiaxed from columnar grain structures in cast strainless steel structural members are presented. The application of ultrasonic velocity measurements to characterize structural ceramics in the green state is also discussed

Nondestructive Evaluation Techniques for Silicon Carbide Heat-Exchanger Tubing

The adequacy of various nondestructive evaluation (NDE) techniques for inspecting silicon carbide heat-exchanger tubing is discussed. These methods include conventional ultrasonics, acoustic microscopy, conventional and dye-enhanced radiography, holographic interferometry and infrared scanning techniques. On the basis of current test results and an examination of the discussions in available literature, these techniques were compared with respect to (a) effectiveness in detecting cracks, pitting, inclusions, and voids, (b) effectiveness in characterizing detected flaws, (c) adaptability to tube geometry, (d) adaptability to in-service inspection, (e) reliability, and (f) extent of development required for commercialization

Preliminary Evaluation of NDE Techniques for Structural Ceramics

A preliminary evaluation of several nondestructive testing methods for flaw detection in high-temperature structural ceramic components is being carried out. The ceramics components being investigated include silicon carbide heat-exchanger tubes and silicon nitride rotors. The nondestructive evaluation techniques under consideration include dye-enhanced radiography, holographic interferometry, infrared scanning, acoustic microscopy, acoustic-emission monitoring, acoustic-impact testing, and conventional ultrasonic testing. The capability of each technique to detect critical-size flaws will be discussed. Preliminary results to date\u27 have shown that (a) dye-enhanced radiographic techniques are capable of detecting tight cracks missed with conventional x-ray methods, (b) acoustic microscopy techniques may be useful in detecting and establishing the size of subsurface defects in reaction-bonded silicon nitride, (c) holographic interferometry techniques should be valuable in locating surface cracks in silicon nitride/silicon carbide components, and (d) the results from various silicon carbide tubes suggests that infrared scanning techniques may reveal changes in heat-flow patterns which are related to variations in physical properties. The results for the other techniques mentioned will be discussed. Future efforts in this program, will be directed toward in-depth investigations of the most useful nondestructive techniques

Thermal stress effects in intermetallic matrix composites

Intermetallic matrix composites develop residual stresses from the large thermal expansion mismatch (delta-alpha) between the fibers and matrix. This work was undertaken to: establish improved techniques to measure these thermal stresses in IMC's; determine residual stresses in a variety of IMC systems by experiments and modeling; and, determine the effect of residual stresses on selected mechanical properties of an IMC. X ray diffraction (XRD), neutron diffraction (ND), synchrotron XRD (SXRD), and ultrasonics (US) techniques for measuring thermal stresses in IMC were examined and ND was selected as the most promising technique. ND was demonstrated on a variety of IMC systems encompassing Ti- and Ni-base matrices, SiC, W, and Al2O3 fibers, and different fiber fractions (Vf). Experimental results on these systems agreed with predictions of a concentric cylinder model. In SiC/Ti-base systems, little yielding was found and stresses were controlled primarily by delta-alpha and Vf. In Ni-base matrix systems, yield strength of the matrix and Vf controlled stress levels. The longitudinal residual stresses in SCS-6/Ti-24Al-llNb composite were modified by thermomechanical processing. Increasing residual stress decreased ultimate tensile strength in agreement with model predictions. Fiber pushout strength showed an unexpected inverse correlation with residual stress. In-plane shear yield strength showed no dependence on residual stress. Higher levels of residual tension led to higher fatigue crack growth rates, as suggested by matrix mean stress effects

Computer-aided analysis of eddy current rotating probe data.

Eddy current (EC) estimate of flaw size obtained from inservice inspection is often the primary means of assessing the structural integrity of steam generator tubes. Reliable prediction of failure pressure and leak rate in tubes with complex cracking requires more detailed information about the geometry and extent of degradation than is generally available from conventional bobbin coil examinations. High-resolution inspections with EC rotating probes are thus carried out on selected regions of tubing to provide the more extensive nondestructive evaluation (NDE) information that is needed to better assess flaw size and distribution. Interpretation of signals from complex cracking that are often distorted by coherent and incoherent noise can be a challenging NDE task. Studies at Argonne National Laboratory have demonstrated that computer-aided data analysis can be used for more accurate and efficient processing of the large amounts of data collected by such probes. The basic structure of a rule-based multiparameter data analysis algorithm is described in this paper. Multiple-frequency inspection data from a standard rotating pancake coil were used for the analyses. The codes were implemented as MATLAB scripts and provide, as the final outcome, profiles of flaw depth in a section of tube. Graphical user interface tools were devised to read the information needed to carry out various stages of data processing. These interactive tools allow conversion, calibration, analysis, and display of data in various formats. Representative cases of estimated flaw profiles are shown for tube specimens with laboratory-grown cracks (with and without simulated artifacts) that were used to assess sizing accuracy. The statistical analyses used to determine NDE performance are also discussed briefly. Results of investigations to date suggest that improved resolution and sizing accuracy can be obtained in a fraction of the time required for manual analysis

Expanding Transformative Experience

We develop a broader, more fine-grained taxonomy of forms of transformative experience, inspired by the work of L. A. Paul. Our vulnerability to such experiences arises, we argue, due to the vulnerability, dependence, and affliction intrinsic to the human condition. We use this trio to distinguish a variety of positively, negatively, and ambivalently valenced forms of epistemically and/or personally transformative experiences. Moreover, we argue that many transformative experiences can arise gradually and cumulatively, unfolding over the course of longer periods of time

Strength and flexibility of bulk high-{Tc} superconductors

Strength, fracture toughness, and elastic modulus data have been gathered for bulk high-temperature superconductors, commercial 99.9% Ag, and a 1.2 at.% Mg/Ag alloy. These data have been used to calculate fracture strains for bulk conductors. The calculations indicate that the superconducting cores of clad tapes should begin to fracture at strains below 0.2%. In addition, residual strains in Ag-clad (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} tapes have been measured by neutron diffraction. An explanation is offered for why many tapes appear to be able to tolerate large strains before exhibiting a reduction in current transport

'Education, education, education' : legal, moral and clinical

This article brings together Professor Donald Nicolson's intellectual interest in professional legal ethics and his long-standing involvement with law clinics both as an advisor at the University of Cape Town and Director of the University of Bristol Law Clinic and the University of Strathclyde Law Clinic. In this article he looks at how legal education may help start this process of character development, arguing that the best means is through student involvement in voluntary law clinics. And here he builds upon his recent article which argues for voluntary, community service oriented law clinics over those which emphasise the education of students