Non-destructive methods of testing (NDT) welded joints are nowadays intensively developing due to their numerous advantages. The most significant of them are the possibility of objects diagnosis in the place of their work without the necessity of disassembling or long outage, lower costs of realization as well as considerably lower insalubrity for people conducting the tests. Study of dynamic characteristics of welded elements creates a good possibility for welded joints assessment in comparison to other known non-destructive testing methods. The main reasons are Fourier analysis (FFT), damping analysis, differences in signals or their answers. Presented method can be used in classical NDT tests as well as in structural health monitoring (SHM). Assumptions for quality evaluation methods of welded plates using spectrums analysis of dynamic characteristics are presented in the article. In order to provide the high quality of research, the measuring devices of Bruel & Kjaer Company are used. Both, the testing methodology and possibility of using vibration method in welded joints testing are presented. The attention is also drawn to the vital testing elements like proper selection of impact hammer ending and impact place as well as the problem of repeatability of diagnostic signals. The value of repeatability of obtained signals will be of critical importance in the comparative method, which is under development. The results of initial testing of plates with proper and faulty welded joints have been analysed. Among welding faults, the boundary bonding and crevice have been considered. The analysis of impact hammer dispersion values in correlation to the spectrum of dynamic characteristic has been conducted. Statistic methods have been used for the assessment.
Rubber and rubber-metal vibration isolators are widely used vibration isolation systems in marine applications. For naval application, shock absorber mounting systems must fulfil two functions. The first one supports the suspended mass in the absence of waving or detonation while providing isolation from vibrations and shock impact. In the second case, during the machine operation, it reduces the force of movement to an acceptable value. Moreover, it returns the insulated mass to the position output without plastic deformation or residual buckling after removing shock stresses or harmonic vibrations. The environment in which marine vibration isolators are to be used strongly influences the selection of a shock absorber. The main environmental problem is the temperature range in marine power plants, which ranges from 20 °C to 55 °C. Temperature fluctuations may cause changes in the physical properties of typical vibration/shock insulators. Both rubbers and elastomers used for shock absorbers tend to stiffen, gain low-temperature damping, and soften and lose damping at elevated temperatures. Factors such as moisture, ozone and changes in atmospheric pressure are usually ignored in shipbuilding. The main environmental factors influencing the ageing of insulators are liquid saturated hydrocarbons, i.e., oils, fuels, coolants, etc., which may come into contact with the surface of the insulators. This work presents the results of the research carried out to determine the effect of overload and the impact of petroleum products on the materials of metal-rubber shock absorbers made of three different rubbers and one polyurethane mixture. For each of the materials, shock absorbers with three different degrees of hardness were tested.
The paper presents two methods of crack detection in ship hulls. The methods are dedicated for structural health monitoring (SHM) of responsible welded joints. The system will be based on vibrodiagnostic-signals will be measured by piezoelectric accelerometers and/or fibre optic sensors. In SHM systems of welded joints of thin-walled structures, a vibrodiagnostic method is the most promising. Its most important advantage is that it is both effective and relatively low costly. There are two general methods of vibrodiagnostic signal analysis: the most frequently used are spectrum analysis and time waveform analysis. The spectrum analysis concerns changes of natural frequency. In marine exploitation conditions, the frequencies changes might be imperceptible. The first method presented in the article is based on the evaluation of the mean value distribution of the amplitude spectrums calculated with the time window method. Second proposed method was based on the determination of damping decrement in function of time. Due to the complexity of the responses run, the proposed method consisted of calculating the damping decrement using the response approximation with different functions. It has been shown that the changes analysis of damping decrement applied to welded plates enables the assessment of the quality associated with the weld. A calculation algorithm as well as and the exemplary results from the proposed methods used for some selected samples with different type of welds are included in the paper. The results of the tests show that the analysis based on proposed methods indicates that they differ significantly depending on the welds, indicating their quality and cracks that are associated with them.
Increasingly popular remote work requires the use of modern network technologies to provide employees in a remote location with access to the company’s IT resources. The answer to the needs of remote access to files and server services can be the use of clouds and VPS. However, this involves high costs and requires entrusting the enterprise’s data to the providers of these services. Both for reasons of data security and too high costs, enterprises sometimes cannot use these technologies. The solution to the problem may be the use of encrypted VPN tunneling, which allows the device to be connected at a remote location to the company’s local network and use its resources as if it was connected to the local network with physical transmission medium.
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