Understanding spherical and sharp microindentations. A reassessment of the contact regimes and mechanical property extractions
- Autores: Daniel Esqué de los Ojos
- Directores de la Tesis: Jorge Alcalá Cabrelles (dir. tes.), María del Carmen Miguel López (codir. tes.)
- Lectura: En la Universitat de Barcelona ( España ) en 2010
- Idioma: español
- Tribunal Calificador de la Tesis: Kubin Ladislas Perre (presid.), Joan Esteve Pujol (secret.), Jan Oiênasek (voc.)
- Materias:
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- Resumen
This thesis is classified into two main parts. First, a new mechanistic understanding into spherical indentation experiments in strain hardening solids is developed.
Extensive finite element simulations provide a general conception about the origin of fully-plastic and elasto-plastic indentation regimes. With this knowledge, a general relation is found for the first time to correlate hardness with the uniaxial stress strain characteristics of the material, enabling the extraction of mechanical properties. The presently found relation thus extends the seminal work by Tabor to any strain hardening solid irrespective/y of the active contact regime. Detailed comparison between the spherical and sharp indentation behaviors allows us to test the present analysis, thus providing a self-consistent view into the indentation behavior of solids that was unavailable in the open literature. Mechanical property extractions are then demonstrated in archetypal metallic polycrystalline aggregates, where such experimental results also provide an insight into the accuracy of the assumed plasticity theory.
The second part concerns extension of the above rationale into the understanding of spherical indentation experiments performed in single crystalline units of material. In this context, systematic finite element simulations are performed by recourse to continuum crystal plasticity theory. The concept of the e|astop|astic and fully plastic single-crystal indentation regimes then emerges in light of the above knowledge gained for polycrystalline aggregates. A fundamental concept introduced in the thesis is the single-crystal representative stressstrain curve. This allows extraction of the uniaxial stressstrain relation of the indented crystal along a specific set of crystallographic orientations. A discussion is then given on the role of crystalline anisotropy and of the hardening behavior upon the indentation-induced plastic zone shape developing in the material. The thesis ends with detailed continuum crystal plasticity simulations performed for the conventionally employed pyramidal indenter shapes in instrumented micro/nano indentation experiments. Along these lines, the concept of the extraction of homogenized mechanical properties from sharp single crystal indentation is discussed, making contact with the above analysis made for sing|e crysta| spherical indentations.
