Non-Destructive Testing Technology
Year:2020 | Volume:2 | Issue:5|Papers Count:8

Defects and damage during the manufacture of composites or metal parts are inevitable. Therefore, non-destructive testing is essential to prevent failure and increase the reliability of composite structures or metal components. Non-destructive thermography technologies have shown many advantages in this regard. In the thermography technology, the temperature variation of the external surface of the work piece was determined by receiving the radiated infrared waves. These waves indicated the point temperature precisely. In this paper, a compelet and comprehensive study of non-destructive infrared thermgraphy test methods for metal and composite inspection, detailed analysis was performed and the developments of infrared therapeutic technologies were investigated. First, the basic concepts for non-destructive test theramography were introduced. Then different types of thermography with radiation stimulation are described and compared. In the following, research examples of the application of thermography methods and some of the strengths and limitations of thermography technologies were compared and described in detail.

In recent years, limitations such as the inability to inspect composite materials in common non-destructive testing methods (NDT) have led to the development of new methods such as optical thermography (OPT) and digital shearography (DISH) which are able to resolve these limitations with non-contact and full field inspection. The aim of this paper is to compare the new and traditional NDT methods and also to mention the main features of these new methods such as detection of the defects by stimulating the specimen and receiving its response as out-of-plane displacement derivative (strain) and temperature gradients. The results show that the loading conditions, type of inspected defects, shear amount and the studied material are effective parameters in DISH to accurately estimating the size and depth of defects and also can show that the phase difference between reflected waves for healthy and defective regions in OPT increases up to a specific and optimum frequency value. Moreover, phase difference of waves can be used to determine the defect depth. Additionally, due to the indirect and non-contacting nature of the new methods in measuring defects, the correct determination of the type, size, depth and position of defects is associated with a small percentage of errors. Finally, it is proved that infrared thermography is a quick and effective method for a pass-fail test. Sonic thermography is capable for semi-quantitative evaluation impact related defects and combination of both OPT and DISH methods demonstrated as applicable for full field inspection of composite components instead of traditional methods.

In recent years, the use of layered composites has become very common in various industries due to specifications and properties like high strength, high strength to weight ratio and high corrosion resistance. One of the methods to construct the composite structures is the mechanical joining. To create these kinds of joints, the composite piece should be drilled. This drilling process results in the damages like interlayer delamination. Among the various methods for damage monitoring in composites, the acoustic emission test has the capability to detect the damages in composite pieces under loading due to high sensitivity, high detectability and the capability for online monitoring of the sample. Until now, extensive studies have been performed to analyze the damages during the drilling process of the composites with flat and smooth geometries. On the other hand, the utilization of curved composites is more common in the industry. There have been a few types of research for drilling of these kinds of composite materials. In this research, by using acoustic emission during the drilling process, the machining force behavior and also, interlayer delamination has been analyzed. According to the results, it has been shown that, count feature in acoustic emission method can presents different damage mechanisms.

Defects in wire rope steel cables can be mainly due to corrosion, loss of cross-sectional metallic area and breakage of steel wires. These defects reduce the allowable strength of rope and eventually failure of the steel cable due to the stresses caused by the combined loads. This study aimed to identify and detect artificial defects on wire rope by using magnetic flux leakage method. First, a number of specific artificial faults created, which included the failure of cable steel wires. Then, using magnetic flux leakage device, the magnetic signals caused by artificial defects were received by magnetic sensors embedded in the device, and then displayed as a color image after analysis. Since the resolution of the images obtained from the magnetic sensor signals is not very clear, the wavelet analysis method has been applied on raw signals to improve quality of the image. In wavlet analysis signal decomposed into different frequency levels and the threshold criterion is applied to reduce the background noise. Then, from the frequency levels, the signal that best describes the faulty content is choosen and used to reconstruct the image. The results show that using the wavelet analysis method improves image analysis capability as well as image quality of the defect.

Electrochemical Impedance Spectroscopy (EIS) is a powerful method for investigating various electrochemical systems. The technic involves application of a small amplitude alternative current (AC) perturbation to the electrochemical system and recording its response, and therefore it is considered a non-destructive monitoring technic. This article describes the scientific fundamentals for the EIS method, instrumentation of the method, especially different electrode configurations (2 or 3 electrode systems and comb-shaped or interdigitated electrodes), and also various fields where corrosion monitoring and analysis has been carried out by EIS. These include: atmospheric corrosion, concrete corrosion, analysis of performance of surface films and coatings, study of inhibitors, high temperature corrosion and oxidation, corrosion in gas and oil industries, microbiologically influenced corrosion (MIC) and stress corrosion cracking (SCC). The most recently published literature has been surveyed and typical equivalent circuit models, capabilities of the EIS technic and limitations of the technic are highlighted for each application. This article is a free translation and re-composition of two chapters about IES from references [1] and [2].

Nowadays, polymer based sandwich panels are widely used in industry because of their excellent physical properties compared to metalic alloys, such as lightness, high strength to weight ratio, and so on. Different mechanisms of damage occur during mechanical loading of the composites. Accumulated defects eventually lead to the composite failure. Matrix cracking, fiber breakage, and delamination are some of the damage mechanisms caused by these types of structures. It is necessary to identify the contribution of each mechanism to the ultimate failure of the composites. Non-destructive monitoring of this type of structures and prediction of damage with simulation by finite element method is very important. In this paper, damage mechanisms under low impact impact for sandwich panel made of glass / polyester shell and polyurethane foam core was investigated. In the present study, the shell and core of the sandwich panel was made manually and the sandwich sample was affected by the impact of 20 Joule, and during the test, acoustic data was stored by the installed sensor and was analyzed. Also, the impact process modeled using Abaqus FE software with explicit dynamic solver and damage mechanisms investigated applying cohesive bonding between layers and the proposed finite element model. The results obtained from the empirical test and simulation were discussed and there is a good agreement observed between them.

In this paper, the measurement of residual stress by the combination of Hole drilling, slitting and digital image correlation methods and history of activities in this area have been investigated. To this end, the principles of the hole drilling, according to ASTM E837 and slitting methods have been discussed. Subsequently, the principles of digital image correlation and the methods used to calculate the correlation coefficient are investigated. To use the proposed method, related works done in recent years have been studied. For this purpose, related articles have been extracted and the main points for evaluation of residual stress using hole drilling and digital image correlation methods have been investigated. By reviewing past research done in the field of residual stress and examining the points made in the research, it has been determined that digital image correlation and central hole drilling methods can be used to measure the residual stresses in any industrial parts with high precision.

Optical Spectroscopy, as a powerful and applicable Non-destructive Testing (NDT) technology, is capable of solving many problems in agriculture based on quality, safety and health assessment of the sample (plant or crop, food, soil, water, etc. ). This non-destructive optical technology can be used for development of smart spectral sensors and systems, the most important objects that can be connected to the Internet with the potential to collect, store, process and analyze the spectral data and information, and control or communicate remotely. Recent advances in non-destructive Spectroscopy technology in combination with emerging and advanced technologies such as Internet of Things (IoT), Big Data, Cloud Computing, and Artificial Intelligence technologies, play an important role in developing Smart Agriculture and improving the agricultural productivity. This article aims to present the role of this Non-destructive Testing technology in the future of Smart Agriculture by introducing its most important applications in solving key challenges facing agriculture based on sample quality, safety and health assessment.