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This issue of Frattura ed Integrità Strutturale contains ten research papers focused on Fracture Mechanics in Central and East Europe.
Four papers from Serbia deal with fatigue crack growth, presenting experimental and numerical results, obtained in the Military Institute, Institute for material testing and Faculty of Mechanical Engineering, all from Belgrade.
Paper Integrity and life estimation of turbine runner cover in a hydro power plant by A.Sedmak, M. Arsić, S. Bošnjak, S. Sedmak and Z. Savić, presents integrity and life estimation of turbine runner cover in a vertical pipe turbine. Fatigue and corrosion-fatigue interaction have been taken into account using experimentally obtained material properties, as well as analytical and numerical calculations of stress state, to estimate appropriate safety factors. Fatigue crack growth rate was also calculated, indicating that internal defects of circular or elliptical shape, detected by ultrasonic testing, do not affect integrity of runner cover.
Paper Experimental examination of fatigue life of welded joint with stress concentration by M. Arsic , A. Sedmak, S. Bosnjak, S. Sedmak and Z. Savic, presents results of experimental examinations of stress concentration influence on fatigue life of butt welded joints with K-groove, produced from the structural steel S355J2+N. Specimens with short cracks (with limited length of initial crack), defined on the basis of the experiences from fracture mechanics by the three points bending examinations, have been examined according to standard for the determination of S-N curve, and used to determine permanent fatigue strengths for different lengths of initial crack.
In the paper Fatigue life prediction of casing welded pipes by applying the extended finite element method, Lj. Lazić Vulićević, A. Grbović, A. Sedmak, Ž. Šarkočević and A. Rajić use the extended finite element (XFEM) method to simulate fatigue crack growth in casing pipe, made of API J55 steel by high-frequency welding, in order estimate its structural integrity and life. Based on the critical value of stress intensity factor KIc, measured in different regions of welded joint, the crack was located in the base metal as the region with the lowest resistance to crack initiation and propagation. The XFEM was first applied to the three point bending specimens to verify numerical results with the experimental ones, and afterwards to simulate fatigue crack growth and estimate its remaining life.
In the paper Influence of exploitation duration and temperature on the fatigue growth parameters in different regions of a welded joints by I. Camagic, Z. Burzic, A. Sedmak, N. Vasic, B. Cirkovic and A. Radovic, the influence of exploitation duration and temperature on the fatigue crack growth parameters in different regions of a welded joint is analysed for new and exploited low-alloyed Cr-Mo steel A-387 Gr. B. Fatigue crack growth parameters, threshold value Kth, coefficient C and exponent m, have been determined, both at room and exploitation temperature. Based on testing results, fatigue crack growth resistance in different regions of welded joint is compared.
The authors of the other six papers are from Germany, Hungary, Romania, Russia, Slovakia.
Paper Numerical Simulation of Dissimilar Metal Welding and its Verification for Determination of Residual Stresses with authors Sz. Szávai, Z. Bezi and C. Ohms presents the through-thickness residual stress distributions on dissimilar metal weld (DMW) mock-up. DMWs, were considered as joints between ferritic steels and either austenitic stainless steels or nickel-based alloys. The numerical simulations were performed using commercial finite element code MSC.Marc, and residual stress measurements were performed on welded joints to validate the simulation results. The validated residual stress distributions can be used for the life time assessment and failure mode predictions of the welded joints.
In the paper Scaling Of Compression Strength in Disordered Solids: Metallic Foams, authors J. Kováčik, J. Jerz, N. Mináriková, L. Marsavina, E. Linul, the scaling of compression strength with porosity for aluminium foams was investigated. Three different compositions Al 99.96, AlMg1Si0.6 and AlSi11Mg0.6 foams of various porosity, sample size with and without surface skin were tested in compression. It was observed that the compression strength of aluminium foams scales near the percolation threshold with Tf ≈ 1.9 - 2.0 almost independently on the matrix alloy, sample size and presence of surface skin.
V. Petrova, S. Schmauder, A. Shashkin in Modeling of edge cracks interaction investigated the effects of the interaction of edge cracks on further crack formation. The solution of singular integral equations is obtained by a numerical method which is based on Gauss-Chebyshev quadrature. The main fracture characteristics, such as, stress intensity factors, fracture angles and critical loads are provided in this study. A series of illustrative examples are presented for different geometries of arbitrarily inclined edge cracks.
Paper titled Failure analysis of dissimilar single-lap joints having authors F.A. Stuparu, D.A. Apostol. D.M. Constantinescu, M. Sandu, S. Sorohan investigates the single-lap joints made of aluminium and carbon fibre adherends of different thickness. The experimental tests and the use of 2D Digital Image Correlation were employed in order to understand better the behaviour of such dissimilar joints. The obtained results are suggesting that a complete monitoring of the failure processes in the overlap region can be fully understood only if local deformation measurements are possible.
The Special Issue is closed by two papers of T. Fekete Review of Pressurized Thermal Shock Studies of Large Scale Reactor Pressure Vessels in Hungary and Methodological Developments in the Field of Structural Integrity Analyses of Large Scale Reactor Pressure Vessels in Hungary. In the first one presents a comparative review of the methodologies used to investigate pressurized thermal shock which appear in the four nuclear power units from Hungary. The concept of structural integrity was the basis of research and development. The second paper presents in the first part of the paper, a short historic overview with the origins of the Structural Integrity concept are presented, and the beginnings of Structural Integrity in Hungary are summarized. In the second part, a new conceptual model of Structural Integrity is introduced. In the third part, a brief description of the VVER-440 V213 type RPV and its surrounding primary system is presented. In the fourth part, a conceptual model developed for PTS Structural Integrity Analyses is explained.
Aleksandar SEDMAK, University of Belgrade, Serbia
Liviu MARSAVINA, University Politehnica Timisoara, Roamnia
Modeling of edge cracks interaction
Failure analysis of dissimilar single-lap joints