Papers by Keyword: Non-Destructive Testing ( NDT)

Abstract: Recent studies showed that electrical conductivity is a valuable technique to identify the different zones of solid-state welded joints with a good correlation with the microstructure and hardness. This is a relevant result since this technique is expedite and, in some cases, non destructive. The concept was applied to other welding processes as the ones involving fusion and to a wide range of materials. For this, a comprehensive study was performed using friction stir welding, tungsten inert gas (TIG) and gas metal arc (MAG) welding processes in either bead on plate or butt joints in: carbon steel, magnesium and titanium. Eddy current non-destructive testing (NDT) was used to measure the electrical conductivity at different depths in transverse sections of the processed materials. The obtained profiles were compared to the hardness profiles in the same sections. As a result, a good correlation was observed in most materials welded by solid state and by fusion processes. The variation of the electrical conductivity closely follows the one detected in the hardness. Another interesting conclusion is that, even for fusion welding of carbon steels, the technique has potential to complement the hardness measurements and microstructural observations, allowing to identify the distinct zones of welds in materials commonly used in industry.

Abstract: The paper presents the application of a new type of a measurement system called Self-excited Acoustical System (SAS). It was applied for stress change monitoring of anchors which are used to secure roofs and walls in mines and in hollowed tunnels. The knowledge about the state of anchors can indirectly indicate the state of rock masses which is crucial for mining safety. One of the main problems so far has been reliable sensor mounting, especially in difficult mining conditions. The SAS system overcomes this problem because it can be mounted easily at the anchors end or even on the anchors flange. The laboratory tests were conducted on a hydraulic tensile testing machine. The mining roof anchor was placed in the machine and then stretched. The changes of the resonance frequency caused by the increase of the tensile strength were observed during the research.

Abstract: This paper deals with finding of defects, such as cracks, breakdowns and inclusions in rails and in ship plates, by ultrasound technique. Pulse echo method and twin beams technique is some of the ultrasonic inspection methods we have used for thickness measurements and for inspection of the welds. Initially, the thickness of rails and ship plates was measured by ultrasound devices using straight beam transducers and then the weldings of these samples were checked by using angle beam transducers.

Abstract: The problem of estimating mechanical properties of buildings materials is a major issue in civil engineering, especially when dealing with existing structures. In such occasion a valuable help is given by Non Destructive Testings, which allow materials characteristics to be evaluated in a non-invasive way. This paper analyses the efficacy of the SonReb method - a non destructive technique which statistically combines the results of Ultrasonic and Rebound Hammer Testing in predicting concrete compressive strength. The SonReb method has been applied on concrete specimens later on exposed to compressive strength test. The effectiveness of several empirical formulas expressing SonReb results is illustrated and discussed.

Abstract: Defect reconstruction of remote field eddy current belonged to electromagnetic inverse problem in materia Non-Destructive Testing. In view of disadvantages in present defect reconstruction methods, such as over-long time or excessive need for training samples, a new defect reconstruction method based on similar model and genetic algorithm was investigated as follows: similar model between non-axisymetric defect and axisymetric defect was represented, and proportionality factor was deduced by skin depth equation. As a result, the time-consuming forward problem solution in defect reconstruction, which using 3D finite element computation conventionally, was simplified to 2D finite element computation. At the same time, a method designed to accelerate convergence of genetic algorithm was adopted, and more times saving were obtained. Computation results show that, total defect reconstruction time is reduced to 7.6%, compared with directly 3D finite elemet computation, while reconstruction accuracy remains almost the same.