Yonka Ivanova

Comparative measurements of the stress state in a rolled carbon steel using magnetic Barkhausen noise and ultrasonic method

We report the results of the stress evaluation of rolled carbon steel cantilever using different non-destructive methods. The paper describes the procedure of calibration and measurements using Barkhausen effect and ultrasonic method. Test object is constant stress cantilever submitted to different loads. Both methods complement and provide better reliability of the stress state evaluation.

Acoustic investigations of the steel samples deformation during the tensile

The paper presents an experimental study of ultrasonic surface waves propagation in the low carbon steel specimens with different degree of degradation of microstructure and mechanical properties, subjected to tensile deformation. The purpose of this paper is to investigate and analyze the dependence between microstructure, mechanical and acoustic properties and to find appropriate parameters for stress state evaluation. For identification of degradation and stress state we use ultrasonic Rayleigh waves (URW) velocity variation obtained by in-line and off-line measurements. The degradation is imitated by structural changes caused by heat treatment.

Non-destructive ultrasonic investigation of the structure state of steam pipelines

The main purpose of the work is to study the dependence of the ultrasonic wave parameters on the structure state in tubes of boilers at thermo-electric power station. The changes of the velocity, spectra and attenuation of ultrasonic surface waves are caused by degradation of the structure and can be used for residual life estimation of the equipment.

Comparison of NDT Techniques for Elastic Modulus Determination of Laminated Composites

The study of dependence of elasticity modulus on the type, shape and structure of the fillers in the composites is an important task. By theoretical point of view, different models are developed to describe the relation between geometrical, mechanical and physical parameters of the fillers and matrix with the macroscopic effective properties of composites. It is reasonably the Young’s modulus of the composites to be determined both experimentally and theoretically.In the present study non-destructive techniques are used for characterization of elastic modulus. NDT methods, static and dynamic ultrasonic and vibration methods are applied to find the relations between internal structure of composites and their elastic properties.For investigating of the elastic properties in different directions of composites are used a methodology based on combination of different kind of vibrations. The bar shaped specimens are examined by free longitudinal, flexural and torsional vibrations.

Computer Aided Modeling of Ultrasonic Surface Waves Propagation in Materials with Gradient of Properties

The present work deals with modeling of generating, propagation and receiving of the Rayleigh impulse in material with gradient of properties. The spectrum of an ultrasonic signal, having passed through a material, is determined by the spectrum of the exciting electrical signal, frequency characteristics of the transmitting and receiving transducers and by material characteristics. The dispersion of the Rayleigh wave is obtained as a result of the simulation done by spectral decomposition of impulse and processing components considering wave penetration and wave velocity changes caused by gradient of mechanical characteristics. Simulated ultrasonic waveforms allow evaluation of the time delay effect induced by stress gradient. Application of ultrasonic wave for stress analyses is possible on the basis of spectral analysis and phase comparisons of ultrasonic impulse.