14 research outputs found
Tensile and nanoindentation tests analysis of Ti6Al4V alloy manufactured by laser powder bed fusion
Additive manufacturing (AM) technologies are widely used in the fabrication of topologically complex components with thin-walled features, such as lattice structures. In this context, Laser Powder Bed Fusion (L-PBF) is one of the most commonly used AM technologies for producing such components. In order to further expand and justify the application of these components in operation and to model their mechanical behavior, it is necessary to know the mechanical properties of the matrix material from which they are formed. Therefore, there is currently a high interest in studying the behavior of these materials when subjected to monotonic or cyclic loading. However, determining the mechanical properties of the matrix material of thin-walled structures using tensile tests is challenging on the required subsize specimens. As a micro- or even nano-scale technology, nanoindentation can be used to probe a small volume of specimen, thus allowing the mechanical properties such as Young modulus, of thin-walled structures to be determined. In this work, Young's modulus of L-PBF Ti6Al4V alloy produced using different laser power and scanning speed combinations, has been determined on nano and macro scale. By comparing obtained results at both scales, it is evident that Young's modulus values determined at nano scale are higher and more scattered when compared to results determined at macro scale. Furthermore, this study implies that a wider range or a higher number of L-PBF process parameters should be considered to model it's influence on Young's modulus with higher accuracy
Advanced prevention against icing on high voltage power lines
Historical meteorological data indicates, that our weather is becoming more and more extreme. For the
electrical utility operators (Distribution System Operators - DSOs and Transmission System Operators -
TSOs), these changes arise in new operation challenges that need to be addressed. For example, frequent icing
phenomenon affects all the components of the power line by a significant mechanical overload: it endangers
the conductors, the insulators and the towers, as well. The result is often fatal and beside serious failures, it
effects on operators’ decisions. These not only endanger the reliability of electrical grids by the loss of a power
line for weeks or even months, but in general, the safety in the surroundings of the power line. As technology
advances, we will be able to collected, analyses and predict very large databases in the field of meteorology
and electrical engineering. The ability of processing mentioned data, combined with know-how results in the
capacity to operate power lines at their thermal limits during different ambient parameters. This technology
called Dynamic Line Rating (DLR) – is not only a great way to increase the transmission capacity of a given
line, but can also be effectively used to prevent, or even solve icing-related issues. Higher currents result in
higher Joule-heats, that consequently heat the conductors. If limits can be reached or approached, icing can be
prevented. If prevention is not possible, detection and removal of ice layer is necessary. The proper handling
of this icing issues, requires advanced algorithms (expert systems) and reliable measuring equipment. The
combination and synchronization between algorithms, weather service and measuring equipment is the key of
the successful operation. An EU H2020 financed project called FLEXITRANSTORE has just been launched
to develop a cross-country co-operation, with objective to improve anti-icing and de-icing solutions. To
establish and analyse different solutions, the project includes several universities, TSOs and DSOs. To solve
mentioned icing issues Budapest University of Technology and Economics’ (BME) developed an advanced
neural-network based algorithm which use OTLM system. It is planned to install and demonstrate the
capabilities of this new technology on the DSOs grid (Electro Ljubljana - ELJ). Besides the introduction of
DLR and icing, this paper also focuses on the preparation/organisation of co-operation between different
companies and universities
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Experimental Characterization and Phase-Field Damage Modeling of Ductile Fracture in AISI 316L
Data Availability Statement: The original contributions presented in the study are included in the article material, further inquiries can be directed to the corresponding author.(1) Modeling and characterization of ductile fracture in metals is still a challenging task in the field of computational mechanics. Experimental testing offers specific responses in the form of crack-mouth (CMOD) and crack-tip (CTOD) opening displacement related to applied force or crack growth. The main aim of this paper is to develop a phase-field-based Finite Element Method (FEM) implementation for modeling of ductile fracture in stainless steel. (2) A Phase-Field Damage Model (PFDM) was coupled with von Mises plasticity and a work-densities-based criterion was employed, with a threshold to propose a new relationship between critical fracture energy and critical total strain value. In addition, the threshold value of potential internal energy—which controls damage evolution—is defined from the critical fracture energy. (3) The material properties of AISI 316L steel are determined by a uniaxial tensile test and the Compact Tension (CT) specimen crack growth test. The PFDM model is validated against the experimental results obtained in the fracture toughness characterization test, with the simulation results being within 8% of the experimental measurements. (4) The novel implementation offers the possibility for better control of the ductile behavior of metallic materials and damage initiation, evolution, and propagation.This research was supported by the Science Fund of the Republic of Serbia, #GRANT No 7475, Prediction of damage evolution in engineering structures—PROMINENT and the Slovenian Research Agency ARIS for the research program P2-0137 Numerical and Experimental analysis of Nonlinear Mechanical Systems
The use of cyclic DJ q as a parameter for fatigue initiation of X52 steel
International audienceThe concept of DJ cyclic has been extended to fatigue initiation emanating from notch. The parameter is then named DJ q. Validation of this parameter is made by fatigue tests made on Roman tile specimens made in X52 pipe steel. Here, fatigue initiation is detected by acoustic emission. It has been found that the fatigue initiation decreases after hydrogen absorption. This can be explained by interaction of hydrogen and plasticity as can be seen for tensile and fracture behaviour of X52 steel after introduction of hydrogen
Fracture toughness analysis of a ductile steel by means of 3D surface displacements
The standards for characterization of fracture toughness of metals are focused on the calculation of fracture parameters based only on in-plane displacements of the specimen tested. Although fracture is a three-dimensional problem, out-of-plane displacements of the specimen tested are not mentioned in those documents. Since three-dimensional displacement measurement is available, it is worth investigating its potential uses in fracture tests. In this work, the fracture toughness of a structural steel was assessed through standard tests, measuring three-dimensional surface displacements. An alternative Crack Tip Opening Displacement calculation was introduced. The fracture initiation was inferred from the out-of-plane displacements, finding good agreement with results from R-curves.Fil: Paolinelli, Luciano Daniel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y TecnologĂa de Materiales. Universidad Nacional de Mar del Plata. Facultad de IngenierĂa. Instituto de Investigaciones en Ciencia y TecnologĂa de Materiales; ArgentinaFil: Carr, Gustavo Eduardo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y TecnologĂa de Materiales. Universidad Nacional de Mar del Plata. Facultad de IngenierĂa. Instituto de Investigaciones en Ciencia y TecnologĂa de Materiales; ArgentinaFil: Gubeljak, N.. University of Maribor; EsloveniaFil: Predan, J.. University of Maribor; EsloveniaFil: Chapetti, Mirco Daniel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y TecnologĂa de Materiales. Universidad Nacional de Mar del Plata. Facultad de IngenierĂa. Instituto de Investigaciones en Ciencia y TecnologĂa de Materiales; Argentin
Micromechanical analysis of constraint effect on fracture initiation in strength mis-matched welded joints
In this paper the micromechanical approach to ductile fracture was applied in a study of constraint effect crack growth initiation in mismatched welded joints. The single edged- notched bend specimens (precrack length â–«â–«) were experimentally and numerically analysed. The coupled micromechanical model prposed by Gurson, Tvergaard and Needleman was used. Constraint effect was tested by varying widths of the welded joints (6, 12 and 18 mm). HSLA steel was used as the base metal in a quenched and tempered condition. The flux-cored arx-welding process in shielding gas was used. Two different fillers were selected to obtain over- and undermatched weld metal. The micromechanical parameters used in prediction of the crack growth initiation on precracked specimen were calibrated on a round smmoth specimen. The difference in fracture behaviour between over- and undermatched welded joints obtained in experimental results was followed by numerical computationsof void volume fraction in front of the crack tip
Micromechanical analysis of constraint effect on fracture initiation in strength mismatched welded joints
In this paper the micromechanical approach to ductile fracture was applied in a study of constraint effect on crack growth initiation in mismatched welded joints. The single-edged notched bend specimens (precrack length a 0/W=0.32) were experimentally and numerically analyzed. The coupled micromechanical model proposed by Gurson, Tvergaard and Needleman was used. Constraint effect was tested by varying widths of the welded joints (6, 12 and 18mm). High-strength low-alloyed (HSLA) steel was used as the base metal in a quenched and tempered condition. The flux-cored arc-welding process in shielding gas was used. Two different fillers were selected to obtain over- and undermatched weld metal. The micromechanical parameters used in prediction of the crack growth initiation on precracked specimen were calibrated on a round smooth specimen. The difference in fracture behavior between over- and undermatched welded joints obtained in experimental results was followed by numerical computations of void volume fraction in front of the crack tip
Micromechanical analysis of constraint effect on fracture initiation in strength mismatched welded
In this paper the micromechanical approach to ductile fracture was applied in a study of constraint effect on crack growth initiation in mismatched welded joints. The single-edged notched bend specimens (precrack length a(0)/W=0.32) were experimentally and numerically analyzed. The coupled micromechanical model proposed by Gurson, Tvergaard and Needleman was used. Constraint effect was tested by varying widths of the welded joints (6, 12 and 18mm). High-strength low-alloyed (HSLA) steel was used as the base metal in a quenched and tempered condition. The flux-cored are-welding process in shielding gas was used. Two different fillers were selected to obtain over- and undermatched weld metal. The micromechanical parameters used in prediction of the crack growth initiation on precracked specimen were calibrated on a round smooth specimen. The difference in fracture behavior between over- and undermatched welded joints obtained in experimental results was followed by numerical computations of void volume fraction in front of the crack tip
Welded Joints Behaviour in Service with Special Reference to Pressure Equipment
Quality and structural integrity of welded pressure equipment are defined by The Pressure Equipment Directive (97/23/EC). The problem is complex, due to welded joint imperfections, matching effect, heterogeneity of microstructure and material properties. Equipment can be fit for service with defects unacceptable by codes, what should be proved by fracture mechanics approach, especially for cracks in the heat-affected-zone