Antonino Pasta

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 for different crack dimensions. Furthermore the effectiveness of the application of an external ring to modify the die stress state during the process, was investigated.

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 finite element method (FEM), are generally lower than those obtained with the ISO rules. Hence, this approach yields a conservative determination of the effective material strength. In all the examined cases, the difference was less than 2.5 per cent. The set FEM technique gives a result accuracy of better than 1 per cent; the difference between the stress obtained by FEM and those obtained by ISO 6336 is less than 2.5 per cent, so that the FEM confirmed, consistent with the ISO rules, that correction of the profile results in significant benefits with respect to determination of the mechanical resistance of spur gears.

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 static characterization of the joints was carried out through tensile tests. Then fatigue tests were made with the application of different levels of load. The fatigue curves were also obtained at the varying the distance between the two rivets in order to better assess the joint strength for a given length of overlap.

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