Metal-Ceramic Composites

Research focus

The Peer review has evaluated this group as Good

This research topic concerns metal-ceramic composites for applications in automotive (brake systems) and aerospace engineering (thermal barrier coatings), energy production (turbines, fuel cells), bioengineering (dental and orthopaedic implants), micromechanics (MEMS, magnetic recording media), precision-cutting tools and so on. The focus is on constitutive modelling of these materials coupled in a variety of modes (coating layers, particle inclusions, interpenetrating network structures, functionally graded distribution, and so on); on their mechanical characterisation via ad-hoc designed experimental tests and parameter identification by deterministic and stochastic techniques; on the simulation of their failure mode, including fracture processes by finite element methods. Part of this research has been fostered by the participation in the inter-disciplinary European Network of Excellence on “Knowledge-based Multi-component Materials for Durable and Safe Performance” (KMM-NoE), which concerns processing, characterisation, experimental mechanics, modelling, simulation and industrial applications of intermetallics, metal-ceramic composites, functionally graded materials. This Network is organising itself into the legally registered European Association named “Virtual Institute on Knowledge-based Multifunctional Materials” (KMM-VIN) intended to promote long-lasting interactions among the Partners, as well as research, building of confidence, development of quality assurance and traceability, implementation of standards and growth of competitiveness at the European level in the field. This research work has been further supported by some PRIN projects co-financed by the Italian Ministry for University and Research (MIUR). Some of the investigated topics can be summarised as follows. Homogenization techniques have been employed to predict the global response up to failure of Metal-Matrix Composites by the use of plasticity theory in conjunction with homogenization theory for periodic media. In this context the macroscopic shakedown domain of unidirectional metal matrix composites has been determined solving a mathematical programming problem defined over a representative volume. The predicted material shakedown domain in the macroscopic stress space was compared to the relevant macroscopic plastic collapse domain and a significant reduction was observed. The optimal design of macroscopically anisotropic solids, such as composites reinforced by different arrays of fibers, was dealt with for several classes of material symmetry (cubic, hexagonal-5, tetragonal-6, orthorhombic). Topology optimization for micropolar solids, such as advanced materials endowed with a microstructure or biological materials, was also dealt with. In particular, a qualitative match between optimal material configurations and microstructure geometry in living tissues was pointed out. Peculiar issues in this research topic are the determination of the local and overall material properties and of the residual stress fields which result from the production processes and their evolution during the lifetime of industrial components. The calibration of local constitutive models through measurements at the macroscale was performed in some situations. The instrumented indentation test, performed at different scales, has been selected as the privileged experimental setup in this framework for several reasons: at the micro-scale, it permits the material properties to be sampled locally; recourse to more traditional techniques is forbidden in many situations, e.g. due to the component dimensions (coating layer thickness); and it is of non destructive nature at the macro-scale. Information relevant to the geometry of the residual imprint has been systematically exploited together with the indentation curves (force exerted on the indenter tip versus its penetration into the material sample) to identify material parameters in a higher number and in a 38 more robust manner. Recourse to inverse analysis techniques is clearly required to extract material parameters from these experimental information sources. Research efforts have been devoted to the interpretation and numerical simulation of fracture in FGMs, where gradual variation of the mechanical properties, unlike the abrupt change encountered in layered materials, is known to improve failure performance. The extended finite element method together with a proper graded element formulation has been developed and applied in this context.

Departments

Dipartimento di Ingegneria Strutturale (DIS)

Professors

Full Professors
Claudia Comi
Alberto Taliercio
Associate Professors
Gabriella Bolzon
Giuseppe Cocchetti
Assistant Professors
Massimiliano Bocciarelli
Valter Carvelli
Roberto Fedele
Stefano Mariani