Vol 55, No 6 (2019)

It is demonstrated that by analyzing the instantaneous spectrum of an ultrasonic signal transmitted in the shadow mode through the product under study, it is possible to determine the degree of difference in the structure of products made of finely dispersed polymer materials with different contents of one of the polymer components. This cannot be achieved with traditional methods of ultrasonic structuroscopy, based on analyzing the degree of attenuation and measuring the velocity of ultrasound in the material.

It was noted that in most ultrasonic tomographs for concrete products, tomograms are constructed based on the velocity of body (longitudinal, transverse) ultrasonic waves, calculated from the easily measured velocity of surface waves. However, in engineering structures exposed to climatic or other impacts, the state of the concrete structure can vary greatly from its surface to its depth, leading to errors in determining the body ultrasound velocity and, consequently, to inaccuracies in displaying defects in the structure and product dimensions. In order to improve defect location accuracy, a new reference-free method has been proposed for measuring the speed of ultrasound in the volume of large-sized engineering structures. The method employs ultrasonic antenna arrays that take advantage of the “focusing to a point” algorithm when constructing tomograms, provided that a point reflector (e.g., an access hole) is present in the product.

A reference-free method is proposed for determining the speed of longitudinal and transverse vertically polarized waves and the thickness of a test object based on comparing the measured and calculated echo signals reflected from the boundaries of the test object when using an antenna array operating on a zero tilt angle wedge in the double scanning mode. Results of numerical and model experiments confirming the efficiency of the method are presented. Using this method in a model experiment, it has proved possible to measure the thickness of a test object and the speed of longitudinal and transverse waves in it with a relative error (accuracy) of approximately 0.25%. The method can be used to characterize anisotropic properties of test objects, providing information about their physical and mechanical properties.

Industrial Radiography is the most widely used NDT technique for weld defect characterization. As it is an indirect technique, an expert radiologist is required at the interpretation end to identify and characterize the defect in radiographs. However radiographs suffer from poor contrast thereby making it difficult to isolate the defect region from the background. Hence it is necessary to develop computer aided analysis tool for automated interpretation of weld radiographs. It involves an efficient contrast enhancement and segmentation technique for isolating the weld defect to its true size. In this work, wavelet based contrast enhancement technique has been developed to highlight the defect region from background. Biorthogonal 6.8 wavelet and Daubechies wavelet of order 4 are used for enhancing root/slag and porosity respectively. Thresholding and region growing are used for segmenting the region of interest.