PSI - Issue 16

Valentyn Uchanin et al. / Procedia Structural Integrity 16 (2019) 192–197 Valentyn Uchanin, Orest Ostash / Structural Integrity Procedia 00 (2019) 000 – 000

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Measurements of the CF were carried out by a KRM- Ts type device on a “river -sea" type cargo ship, which has been in operation since 1980. The material of investigated ship coaming is 09G2S steel. The longitudinal coordinate of the points of CF measurements was determined by the number. CF was measured at points on the coaming horizontal desks, which correspond to each 5th bulkhead. For the inspected ship, the distance between each fifth bulkhead was equal to 2.5 m. Distributions of measured CF values along the inspected ship coaming are presented in Fig. 5. CF values were measured for 2 directions of the magnetization field – longitudinal and transverse. Measurements of the CF H c distribution were conducted in different loading modes. The H c distribution on the point numbers № in ballast state show that the highest CF H c values are observed in the areas of a points 4 ( № 50), 5 ( № 57), 6 ( № 85), 7 ( № 135) and 8 ( № 190) (Fig. 5). These areas can be recognized as individual critical ones for inspected ship and can be used for further monitoring. It was revealed that the critical areas coincide for the ballast mode and for ship under full loading. Consequently, the identified critical areas are available under different ship loading conditions and are individual for each ship. To determine the mechanical stresses of ship structures in critical areas, an appropriate correlation between the stress state (yield strength and ultimate strength) and CF were used. For the investigated steel, the corresponding values of the CF are 7.5 A/cm and 9.5 A/cm respectively.

Fig. 5. Distribution of the CF H c along the coamings according to the bulkhead numbers in ballast conditions: 1 – longitudinal H c component; 2 – transverse H c component; 3 – midship section; 4 – 8 – revealed critical areas.

It should be noted that areas of highest CF (and mechanical stresses) are not in compliance with the recommendations of the International Maritime Organization concerned the strain gauge placement. New concept for ship structure monitoring was proposed. Due this concept the monitoring must be carried out by placing the CF sensors in the preliminary defined critical areas and measuring the CF changes during the exploitation. Such strategy based on the CF measurements (as indirect method for determining the level of mechanical stress) in preliminary determined critical areas takes into account the individual peculiarities of a inspected ship (Zavalnuk et al. (2013)). 6. Determination of stresses in steel components by EC method Any types of stress determine the residual life of the structures. For example, residual stresses, created by the welding process provoke the brittle fracture and stress-corrosion cracking. Proposed EC method based on the magnetic permeability changes in the ferromagnetic material is concerned with the rearrangements of the magnetic domains under stresses due to the reverse magnetostrictive effect (Villari effect). It is known, that the tensile and compressive stresses influence the magnetic domains alignment in a different way and the elliptical diagram for angular distribution of directional permeability for material under stress was assumed. Our investigations show the better sensitivity to stress induced MA, when new double differential type EC probe with 18 mm operational diameter were applied (Uchanin (2013)). These probes are composed of two excitation coils and two sensing coils situated in the tetragon corners. Our investigations were carried out with the application of the specially developed set-up for four-point loading by pure bending scheme. The dependences of EC probe signal amplitude U on the tensile and compressive mechanical stresses σ m on the operational frequency 5.0 kHz are presented in Fig. 6. The EC probe signal amplitudes were measured during loading trials up to 225 MPa and subsequent unloading. The existence of the magneto-mechanical hysteresis can be observed for tensile and compressive loading even in the elastic loading range (Fig. 6). This hysteresis can produce the relevant errors during the stress measurements. On the other hand, it is not essential for comparative inspection. The invariant property of MA EC probe signal under