Issue 10

A. Pirondi, Frattura ed Integrità Strutturale, 10 (2009) 21-28; DOI: 10.3221/IGF-ESIS.10.03 21 Failure prediction of T-peel adhesive joints by different cohesive laws and modelling approaches Alessandro Pirondi University of Parma, Department of Industrial Engineering, Parco Area delle Scienze, 181/A - 43100 Parma, Italy alessandro.pirondi@unipr.it R IASSUNTO . In questo articolo si è simulato mediante il modello di zona coesiva il cedimento di un giunto T- peel incollato. Gli aderendi sono lamiere di acciaio Fe360 e sono unite mediante l’adesivo strutturale Loctite Multibond 330. I parametri del modello di zona coesiva sono stati calibrati sulla base di esperimenti di frattura condotti in precedenza su provini Double Cantilever Beam (DCB) incollati con il medesimo adesivo. La simulazione è stata condotta utilizzando il software di analisi ad elementi finiti ABAQUS, sviluppando modelli 2-D. Il cedimento avviene in uno strato modellato utilizzando elementi di tipo coesivo disponibili nel software. L’analisi è volta ad individuare l’influenza di: i) differenti formulazioni della legge coesiva, ii) la modellazione o meno dello strato di adesivo con le sue proprietà elasto-plastiche. A BSTRACT . In this work, Cohesive Zone Modelling (CZM) was used to simulate failure of T-peel bonded joints with 1.5mm thick adherends, respectively, bonded toghether with Loctite Multibond 330 adhesive. The fracture toughness and load-opening behaviour recorded in previous experiments on bonded Double Cantilever Beam (DCB) specimens were taken as reference to calibrate CZM parameters. Two-dimensional models were analysed using the FE code ABAQUS. The failing interface was modeled with the cohesive elements available in this software. The influence of: i) different cohesive law shapes, ii) modeling the presence of the adhesive layer explicitly, was studied. K EYWORDS . Adhesive joints, Fracture, Cohesive zone modeling. I NTRODUCTION he use of adhesive joining in civil, aerospace and mechanical constructions has considerably increased in the last decades thanks to the advantages over traditional joining techniques such as: i) ability to join dissimilar materials, ii) stress distribution over a wider area, iii) potentially lower weight. However, joint fabrication procedures and component service loads may introduce or initiate defects, whose evolution will control the performance and the reliability of the bonded joint. In those cases, Fracture Mechanics (FM) can be used to assess the structural integrity of a bonded join t [1]. The FM approach consists in the comparison of a parameter, function of load and geometry of the cracked body (for example the strain energy release rate, G), with the fracture resistance (G c ). The simulation of fracture therefore requires to implement a criterion that triggers propagation when G=G c . An attractive way to simulate the effect of a defect on joint strength is to incorporate a model of the rupture process (i.e. the criterion to trigger propagation). In particular, the fracture of bonded joints has been successfully simulated using the Cohesive Zone Model (CZM) in [2-7]. According to this approach, the zone in front of the physical crack tip opens and then tears progressively apart following a given traction-separation behaviour. Although straightforward methods to evaluate experimentally CZM parameters in adhesive joints have been recently presented [8], questions on the physical meaning or, in other words, on the transferability of the parameters to joint geometries different from the one from they were extracted is still an open issue. In particular, studies have been carried T