Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

CAE methodology for the design of new materials

A complete CAE methodology for the design of ceramic and intermetallic structural components was developed, mainly targeting light weight valves, with the prevision of the operative life according to the real loadings and to the specific thermo mechanical materials properties of the materials.

On the basis of the specific materials properties (measured on hypereutectic aluminium alloys for intake valves, gamma-TiAl intermetallics and Si3N4 ceramics for exhaust ones), the valves? design optimisation by means of Finite Element Modelling and appropriate simulation, based on the statistic failure prediction according the up to date methodologies for brittle materials, was accomplished.

The development of low cost, reliable and light weight valves with innovative, less ductile materials required the integration of various disciplines, from materials sciences to mechanical engineering. Fundamental research on the advanced light weight materials considered in the Project and the basic system requirements have been considered as starting points. Then the peculiar mechanical behaviour of brittle ceramic materials has required the development of a different design procedure than the standard methodologies applied with conventional metallic alloys.

The methodology to overcome this lack of design procedures has been developed: after the selection of the material on the basis of the operating conditions, by means of FEA (Finite element Analysis) simulation tools, the stress distribution within the operating valves and in the contact area between valve and valve seat has been modelled and, as a result, the design is modified in order to possibly reduce the peak stress concentrations and to improve the material utilisation. Then the failure probability for the valves has been calculated taking into account the real mechanical characterisation of the considered brittle material (for example bending tests for silicon nitride) and the calculated stress distribution, utilising the well-established concepts of linear fracture mechanics and of Weibull statistics. After this process is accomplished, the prediction of the operating life of valves can be evaluated using both dynamic and static fatigue of the material: if the calculated results cannot meet the required conditions, then design and/or material have to be opportunely modified.

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