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The advent of additive manufacturing technologies significantly encouraged the development and usage of lattice structures. This paper aims to experimentally investigate the influence of dimension, building position, and orientation on the mechanical properties of Ti6Al4V trusses, manufactured by electron beam melting process, to be used in lattice cells. Specimens were manufactured considering the following parameters: truss diameter (1, 1.5, 2 mm), growth orientation (0°, 45°, 90°), and specimen position inside the building chamber. Trusses with diameter of 1 mm showed inconsistent mechanical properties caused by the poor manufacturing quality. Specimen position was found to influence the analyzed mechanical properties. Unmelted powders were observed to affect the outer surfaces of all specimens and the whole cross-sections of specimens manufactured at 0°. Specimens manufactured at 45° with diameter of 2 mm demonstrated the best performances, whereas specimens manufactured at 90° with diameter of 2 mm displayed the highest elongation at fracture. [ABSTRACT FROM AUTHOR]

This paper presents a novel numerical model, based on the finite element (FE) method, for the simulation of a welding process aimed to make a two‐pass V‐groove butt joint, paying attention on the prediction of residual stresses and distortions. The 'element birth and death' technique for the simulation of the weld filler supply has been considered within this paper. The main advancements with respect to the state of the art herein proposed concern: (i) the development of a modelling technique able to simulate the plates interaction during the welding operation when an only plate is modelled. This phenomenon is usually neglected in literature; (ii) the heat amount is supplied to the FEs as volumetric generation of the internal energy, allowing overcoming the time‐consuming calibration phase needed to use the Goldak's model, commonly adopted in literature. Predicted results showed a good agreement with experimental ones. [ABSTRACT FROM AUTHOR]

In this work laser‐welded tube‐tube specimens made of aluminium alloys AlMg3.5Mn and AlSi1MgMn T6 were experimentally tested under constant and variable amplitude loading, under pure axial and pure torsion loading. In order to evaluate the influence on fatigue behaviour of the residual stresses, because of the welding process, some specimens were subjected to postweld heat treatment and then were tested. The numerical analyses, using finite element (FE), were carried out to obtain a reliable estimation of the residual stress in the specimen. The numerical results were in a good agreement with experimental ones obtained by means of hole‐drilling method. Finally, the residual stress distribution was superimposed to stress distribution because of fatigue loads obtained by FE analyses applying local concept, to calculate the stresses in the crack initiation zone and to understand the different types of failure that occurred in as‐welded and relieved specimens. [ABSTRACT FROM AUTHOR]

This work deals with the investigation and characterization of Ti6Al4V parts produced with an intriguing manufacturing process belonging to the Wire Arc Additive Manufacturing (WAAM) family: the Cold Metal Transfer technology (CMT). Wall‐shaped parts were produced according to different process parameters, namely the wire feed speed and voltage–current combinations, leading to different energy inputs. The parts were characterized in terms of surface morphology, microhardness, microstructure, tensile properties, and fatigue crack growth. The results suggested that the investigated deposition parameters led to similar results. Moreover, the mechanical and fatigue crack growth behavior was in line with parts of the same alloy produced through other manufacturing routes, whereas the microstructure type was the result of the fast cooling of the molten material. Finally, considering the simple system adopted to avoid oxidation during the deposition stage, the results suggested that CMT is a promising manufacturing technique for titanium alloy semifinished parts. Highlights: Wall‐like parts made of Ti6Al4V alloy were produced through WAAM‐CMT technologySound parts with minimum oxidation were produced through a simple enveloping systemThe parts had properties similar to those of more traditional manufacturing routesThe microstructure, tensile, and fatigue crack growth behavior were quite isotropic [ABSTRACT FROM AUTHOR]

A fatigue test on a full scale panel with complex loading condition and geometry configuration has been carried out using a triaxial test machine. The demonstrator is made up of two skins which are linked by a transversal butt-joint, parallel to the stringer direction. A fatigue load was applied in the direction normal to the longitudinal joint, while a constant load was applied in the longitudinal joint direction. The test panel was instrumented with strain gages and previously quasi-static tests were conducted to ensure a proper load transferring to the panel. In order to support the tests, geometric nonlinear shell finite element analyses were conducted to predict strain and stress distributions. The demonstrator broke up after about 177000 cycles. Subsequently, a finite element analysis (FEA) was carried out in order to correlate failure events; due to the biaxial nature of the fatigue loads, Sines criterion was used. The analysis was performed taking into account the different materials by which the panel is composed. The numerical results show a good correlation with experimental data, successfully predicting failure locations on the panel. [ABSTRACT FROM AUTHOR]

Numerical analyses by finite element method and experimental tests are used to determine static and dynamic behaviour of railway vehicles. Experimental measurements are very time consuming and expensive, so they cannot be used at all stages of design. Numerical simulations do not have the disadvantages of experimental methods, but it is necessary to verify them by experiments to obtain realistic results. Full-width/full-length, half-width/full-length and half-width/half-length modeling approaches can be used to determine static and vibrational behaviours of railway vehicles depending or not on the symmetry of roof structure and applied load. Different static loading cases defined in standards such as EN 12663, UIC CODE OR 577 and ERRI B12/RP17 have to be considered in FE analyses. Evaluation of stress states, buckling and vibrational behaviours for a roof structure of a railway freight refrigerated car are presented. To highlight the vibrational behaviour of the structure normal mode (free vibration) analyses are performed. As a result of the relevant simulations, structural characteristics and structural weaknesses of the design are determined. [ABSTRACT FROM AUTHOR]

Sintered gears manufactured through powder metallurgy technology contain residual porosity that can make them inadequate for high power supply. Crack propagation is significantly enhanced by both residual porosity and cyclical stresses involving the teeth. The use of densification processes can highly improve their performances, permitting the reduction of the residual porosity. Among the densification processes, the rolling assumes a key-role. The process permits the densification of the tooth flanks, the most stressed parts of the wheel. However, the performances of the rolled wheel depend on several process parameters, whose setup phase requires several efforts and many experiments. Finite element (FE) model can be a helpful tool, allowing a faster estimation of the process parameters, reducing waste and costs linked to the experimental tests. In this sense, FE modelling techniques discussed in literature only cover the simulation of spur gears densification process, since they consist of in-plane 2D finite elements. In this paper, different numerical modelling techniques, based on 2D finite elements, are proposed to simulate the densification process of spur gears and used to perform a tendency analysis to explore the effects of wheelbase reduction between the forming rollers on the material densification. Material densification appeared higher for reduced wheelbases, but an increasing cavity was observed at the tooth root as the wheelbases decreases. Moreover, a FE model based on 3D finite elements is proposed to reproduce numerically the rolling process of a helical gear. The accuracy of the 3D FE model was measured against the results provided by some experimental tests, herein discussed too. A good agreement between numerical and experimental results was observed. [ABSTRACT FROM AUTHOR]

Three‐dimensional numerical analyses, using the finite element method (FEM), have been adopted to simulate fatigue crack propagation in a hollow cylindrical specimen, under pure axial or combined axial‐torsion loading conditions. Specimens, made of Al alloys B95AT and D16T, have been experimentally tested under pure axial load and combined in‐phase constant amplitude axial and torsional loadings. The stress intensity factors (SIFs) have been calculated, according to the J‐integral approach, along the front of a part through crack, initiated in correspondence of the outer surface of a hollow cylindrical specimen. The crack path is evaluated by using the maximum energy release rate (MERR) criterion, whereas the Paris law is used to calculate crack growth rates. A numerical and experimental comparison of the results is presented, showing a good agreement in terms of crack growth rates and paths. [ABSTRACT FROM AUTHOR]

Abstract Wendelstein 7-X (W7-X), the world's largest nuclear fusion experiment of modular stellarator type, started operation in 2015 and will be upgraded with a water cooled first wall for steady state operation in 2020. The first wall consists of a CFC armored island divertors, adjacent baffles, heat shields, and stainless steel wall panels. Baffle and heat shield segments consist of graphite tiles, bolted with low pre-stress onto heat sinks of CuCrZr that are in turn brazed onto water cooled steel pipes. Cracks were detected before installation in the baffles in the root of the brazed seam in over 100 locations. Such cracks are attributed to the imposed plastic deformation of the pipes to bring them into the final shape following the complex 3D geometry of the plasma vessel. This paper gives an overview of the experimental and numerical work using finite element method (FEM) and dual boundary element method (DBEM), including sub-modeling to assess the risk of a water leak during operation. Details of the numerical work is published in Giannella et al. (2017), Lepore et al. (2017) and Citarella et al. (2018). First fatigue crack growth experiments were carried out on pipe material and thermal-mechanical crack growth predictions were made with FEM and DBEM. It appeared that the Stress Intensity Factor (SIF) threshold of the ductile steel is only reached when large plastic strains occur, thus violating the field of application of linear elastic fracture mechanics to forecast crack growth. Afterwards, representative brazed pipe samples were manufactured and subjected to initial plastic deformation causing cracks in 11 out of 12 samples. Some samples were tested up to 60,000 bending load cycles. Two out of four samples failed after ∼35,000 cycles. Before and after the test, the shape of the cracks was measured using 3D computer tomography scans. Equivalence between thermal load in W7-X and the mechanical load in the cyclic test was determined with the numerical models to allow for a prediction of the fatigue life in W7X. Additional modeling showed that also plastic zones away from the cracks can limit the fatigue life. [ABSTRACT FROM AUTHOR]

Ti-6Al-4V is an alloy increasingly used in aeronautics due to its high mechanical properties coupled with lightness. An effective technology used to manufacture titanium components with a reduced buy-to-fly ratio is laser beam welding. Previous studies showed that the key factor that rules the mechanical properties and the fatigue life of the joint is its morphology. The aims of this paper were to investigate the influence of the geometrical features of the joints (height of the top and root reinforcement, depth and radius of the underfill, and the valley-valley underfill distance) on their mechanical properties and also to conduct a finite element (FE) analysis on the real geometry of the welded joints. Ti-6Al-4V rolled sheets 3.2 mm thick were welded in butt joint configuration using a laser source and their performance was studied in terms of weld morphology, microstructure, Vickers microhardness and fatigue life. A full factorial plan, designed varying the welding speed and laser power, was carried out. The real geometry and then the joint morphology were studied through an innovative approach: for each specimen, both the total weld face and the total root surface were acquired using a confocal microscope. Finally, through these acquisitions, the clouds of points of the scanned surfaces were used in order to carry out a FE analysis capable of providing a stress concentration factor, K , value for each detected joint. The main results are the realization of a reliable FE model by an experimental agreement and the relationship found amongst the fatigue performances and some noticeable metallurgical and geometrical features, such as the underfill depth and the aspect ratio defined as the ratio between the maximum height of the joint and the valley-valley underfill distance. [ABSTRACT FROM AUTHOR]