Time of flight diffraction technique

The PS-4 ultrasonic examination system provides many new features, which allows the operator to perform several inspections simultaneously. Both pulse-echo and time-of-flight-diffraction technique can be applied together with storage of digital A-scan data at the same time. 

Time of flight diffraction technique is a hybrid of the direct and indirect pitch and catch tests. Ultrasonic waves from a transmitter probe are diffracted from the tips of a crack as well as transmitted along the scanning surface and reflected from the back wall. 

Unfortunately, now that such methods have become available, such as the Time Of Flight Diffraction (TOFD) technique, this revolution does not happen. What we see instead is a much slower process towards quantitative NDT, in combination with adapted acceptance criteria for weld defects. 

Time of flight (TOF), 75 660-661 Time-of-flight (ToF) mass analyzers, 24 109 Time of flight diffraction (TOFD), 79 486 Time-of-flight instrumentation, in particle counting, 78 150—151 Time-of-flight-SIMS technique, 24 109 Time-resolved fluorimetry, 74 148-149 Time-resolved spectra, analysis of, 74 613 Time standards, 75 749—750 Time-temperature parameters (TTP), 73 471, 478, 479 creep properties and, 73 480 Time-temperature superposition, 27 746-747... 

Planar tomography could be complementarily adopted to indicate cracks and determine their depth propagation with high resolution, while time of flight diffraction (TOFD) has been considered not suitable as a surface crack inspection. Ultrasonic equipment such as phased array technique, on the other hand, allows complete weld inspections, improving, for instance, the separation between back wall and defect indication [10]. 

Residual stresses induced by variable polarity plasma arc (VPPA) welding in an A1 alloy 2219-T851 plate (6.5 mm thickness - Z direction, 62 mm in the direction parallel to the weld axis - Y direction, 48 mm in the direction perpendicular to it - X direction) were investigated by neutron diffraction [5], Measurements were performed by neutron diffraction, using the time of flight (TOF) technique, with a 2x10x2 mm3 sampling volume. 

Time-of-flight diffraction (TOFD) systems measure the time required for an ultrasonic wave to reach a flaw and return to the transducer. Defect depth and visualization of defect regions can be obtained with this technique. Incident ultrasonic energy propagates differently within a material as follows ... 

The time-of-flight Laue diffraction technique used at pulsed sources samples a large three-dimensional volume of reciprocal space in a single measurement with a stationary crystal and detector. This is due to the combination of the wavelength sorting inherent in the time-of-flight (TOP) technique with large area position-sensitive detectors (PSDs). 

Methods for analysis of the particle size distribution in the aerosol cloud include techniques such as time of flight measurement (TOE), inertial impaction and laser diffraction. Dynamic light scattering (photon correlation spectroscopy) is confined to particles (in suspension) in the submicron range. In addition to the size distribution, the particle velocity distribution can be measured with the Phase Doppler technique. 

In pulse-echo-based techniques, the time of flight in a sample cannot be determined simply from the observation of the time span between adjacent echoes in the echo pattern if plane parallel transducers operated at resonant frequencies are employed. Transducers introduce substantial errors if the velocity is derived from such measurements, especially if relatively short samples are used. Various correction approaches have so far been developed in order to consider the influence of resonant transducers and the effects of diffraction [31-33]. The need for corrections can be avoided and a broad operational bandwidth obtained by using short pulses of duration equal to or shorter than the transduction [34] this requires a time resolution better than the transit time in the transducer. This short-pulse excitation (e.g. the maximum for a 10-MHz transducer is 50 ns) requires a high-power wide-band ultra-linear amplifier to ensure the detection of US signals with sufficient resolution under non-resonant conditions. 

Figure 1 Compilation of data collected from Refs. 12 and 23 to 30 showing fine particle fraction (FPF), versus volume mean aerodynamic diameter c/a, for micronized and SCF-processed powders investigated. Values of c a obtained by using the AeroSizer time-of-flight technique when available (23,24,26,30) or recalculated from the mean volume (geometric) particle diameters cfy- obtained from laser diffraction and scanning electron microscope data (12,25,29) by applying the conversion algorithm developed by Shekunov et al. (24).

Transient intermediates are most commonly observed by their absorption (transient absorption spectroscopy see ref. 185 for a compilation of absorption spectra of transient species). Various other methods for creating detectable amounts of reactive intermediates such as stopped flow, pulse radiolysis, temperature or pressure jump have been invented and novel, more informative, techniques for the detection and identification of reactive intermediates have been added, in particular EPR, IR and Raman spectroscopy (Section 3.8), mass spectrometry, electron microscopy and X-ray diffraction. The technique used for detection need not be fast, provided that the time of signal creation can be determined accurately (see Section 3.7.3). For example, the separation of ions in a mass spectrometer (time of flight) or electrons in an electron microscope may require microseconds or longer. Nevertheless, femtosecond time resolution has been achieved,186 187 because the ions or electrons are formed by a pulse of femtosecond duration (1 fs = 10 15 s). Several reports with recommended procedures for nanosecond flash photolysis,137,188-191 ultrafast electron diffraction and microscopy,192 crystallography193 and pump probe absorption spectroscopy194,195 are available and a general treatise on ultrafast intense laser chemistry is in preparation by IUPAC. 

B. Buras Time-of-flight diffractometry. Reactor Centrum Netherland Report -234 New methods and techniques in neutron diffraction (1975) pp. 307-346. 

Particle size measurement techniques (Fig. 1) with various higher dispersion energies at very low (time-of-flight method) and at high silica aerosol concentrations (cascade impactor, laser diffraction method with air-jet injection) seem to be a powerful tool to investigate particle interactions. 

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