[Show abstract][Hide abstract] ABSTRACT: Nowadays, finite element analysis assumes a key-role in the automotive industry. Predictivity of FE models has been strongly improved during the last years and the research on this topic involves both industrial and academic fields. The main focus of this paper is the prediction of the failure of aluminum alloys used for extruded components. Material fracture affects the capacity of absorbing energy and the crashworthiness of the structure as well. In extracting the samples directly from the components involved in the crash event, it has been possible to take into account the whole manufacturing process. The methodology has been developed to improve the correlation of the FE models as well as to answer to the industrial requirements.
Preview · Article · Dec 2015 · Procedia Engineering
[Show abstract][Hide abstract] ABSTRACT: Several typical and uncommon failure modes in con-rods for internal combustion engines are commented from the stress level viewpoint. The interpretation of the fractures is supported with traditional calculations, with more advanced analytical models, and with Finite Element (FE) predictions. The repertoire of failures in a con-rod is presented by separately addressing the parts composing the con-rod itself, namely the shank, and the small and big ends.
No preview · Article · Nov 2015 · Engineering Failure Analysis
[Show abstract][Hide abstract] ABSTRACT: The elastic stress concentrations are addressed that are developed from the keyless frictionless press fit of a shaft subjected to bending into a hub with rounded bore edges. Derived from a formal modelling of the title problem in terms of an integral equation, a set of normalised parameters is proposed that accounts for the combined effects on the hub stress concentration of the fillet radius, the shaft radius, the hub outer radius, the hub axial length, the interference, the Young's modulus, and the bending couple. A numerical validation of the normalised parameters is presented. With the aid of Finite Elements, various design charts are compiled that (a) forecast the bending couple initiating the detachment between the shaft and the hub, and (b) report the elastic stress concentrations within the hub versus the proposed normalised parameters in the absence of shaft-hub detachment. Such charts assist the designer in dimensioning an interference fit in the presence of a bending couple.
No preview · Article · Sep 2015 · Mechanics Based Design of Structures and Machines
[Show abstract][Hide abstract] ABSTRACT: A methodology is developed for fatigue driven shape optimization of industrial me- chanical components by means of mesh morphing. The methodology is integrated in commer- cial software platforms to increase its productivity and performance in industrial applications. It is well known that shape optimization is a way to improve the structural performance of components, yet it is mostly applied to linear elastic load cases. The idea of including fatigue analysis into the optimization process is of great interest for mechanical components design. Tools based on parametric geometries are becoming standard for fine-tuning optimization processes in industry. These tools can handle multiaxial fatigue analysis, but they are limited by difficulties in maintaining geometry coherence. The use of finite element models in place of parametric geometries results in a faster and more flexible methodology. In fact, mesh morphing avoids geometry coherence problems and the need of re-meshing. The aim of this work is the integration of mesh morphing and multiaxial fatigue in the context of shape opti- mization. A tool for achieving this was created and is presented here together with its appli- cation to part of a cast iron component subject to multi-axial high-cycle fatigue. The results obtained with the proposed methodology are closer to the industrial needs than those that can be obtained from shape optimization based on structure stiffness alone.
[Show abstract][Hide abstract] ABSTRACT: The applicability of the Boussinesq influence function in modelling the frictionless elastic contact between a rectangular indenter with rounded edges and a half-plane is numerically explored. The potential of the asymptotic matching method combined with classical fracture mechanics results is investigated. Manageable design formulae for evaluating the maximum equivalent stress are analytically derived with the aid of the asymptotic matching method.
No preview · Article · Apr 2014 · ARCHIVE Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science 1989-1996 (vols 203-210)
[Show abstract][Hide abstract] ABSTRACT: Difficult-to cut-materials are associated with premature tool failure, most likely in the case of complex geometries and this shapes. However, Nickel-based alloys are commonly used in high-temperature and aerospace applications, where thin deep holes are often required. Then, the only viable manufacturing solution relies on non-contact processes, like electrodischarge (ED) drilling. Morphology of ED machined surfaces is significantly different than obtained by metal-cutting operation and is known to jeopardize fatigue strength, but the extent needs to be gauged and related to the process parameters. Aim of the paper is to study the effect of holes (0.8 mm diameter, aspect ratio 10) produced by ED drilling on the fatigue life of Inconel 718. Rotating bending fatigue tests are carried out on specimens drilled under two ED setups, as well as with a traditional cutting tool. Specimens free from holes are fatigued under the same conditions for comparison. Based on previous studies, extremal ED parameters are selected, giving best surface finish versus highest productivity. S-N curves show that the ED process causes a decrease of the fatigue resistance with respect to traditional drilling, whereas the effect of different ED setups is negligible. Maximum productivity can thus be pursued with no threat to fatigue performance. The fatigue limit variation is quantified by using the superposition effect principle: ED drilling causes an increase of the stress concentration factor around 25% if compared to traditional drilling. The macroscopic fatigue behavior is integrated with a study of the effects of the different drilling processes in the micro-scale, by means of a microstructural and fractographic analysis.
[Show abstract][Hide abstract] ABSTRACT: Specific polymeric and asphaltic materials are widely used for NVH automotive applications. If patches of such materials are properly collocated on vehicle’s panels, they are able to improve significantly noise and vibration performance by modulating damping and stiffness.This work presents a methodology for tuning a FE composite model, using optimization techniques to improve the correlation with the experimental modal tests performed.In particular, plain and ribbed aluminum plates have been considered for several covering ratios of three damping materials.The correlation between numerical and experimental data is achieved by monitoring dynamic parameters such as natural frequencies, mode shapes, and frequency response functions (FRFs). The optimization strategy consists of two steps and makes use of evolutionary and gradient-based algorithms. LMS Virtual.Lab® is used in this part of the work as an environment for correlation and optimization.In order to verify the reliability of the correlation, modal tests are performed on a particular vehicle’s panel.
[Show abstract][Hide abstract] ABSTRACT: In the last few years, the restrictive safety standards and the need for weight reduction have brought the crashworthiness research to focus on composite materials because of their high energy absortion-to-mass ratio. On the other hand, the possibility of obtaining predictive dynamic FEA models for these new materials is still an open issue: the present work aims at developing a methodology for the characterization of composite materials with particular interest for the head impact simulation.Composite materials behavior, defined through the mathematical models implemented in FEA codes, is very complex and requires a large amount of physical and numerical setting parameters. The majority of these parameters can be obtained by an experimental campaign that involves several kind of different tests. The presented methodology allows to obtain a good numerical-experimental correlation simply performing few tests which emulate the behavior of the component during the head impact event.A software tool based on a genetic optimization technique has been developed in order to determinate automatically the material properties values that guarantee the best numerical-experimental correlation.
[Show abstract][Hide abstract] ABSTRACT: The current emissions regulations lead car manufacturers to look carefully for weight reduction. In the automotive industry the classic trial-and-error approach to design is becoming inadequate and techniques based on optimization are necessary to improve the design process. In this study a methodology to design a sport-car front hood is proposed. The process carried out could also be extended to car components characterised by a similar configuration.Starting from the geometry of the actual part, a design volume has been defined. The first step consists of a topology optimization performed considering the material as isotropic (aluminium properties): the output is a rough structure which accomplishes all the imposed targets. The interpretation of the topology results brings to a re-design phase aimed at realising a feasible component.The subsequent optimization step is dedicated to composite material structures and acts on the component plybook, varying thickness and orientation of each ply to find the best solution complying with targets. Finally, the component has to be reviewed from a technological point of view in order to be virtually delivered and to proceed with the prototype phase.
[Show abstract][Hide abstract] ABSTRACT: A mass-conserving formulation of the Reynolds equation has been recently proposed by some of the authors to deal with cavitation in lubricated contacts . This formulation, based on the mathematical derivation of a linear complementarity problem (LCP), overcomes the drawbacks previously associated with the use of such complementarity formulations for the solution of cavitation problems in which reformation of the liquid film occurs. In the present paper, the methodology favoured in , already successfully applied to solve textured bearing and squeeze problems in the presence of cavitation in a one dimensional domain for incompressible fluids, has been extended to include the effects of fluid compressibility, piezoviscosity and the non-Newtonian fluid behaviour and it has been also applied to the analysis of two dimensional problems. The evolution of the cavitated region and the contact pressure distribution are studied for a number of different configurations which can be considered as relevant benchmarks. In particular, some of the results obtained with the proposed scheme are critically analysed and compared with the predictions obtained using alternative formulations, including full CFD calculations. The stability of the proposed algorithm and its flexibility in terms of implementation of different models for compressibility, piezoviscosity and non-Newtonian behaviour are highlighted.
No preview · Article · Nov 2013 · Tribology International
[Show abstract][Hide abstract] ABSTRACT: Objective:
The purpose of this work is to determine the surface morphology obtained by sandblasting and double treatment with acids of titanium implants (BioActive Treatment, B&B Dental Implant Company S.r.l., Bologna, Italy).
Implant surfaces are sandblasted with alumina oxide (Al₂0₃) by using a dedicated appliance. The surface is treated with a double etching by using mineral acids (phosphoric acid). Implant surfaces are cleaned with Argon plasma in a class 10.000 clean room, to guarantee the absence of environmental contamination. As an efficacy test, surfaces undergo x-ray photoelectron spectroscopy (XPS or ESCA). The surface topography of the implants was evaluated by Scanning Electron Microscope (SEM). Roughness was evaluated quantitatively using dedicated software to convert conventional SEM images into three-dimensional data (Mex 4.2, Alicona Imaging GmbH, Graz, Austria). EDX (Energy Dispersive X-ray spectroscopy) analysis was performed.
The SEM observation shows, in a low magnification (200x), a nice machining work, together with a homogeneous surface finish without particles or blasting residuals. Increasing the magnification, (2500-5000x) show the typical structure of micro-roughness surfaces treated with double acid attack. Values emerged from stereo SEM analysis:Ra 3.19 ± 1.06, Rq 4.78±1.15, Rt 11.41±1.06. EDX analysis confirms that the only elements detected are Ti, Al and V.
As known and reported in the scientific literature, this micro-topography enables the surface to act as a “sponge”, interacting strongly with the clot and stimulating bone regeneration. The initial roughness level favours osteoblast cells anchor and the integration with the bone tissue, reducing the osseointegration time. With the limits of this study, this treatment seem to obtain by subtraction an implant surface with a controlled micro-roughness and absence of contaminants or foreign deposits. Student Presenter This abstract is based on research that was funded entirely or partially by an outside source: B&B Dental Implant Company S.r.l., Bologna, Italy
Keywords: Acid etch, Biocompatibility, Dental materials, Implants and SEM
[Show abstract][Hide abstract] ABSTRACT: In this article, the achievement of a uniform elastic contact pressure in a frictionless, keyless, shaft–hub interference fit obtained by properly shaping the mating profiles is examined. The peculiarity of the hub mechanical response according to which, under the effect of a uniform pressure applied to the hub bore, the bore axial profile moves radially without any distortion, is exploited to simplify the determination of the mating profiles that return a uniform pressure. In particular, the hub radial deflection may be computed with a simple plane model, whereas only the shaft radial deflection requires a more complex analysis in cylindrical coordinates. Explicit approximate expressions are reported for the shapes to be conferred to the mating profiles to achieve a uniform pressure. Selected examples are presented to clarify the proposed design procedure and to preliminarily explore the effect on the pressure profile of simple shape errors.
No preview · Article · Mar 2013 · ARCHIVE Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science 1989-1996 (vols 203-210)
[Show abstract][Hide abstract] ABSTRACT: The elastic stress concentrations developed from the keyless, frictionless, static press-fit of a solid shaft into a hub with bore rounded edges are addressed. Derived from an analytical approach, a normalising parameter Φ is employed that accounts for the combined effects on the hub stress concentration of the fillet radius of the hub bore, the shaft radius, the interference, and the Young’s modulus. Compiled with the aid of Finite Elements, several design charts are presented that report the elastic stress concentrations within the hub versus the normalising parameter Φ. Each curve is valid for prescribed ratios of a) the hub inner radius to the outer radius, and b) the fillet radius to the shaft radius. An approximating expression of ample validity is also presented for a prompt evaluation of the hub stress concentration factor.
[Show abstract][Hide abstract] ABSTRACT: Improvements in structural components design are of- ten achieved on a trial-and-error basis guided by the designer know-how. Despite the designer experience must remain a fundamental aspect in design, such an approach is likely to allow only marginal product enhancements. A different turn of mind that could boost structural design is needed and could be given by struc- tural optimization methods linked with finite elements analyses. These methods are here briefly introduced, and some applications are presented and discussed with the aim of showing their potential. A particular focus is given to weight reduction in automotive chassis de- sign applications following the experience matured at MilleChili Lab.
[Show abstract][Hide abstract] ABSTRACT: The loosening mechanism is explored of a bush press-fitted into the small end bore of a con-rod. A modelling of the bush loosening mechanism is proposed. Numerical and analytical forecasts of the tensile inertial force responsible for the bush loosening are presented for a purely elastic model. Proper design charts are compiled that allow (a) the initial interference precluding any bush loosening to be determined within the respect of an imposed safety factor and (b) the maximum elastic stress within the small end to be computed for a general inertial load.
No preview · Article · Mar 2012 · Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering
[Show abstract][Hide abstract] ABSTRACT: Various design charts of ample validity and prompt access are presented, which permit the contact stresses within the lug of a pinned connection to be forecast in the presence of an initial clearance between the pin periphery and the lug bore. To cover the range of the practically encountered geometries and loadings, round-ended lugs of various widths and with a variously tapered shank are considered, and several inclinations of the applied load are addressed. The charts are compiled with the aid of finite elements. The employment of the recently proposed load factor Φ allows the combined effects on the peak contact stresses of the load intensity and of the initial clearance to be predicted.
No preview · Article · Nov 2011 · The Journal of Strain Analysis for Engineering Design
[Show abstract][Hide abstract] ABSTRACT: The elastic stress concentrations developed from the keyless frictionless static press-fit of a shaft into a hub are addressed. Two configurations are examined, namely (a) an infinitely long solid shaft press-fitted into a hollow hub with bore rounded edges, and (b) a shaft with filleted extremity, partially inserted into a hub. Derived from an analytical approach, a normalizing parameter is proposed that accounts for the combined effects on the stress concentrations of the fillet radius, the shaft radius, the interference, and Young’s modulus. With the aid of finite elements, various design charts are compiled that report the elastic stress concentrations within the hub versus the proposed normalizing parameter. Each curve is valid for a fixed ratio of inner to outer hub radii.
No preview · Article · Aug 2011 · The Journal of Strain Analysis for Engineering Design