Search

Highlights • The radial impact test is simulated, for a number of different aluminium wheels, by means of a finite element model. The model includes tyre, wheel, striker and supporting structure. The actual structure of the tyre is modelled. • A wheel instrumented with strain gauges has been used to validate the finite element model. An additional set of four families of different wheel types, equipped with different tyres, has been considered to enlarge the validation activity. • The modelling approach has proved to be effective in reproducing the final plastic deformation of the wheel and thus to predict the compliance of the wheel design with the requirements coming from standards. Abstract Safety is a crucial issue for automotive wheels, normally subject to severe dynamic working conditions. Severe indoor tests have been conceived and standardised to guarantee the required safety standards of vehicle wheels. This paper is devoted to the analysis and virtual simulation of the radial impact test of aluminium wheels, one of the most severe tests the wheel has to pass before production. The radial impact test is simulated, for a number of different aluminium wheels, by means of a finite element model. The model includes tyre, wheel, striker and supporting structure. The actual structure of the tyre is modelled. Tyre damping is included through a Rayleigh model, whose parameters are experimentally identified. The wheel material inhomogeneity is taken into account by assigning different stress/strain curves to wheel rim and spokes. A wheel instrumented with strain gauges has been used to validate the finite element model. An additional set of four families of different wheel types, equipped with different tyres, has been considered to asses the experimental variability and to compare the outputs of the corresponding impact models realized by the same procedure. The finite element model of the radial impact test has proven to be effective in reproducing the final plastic deformation of the wheel and thus to predict the compliance of the wheel design with the requirements coming from standards. [ABSTRACT FROM AUTHOR]

The mechanical properties of three different silicone gels were characterized by means of tension, shear and compression tests at large deformations. The non-linear behavior of the materials is taken into account and three material models (Neo-Hook, Yeoh, Ogden) for rubber-like materials have been considered in order to assess their capability to describe the behavior of the gels. The parameters of the material models are reported. [ABSTRACT FROM AUTHOR]

The paper deals with the conceptual design of a beam under bending. The common problem of designing a beam in a state of pure bending is discussed in the framework of Pareto-optimality theory. The analytical formulation of the Pareto-optimal set is derived by using a procedure based on the reformulation of the Fritz John Pareto-optimality conditions. The shape of the cross section of the beam is defined by a number of design variables pertaining to the optimization process by means of efficiency factors. Such efficiency factors are able to describe the bending properties of any beam cross section and can be used to derive analytical formulae. Design performance is determined by the combination of cross section shape, material and process. Simple expressions for the Pareto-optimal set of a beam of arbitrary cross section shape under bending are derived. This expression can be used at the very early stage of the design to choose a possible cross section shape and material for the beam among optimal solutions. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the fatigue life of pneumatic tires is investigated with particular focus on the phenomenon of belt separation. This phenomenon yields the propagation of fatigue cracks in the rubber separating the belts; not the separation of the rubber at the interfaces with the belts. Cracks at the belts edges are related among others to the high stress concentration due to the very different stiffness of the two materials. A steady-state rolling finite element model of the full tire is used to evaluate the stress and strain fields in the rubber at the edges of the belts. Suitable life predictors are defined and computed for the identification of the zones with a higher expectation of failure. For the evaluation of crack propagation in the bulk rubber material between different belts, in principle, two different approaches are employed associated with crack nucleation and crack growth. The two approaches are applied to the study of crack propagation in a truck tire and the results of different predictors are compared to crack propagation found in a real tire. [Copyright &y& Elsevier]

A method for the measurement of the inertia properties of bodies with aerofoils (such as spacecraft or aircraft) is dealt with. Two different test rigs have been realized and used to validate the proposed method. Each test rig is a spatial multicable pendulum carrying the body under investigation. The method is based on a simple procedure. The spatial pendulum is displaced from its rest configuration, and then a free motion evolves in a complex manner under the action of the gravitational field. The motion and the forces acting on the pendulum are measured, and then the inertia parameters are identified offline by a suitable and very quick numerical procedure. The proposed method does not require any dynamic excitation device, and it could be applied to measure the inertia properties of huge bodies, such as those pertaining to spacecraft or aircraft. The paper focuses particularly on how the aerodynamic forces acting on the body under investigation can influence the measurement uncertainties. Such a problem is of relevant importance for bodies with aerofoils (such as aircraft, spacecraft, or their subsystems). It is shown, both analytically and experimentally, that the developed method could be applied for the measurement of the inertia properties of full-scale aircraft or spacecraft. [ABSTRACT FROM AUTHOR]

In this paper the error analysis, construction and experimental assessment of performances of a new high precision six-axis load cell are presented. In a previous companion paper the conceptual design, modelling and embodiment design of the load cell were described. The new load cell is able to measure the three components of respectively a force and a moment acting on the load cell itself. The new six-axis load cell, patented by Politecnico di Milano, performs well in terms of linearity, sensitivity, accuracy and repeatability. [ABSTRACT FROM AUTHOR]

• full digitalization of the design process of road vehicle wheels. • Reduction of indoor impact tests to assess rim structural safety. • A method for the realization of finite element models of different impact tests is presented. • The method is successfully applied to different radial and side impact tests. • For some impact configurations, the possibility to use an implicit solver to increase the stress accuracy is explored. In the design of automotive wheels, safety is a crucial factor. Homologations, legislation and standards require severe impact tests before a new wheel can be released on the market. Impact tests are usually performed after the wheel has been already designed and the first prototypes have been produced. In case of test failure, significant delays and costs have to be sustained before the wheel can be actually produced. Numerical simulation of wheel impact tests can reduce the risk of test failure and be a valuable tool for the designer to obtain more efficient and light wheels.The paper deals with the full digitalization of the design process of road vehicle wheels. The aim is to reduce as much as possible indoor impact tests to assess wheel rim structural safety. The numerical simulation of impact tests is accomplished by complex finite element models comprising wheel, tyre and test rig structure. Several data can be required for the modelling of the tyre, which are not usually known to the wheel designer. In this paper, a method for the realization of finite element models of different impact tests is presented. By the proposed method, finite element models with a sufficient level of accuracy for the design of the wheel, at a relatively low computational cost, can be obtained by means of a well defined procedure. For tyre characterisation, only simple measurements related to geometrical features, stiffness and frequency response are required. The method is successfully applied to different impact tests such as radial impact tests with flat or V-shaped striker and 13∘ side impact test. For all the considered tests, experimental validations are performed on different wheels, instrumented with strain gauges located at the most stressed areas. The striker accelerations are also reproduced accurately. The method for the numerical simulation of indoor impact tests of road vehicle wheels enables the full digitalisation of design process, with relevant results in terms of "time to market" reduction and structural safety assessment. The proposed method is useful not only to design wheel rims, but also to design pneumatic tyres. [ABSTRACT FROM AUTHOR]

new high precision six-axis load cell is presented in two companion papers. The first paper (this one) is focused on the presentation of the load cell, the conceptual design, the modelling and the embodiment design. The second paper refers to the error analysis, the construction and the experimental assessment of the performances. The new load cell is able to measure the three components of both a force and a moment acting on the load cell itself. The sensing structural element of the six-axis load cell is basically a three spoke structure. Strain gauges are conveniently located on highly stressed areas. The sensing structural element is constrained to the frame of the load cell by means of special joints conceived to avoid friction. The mechanical behaviour of the load cell is described by means of analytical equations that allow a quick preliminary design focused on the given technical specifications. A finite element model has been used to asses the mechanical behaviour of the load cell. [ABSTRACT FROM AUTHOR]

Abstract: A method for the measurement of the inertia properties of rigid bodies is presented. Given a rigid body and its mass, the method allows to measure (identify) the centre of gravity location and the inertia tensor during a single test. The proposed technique is based on the analysis of the free motion of a multi-cable pendulum to which the body under consideration is connected. The motion of the pendulum and the forces acting on the system are recorded and the inertia properties are identified by means of a proper mathematical procedure based on a least square estimation. After the body is positioned on the test rig, the full identification procedure takes less than 10min. The natural frequencies of the pendulum and the accelerations involved are quite low, making this method suitable for many practical applications. In this paper, the proposed method is described and two test rigs are presented: the first is developed for bodies up to 3500kg and the second for bodies up to 400kg. A validation of the measurement method is performed with satisfactory results. The test rig holds a third part quality certificate according to an ISO 9001 standard and could be scaled up to measure the inertia properties of huge bodies, such as trucks, airplanes or even ships. [Copyright &y& Elsevier]

A feasibility study on a short fibre reinforced Polymer Metal Hybrid (PMH) solution of a car's suspension control arm has been conducted through a simplified demonstrator, representative of the most critical portion of this component. It was injection moulded in two versions: an all composite one and a PMH version, in which the short fibre reinforced composite was over-moulded on to an aluminium insert. The demonstrator underwent quasi-static, creep and impact tests to simulate most of the loading conditions experienced by a suspension arm during its lifetime. The mechanical behaviours of the two demonstrator versions were compared to highlight the differences introduced by the proposed novel PMH solution. In particular, the ductile metal insert ensured the compliance of the PMH demonstrators with the automotive specific safety requirement of avoiding the complete separation at failure, which was successfully obtained in all testing conditions. [ABSTRACT FROM AUTHOR]

An innovative six axis load cell is presented and employed for frontal impact tests on a Hybrid III 50th percentile dummy. The new six axis load cell, designed at Politecnico di Milano (Technical University of Milan), is a quasi-statically determined structure consisting of a central three spoke element fixed to an external frame by means of special joints appositely designed to minimize friction. A specifically designed electronic board is embedded in the load cell and allows real-time signal processing. The developed load cell has been employed during frontal impact tests on a Hybrid III dummy. An impact force is applied to the dummy’s head by means of an impact pendulum. The accelerations in two different points of the dummy’s head as well the impact force have been measured. A simple 1 DOF analytical model of the head and neck has been developed. Neck stiffness and damping have been identified directly from experimental data. [ABSTRACT FROM AUTHOR]

The Fritz John conditions for Pareto-optimality have been set in matrix form and used for introducing a procedure for the analytical derivation of the Pareto-optimal set in the design variables domain. Subsequently, the derivation of the Pareto-optimal set in the objective functions domain can be obtained, if possible, by a proper analytical derivation. Both the objective and constraint functions are assumed to be available in analytical form and twice differentiable and convex (or pseudo-convex). The proposed procedure to find the Pareto-optimal set is relatively simple. The computation of the determinant of a matrix is required. A symbolic manipulator can be exploited. If there are two design variables and two objective functions, the Pareto-optimal set can be easily computed by applying a simple formula derived in the paper. If the number of design variables equals the number of objective functions, the Pareto-optimal set in the design variables domain can be found by computing the product of the constraint functions times the determinant of the Jacobian of the objective functions. A number of case studies have been proposed to test the effectiveness of the proposed procedure. The optimal structural design of, respectively, a pair of compressed spheres, a cantilever with rectangular cross section have been faced and solved. Additionally the test problem proposed by Fonseca and Fleming has been addressed and solved analytically. Optimization problems with low dimensionality (2 or 3 design variables and 2 objective functions, 2 or more constraints) have been easily solved. The proposed procedure can be useful in the actual engineering practice at the earliest design stage. In this case the designer can be made aware on the proper design variables setting to obtain the desired tradeoff among conflicting objective functions. [ABSTRACT FROM AUTHOR]

In this paper the design, the accuracy assessment and the calibration procedure of an innovative six axis load cell are presented. The load cell is able to measure the three forces and three moments and has been designed at the Politecnico di Milano (Technical University of Milan) as a result of 10 years of research in this field. The sensing structural element of the six-axis load cell is a three spoke structure constrained to the frame of the load cell by means of special joints conceived to avoid friction. Strain gauges are conveniently located on highly stressed areas. Mathematical models, both analytical and numerical, are implemented and presented in order to describe the behaviour of the load cell, to optimize its parameters and to theoretically assess its accuracy. A special device has been designed and constructed in order to accurately and quickly calibrate the load cell. Particular attention has been devoted to the processing of the strain gauges signals. An electronic DSP board, located inside the load cell, has been realized able to compute the six components of the generalized force from the strain gauge signals and return six voltage signals proportional to the measured forces. Software selectable filters and gains are implemented on the DSP board. [ABSTRACT FROM AUTHOR]