Influence of the distance between rivets in self-piercing riveting bonded joints made of carbon fiber panels and AA2024 blanks

Abstract The increasing use of new materials alternative to steel in manufacturing industry has led to a greater emphasis on the improvement and the development of specific joining approaches allowing to get effective mechanical properties even when different materials are joined together. It should be observed that often the traditional welding techniques show several limitations as aluminum or magnesium alloys are used, and, what is more, they are not compatible with composite materials. The development of structures made of these materials has renewed the use of mechanical fastening operations. The present paper investigates the influence of the distance between rivets in self-piercing r…

Damage and fracture study of cold extrusion dies

Abstract In the present paper die fracture in cold extrusion was investigated considering a few different die reduction zone geometries. A former finite element method (FEM) analysis of the process was developed to obtain the contact pressure distribution at the workpiece–die interface for each of the investigated geometries; subsequently a stress and strain analysis utilizing the BEM code Franc3D was carried out, with the aim to evaluate the crack propagation at each loading cycle, i.e. at each extrusion process. In this way the die life for each of the investigated extrusion die geometries was compared utilizing the Paris law and the values assumed by the stress concentration coefficient …

Modello di previsione della crescita di una cricca in un giunto incollato

IMPIANTO DI STABILIZZAZIONE DI UNA IMBARCAZIONE A SOSTENTAMENTO ALARE

Lo studio, frutto dell’attività di ricerca svolta dal DICGIM dell’Università degli Studi di Palermo in partnership con l’Engineering Department della Ustica Lines S.p.A. nell’ambito di un progetto finanziato con fondi PON Ricerca e Competitività 2007-2013, analizza preliminarmente le cause di guasto comportanti la fermata di un battello a sostentamento alare HSC per trasporto passeggeri al fine di individuare i componenti critici del mezzo. Individuato tale componente nel sistema di stabilizzazione, viene valutato l’impatto economico che il fermo del battello comporta sui costi operativi della Compagnia di navigazione. L’entità di tali costi, anche in termini di mancata utilizzazione del me…

Finite Element Method Analysis of a Spur Gear with a Corrected Profile

The difference between the stress value calculated by a two-dimensional finite element model of spur gears and those obtained by the rules in ISO 6336 was evaluated. Hertz theory, which provides information on the extension of the contact area and the maximum value of the contact pressure, was used to choose the dimensions of the elements. The mesh was created using the stress analytical solution relative to a model consisting of two cylinders in contact. Analogous optimization was executed for the mesh of the teeth feet; a mesh of 15 elements was considered optimum, because it minimized the difference to 0.5 per cent in the bending stress calculation. Stress values, obtained using the fin…

Analysis of the mechanical performance of hybrid (SPR/bonded) single-lap joints between CFRP panels and aluminum blanks

Abstract The increasing use of innovative materials in manufacturing of modern mechanical components has led to the development of reliable joints between innovative (composite materials etc.) and traditional materials (steel, aluminum etc.). In the last few years, hybrid joints, combining the advantages of the adhesive joints and traditional mechanical joints as bolted or riveted joints, have been shown an increasing industrial interest especially in automotive and aerospace sectors. In the present paper a systematic experimental study of hybrid lap joints was carried out with the aim to detect the optimal joint configuration. Tensile tests on hybrid joints made by combining adhesive bondi…

Studio sperimentale di giunti ibridi CFRP-alluminio

Experimental and numerical analysis of aluminum-aluminum bolted joints subject to an indentation process

Abstract The increasing interest of the industry (especially automotive, aviation and marine) in the fastener joints (riveted, bolted, etc.) between metallic materials, has re-opened the study on the possibility to improve the performance of the drilled structure using plastic deformation processes. Indentation process, performed before the drilling operation, creates circumferential compression stresses around the hole which increase significantly the mechanical performance of the drilled structures. In this paper, static and the fatigue performances of aluminum–aluminum (AW 6082-T6) single-lap bolted joints are studied. In particular, the study compares the mechanical strength of only dri…

Ottimizzazione di Giunti Ibridi(Spr/Incollati) Gfrp-Al

Fatigue strength of a single lap joint SPR-bonded

In the last years, hybrid joints, meaning with this the joints which consist in combining a traditional mechanical joint to a layer of adhesive, are gradually attracting the attention of various sectors of the construction of vehicles and transportation industries, for their better performance compared to just mechanical joints (self-piercing riveting SPR, riveting, and so on) or just to bonded joints. The paper investigates the fatigue behavior of a single lap joint self-piercing riveted (SPR) and bonded throughout fatigue tests. The considered geometric configuration allowed the use of two rivets placed longitudinally; an epoxy resin was used as adhesive. In the first part of the work sta…

Fatigue behaviour of self-piercing riveting of aluminium blanks and carbon fibre composite panels

In this article, the fatigue behaviour of self-piercing riveted joints in 2024-T6 aluminium sheets and carbon fibre composite panels is studied through experimental tests and numerical simulations. This study, aimed to evaluate the best process conditions and the mechanical behaviour of the joint itself, can be divided into few phases: the first one in which the static mechanical behaviour was investigated in order to evaluate the best process conditions (such as the best value of oil pressure of the riveting system) and the second one which had the purpose to determine the fatigue behaviour of the joint. Finally, a finite element method analysis of the riveting process was developed in or…

Influence of parameters in a hybrid joint (SPR/bonded) GFRP-aluminum

Cyclic Delamination Analysis: Experimental and Cohesive-Frictional interface Finite Element Modelling

EFFETTO DELL’ATTRITO NELL’AVANZAMENTO DELLA DELAMINAZIONE PER MODO II DI CARICO

Il lavoro valuta l’influenza della dissipazione energetica dovuta agli effetti attritivi che si sviluppano all’interfaccia tra le lamine di provini sollecitati a Modo II di carico. Sono state effettuate diverse prove sperimentali su compositi in fibra di vetro e resina epossidica soggetti a condizioni di carico cicliche e valore medio crescente, tali da mantenere le lamine del composito in continua aderenza. Al fine di valutare l’incidenza dell’attrito interlaminare nella delaminazione per Modo II, i risultati delle prove sperimentali sono stati riprodotti per mezzo di analisi agli elementi finiti utilizzando il programma di calcolo FEAP (con codice sorgente aperto), nel quale è stato imple…

ANALISI NUMERICO-SPERIMENTALE SUL COMPORTAMENTO A FATICA DI COMPOSITI CARALL RIVETTATI

Nel lavoro è descritto un modello di danneggiamento per provini CARALL (CArbon Reinforced ALLuminium), rivettati e non rivettati, sottoposti a prove di fatica mediante flessione pulsatoria a tre punti in controllo di spostamento. I provini sono realizzati sovrapponendo 8 lamine di tessuto intrecciato di carbonio [0°/90°] e resina epossidica con interposta una lamina in lega di alluminio 6061-T6 dello spessore di 0.8mm. Le prove sono state condotte su provini non rivettati (Tipo 1), su provini con due rivetti disposti simmetricamente ad una distanza d=22 mm dalla mezzeria (Tipo 2) e su provini con 2 rivetti disposti ad una distanza d=44 mm dalla mezzeria (Tipo3). L’analisi dei risultati sper…

Thermal NDT of glass reinforced composite panels for naval applications by means of a linear infrared scanner

The work describes the development and application of a low cost Thermal NDT set-up to investigate the influence of delamination defects on thick glass fibre reinforced composite laminates simulating typical hull monolithic GRP panels. Two active thermographic techniques have been implemented in particular: a pulsed thermography and a step heating scheme. A 12 mm thick cross-ply panel has been manufactured and delamination defects simulated in two different ways: by embedding patches of folded Teflon sheets, and by drilling flat bottomed back holes. A number of defects was then positioned at three different depths form the scanned surfaces, measuring ¼, ½ and ¾ of the laminate thickness. A …

Progetto e messa a punto di una macchina prova materiali a fatica a flessione piana per provini in composito

Determination of the Stress Intensity Factor by Means of the Espi Technique

The experimental determination of stress intensity factors by means of non-destructive techniques is a research topic of actual interest, In fact there are many applications, where a reliable and accurate experimental procedure is needed to evaluate numerical or theoretical models about the behaviour of cracked or notched structures.

Numerical and Experimental Analysis of the Frictional Effects on 4ENF Delamination Tests Performed on Unidirectional CFRP

Abstract Progressive delamination in composite materials under static or fatigue loading condition are, in many structures, one of the predominant cause of failure. In the paper, an accurate study of quasi-static delamination growth under mode II loading condition is conducted. Several experimental tests are performed on composite laminates consisting of unidirectional carbon/epoxy layers. Four-point end-notched flexure (4ENF) test is employed in order to characterize the mode II interlaminar fracture toughness. The R-curve is obtained by means of optical and numerical determination of crack tip position. The energy release rate and the crack length are calculated through experimental deter…

Effect of the indentation process on fatigue life of drilled specimens

Design and manufacture of mechanical elements are strongly influenced by the evaluation of the residual stresses due to their effects on the material strength. This paper presents numerical and experimental results performed on AW 6082-T6 aluminum alloy drilled specimens when the hole is created after a bilateral indentation process. The plastic deformation induced by the indenters creates a compressive residual stress field around the hole, which persists after the drilling operation. Several numerical analysis have been carried out in ANSYS APDL explicit solver for different indentation depths and hole diameters in order to evaluate the compressive circumferential stresses, optimal proces…

ANALISI DI GIUNTI A DOPPIA SOVRAPPOSIZIONE GFRP-ALLUMINIO INCOLLATI E BULLONATI

Valutazione della vita a fatica di giunti complessi saldati tramite Friction Stir Welding

Comportamento a Fatica di Giunti Ibridi (Spr/Incollati) Cfrp-Alluminio

EFFETTI DEL PROCESSO STRESSWAVE SULLA VITA A FATICA DI PROVINI FORATI IN LEGA DI ALLUMINIO: OTTIMIZZAZIONE DELLA DISTANZA TRA FORI ADIACENTI

Determination of the Stress Intensity factor by means of the Electronic Speckle Pattern Interferometry technique

FEM model achievement for dental implant characterization

Frictional effect in mode II delamination: Experimental test and numerical simulation

Abstract The present paper proposes an experimental and a numerical analysis of the frictional effect on the mode II delamination. Frictional stresses between the crack edges can absorb and dissipate significant energy contributions in the delamination zones, especially under cyclic loading conditions. The experimental tests are performed for a set of unidirectional End-Notched Flexure (ENF) composite specimens, which are subjected to fatigue loading law with increasing mean value. The numerical analyses are performed considering a cohesive–frictional constitutive model, which is able to reproduce the transition of the interface behavior from the sound elastic condition to the fully cracked…

Valutazione dell'usura nei carrelli per serramenti

Nel lavoro è valutato il comportamento di carrelli per serramenti in condizioni di carico variabile al fine di valutarne l’usura. Le prove dinamiche sono state condotte su una macchina di semplice concezione appositamente realizzata e adatta a garantire un moto alterno sotto carico. Per la valutazione dell’usura è stata eseguita una scansione molto accurata della geometria delle rotelle (prima e dopo aver effettuato le prove dinamiche) attraverso un sistema di rilevazione a luce strutturata COMET V STEINBICHLER. Il processo di scansione ha permesso di digitalizzare le rotelle con un’accuratezza dell’ordine di 5µm. I dati della scansione hanno evidenziato un aumento pressoché uniforme del di…

Analisi dei meccanismi di delaminazione in un materiale ortotropo ed all'interfaccia di un composito ibrido

STUDIO NUMERICO-SPERIMENTALE SUGLI EFFETTI DEL PROCESSO STRESSWAVE IN PIASTRE FORATE IN LEGA DI ALLUMINIO

On the self-piercing riveting of aluminium blanks and carbon fibre composite panels

In the present paper the possibility to join aluminium alloys blanks and carbon fibre composites panels by self-piercing riveting operation is considered. In particular a few case studies were carried out at the varying of the process parameters. The effectiveness of the obtained joints was tested through tensile tests and through fatigue ones; what is more the process mechanics was highlighted through proper macro and micro observations of the transverse sections of the joints. The failure mechanics of the obtained joints were also considered in order to highlight the mechanisms which occur and determine the lost of the load carrying capability of the joints. Finally a numerical model of t…

STUDIO NUMERICO E SPERIMENTALE SU GIUNZIONI DI ELEMENTI IN POLIETILENE SALDATI DI TESTA ED ELETTROFUSI

Fatigue behavior of self-piercing riveting of aluminium blanks and carbon fiber composite panels

Analisi numerico-sperimentale per la determinazione delle tensioni residue in un giunto saldato

La durata di un componente dipende dall’interazione tra le caratteristiche meccaniche del materiale con cui è costruito e gli sforzi a cui esso è sottoposto. Per la determinazione dello stato tensionale agente, oltre agli sforzi dovuti ai carichi imposti durante l’esercizio, è necessario conoscere accuratamente gli stati tensionali residui derivanti dal processo di produzione. Generalmente, le tensioni residue sono indesiderate poiché possono essere di entità elevata e tale da ridurre la resistenza complessiva del componente meccanico. Un aspetto particolarmente insidioso delle tensioni residue è che la loro presenza viene generalmente riconosciuta solo dopo il verificarsi di un malfunziona…

Analisi numerico-sperimentale sull’influenza dell’attrito nella delaminazione in Modo II

Ingegnerizzazione di giunti SPR a semplice sovrapposizione CFRP-Al

WELDING MISMATCHING INLUENCE ON CRACK PROPAGATION

Valutazione delle caratteristiche di assorbimento delle resine proteiche mediante un metodo RGB

Studio dei fattori di intensificazione delle tensioni per cricca che avanza in un pannello forato mediante analisi fotoelastica

Numerical simulations and experimental measurements of the stress intensity factor in perforated plates

A numerical procedure, which combines two hybrid finite element formulations, was developed to analyse the stress intensity factors in cracked perforated plates with a periodic distribution of holes and square representative volume elements. The accuracy of the method in predicting the stress intensity factor was verified by a comparison with experimental measurements, carried out by a photoelasticity method, and by commercial finite element software. Several simulations were executed by varying both the crack length and the hole diameters, and the effects of the holes on the stress intensity factor are illustrated. The method shows high accuracy and efficiency, as small differences were ob…

SISTEMA INNOVATIVO PER LA STABILIZZAZIONE DI UN HSC

Studio numerico e sperimentale del danneggiamento a fatica dei materiali compositi ibridi

Effect of the mutual position between weld seam and reinforcement on the residual stress distribution in Friction Stir Welding of AA6082 skin and stringer structures

Abstract In the paper, a numerical and experimental study was carried out to highlight the effect of the distance d between the weld seam and the reinforcement on the residual stress distribution in Friction Stir Welded AA6082-T6 structures. An L-shaped profile was welded to a sheet metal with varying tool rotation and distance d from the weld seam. The Cut Compliance method was used to determine the resulting longitudinal residual stress. A dedicated FE model for FSW was set up, validated and utilized to predict the longitudinal residual stress in the assembled part. The analysis allowed the identification of a few design guidelines in order to reduce the detrimental effects of the residua…

Verifica dei risultati della normativa ISO 6336 sulle ruote dentate per mezzo di simulazione numerica

Design and use of a Fatigue Test Machine in Plane Bending for Composite Specimens and Bonded Joints

Polymeric and composites materials are increasingly used in industry as structural parts, so that specific information on their mechanical properties "at long term" (creep, relaxation, fatigue) are requested. The design and implementation of these components also requires that they are permanently connected together to perform certain functions. The use of adhesives in structural joints has increased over recent years thanks to the continuous development by companies which provide the market with adhesive having better and better mechanical properties. The main areas relate to the aerospace, aeronautical and automotive industries, where requirements are required for lightness and reliabilit…

Ingegnerizzazione di una macchina prototipale per processi di saldatura linear friction welding

DETERMINAZIONE DELLE TENSIONI RESIDUE IN PROFILATI IN LEGA DI ALLUMINIO SALDATI DI TESTA MEDIANTE FRICTION STIR WELDING

A model for predicting the mixed-mode fatigue crack growth in a bonded joint

Bonded joints are highly sensitive to the presence of defects and to the degradation phenomena, and this aspect represents the primary obstacle to their use in different structural engineering applications. Delamination in a bonded joint represents, in fact, one of the primary, most common and insidious causes of damage. In this paper, a numerical–experimental study on the crack propagation along the adhesive layer of a bonded joint specimen is carried out. Experimental study is focused on the evaluation of the damage modalities of a bonded joint when the specimens are subject to fatigue load. Experimental tests are compared with the results of several numerical analysis performed in ANSYS …

An analysis of interface delamination mechanisms in orthotropic and hybrid fiber-metal composite laminates

Abstract The onset and propagation of interlaminar defects is one of the main damage mechanisms in composite materials. This is even more the case when considering layered materials comprising metallic laminae (typically Aluminium) and FRP laminae. Propagation of delamination mainly depends on the initial crack extension and its loading mode. This work presents some results of a combined analytical–numerical–experimental study on the onset and propagation mechanisms regarding interlaminar defects. Two cases have been analysed in particular, the first consisting of a glass-fibre reinforced epoxy resin laminate, and the second consisting of a hybrid laminate where a lamina of aluminium is lay…

GIUNZIONI BULLONATE FRA COMPOSITO E ALLUMINIO: STUDIO DEL GIOCO MEDIANTE FIBRE OTTICHE INGLOBATE NELLO SPESSORE

Le giunzioni bullonate di elementi in composito sono state da sempre utilizzate per applicazioni impegnative. Sono stati annegati estensimetri a fibra ottica nello spessore di un pannello in composito in prossimità della superficie di contatto piastra-bullone in un giunto ibrido composito-alluminio. Sono state eseguite diverse prove di trazione su provini single-lap joint con differenti valori del gioco tra bullone e foro. Le prove consentono di determinare una relazione fra il gioco tra bullone e foro e i valori delle deformazioni misurate dagli estensimetri a fibra ottica. Risulta che ad un incremento dei valori del gioco corrisponde un incremento dei valori di deformazione in prossimità …

Strumenti numerici avanzati per il cae di processi di formatura di leghe di titanio