Ultrasonic characterization of microstructure in powder metal alloy

The ultrasonic wave propagation characteristics were measured for IN-100, a powder metallurgy alloy used for aircraft engine components. This material was as a model system for testing the feasibility of characterizing the microstructure of a variety of inhomogeneous media including powder metals, ceramics, castings and components. The data were obtained for a frequency range from about 2 to 20 MHz and were statistically averaged over numerous volume elements of the samples. Micrographical examination provided size and number distributions for grain and pore structure. The results showed that the predominant source for the ultrasonic attenuation and backscatter was a dense (approx. 100/cubic mm) distribution of small micropores (approx. 10 micron radius). Two samples with different micropore densities were studied in detail to test the feasibility of calculating from observed microstructural parameters the frequency dependence of the microstructural backscatter in the regime for which the wavelength is much larger than the size of the individual scattering centers. Excellent agreement was found between predicted and observed values so as to demonstrate the feasibility of solving the forward problem. The results suggest a way towards the nondestructive detection and characterization of anomalous distributions of micropores when conventional ultrasonic imaging is difficult. The findings are potentially significant toward the application of the early detection of porosity during the materials fabrication process and after manufacturing of potential sites for stress induced void coalescence leading to crack initiation and subsequent failure

Measurements of Scattering from Bulk Defects

This report presents results of measurements of longitudinal wave ultrasonic scattering from complex defects embedded in Ti-alloy by the diffusion bonding process. The defects examined are: circular and elliptical cracks, two overlapping voids consisting of a sphere and a prolate spheroid, two adjacent spherical voids, and a spherical void with an encircling crack. Representative plots are given for the raw waveforms, magnitude (and sometimes the phase) of the deconvolved Fourier transform, and in some cases the time impulse response function. The data are compared to or analyzed in terms of several current theories. While good quantitative agreement was observed over certain ranges, the comparisons point to definite (in some cases not unexpected) limitations in either the pertaining theory or experiment or both. Finally, the results are discussed with an eye toward applications

Crack Depth Measurements with the Aid of SAW NDE

This report presents results of measurements of crack depth with the aid of acoustic bulk and surface waves. Both simulated and real fatigue cracks were examined. Two techniques were employed, one took advantage of the very efficient mode conversion between acoustic surface waves and shear waves at the crack tip; the other technique used the diffraction of shear waves at the crack tip. Both techniques were used on a number of simulated {spark eroded) and real cracks in Al 2024. In one fatigue specimen which contained an elliptical crack 4.5 mm in length and 1.25 mm in depth, crack closure studies were carried out. The precision of crack depth determination was judged to be better than 10%

Low Frequency Characterization of Flaws in Ceramics

There is an increasing need for the characterization of small flaws in ceramic components. This project is concerned with detecting and characterizing flaws in the bulk of ceramic parts. Cylindrical tensile test specimens of hot pressed Si3N4 are being prepared and, when available, will be inspected. In preparation for the arrival of the samples, measurement techniques have been developed for inspection of cylindrical shaped samples, signal processing techniques have been developed for obtaining flaw scattering data over a broad range of frequencies and analysis techniques have been developed to automatically extract flaw characteristics from measured data

Long Wave Ultrasonic Characterization of Inclusions in Silicon Nitride

The size and material content of Fe and Si inclusions in Si3N4 have been measured by means of pulse-echo scattering of elastic waves in the frequency range 5 to 100 MHz. The inclusions were of 100 μm and 400 μm nominal diameters and were located 3 mm deep in the Si3N4. The electronic noise was reduced by signal averaging and, in some cases, the noise due to grain scattering was reduced by averaging over transducer position. The scattering amplitude A(ω) and the impulse function R(t) were obtained by a desensitized deconvolution of the reference waveform obtained by reflecting the transmitted pulse from the back surface of the sample in a defect-free region. Comparison of theory and experiment are given for A(ω) and estimates of flaw size and material content are presented

Safety and tolerability of NXY-059 for acute intracerebral hemorrhage: the CHANT trial

<p><b>Background and Purpose:</b> NXY-059 is a free radical-trapping neuroprotectant developed for use in acute ischemic stroke. To facilitate prompt administration of treatment, potentially before neuroimaging, we investigated the safety of NXY-059 in patients with intracerebral hemorrhage (ICH).</p> <p><b>Methods:</b> We randomized 607 patients within 6 hours of acute ICH to receive 2270 mg intravenous NXY-059 over 1 hour and then up to 960 mg/h over 71 hours, or matching placebo, in addition to standard care. The primary outcome was safety: the mortality and the frequency of adverse events, and the change from baseline for a variety of serum, imaging, and electrophysiological measurements. We also studied the overall distribution of disability scores on the modified Rankin Scale (mRS) and the Barthel index.</p> <p><b>Results:</b> We treated 300 patients with NXY-059 and 303 with placebo. Treatment groups were well matched for prognostic variables including Glasgow Coma Scale, risk factors, and age. The mean National Institute of Health Stroke Scale score on admission was 14 in both groups. The baseline hemorrhage volume was 22.4±20.1 mL in the NXY-059 group and 23.3±22.8 mL in the placebo group (mean±SD). Most hemorrhages were related to hypertension or anticoagulant use. Mortality was similar in both groups: 20.3% for NXY-059 and 19.8% for placebo-treated patients. The proportion of patients who experienced an adverse event was the same for both groups, whereas for serious adverse events the proportion was slightly higher in the NXY-059 group. However, no pattern emerged to indicate a safety concern. Serum potassium fell transiently in both groups, lower in the NXY-059 group. There were no differences in 3-month function, disability, or neurological deficit scores. The odds ratio for an improved outcome in 3-month mRS scores in the NXY-059 group was 1.01 (95% CI 0.75, 1.35).</p> <p><b>Conclusions:</b> NXY-059 given within 6 hours of acute ICH has a good safety and tolerability profile, with no adverse effect on important clinical outcomes.</p&gt