Raffaele Sepe

DBEM crack propagation in friction stir welded aluminum joints

This paper deals with the simulation of multiple crack propagation in friction stir welded butt joints and the aim is to assess the influence of process induced residual stresses on the fatigue behavior of the assembly. The distribution of the process induced residual stresses is mapped by means of the contour method; then, the computed residual stress field is superimposed, in the DBEM environment, to the stress field due to a remote fatigue traction load and the crack growth is simulated.A two-parameters crack growth law is used for the crack propagation rate assessment. The Stress Intensity Factors are evaluated by the J-integral technique. Computational results have been compared with experimental data, provided by constant amplitude crack propagation tests on welded samples, showing the subdivision of the overall fatigue life in the two periods of crack initiation and crack propagation.

Tensile Testing of Hybrid Composite Joints

In the present paper, results of experimental tests carried out on hybrid (bonded/bolted) and adhesive composite single-lap joints are showed. The laminate adherends were made by unidirectional carbon fiber/epoxy with symmetric stacking sequence. In particular, the tests were carried out to evaluate strength and failure mode of the different joints. These joints were subjected to quasi-static tensile displacement and tests were conducted using a universal testing machine. The maximum tension load that the specimen can bear is determined and the failure process is correlated to the lay-up of the composite and joint type.

Evaluation by FEM of the Influence of the Preheating and Post-Heating Treatments on Residual Stresses in Welding

During 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. In this paper the temperature distribution and residual stresses were determined in a single-pass butt joint welded by GMAW (Gas Metal Arc Welding) process by finite element model (FEM). A 3D finite parametric element model has been carried out to analyze temperature distribution in butt weld joints and thermo-mechanical analyses were performed to evaluate resulting residual stresses. Temperature fields have been investigated by varying an initial preheating treatment. Moreover the technique of “element birth and death” was adopted to simulate the process of filler metal addition The high stresses were evaluated, with particular regard to fusion zone and heat affected zone. The influence of preheating and post-heating treatment on residual stresses was investigated. The residual stresses decrease when preheating temperature increases. The maximum value of longitudinal residual stresses without pre-heating can be reduced about 12% and 38% by using the preheating and post-heating process respectively.

Finite-Element Simulation of Temperature Fields and Residual Stresses in Butt Welded Joints and Comparison With Experimental Measurements

Welding is used in fabrication of structures ranging from small components to large and important structures. One of the important problems associated with welded structures is development of residual stresses and deformations due to welding temperature. In fact when structures are manufactured by welding, a non-uniform temperature distribution is produced. This distribution initially causes a rapid thermal expansion followed by a thermal contraction in the weld and surrounding areas, thus generating inhomogeneous plastic deformation and residual stresses in the weldment when it is cooled. High residual stresses in regions close to the weld may promote brittle fracture, fatigue, or stress corrosion cracking. Meanwhile, distortion in base plate may reduce the buckling strength of structural members. Therefore estimating the magnitude and distribution of welding residual stresses and distortion are necessary for achieving the safest design.In the present work an elastic-plastic finite element model considering temperature dependent mechanical properties is used to evaluate residual stresses. In this study a parametric model is adopted and the elements birth and death are used in single-pass butt welded joint to simulate the weld filler variation with time. Then numerical results are compared with experimental data.© 2014 ASME

Fatigue Behaviour of Full Scale Flat Stiffened Aeronautic Panels

This paper concerns the experimental characterization of static and fatigue strength of a flat panel stiffened by bonded pad made of aluminum alloy. The panels were full scale and tested under both static and fatigue loads, applied by means of an in house designed and built multi-axial static and fatigue machine. The fatigue crack propagation life of the stiffened panel has been compared to that of a simple flat panel and to that of a flat panel with chemical milling pad-up, getting that the fatigue crack growth life can be significantly improved.

Finite Element Analysis of Residual Stresses on Butt Welded Joints

Localized 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.© 2006 ASME

Evaluation of Residual Stresses in Butt Welded Joint of Dissimilar Material by FEM

The study proposed within this paper deals with an application of finite element techniques to the thermo-structural analysis of a dissimilar butt-welded joint. Residual stresses induced by the fusion arc-welding of steel joints in power generation plants are a concern to the industry. Nowadays, the application of finite element method appears to be a very efficient method for the prediction and the investigation of the weld-induced residual stresses, nevertheless the detailed modelling of all phenomena involved in such process is still challenging. The structural integrity assessment of welded structures strongly requires a deep investigation of weld-induced residual stresses in order to be compliant with safety requirement of power plant. The longitudinal and transversal residual stresses in dissimilar material butt joints of 8 mm thick for V-groove shape were studied. The developed thermo-mechanical FE model as well as the simulation procedures are detailed and results are discussed. As a result of such work, it has been found out that residual stresses in the two dissimilar plates are characterized by very different magnitudes and distribution.

Performance evaluation of CFRP-rubber shock absorbers

In the present work a numerical investigation on the energy absorbing capability of dedicated structural components made of a carbon fiber reinforced polymer and an emulsion polymerised styrene butadiene rubber is reported. The shock absorbers are devices designed to absorb large amounts of energy by sacrificing their own structural integrity. Their aim is to cushion the effects of an impact phenomenon with the intent to preserve other structures from global failure or local damaging. Another important role of shock absorbers is reducing the peak of the acceleration showed during an impact phenomenon. This effect is of considerable interest in the case of vehicles to preserve passengers’ safety. Static and dynamic numerical results are compared with experimental ones in terms of mean crushing forces, energy and peak crushing. The global performance of the absorbers has been evaluated by referencing to a proposed quality index.

FEM Simulation of a FML Full Scale Aeronautic Panel Undergoing Static Load

This paper concerns the numerical characterization of the static strength of a flat stiffened panel, designed as a fiber metal laminates (FML) and made of Aluminium alloy and Fiber Glass FRP. The panel is full scale and was tested under static loads, applied by means of an in house designed and built multi-axial fatigue machine. The static test is simulated by the Finite Element Method (FEM) in a three-dimensional approach. The strain gauge outcomes are compared with corresponding numerical results, getting a satisfactory correlation.

Development and stress behaviour of an innovative refrigerated container with PCM for fresh and frozen goods

Purpose – 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 ...