A. Risitano

Rapid determination of the fatigue curve by the thermographic method

Abstract The available methods for the rapid determination of the fatigue limit (Metall. Ital. 27 (1935) 188; Rev. Metall. XVIII (1951) 11) and for the analysis of the dynamic parameters of crack mechanics (ASTM-STP 519, 246; J. Mater. 5 (1970) 4; J. Appl. Mech. 67 (1945) A159; Exp. Mech. 5 (1965) 193; Fatigue Engng Mater. Struct. 1 (1979) 37; J. Basic Eng. Trans. ASME, Ser. D 85 (1963) 528) require the determination of parameters which are highly specialised (KI, J-integral) and often too closely linked to the micro-mechanics of the material, downgrading the engineering aspects of the problem and its design definition. Following their research into the use of the thermographic method to determine the dynamic properties of materials and components commonly used in the industrial sector (hereafter called the Risitano method [Int. J. Fatigue Mater. Struct. Components 22/1 (1999) 65]), the authors now present a procedure for the definition of the whole fatigue curve.

Indicators for environmentally conscious product design

The aim of the present study was to develop effective instruments which permit the choice of materials and architecture of an industrial product to be optimized, while conferring a high degree of eco-compatibility on the products life cycle by means of different types of recycling at the end of its operating life. Having introduced the principles of life cycle analysis and outlined a design methodology which uses this instrument it was possible to analytically define some green indicators considered particularly significant. Dependent on the recovery plan envisaged at the end of the products life, these indicators are able to quantify, the energy and emission content of the product as a function of the main design choices (materials and architecture). The indicators defined allow the architecture and the choice of materials to be optimized during the design phase, guaranteeing both a limited environmental impact for the products entire life cycle and the recovery of resources by means of an efficient plan for recycling parts and materials at the end of the products life.

Development of an algorithm for the analysis of surface defects in mechanical elements

The non-destructive tests allow to establish the physical and structural conditions of a mechanical part, to verify its condition, the superficial wear and tear and then evaluate its `remaining efficiency. The non-destructive tests are applied in all those fields of engineering in which the determination of the mechanical and structural characteristics of elements in use is requested, without making them undergo destructive or damaging tests. In the present work an application program has been developed which, examining the surface of mechanical parts under an optical microscope and a blaster video, is able to characterize the material and to recognize and identify the possible presence of a superficial crack. The program constitutes the first step towards the realization of an industrial prototype which, thanks to the utilization of a plan moved by step-by-step motors, allowing the scanning of the whole surface of a part and the recognition of the crack in an automatic way, that is without the presence of an operator, and its characterization, in case it is identified, through the determination of some geometric parameters useful to ascertain the structural integrity of the element under examination. For the realization of the program different techniques of image analysis have been applied and the use of an artificial neural network preset for the recognition of the crack has been necessary. The program has been realized in C language and it works in Linux system.

Product Recovery-Cycles Design

This paper reports the development of a tool to aid designers in making the best choices in order to plan recovery cycles for a product at the end of its working life. Having outlined an effective design methodology for this purpose, a calculation model was developed to support the methodology. The model was based on the quantification of determining factors, allowing the definition of the reusable parts of the architecture and the evaluation of the values assumed by an indicator which translates the environmental effects of recovery cycles in terms of extension of the product’s useful life. A trial conducted on a commonly used industrial unit, a heat exchanger, demonstrated the value of the design tool in comparing different architectures of a product and their optimisation, confirming its effectiveness as calculation model for the environmental quality-oriented product design.

A soft-computing robotic shift for a hybrid vehicle

In the present paper we present a control system of robotic shift in hybrid vehicles that utilizes fussy logic as well as optimization techniques (genetic algorithms) aimed at improving, with the automatic choice of the shifting, the objective-functions previously chosen (minimum consumption, suitable dynamic performances). Following the working out of a model in Simulink environment, which is suitable for the simulation of the behavior of a hybrid vehicle equipped with different shifts (manual, robotic, robotic fussy-logic) we carried out tests in a virtual lab and compared the results with those obtained with models previously built by others (CRF) that had been validated on real vehicles. The results of the simulations have shown, on the one hand, the validity of the robotic shift relative to the manual shift, and, on the other hand, the effectiveness of the application of soft-computing for the development of the robotic shift relative to a vehicle equipped with a traditional robotic shift, in which the logic of shifting is managed by static maps

Numerical evaluation of a material-independent necking shape factor

The best degree of approximation for the determination of a ductile material hardening curve today is represented by the Bridgman method. This procedure requires measurements of the necking curvature radius other than the load and the neck diameter, and in literature it is usually carried out without dealing with the increasing porosity of the material. The obtained curve is approximate because refers to values of the equivalent stress and strain averaged onto the entire neck section and, when it is evaluated without any void measurement, because of the difference between the apparent and the effective resisting cross section. Furthermore, it has been shown that the response of this method is strongly dependent on the initial specimen shape, showing a certain lack of precision in the triaxiality estimation, In this work a new method for the evaluation of the flow stress-equivalent plastic strain curve has been used, adopting some of the hypotheses flom the Bridgrnan theory, but eliminating the need of curvature radii measurements. “ The relationships found between some variables characteristic of the plastic behavior are almost independent from the materials except for their Consider& strain, and the derived characterization method proposed is also independent of the initial specimen shape.

A cellular neural networks approach for non-destructive control of mechanical parts

An approach is proposed using cellular neural networks applied image processing, for the detection and characterisation of superficial faults in mechanical parts. There are above all two advantages deriving from an application of the proposed methodologies: the automization of a procedure, that of non-destructive tests (NDT), which is today carried out manually, and the possibility to reduce to a negligible amount the time spent on checking operations at present estimated to be in the order of a number of hours for each separate mechanical part.