1,721,000 research outputs found
The influence of thermal properties and preheating on residual stresses in welding
No full textA 2D finite element model has been carried out to analyse temperature distribution in butt weld joints. Temperature fields have been investigated by varying both thermal properties and an initial preheating treatment. Successive thermo-mechanical analyses were performed to evaluate resulting residual stresses. Temperature distribution and residual stresses were determined in a single-pass butt joint welded by Gas Metal Arc Welding (GMAW) process. A finite element parametric model was carried out and the technique of âelement birth and deathâ was adopted to simulate the process of filler metal addition. By means of finite element analysis high stresses were evaluated, with particular regard to Fusion Zone (FZ) and Heat-Affected Zone (HAZ). The influence of thermal properties and preheating on residual stresses in welding was also investigated. In the last few years, various experimental destructive and non-destructive methods were developed to evaluate residual stresses. However it is impossible to obtain a full residual stress distribution in welded structures by means of experimental methods. This disadvantage can be solved by means of computational analysis, which allows to determine the whole stress and strain fields in complex structures. This paper demonstrates that the technique of âelement birth and deathâ is suitable to simulate welding processes. Moreover, the study of welded joints should take into consideration the effect of material thermal properties and preheating treatment
The effect of thermal properties and weld efficiency on residual stresses in welding
Full text linkA parametric model is adopted and the technique of element “birth and death” is used to estimate the effect of thermal properties and weld efficiency on residual stresses in butt weld joints. Residual stresses and distortions on butt welded joints are numerically evaluated by means of finite element method. The FE analysis allows to highlight and evaluate the stress field
and its gradient around the fusion zone of welded joints, higher than any other located in the surrounding area.
The main conclusion is the significant effect of varying the value of the conductivity on residual stresses.
Several experimental destructive and non destructive techniques for directly measuring
residual stress have been developed. However, the application of these methods in practice is usually limited
by either cost or accuracy. Numerical simulation based on finite element techniques, therefore, offers a
comprehensive solution for the prediction of residual stress and strain as well as welding distortion in complex
welded structures. In this study it is shown that the technique of element “birth and death” can be usefully
applied to welding process in order to take in account the effect of the thermal properties of materials
Macchina per prove di fatica su elementi unificati da sottoporre a misure mediante tecnica di diffrazione neutronica
No full textDevelopment and stress behaviour of an innovative refrigerated container with PCM for fresh and frozen goods
No full textPurpose - The major objectives of this study are the engineering development and the structural analysis with finite element method (FEM) of a refrigerated container having a passive equipment and a remote control system to carry both fresh (+4°C÷±1°C) and frozen (-18°C ÷-20°C) goods. The purpose of this paper is to offer some solutions to the many disadvantages of using phase change material (PCM) to refrigerate the insulated container for transporting both fresh and frozen goods. Design/methodology/approach - In order to transport both fresh products (+4°C÷±1°C) and frozen products (-18°C ÷-20°C), the PCM elements are filled with one eutectic liquid only, so as to avoid problems related to filling and emptying the eutectic plates, and to plate corrosion. Moreover, specially shaped air ducts and a cool flow control system are designed to maintain a uniform circulation of cool air and constant humidity values. All the structures of the container are correctly designed by means of FEM calculations to assure that all the structural, safety standards parameters are satisfied. Findings - An innovative refrigerated container with PCM and a remote control system used to transport both fresh (+4°C÷±1°C) and frozen (-18°C ÷-20°C) products, in which it is possible to maintain the temperature values for almost seven days, has been considered here. Many disadvantages due to the use of PCM have been eliminated. It is possible to maintain a uniform circulation cool air and humidity values within the design parameters by means of fans; moreover, this container is light and environmentally friendly. All structures of the container are designed using FEM. Originality/value - This paper presents a refrigerated container with passive equipment and a remote control system to carry both fresh (+4°C÷±1°C) and frozen (-18°C ÷-20°C) goods in which it is possible to maintain the temperature values necessary for almost seven days. The container is equipped with a remote control system powered by photovoltaic panels which works in real time, is capable of giving information about the environmental parameters set in it and monitors the state of products by means of a network of sensors. Furthermore, the remote control system can send information about the position of the container to a remote control centre. The relevant structural conditions are numerically (FEM) evaluated and reported
Finite element analysis of residual stresses on butt welded joints
No full textLocalized heating during welding, followed by rapid cooling, usually generates residual stresses in the weld and in the base metal. Residual stresses in welding processes give significant problems in the accurate manufacture of structures because those stresses heavily induce the formation of cracks in the fusion zone in high strength steels. Therefore, estimating the magnitude and distribution of welding residual stresses and characterizing the effects of certain welding conditions on the residual stresses are deemed necessary. In this work, residual stresses and distortions on butt welded joints are numerically evaluated by means of finite element method. The FE analysis allows to highlight and evaluate the stress field and his gradient around the fusion zone of welded joints, higher than any other located in the surrounding area. Temperature-dependent material properties, welding velocity, external mechanism constraints, technique of 'element birth and death' and latent heat of fusion are also taken into account. Some numerical results are compared with experimental data showing a very good correlation
Static and modal numerical analyses for the roof structure of a railway freight refrigerated car
Full text linkNumerical 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. Fullwidth/
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
Hybrid technique to assess the fatigue performance of multiple cracked FSW joints
Full text linkIn this paper a numerical-experimental procedure useful to numerically assess the fatigue performance of friction stir welded aluminium joints is presented. The impact of manufacturing residual stresses on crack propagation in the joint driven by a remote fatigue load can be predicted. The proposed sequential procedure starts with the experimental residual stress assessment by the contour method and proceeds through the multiple crack growth simulation by the Dual Boundary Element Method. In the frame of Linear Elastic Fracture Mechanics, the superposition principle is invoked to provide the mathematical foundation supporting the proposed modelling strategy. In order to validate the proposed procedure, simple specimens are fatigue tested, obtaining multiple crack propagation scenarios that are monitored, in order to compare experimental and predicted crack growth rate
Multiaxial Fatigue Crack Propagation of an Edge Crack in a Cylindrical Specimen Undergoing Combined Tension-Torsion Loading
No full textA three-dimensional crack propagation simulation of a hollow cylinder undergoing coupled traction and torsion loading conditions is performed by the Dual Boundary Element Method (DBEM). The maximum tension load and torque are equal to 40 kN and 250 Nm respectively. Specimens, made of Al alloys B95AT and D16T, have been experimentally tested with in-phase constant amplitude loads. The Stress Intensity Factors (SIFs) along the front of an initial part through crack, initiated from the external surface of the hollow cylinder, are calculated by the J-integral approach. The crack path is evaluated by using the Minimum Strain Energy Density (MSED) criterion whereas the Paris’ law, calibrated for the material under analysis, is used to calculate crack growth rates. A cross comparison between DBEM and experimental results is presented, showing a good agreement in terms of crack growth rates and paths
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