Giuseppe Di Franco

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

Self-Piercing Riveting (SPR) is receiving more recognition as a possible and effective solution to join body panels and structures. For example self-piercing riveting is still the first choice for the most well-known automotive car industries when considering the intensive use of aluminum alloy. To combine the advantages of the two joints techniques, in the last years hybrid joints combining a classical mechanical fastening (riveting) and a classical adhesive bonding, or a co-cured joint, have attracted great interest.In the present paper the static behavior of single-lap hybrid joints (SPR-bonded) between GFRP and aluminum through experimental tests. In particular, tensile strength, energy absorption and failure modes of studied joints were investigated through tensile tests.

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 order to compare the obtained results with the experimental ones. The joining process was simulated using a finite element method code specific for plastic deformation processes, namely DEFORM™, to predict the deformed shape and mechanical fastening mechanism. Results showed how this procedure can be a powerful tool to carry out a proper computer-aided process engineering. The experimental tests showed that the hybrid joint (metal/composite) has good mechanical characteristics both under static and fatigue loads.

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

Polymeric and composites materials are used increasingly as structural parts in industry and therefore many informations on mechanical properties (creep, relaxation, fatigue life) are necessary. Composite materials behavior subjected to fatigue load is very complex due to non homogeneous and anisotropic properties, and it has been studied for a long time; however, composite materials design is still based on very long fatigue tests and high safety factors are used. Composites industry uses various types of resin (usually epoxy or polyester resin) and reinforced fibers (usually fiberglass). Many industrial components and consumer goods are made in this way, such as parts for boats, car components, etc. Composites with polymer matrix are used by the industries with much performed resins and stubborn and rigid reinforced fiber. Composite materials are used primarily in aerospace, military and automotive industries, however, are also utilized in sports such as golf, fishing, skiing (and snowboarding) and in the naval industry (Marannano & Virzi Mariotti 2008). These materials have very high mechanical properties such as low weight, high strength and stiffness, good formability and high design flexibility. Many theoretical studies (Van Paepegem & Degrieck, (b) 2001; Van Paepegem & Degrieck, 2002 ;Marannano & Pasta 2006; Natarajan et al. 2005) are dedicated to the study of crack propagation, applying the concepts of fracture mechanics. Fatigue failure can be described as a sequence of two phases: • crack formation; • crack propagation. The crack propagation has been studied carefully, ignoring the formation crack, and precracked specimens are used for this purpose; the study requires the development of equipping, methodologies and specialist analysis. Fatigue studies usually require several days (sometimes weeks) of load cycles to obtain an appreciable damage. The tests show inhomogeneous results, so it is necessary to do many repetitions to get a more accurate

Analysis of the accuracy of fiber-optic strain transducers installed by using composite smart patches:

The aim of this work is to investigate the accuracy of fiber-optic strain transducer related to the incomplete load transmission that can occur on composite smart patches used as base support for the installation of such transducer, commonly used for structural monitoring of concrete elements. In detail, since the dimensions of the transducer are generally very small compared to those of the structural element being monitored, attention is given not to the global reinforcement effect, which occurs when the transducer alters the entire strain field of the transversal section of the monitored element, but rather to the so-called local reinforcement effect, which is due to an incomplete load transmission from the analyzed structure to the transducer and results in a localized variation of the strain field, without affecting the global structural response of the monitored element. Theoretical studies carried out in this work have permitted the evaluation of a correction coefficient (C), which allows the user the correction of the measured strain or the proper transducer calibration, according to the elastic characteristics of the materials and the geometry of the structure-transducer system. The accuracy of the proposed theoretical model has been verified by finite element method analysis, varying the main factors that influence the local load transmission. Successive experimental tests have corroborated the accuracy of the formula proposed for the correction of the measured strain. In summary, the results of this study showed that the use of thick patches made by high-modulus composite materials (carbon fiber–reinforced polymer etc.), or the use of short patches, can lead to coarse error on the strain measurement; on the contrary, for thin patches made by low-modulus composite materials (fiberglass etc.) and having sufficient base length, the error is less than ±1%.