Time-of-flight diffraction ultrasonics

About: Time-of-flight diffraction ultrasonics is a research topic. Over the lifetime, 544 publications have been published within this topic receiving 3189 citations.

Sparse Representations to Replace TOFD Images in Non-destructive Testing of Materials

Abstract: This paper describes a proposed method for the selection of relevant samples of ultrasonic signals during automatic material inspection. Instead of the well-known time of flight diffraction (TOFD) images, data are stored as a sparse matrix in which the elements only indicate whether a defect has been detected. This technique avoids storage of useless signals received during probe displacement in cases of low and high signal-to-noise ratios that correspond to coarse-grained and fine-grained materials, respectively. The approach is based on comparing the positions of maximum amplitudes, which are randomly located when signals only consist of noise but are in the same signal range when a defect is detected. The matrix elements are then applied as inputs to a self organizing map by neural networks to produce a normalized sparse matrix as the output, with a constant number of elements. This approach will be beneficial to enable the use of selected data in intelligent systems requiring a fixed number of inputs to characterize defects.

Ultrasonic time-of-flight diffraction method by cylinder focusing wedge

Abstract: An ultrasonic time-of-flight diffraction method by a cylinder focusing wedge relates to the field of ultrasonic detection and solves the problem that an existing time-of-flight diffraction method for detection is low in energy level of defective diffraction signals and needs improvement of detecting sensitivity. The ultrasonic time-of-flight diffraction method includes the specific steps: firstly, determining known conditions including the diameter of a probe wafer, the longitudinal wave velocity of the wedge, the longitudinal wave velocity of a detected workpiece and the velocity of longitudinal waves in water; secondly, setting needed conditions including the water path of an acoustic beam of a spindle, the refraction angle of longitudinal waves in the detected workpiece and the focusing vertical depth of the acoustic beam of the spindle in the workpiece; and thirdly, computing the curvature radius of a cylinder of the wedge according to the conditions and detecting by the ultrasonic time-of-flight diffraction method through the manufactured cylinder focusing wedge. The ultrasonic time-of-flight diffraction method is used for ultrasonic detection.

Study and Evaluation of Advanced TOFD Method for Inspection of Polyethylene Pipes but Welding

Abstract: Polyethylene material has some specification that makes very difficult any kind of inspection based on ultrasonic. The acoustic impedance and sound velocity in this kind of material are near to the materials commonly used in ultrasonic wedges. Also this kind of materials are highly attenuative materials for ultrasound. To inspection of polyethylene circumferential but welds and overcome to all the problems mentioned, the especial technique of TOFD (Time of Flight Diffraction) method which employs low frequency probe and concentrate on the inspection area that longitudinal waves turn into transverse waves has been used. The purpose of inspection is determining the exact location of surface and internal welding defects. For this purpose, two separate polyethylene pipes with 10 inch in diameter, 15 mm thickness and also 25 inch diameter, 28 mm thickness, were selected. In total 40 artificial defects which involve 28 side drill holes in deferent depths and 12 surface and sub-surface notches were created. All artificially created defects were detected with very good accuracy. Unlike the conventional TOFD method which have 2 to 3 mm dead zone, by using the above method even surface notch with 0.5 mm has been detected.

Defect depth automation measurement based on image processing for tofd parallel scanning

Abstract: To get more precise defect depth in parallel scanning of ultrasonic time-of-flight diffraction (TOFD) technique, a method for automatically measuring defect depth using defect image data is proposed in this paper. The method extracts defect image data from B-scan image through a series of image processing to fit a parabolic curve. Defect depth will be easily obtained by combining the quadratic coefficient of fitted parabolic curve with that of formula based on the principle of ultrasonic TOFD parallel scanning. Experiment result shows that the defect depth measuring error is less than 0.5 mm with this method and demonstrates strong practicability, high degree of automation and high measurement precision of the proposed method, reducing ultrasonic testing workload of the operator.

THz-ToF techniques for the detection of inherent discontinuities in dielectric materials based on a SAFT – and an optical layer reconstruction algorithm

Abstract: Electromagnetic waves with frequencies between 0.1 and 10 THz are described as THz-radiation (T-ray). The ability to penetrate dielectric materials makes T-rays attractive to reveal discontinuities in polymer and ceramic materials. THz-Time Domain Spectroscopy Systems (THz-TDS) are available on the market today which operates with THz-pulses transmitted and received by optically pumped semiconductor antennas. In THz-TDS the travelling time (ToF) and shape of the pulse is changed if it interacts with the dielectric material and its inherent disconti-nuities. A tomogram of the object under the test can be reconstructed from time of flight diffraction (ToFD) scans if a synthetic focusing aperture (SAFT) algorithm is applied. Otherwise, planar discontinuities like cracks in plastics or delaminated lay-ers in composites can be abstracted as layers located at any angle in relation to the outer sample surface direction. A tomogram from the scanned sample can then be reconstructed in case the interactions of electromagnetic pulses with the existing in-herent interfaces are detectable and a model is assumed which describes the device under the test as multilayer structure composed of thin layers with different dielec-tric properties. A short description of both the SAFT – and Optical Layer algorithm for the recon-struction of the inherent structure is initially given. Measurements on representative samples with a variety of artificially produced small and large scale. Reconstructed tomograms are presented to discuss and evaluate the benefits and limits of the two different reconstruction approaches.