جستجوی مقالات مرتبط با کلیدواژه "امواج هدایت شده فراصوت" در نشریات گروه "مکانیک"

In this research side ratio effect of ultrasonic guided waves in a bar with rectangular cross section is investigated and wave structure is calculated and plotted. The motion of ultrasonic guided waves in the mentioned bar is considered as a three dimensional problem. In the homogenous equation system that is obtained to satisfy stress free surface boundary conditions, the ratios determinant of this system should equal zero. So, the frequency equation is obtained. The real roots of this equation are extracted and frequency spectrum, phase and group velocity diagrams and wave structure for longitudinal, torsional and bending waves are plotted by a written computer program by Matlab. Increasing cross section bar side ratio shows when the frequency increases the longitudinal and torsional waves phase velocity decreases and bending waves phase velocity increases. Also, for some modes replacing particles on the bar surface is considerable and for some others is negligible.

In this study, the structural health of a thick steel beam, made of ST-52, is inspected by ultrasonic guided wave propagation method using piezoelectric wafer active sensors that is one of the most important techniques of on-line structural health monitoring. The key parameters of the diagnostic waveform such as excitation frequency and cycle number are determined in relation to beam dimensions as well as pulse-echo configuration of PZT active sensors attached to the beam. Finite element simulations were conducted to characterize wave propagation in the beam, and the signals of wave propagation were experimentally measured. For signal processing and feature extraction, continuous wavelet transform and scaled average wavelet power technique are used. Using the extracted features, probable existing damage in the structure is detected, localized, and intensified. The acquired results are representing a higher precision of the implemented method for damage identification and characterization with respect to a previous study.

These days machinery، devices and tools that are used in industry، are very complex and costly. Therefore using producing and inspecting methods with maximum reliability that supply equipments، are required. Non-destructive testing is one of those methods that are used to inspect equipment that already have been mentioned. One of the non-destructive testing، which has more industrial application، is ultrasonic test. In this paper، examine of the ultrasonic guided waves in laminated isotropic plates has been discussed. With the assumption that there is not space between layers andthey are connected to each other and as boundary conditions، on the top and bottom of plate’s surfaces، tension is zero. The purpose of this study are extracting diagrams of frequency spectrum (frequency depending on the wave number)، phase velocity depending on frequency، group velocity depending on frequency and eventually the wave structure and stress distribution in a two-layers plate، the equations for multi-layer plates are solved and diagrams that discussed above are extracted. How to stimulate a particular mode at a probe frequency for two layers plate is investigated in continuance and graphs of radiation angle at frequency are plotted.