Papers by Author: Marco Alfano

Abstract: Aluminum (Al) and Magnesium (Mg) alloys are nowadays widely employed in order to produce lightweight automotive and aeronautical components and to gain fuel saving and reduced emissions. However, the joining of Al and Mg alloys poses well known technical problems and the application of conventional joining techniques, e.g. welding, may be ineffective. On the other hand, adhesive bonding may be considered as a candidate replacement of the traditional techniques and for this reason it has been recently proposed as an alternative technology for Al/Mg joints. In particular, it has been demonstrated that adhesive bonding, in conjunction with state-of-the-art surface treatments, can provide Al/Mg joint with enhanced strength. However, in order to evaluate the potential of adhesive bonding to outperform the conventional joining techniques a systematic comparative analysis is needed. Therefore, the aim of this work is to supplement the existing studies on Al/Mg bonding providing a comparative analysis between Al/Mg joints prepared using gas metal arc (MIG) welding, riveting and adhesive bonding. Probably, the use of adhesive bonding as complementary joining process will be the industrial answer to the hybrid joints performance needs.

Abstract: This paper deals with the application of Cohesive Zone Model (CZM) concepts to study mode I fracture in adhesive bonded joints. In particular, an intrinsic piece-wise linear cohesive surface relation is used in order to model fracture in a pre-cracked bonded Double Cantilever Beam (DCB) specimen. Finite element implementation of the CZM is accomplished by means of the user element (UEL) feature available in the FE commercial code ABAQUS. The sensitivity of the cohesive zone parameters (i.e. fracture strength and critical energy release rate) in predicting the overall mechanical response is first examined; subsequently, cohesive parameters are tuned comparing numerical simulations of the load-displacement curve with experimental results retrieved from literature.

Abstract: The use of non destructive techniques for the elastic characterization of isotropic materials is continuously increasing and those based on the modal vibration testing of plate-like specimens is very widespread. In the present paper, an optimized search procedure is proposed which allows the material constants of isotropic plates to be non-destructively identified from vibration testing data and using finite element analyses. The identification process is performed by an optimizing algorithm in which the error function to be minimized depends on the difference between the natural frequencies obtained by finite element analyses and the measured ones. In order to verify the proposed identification procedure a comparison with the results reported in literature has been made.

Abstract: The present paper describes a numerical method which is able to calculate the stress intensity factor in two dimensional heterogeneous materials under mechanical and thermal loads. The proposed method uses two hybrid element formulations to model the second phase heterogeneities of the material and the crack tips. The method was used to analyse alumina-zirconia ceramic materials, and the effects due to the zirconia t→m phase transformation and the thermal stresses, which develop during the cooling stage of sintering, were taken into account in calculating the stress intensity factor.

Abstract: The aim of the present paper is to evaluate the interfacial fracture toughness of an Al/Epoxy adhesive system with a crack lying at the interface. A cracked lap shear specimen loaded in four point bending is adopted and the fracture toughness is pointed out in terms of the critical complex stress intensity factor. To this aim numerical analyses of the fracture specimen have been carried out using a commercial finite element code. In addition, fracture surfaces are analyzed and the locus of failure is discussed.

Abstract: The paper presents a procedure whereby the Poisson’s ratio and dynamic Young’s modulus of isotropic and homogeneous materials are determined using two of the first four frequencies of natural vibration in thin square plates. The procedure is based on suitable approximate relationships relating the resonant frequencies to the elastic constants of the material. These relations were derived from an extensive series of numerical analysis carried out by a finite element code. To measure the fundamental resonant frequencies, inexpensive computerized equipment is proposed. The procedure has been validated on Carbon Steel specimens.