A one-dimensional model for variations of longitudinal wave velocity under different thermal conditions

Ultrasonic testing is a versatile and important nondestructive testing method. In many industrial applications, ultrasonic testing is carried out at relatively high temperatures. Since the ultrasonic wave velocity is a function of the workpiece temperature, it is necessary to have a good understanding of how the wave velocity and test piece temperature are related. In this paper, variations of longitudinal wave velocity in the presence of a uniform temperature distribution or a thermal gradient is studied using one-dimensional theoretical and numerical models. The numerical model is based on finite element analysis. A linear temperature gradient is assumed and the length of the workpiece and the temperature of the hot side are considered as varying parameters. The workpiece is made of st37 steel, its length is varied in the range of 0.04-0.08 m and the temperature of the hot side is changed from 400 K to 1000 K. The results of the theoretical model are compared with those obtained from the finite element model (FEM) and very good agreement is observed.</span

Application of signal processing techniques to ultrasonic ToFD testing of austenitic welds

The desired properties of austenitic steels lead to their numerous applications in many industries. Welded austenitic materials have columnar grains, anisotropic elastic properties, and a heterogeneous structure. These properties are controlled by both the procedure and parameters of welding. The complex structure of austenitic welds can distort and scatter the ultrasonic beams. In ultrasonic testing of austenitic welds, this situation can lead to low signal-to-noise ratio and make the interpretation of results quite difficult. In this paper, the relatively new ultrasonic technique of time-of-flight diffraction (ToFD) is used for inspection of austenitic welds. Special signal processing techniques are implemented in order to improve the low signal-to-noise ratio of ultrasonic signals and make the interpretation of results easier

بررسی اثر درز جوش طولی لوله در هنگام بازرسی فراصوتی لوله با امواج هدایت شده متقارن

Low-pressure fluid transmission lines are largely manufactured by cold rolling of a plate followed by resistance welding of the two edges of the plate. Consequently, these pipes have a straight weld seam along their length. In this paper, a finite element method is used for simulating the propagation of symmetric guided wave modes L(0,2), L(0,1) and T(0,1) in straight seam welded pipes. A comparison is made between the propagation of these wave modes in seamless and seam welded pipes. Results indicate that the angular amplitude profiles of the L(0,2) and T(0,1) modes do not change much in the presence of the seam weld. However, the presence of the straight seam weld significantly affects the propagation of the L(0,1) mode along the pipe. While the angular displacement profile for the L(0,2) and T(0,1) modes are almost symmetric, for the L(0,1) mode, the angular displacement profile shows high asymmetry. This asymmetric behavior impairs the sensitivity of this mode to the detection of defects in the proximity of the weld line. As a result, the guided wave modes L(0,2) and T(0,1) are considered to be suitable for inspection of straight seam welded pipes but L(0,1) is not recommended for this purpose

Application of Model-Based Estimation to Time-Delay Estimation of Ultrasonic Testing Signals

Time-Delay-Estimation (TDE) has been a topic of interest in many applications in the past few decades. The emphasis of this work is on the application of model-based estimation (MBE) for TDE of ultrasonic signals used in ultrasonic thickness gaging. Ultrasonic thickness gaging is based on precise measurement of the time difference between successive echoes which reflect back from the back wall of the test piece. The received echoes are modelled by Gaussian pulses and the desired system response is estimated using Gauss-Newton and Space Alternating Generalized Expectation Maximization (SAGE) algorithms. In addition to the model-based estimation approach, five other TDE techniques including peak-to-peak measurement, cross-correlation, cross-correlation with interpolation, phase-slope, and cross-correlation with Wiener filtering are also considered and compared with the SAGE. The main advantage of the SAGE algorithm, in addition to its higher accuracy, is its ability to deconvolve the overlapping echoes

تحلیل اجزای محدود آزمون غیرمخرب دمانگاری ارتعاشی به کمک فرکانس تشدید عیب

Vibro-thermography is an emerging and promising technique that uses ultrasonic elastic waves as an excitation source to detect and evaluate surface and subsurface defects. Friction of the edges of defects, viscoelastic behavior and non-linear vibrations of the defect region are the main sources of heating and the temperature gradient that shows up synchronously with variations of non-linear elastic energy. The temperature gradient in the defect region can be imaged by an infrared camera in order to estimate the location and size of the defects. In this paper, the vibro-thermography is simulated in COMSOL Multiphysics software. Lamb waves are used to excite an aluminum plate containing a flat-bottomed hole. First, the resonance frequency of the defect is found by means of the theory of vibrations and also by finite element method (FEM). An algorithm that incorporates frequency analysis as a function of out-of-plane displacements is used to verify this frequency and the results are compared with the eigenfrequency analysis results. The agreement observed between the theoretical and numerical models is found to be very good. The plate is then excited by an amplitude modulated sine-burst at the local defect resonance (LDR) frequency and a frequency related to the thermal penetration depth. Thermal image processing is carried out on the thermal waves to obtain their amplitude and phase images. By considering a four-point algorithm, the location, size and geometry of the defect is estimated with good accuracy

Nondestructive evaluation of cylindrical components by resonance acoustic spectroscopy

grantor: University of TorontoPotential applications of resonance acoustic spectroscopy (RAS) for the purpose of nondestructive evaluation (NDE) and on-line monitoring of isotropic clad rods and transversely isotropic cylinders are investigated in this thesis. Mathematical models are developed for the scattering of an infinite plane acoustic wave from infinite elastic and viscoelastic clad rods and infinite transversely isotropic cylinders. In these mathematical models, the scattered pressure field is obtained in terms of normal-mode Rayleigh series. Experimental measurements of the scattered pressure fields of various cylindrical components are performed using the short-pulse method of isolation and identification of resonances (MIIR). The method is applied to: copper-clad aluminum rods, Epon-815-clad steel rods, and fiber reinforced composite rods. The experimental results show good consistency with the results obtained from mathematical models. It is concluded that RAS is a potentially powerful technique for nondestructive evaluation and on-line monitoring of various cylindrical components.Ph.D