Funding body: National Science Centre (NCN)
Start date: 3 Aug. 2015; duration 36 months
NCN (OPUS 8) contribution: 1 043 300 PLN
Research objectives/ hypotheses
The primary scientific objective of this project is to investigate in a comprehensive and systematic manner through a carefully designed experimental programme and microstructure-based numerical modelling the effects of processing-induced thermal residual stresses on the fracture behavior and selected mechanical properties of metal-ceramic composites (sintered or infiltrated). The scientific problem to be tackled is the interplay between the microstructure, thermal residual stresses and fracture behavior of metal-ceramic bulk composites for a wide spectrum of material microstructures including metal-matrix composites (MMC) and ceramic matrices reinforced with metal particles (CERMETS). Interpenetrating phase composites (IPC) will be included in this research for comparison with the MMC and CERMETS to provide more evidence for validation of research hypotheses.
Research hypotheses of the project can be expressed as follows: (i) thermal residual stresses have a significant effect on the fracture toughness of metal-ceramic composites, (ii) material microstructure strongly affects the TRS field and can alter the crack toughening mechanism and type of final failure, (iii) by research-based design of the composite microstructure one can reduce the level of processing-induced TRS and obtain materials with better fracture characteristics and other mechanical properties. A necessary pre-requisite for that is the proposed exploratory research programme consisting of a fully controlled material processing phase, materials characterization and computational modelling aimed at a better understanding of the origins and the effects caused by TRS on the integrity and load bearing capacity of the composite materials under investigation.
Research methodology
The project objectives require an interdisciplinary research team with complementary expertise and skills in the following fields: (i) material science and engineering, with particular focus on metal-ceramic composites and powder metallurgy and experimental techniques for microstructure characterisation, mechanical testing including fracture parameters and residual stresses measurements; (ii) mechanics of materials, especially modelling of thermal stresses, effective properties, damage and fracture processes, (iii) numerical methods, i.e. FEM. A highlight of the research methodology adopted in this project is its complementarity in tackling the problem of the TRS influence on the fracture behaviour of composites, comprising materials processing, characterisation of microstructure, testing of mechanical properties and modelling of TRS and fracture. Composite samples will be scanned by micro-CT to provide a basis for FE mesh development; TRS will be measured by neutron diffraction. The fracture behaviour will be determined experimentally in three point bending and Compact Tension tests and will be used in the assessment of the effect of TRS on the fracture behaviour. In parallel to experimental testing, numerical models using micro-CT based FE meshes will be developed for fracture toughness with account of TRS and stresses from crack toughening mechanisms (e.g. crack bridging). Numerical models will be validated by comparison with the experimental results.
Expected impact
The project will generate a large amount of new knowledge in the field of thermal residual stresses and fracture. The use of micro-computed tomography to precisely mimic the complex microstructure to be used as a mesh for FEM modelling of TRS and its effect on the fracture toughness and toughening mechanism falls within the mainstream of research directions in multi-component materials.
The project will have an economic and social impact in this sense that it will contribute to a better understanding of the detrimental effect on TRS on the mechanical properties and fracture behaviour of an important class of structural and functional materials. The conclusions will help design metal-ceramic composites with lower TRS levels and less susceptible to TRS induced fracture. Development of more reliable materials with enhanced properties has a clear economic aspect as metal-ceramic composites are used in many industry sectors such as automotive and aerospace transport, energy and electronics. Improved or new materials are associated with new jobs for people producing them or transforming them into products, which can be seen as a social aspect of the materials development.