Papers by Keyword: Elastic Wave

Abstract: In this study, elastic waves were detected when different bending stresses were applied to cracked specimens of high-strength steel (SKD11: HV550) immersed in a 0.057 M solution of acetic acid (CH₃COOH), and frequency characteristics were analyzed using time-frequency analysis. The dominant frequency obtained using the tensile test was approximately 103 kHz, and those in the acetic-acid solution without stress were approximately 32 and 101 kHz. The dominant frequencies of the crack specimens in which cracks propagated were approximately 30–40 (F1), 60–85 (F2), and 100–110 (F3) kHz. An elastic wave was obtained by corrosion, pitting, crack initiation, and propagation but not during the hydrogen aggregation time. The dominant frequencies of the crack specimens without crack propagation were approximately 28–33 (F1) and 94–109 (F3) kHz. These were the same as the dominant frequency in the acetic-acid solution under nonstress conditions. The fractured surface showed many traces of pitting and corrosion regardless of the applied stress, resulting in microcracks in the Cr carbide. -----------------------------------------------------------------------------------------------------------

Abstract: Ultra-high-strength steel (UHSS) structures are exposed to corrosive environments during service, and hydrogen-assisted cracking (HAC) may occur owing to stress corrosion cracking and hydrogen embrittlement. In this study, the HAC threshold stress intensity factor and fatigue life of UHSS steel were evaluated by applying stress in a corrosive environment to prevent structural fracture. For specimen with semicircular slits by electric discharge machining, fatigue limit was obtained by static fatigue test under corrosive environment. The fatigue limit of the crack specimen was evaluated by the fatigue limit of the experiment and HAC threshold stress intensity factor, and comparative evaluation was performed. On the surface of cracks, grain boundaries were embrittled by corrosion, and grains were clearly observed. Meanwhile, cracks in the surface direction propagated slightly, unlike cracks in the depth direction. The static fatigue limit of UHSS (SKD11:HV670) was determined to be 400 MPa, and the fatigue limit of the crack specimen could be evaluated. The experimental results agreed well with the evaluation results.

Abstract: The paper presents a non-isothermal model of the initial stage of ion implantation process. The model takes into account the existence of internal interfaces. The model assumes that the implantable impurity generates mechanical perturbations. These disturbances can propagate at different speeds before and after internal boundary. The examples of the waveform evolution in transition across the border are shown.

Abstract: The coupled model is presented to describe the elements penetration into the surface layer of metal during the process of ion implantation. Mechanical stresses arising due to the interaction of particles with the surface affect the redistribution of the implanted impurity. In addition, the existence of vacancies in the metal surface and their generation under the stresses influence are taken into account. The kinetic law is written on the basis of the thermodynamics of irreversible processes. The solution had been found numerically. As a result, the distributions of impurity concentration and deformations have been obtained for various time moments. The comparison of the concentration profiles with vacancies and without their have been given.

Abstract: A coupled isothermal model at the initial stage of a solid body surface treatment with particle flux is presented in this paper. The model takes account of the interaction of two different scale processes: impurity diffusion and mechanical stress wave propagation. The transition to dimensionless variables is briefly described. The examples of the coupled problem solution illustrating the wave interaction under the action of one pulse and two successive pulses are given.

Abstract: Aging and deterioration (such as weakening of concrete strength and loss of prestress) of various degree will inevitably happen to prestressed concrete beam in service. In making the prestressed concrete beam, it is of vital importance to ensure that the prestress tension is sufficient, duct grouting is compact enough and concrete pouring is in good quality. Otherwise, structure will deteriorate faster and safety hazard and even bridge collapse may ensue, causing considerable economic losses.

Abstract: In this study, to accurately identify the functions of piezoelectric actuators and sensors for the generation and collection of elastic waves in typical engineering structures, several effective models of surface-bounded flat PZT disks are further developed and validated for numerical modelling of elastic wave propagations. Based on these models, a series of finite element models of elastic waves in plates are devised using both implicit and explicit dynamics analysis techniques and those numerical simulations are conducted and verified one another. The results flowed from the present research is being used to study the elastic wave propagation in pipes and develop an online structural health monitoring (SHM) system with an integrated piezoelectric actuator-sensor network.

Abstract: The matrix Greens function of coupled spin and elastic waves for media with the 3D inhomogeneities of the coupling parameter is studied. It has been shown that the difference in shapes of the Greens functions for the cases of 1D and 3D inhomogeneities appears only for the sufficiently large correlation wave number of the inhomogeneities.

Abstract: In the case of fracturing of rocks in subcritical stress state, the stress release due to fracturing could be accompanied by stress increase near the fracture tips, so the rock deformation near the tips could also generate elastic waves (so called "stopping-phase"). Results of experimental modeling of elastic wave generations by fatigue tensile fractures are considered. The model sample consisted of elastic layer made of rubber and fragile layer made of paraffin, the layers were bounded. The elastic layer was stretched and fixed, so the fragile layer was under static tension and started fracturing by tensile fractures. First fractures appeared in visually intact material, later fractures were preceded by a cloud of small "micro" fractures. The fracturing generated elastic waves, which had two components: one corresponded to fracturing of the fragile layer and had characteristic frequency 5-10 kHz; another one had frequency 100-300 Hz, opposite onset and corresponded to tension of elastic layer. It was concluded that tensile fractures in stressed rocks could be considered as a kind of a double-source of elastic waves: one source is the fracture itself, another source is an area of deformations due to stress increase in the vicinity of the fracture tips.

Abstract: This paper deals with the damage assessment in stone blocks dismantled from a historic bridge construction. Nonlinear ultrasonic spectroscopy and impact echo methods were used for evaluating the stone block integrity structure. Harmonic analysis of the sample response on well defined ultrasonic excitation was used in the case of nonlinear ultrasonic method application. The amplitude dependent spectral changes of the probing signals were measured in the damaged blocks. Measurement results showed that the analysis of amplitude dependent spectral changes is a promising method for the damage assessment in structures. The Impact-Echo method is a technique for detecting defects in material structure such as stone blocks. It is based on monitoring the propagation of elastic waves from a short-duration mechanical impact. The aim of this paper is to provide an overview of the technique and to discuss the important parameters involved in this type of testing. The impact echo method is used to generate low-frequency stress waves from 500 Hz to 50 kHz that propagate into the structure and are reflected by defects and external surfaces.