Thermography is one of the new, fast and low-cost methods for nondestructive testing. In this method, the workpiece is subjected to heating under the modulated heat source, and the images of the process are stored by the thermal camera. In this research, the feasibility of this method was performed on a plastic cutter. The results showed that deeper and smaller defects are better identified in the image of the amplitude of the heat wave amplitude. It was also found that the quality of phase images is higher than the image of the domain and is less affected by the test conditions, such as asymmetric heating and light reflection. By optimizing the test conditions, the defects can be displayed with the use of domain images. Also, two different frequencies with a relatively high spacing of 0. 5 Hz and 1 Hz were used to obtain a suitable frequency for the workpiece. Due to the appropriate heat transfer, lower frequency use in the test is recommended to provide a more appropriate time interval for detecting defects.

Shearography is a powerful optics method, which is capable of measuring derivatives of displacement, surface strains, and nondestructive testing. Time-average shearography and stroboscopic shearography have been developed for full-field vibration analysis. In this paper, the capability of time-average shearography and stroboscopic shearography for nondestructive testing has been compared using a proposed shearography configuration. In order to generate vibration, the proposed experimental system was equipped with a piezoelectric excitation mechanism. The time-average and stroboscopic shearography inspections were carried out by sweeping the excitation frequency of the piezoelectric. Stroboscopic shearography successfully detected the defect in the frequency ranges of 1300-1600, 6000-8000 Hz and 12600-13300 Hz, while time-average shearography detected the defect only in the frequency ranges of 6000-8000 Hz, and 12900-13100 Hz. The results of inspections of propylene specimen with a 10 mm circular hole indicated that stroboscopic shearography provides a more reliable assessment than time-average shearography. Compared to time-average shearography, stroboscopic shearography gives more clear fringes in the all frequency range. In addition, stroboscopic shearography could recognize the defect in wider frequency ranges.

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.

The deterioration of railway tracks raises great concerns about the integrity of assessments and evaluations of railway tracks currently in service. Integrated inspection strategies coupled with innovations in inspection technology can lead to significant improvements in operational cost efficiency and reliability without the requirement of a fundamental shift in the existing understanding of the inspection process and standards. This review provides a discussion of the current state-of-the-art in nondestructive testing (NDT) for inspection, testing, and monitoring approaches for internal and surface defects, and condition assessment of railway tracks in general. A critical analysis is made between NDT and visual approaches, including a review of background theory and the techniques used to incorporate condition data into maintenance procedures. Various image processing techniques, along with their applications to different NDT imaging methods and some specific applications in railway tracks, with a discussion of their advantages and shortcomings, as well as future developments and novel inspection methodologies in the field are also presented, in order to show the potential of these approaches for rail infrastructure.

Digital shearography is widely used as a nondestructive inspection method in detection of subsurface defects and strain measurement in experimental mechanics. In addition, full field measurement and low vibration isolation requirements cause to higher application of this method in quality control applications. In this paper, the application of digital shearography in inspection of metallic samples has been studied. The subsurface defects of aluminum samples have been investigated by using a proper setup of digital shearography. The thickness of samples is 3mm and 5mm and the shear size in experiments is equal to 4mm. The samples are irradiated by a 660nm diode laser and recorded shearograms before and after thermal load have been analyzed by means of appropriate software. The results showed that, the diameter to depth ratio of defects employs important role in detectability of subsurface defects. By using this method, the minimum detectable diameter of defect is 2. 5 times of its depth.

In tire industry, it is very crucial to evaluate physical and mechanical properties of rubbers which are used for production of tires, to ensure the quality of the final product. Resilience is an important property of a rubber, which cannot be evaluated through direct measurement in production cycle in this industry. Therefore, Non-destructive ultrasonic testing, which has been used in many applications for examination of various material properties, can be used as an alternative approach for this purposes. In this study, the Non-destructive ultrasonic testing method has been employed to investigate the resilience of nanoclay reinforced rubber compounds. By changing physical and mechanical properties of materials, ultrasonic wave velocities are changed. For this purpose, sixteen different samples of nanoclay reinforced rubber compounds with different formulations were prepared and both their resilience and the longitudinal ultrasonic wave velocity through them were measured. In the next step, using the relevance vector machine regression analysis, a mathematical expression for the rubber resilience based on the longitudinal ultrasonic wave velocity was developed, which was proven to be qualified with acceptable accuracy and generalization capability. The results of this research can be used for online evaluation of the rubber resilience in tire production cycle.

The eddy current nondestructive testing (ECT) is one of the electromagnetic methods that can be used to evaluate and control the metallurgical quality of industrial alloys. The rapid implementation and digital nature of the answers have led to its use in setting up automatic inspection and quality control lines. The purpose of this paper is to investigate the metallurgical quality control conditions of 7075 aluminum alloy sheets after aging heat treatment using the ECT method. For this purpose, the destructive tests of metallography, hardness and electrical conductivity were performed along with the eddy currents Nondestructive testing and then their data were compared with each other. The sheet samples of this alloy were prepared in the form of a 1. 2 mm thickness. The solution heat treatment was performed at 470 centigrade for 20 minutes and then artificial aging heat treatment was performed at different temperatures and times. Microstructural studies were performed by optical and scanning electron microscopes, standard conductivity (% ICAS) and Brinell hardness methods. Then, using a eddy current apparatus at 8 kHz, the electromagnetic responses of the samples were evaluated and compared. The results showed that to quality control and assurance of the aged products, the use of hardness index alone cannot suffice. In addition, the metallographic method has executive limitations in production processes. It was found that the eddy current responses are affected by microstructural changes resulting from aging process. Using this method, different parts of 7075 aluminum alloy can be Nondestructively separated from each other.

In this laboratory study, a mixing design was made of ordinary concrete containing Portland cement with a grade of 500 kg/m 3 and a mixing design was made of alkaline concrete based on slag from the composing furnace. To investigate the mechanical properties, a nondestructive test was performed to determine the velocity of ultrasonic vibrations in concrete at 21 and 600 °, C at a 90-day curing age. In order to evaluate the microstructure of theconcrete and verify the results of ultrasonic test, compressive strength test and scanning electron microscopy imaging was performed on concrete samples. The results showed a decrease in the speed of ultrasonic vibrations after applying high temperature (600 °, C) in concrete, so that in ordinary concrete and hard concrete, the deceleration rate was 44. 79% and 40. 58% in the results after and before, respectively. In this regard, the velocity of ultrasonic waves in ferrous concrete were lower than ordinary concrete, so that at 21 and 600°, C, the percentage of velocity drop in ferrous concrete compared to conventional concrete was equal to 10. 48 and 3. 66%, respectively. The results of the compressive strength test and the images obtained from the scanning electron microscope were in good agreement with the results of the ultrasonic tests in concrete at 21 and 600°, C.