[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: 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: 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.
ASME 2013 International Mechanical Engineering Congress and Exposition; 11/2013
[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.
ASME 2013 International Mechanical Engineering Congress and Exposition; 11/2013
[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.
ASME 2013 International Mechanical Engineering Congress and Exposition; 11/2013
[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.
ARCHIVE Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science 1989-1996 (vols 203-210) 03/2013; 227(3):405-419. · 0.59 Impact Factor
[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.
ASME 2012 International Mechanical Engineering Congress and Exposition; 11/2012
[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.
Problèmes Inverses, Contrôle et Optimisation de Formes 2012, Paris, France; 04/2012
[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.
Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering 03/2012; 226(3):312-324. · 0.65 Impact Factor
[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.
The Journal of Strain Analysis for Engineering Design 11/2011; 46(8):760-771. · 1.01 Impact Factor
[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.
The Journal of Strain Analysis for Engineering Design 08/2011; 46(6):478-491. · 1.01 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Weight reduction is a major issue for carmaker companies due the need to comply with the emission regulations without reducing the vehicle safety. A classic trial-and-error approach to design in the automotive industry is becoming inadequate and new means are needed to enhance the design process. A major improvement on the end product can be achieved by adopting suitable optimization techniques from the early design stage. In the present paper the problem of automotive chassis design in view of weight reduction is tackled by means of topology optimization. The design methodology proposed is applied twice: at first addressing a chassis for spider vehicles, then for coupe ́ vehicles. The two chassis, together with some intermediate result are discussed and compared. The methodology has been proven to be successful in finding innovative and efficient layouts for automotive chassis.
World Congress on Engineering 2011 - The 2011 International Conference of Mechanical Engineering, London, UK; 07/2011
[Show abstract][Hide abstract] ABSTRACT: Automotive chassis design in view of car weight reduction is a challenging task due to the many performance targets that must be satisfied, in particular in terms of vehi- cle safety. In this paper a methodology for automotive chas- sis design in involving optimization techniques is presented. In particular, topology, topometry and size optimizations are coupled with F E M analyses and adopted in cascade for reaching an optimum chassis configuration. The methodol- ogy is applied to the design process of a rear-central engine high performance vehicle chassis. The objective of the op- timization process is the chassis weight reduction, yet in fulfilment of structural performance constraints as required by Ferrari standards. The results demonstrate the general ap- plicability of the methodology presented for obtaining the general trusses layout and thicknesses distribution of the structure. The numerical model at this stage shows a sig- nificant weight reduction when compared to the chassis of the Ferrari F458 Italia.
Structural and Multidisciplinary Optimization 01/2011; 44(1):45-56. · 1.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Purpose: A recent procedure called All-on-four " provides the rehabilitation of atrophic edentulous jaws by means of a fixed prosthesis supported by 4 implants. Purpose of this work is the comparative evaluation between the biomechanical features of the All on Four versus traditional therapy
Methods: it was created a 3D model (SolidWorks - Dessault Systems SolidWorks Corp - Concord, MA, USA) of a clinical case with 6 mandibular implants and a screwed framework. The FEM analysis was performed by varying the number and position of the implants and the superstructure material. 9 different models were analyzed. The load was 300 N on the distal part of the framework.
Results: Implants closest to the application of the force are the more loaded. In the superstructure there was a stress peak that exceeds the plasticization value of one material (titanium), although the area is very limited. In the bone, maximum stress occurs in the cortical component, while the medullary component is less interested. The distal implant (closer to the force) has a compressive load, while the mesial one has a tractive stress.
Conclusion: The strategic distribution of implants appears to be the key factor that governs the distribution of loads. A limited number of implants, strategically placed, can be an effective alternative rehabilitation in selected cases. This suggests a possible effectiveness of the fixed implant prosthesis on 4 implants, accompanying the reduction of, costs, post-operative morbidity and the difficulty of the prosthesis than other procedures.
[Show abstract][Hide abstract] ABSTRACT: The contact problem between a split ring and a circular housing is mechanically examined. This contact is revisited in terms of receding contact, the zones along which the ring beds over the housing are investigated, and normalizing design parameters are evidenced. The split ring is modelled in terms of a straight, purely flexural beam as well as of a curved, shear-elastic beam; for both models, analytical solutions are obtained. Various easy accessible design diagrams, useful for estimating the maximum elastic stresses within the split ring and the axial insertion force, have been prepared with the aid of these two beam models and using finite elements. The mechanical response of the split ring when its angular width is appreciably lower than π is clarified.
The Journal of Strain Analysis for Engineering Design 11/2009; 44(8):671-688. · 1.01 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The stress increase that is caused by the presence of an initial clearance within the small end of connecting rods for motorbike and car engines is investigated. Plane analytical and numerical modellings of the dry contact between the small-end and piston pin are adopted. Based upon a recent analytical result, a normalizing parameter is introduced, which allows the stress concentration factor at the small-end bore sides to be expressed as a function of a proper combination of the initial clearance between the small end and gudgeon pin, the applied load, and Young's modulus, for prescribed aspect ratios of the small end and hollow pin. Design diagrams summarizing the consequences of an initial clearance between the small-end bore and gudgeon pin on the eye peak stress are reported, which cover a wide range of geometries, clearances, and loadings. Selected comparisons between two-dimensional and three-dimensional models are carried out.
Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering 06/2009; 223(6):769-782. · 0.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A normalizing loading parameter useful in summarising the mechanical response of plane pin-in-plate-like contacts is extended to axisymmetric ball-in-socket-like contacts. An example addressing a compliant layered artificial hip joint is presented, and the usefulness of the normalizing loading parameter is evidenced.
Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine 09/2007; 221(6):601-11. · 1.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, the stress state in a round-ended, taper-shanked lug loaded by an oblique point force is investigated. Numerical, analytical and, partially, photoelastic studies were carried out. In the analytical model, the lug is modelled as a plane problem, and it is partially likened to a ring examined with a Michell-type series solution; the differences in shape between lug and ring are overcome by endowing the series solution with degrees of freedom suitable for adapting the ring solution to the lug actual geometry. Three prompt access design charts are presented, which report the normalised stress concentration for three lug shank taper angles, for selection of five aspect ratios between bore radius and radius of the rounded extremity, and for load inclinations ranging from longitudinal to transverse directions.
[Show abstract][Hide abstract] ABSTRACT: In cases of completely conforming frictionless contact, the contact area generally either decreases or stays the same under load, in which case the extent of the contact area is subsequently independent of load and the stress and displacement fields vary linearly with the loading parameter. Dundurs and Stippes describe such cases as receding contact problems. Here, we demonstrate that similar results apply in the presence of Coulomb friction, in which case the extent of the stick and slip zones and the local direction of sliding are independent of load. We also show that if there is a small initial gap or interference throughout the potential contact area, the extent of the contact area and the stress and displacement fields will approach those of the corresponding receding contact problem as the applied load is increased. If the interface conditions permit adhesion between the contacting surfaces, the extent of the adhesion zone shrinks to zero as the load increases without limit. Progress of the contact configuration towards the limit is governed solely by a dimensionless load factor involving the ratio between the applied load and the initial clearance or interference. This permits results for a variety of initial geometries (due to tolerance variations) to be obtained from a set of finite element results for a single case. Some of these characteristics are demonstrated using a finite element solution of a connecting rod/bushing/gudgeon pin contact. Other interesting applications are those with complex geometries, ranging from biomechanics, as in prostheses, to the design of multiple fasteners.
International Journal of Mechanical Sciences 09/2006; · 2.06 Impact Factor