Tesis doctoral de Ovidi Casals Boixados
Advanced mechanical applications and structural integrity assessments rely on advanced tools to probe local mechanical properties. Inthis context, indentation techniques constitute an appealing alternative tool to conventional uniaxial tests for the assessment of fundamental properties that are crucial for mechanical design. Significant research efforts are directed to determine the viability of new methodologies to evaluate mechanical properties from contact parameters measured in hardness tests and more advanced instrumented indentation techniques. With the enhancement of computational capabilities, it is also possible to conduct extensive 3-d simulations of pyramidal indentation experiments. Finite element simulations provide amethod for virtual material testing, where prior dimensional analysis illustrate the dependency between indentation parameters and mechanical properties. The combination of dimensional analysis and simulations give a detailed mathematical description to the indentation experiment which is required for the development of methodologies for mechanical property evaluations. some of these methodologies have shown to be useful in the characterization of the elastic behavior of materials. Assessment of elasto-plastic mechanical properties has also been addressed by different authors prior or during the course of this investigation. In spite of this, application of the aforementioned methods is still limited by their accuracy and actual range of validity. The lack of accuracy may be related to the precision of the mathematical formulations describing the indentation experiments, as well as to the convenience of the constitutive model selected for computational analysis at a given indentation length scale. In this regard, indentation experiments performed at different loads provide information on the various deformation phenomena occurring at the different material length scales ranked during the indentation experiment. All these factors strongly condition the interpretation of experimental results, which are thus extremely sensitive to the development of so-called indentation size effects. the present dissertation concerns the indentation of metallic polycrystalline aggregates and single crystals through continuum mechanics theories. efforts are first directed to the development of a new methodology for mechanical property extractions from instrumented indentation techniques in imprints made at sufficiently large loads, which encompass a representative number of grains. The work is predicated on comprehensive dimensional analysis and extensive finite element simulations of pyramidal (vickers and berkovich) and conical indentation of strain hardening solids. Theresulting intrinsic duality of mechanical property extractions from instrumented indentation experiments is related to the lack of measurement of the amount of pileup or sinking-in, which cannot be fully compensated through further analysis of the p-hs curve. This work also shows that qualitative observations on whether bulging or pincushion effects occur around the imprint are sufficient to establish which of the two potential sets of inferred properties corresponds to the indented material. the second part of this thesis is devoted to the analysis of experiments performed at the micro-indentation range. An effort is herein made to use crystal plasticity models to understand pyramidal indentation experiments made within single crystals. Issues under examination are the physical consistency of the continuum crystal plasticity theories in the modeling of indentation experiments, and the influence of crystal slip anisotropy and of prior straining on the dislocation density patterns underneath sharp indenters.. Agreement between experiments and simulations is predicated in terms of hardness, instrumented indentation applied load (p)-penetration depth (hs) curves, and material pileup and sinking-in development at the contact boundary.
Datos académicos de la tesis doctoral «Micromechanical analysis of indentation experiments in metallic single crystals and isotropic polycrystals«
- Título de la tesis: Micromechanical analysis of indentation experiments in metallic single crystals and isotropic polycrystals
- Autor: Ovidi Casals Boixados
- Universidad: Politécnica de catalunya
- Fecha de lectura de la tesis: 13/07/2009
Dirección y tribunal
- Director de la tesis
- Jorge Alcalá Cabrelles
- Tribunal
- Presidente del tribunal: enrique Fernández aguado
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