Gruppo Italiano Frattura (IGF)
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Cold spray technology: future of coating deposition processes
No full textCold spray (CS) belongs to a wide family of thermal spray technology with the difference that it is a solid state process in which spray particles are deposited via supersonic velocity impact at a temperature much below the melting point of the spray material. This paper briefly describes the various aspects of this rapidly emerging technology, with almost all the important parameters which affect the deposition behavior along withadvantages and limitations; applications and history of emergence of this process is also reviewed. Though this technology emerges three decades ago but still it could not establish itself as viable practical industrial technology. Hence, the efforts, along with funding from public/private sources are required to commercialize this coating process. It is expected that next decade will saw the growth of cold spray as a viable coating processaround the globe
Crack path dependence on inhomogeneities of material microstructure
No full textCrack trajectories under different loading conditions and material microstructural features play animportant role when the conditions of crack initiation and crack growth under fatigue loading have to beevaluated. Unavoidable inhomogeneities in the material microstructure tend to affect the crack propagationpattern, especially in the short crack regime. Several crack extension criteria have been proposed in the pastdecades to describe crack paths under mixed mode loading conditions. In the present paper, both the Sihcriterion (maximum principal stress criterion) and the R-criterion (minimum extension of the core plastic zone)are adopted in order to predict the crack path at the microscopic scale level by taking into account microstressfluctuations due to material inhomogeneities. Even in the simple case of an elastic behaviour under uniaxialremote stress, microstress field is multiaxial and highly non-uniform. It is herein shown a strong dependence ofthe crack path on the material microstructure in the short crack regime, while the microstructure of the materialdoes not influence the crack trajectory for relatively long cracks
Analysis of the causes of failure in 5Cr-1Mo pipes mounted in a preheating furnace
No full textThe oxidation resistance of iron-based alloys depends on the formation of thin protective films consisting ofreaction products between the alloys and the ambient atmosphere. The high corrosion resistance of Fe-Cr-Mo alloys hasbeen attributed to the rapid formation of a uniform, highly protective passive film. The pipes hardness and resistance tovarious forms of corrosion are determined by the composition of the oxide layer that plays an important role indetermining the lifetime of the pipes themselves. The thermal stability of the oxide layer is influenced by its compositionand thickness as well as by the bond to the underlying metal.Determining factors for the high temperature corrosion are generally: temperature, metallurgy, TAN (chloridric andnaphthenic acid), local flow conditions, sulphur compounds
Effect of pressure on the physical properties of magnetorheological fluids
No full textTo date, several applications of magnetorheological (MR) fluids are present in the industrial world,nonetheless system requirements often needs better material properties. In technical literature a previous workshows that MR fluids exhibit a pressure dependency called squeeze strengthen effect. Since a lot of MR fluidbased devices are rotary devices, this paper investigates the behaviour of MR fluids under pressure when arotation is applied to shear the fluid. The system is designed in order to apply both the magnetic field and thepressure and follows a Design of Experiment approach. The experimental apparatus comprises a cylinder inwhich a piston is used both to apply the pressure and to shear the fluid. The magnetic circuit is designed toprovide a nearly constant induction field in the MR fluid. The experimental apparatus measures the torque as afunction of the variables considered and the yield shear stress is computed. The analysis of the results showsthat there is a positive interaction between magnetic field and pressure, which enhances the MR fluidperformances more than twice
Properties and applications of Magnetorheological fluids
No full textThis brief introduction describes the mechanical, rheological and magnetic properties of themagnetorheological (MR) fluids for feasible engineering applications. The typical modes of exploiting thistechnology are shown and discussed. An increasing number of industrial applications illustrate how the MRfluids peculiar properties may be used to provide optimal performance in semi active damping and dissipativedevices
A mechanical model for FRP-strengthened beams in bending
No full textWe analyse the problem of a simply supported beam, strengthened with a fibre-reinforced polymer (FRP) strip bonded to its intrados and subjected to bending couples applied to its end sections. A mechanical model is proposed, whereby the beam and FRP strip are modelled according to classical beam theory, while the adhesive and its neighbouring layers are modelled as an interface having a piecewise linear constitutive law defined over three intervals (elastic response – softening response – debonding). The model is described by a set of differential equations with appropriate boundary conditions. An analytical solution to the problem is determined, including explicit expressions for the internal forces, displacements and interfacial stresses. The model predicts an overall non-linear mechanical response for the strengthened beam, ranging over several stages: from linearly elastic behaviour to damage, until the complete detachment of the FRP reinforcement
Electro-mechanical coupled design of self-powered sensing systems and performances comparison through experiments
No full textRecent advances in low-power sensors and electronic components open to innovative strategies instructural monitoring and real-time data processing, in particular for industrial and vehicular fields. Dedicateddevices for harvesting the energy dissipated by mechanical vibrations of machines are showing their applicabilityin supplying autonomous distributed sensing systems. The harvester will replace cables and storage batteries,with relevant benefits on the sensing system capillarity, accessibility and applicability. The design of theinterfaces of the electric, magnetic and structural coupled systems forming the harvester include static anddynamic modeling and simulation of the interactions involved; smart and effective architectures are need tosatisfy the general requirements of bandwidth, tunability and efficiency required by each application. This paperreports the research advances in this field as a result of laboratory tests and design studies, with particular focuson the design methodologies involved in the definition of energy harvesters
Experimental methods for the characterization of fatigue in microstructures
No full textThe mechanical fatigue behavior of gold microbeams is analyzed. Dedicated devices have beendesigned and built able to produce alternate loading on gold specimens; the electrostatic actuation is used asdriving force. Gold beams are tested under both bending and tensile alternate loadings. Results were used toplot S-N curves and fatigue Goodman-Smith diagram in order to estimate the fatigue limit of the material inpresence of mean and alternate stress conditions. The surface topography evolution is studied and failure modesare discussed
Indentation response of a NiTi shape memory alloy: modeling and experiments
No full textThe indentation response of a pseudoelastic nickel-titanium based shape memory alloy (SMA) has been analyzed. Indentation tests have been carried out at room temperature using a spherical diamond tip and indentation loads in the range 50-500 mN in order to promote a large stress-induced transformation zone in the indentation region and, consequently, to avoid local effects due to microstructural variations. The measured load-displacement data have been analyzed to obtain information on the pseudoelastic response of the alloy. To aid this analysis numerical simulations were performed, by using a commercial finite element (FE) softwarecode and a special constitutive model for SMAs, so as to understand better the microstructural evolution occurring during the indentation process. Finally, the FE model has been used to analyze the effects of temperature on the indentation response of the alloy. This analysis revealed a marked variation of both the maximum and residual penetration depths with increasing test temperature
Sn and Ti influences on intermetallic phases damage in hot dip galvanizing
No full textProtection against metallic materials corrosion is one of the most important means to reduce both maintenance costs and environmental impact. In the last years new studies on chemical baths compositions and fluxes have been performed in order to improve processes, corrosion resistance and mechanical behavior of Zn based coatings. Chemical bath composition is often improved by the Sn addition which increases the fluidity ofthe melt. Ti addition makes the coatings to change color under appropriate heat treatment. In this work a comparative microstructural analysis, in Zn-Sn and Zn-Ti coatings, is performed to evaluate intermetallic phases formation kinetics and the influence of intermetallic microstructure on coating damage under constant bending deformation