Tesis doctoral de Clara Beatriz Picallo González
Understanding how materials deform and break is a subject of critical importance in industry. At the same time, it requires from the knowledge of the basic processes governing the phenomenon and hence, fundamental physics research is a must. Many subjects get straightforward benefits from the advances in fracture and deformation mechanics. For instance, nanomaterials are of crucial importance for new developing technologies and hence the knowledge of how size affects their behavior is essential for the good performance at those scales. It has been observed in many materials and experimental setups that small size samples exhibit surprisingly higher strengths than macroscopic samples of the same material. The design of new materials í la carte relies on the knowledge of how temperature, chemical composition, microstructure, etc., Affect the mechanical response of the material. the presence of power law distributions in both temporal and spatial properties and the universality of the behavior seem to suggest that fracture and plasticity could be explained as some type of critical phenomena. This means that there should be some general principles that rule the process and that are more important than a detailed description of the interactions and atomic structure of the media. Hence, simplified theoretical approaches based on fundamental concepts can help to capture the essential ingredients in the system. In this sense, tools coming from statistical mechanics can help to deal with disorder, long range interactions and scaling laws. In the last decade several steps have been given in this direction and, to this aim, some simplified models have been developed and studied. This thesis is devoted to the study of the deformation and failure of materials in the presence of disorder with the help of statistical mechanics tools and models. the outline of this thesis is as follows. Chapter 2 serves as a brief review of solid mechanics and the different approaches to modeling the response of materials. We focus on the statistical physics approach to the problem, describing the models and the insight gained from this perspective. We give special attention to the random fuse model (rfm) a simple scalar model based on the formal analogy of electrical and mechanical equations that has become the cornerstone of lattice models for fracture and will be used throughout this thesis. in chapter 3 we numerically study the brittle fracture of materials by means of the acoustic emission produced during the load of an amorphous medium simulated with the rfm. Acoustic emission is a typical experimental tool for monitoring damage in materials. After introducing the subject of crackling noise in section 3.1, in section 3.2 we study the differences between several energy estimators and derive scaling relations that account for their statistical behavior. We also study the temporal evolution of the energy dissipation in the search for traces of the proximity of final failure. Finally, the consequences of relaxing the quasistatic loading condition to mimic dynamic fracture are also studied. chapter 4 deals with elastic-perfectly plastic behavior. A brief introduction to the basic concepts is found in 4.1 where the elastic-perfectly plastic version of the rfm is presented as well as the conjectured equivalence of this problem to the classic topic of directed polymers and minimum energy surfaces. In section 4.2 we numerically and theoretically revise the relation between minimum energy surfaces and the yield surfaces produced with an elastic perfectly plastic rfm. chapter 5 begins with a description of the experimental findings and existing numerical models of plasticity in section 5.1. In section 5.2 we introduce a lattice model for ductile fracture based on the rfm but able to account for both brittle and ductile behavior. In section 5.3 we study the transition from brittleness to ductility as plastic deformation is accumulated prior to fracture. Ductile fracture surfaces are compared to minimum energy surfaces and crack surfaces resulting from brittle fracture. The burst avalanches are also studied and compared with the current theoretical and experimental understanding.
Datos académicos de la tesis doctoral «A mesoscopic study of plasticity and fracture in disordered materials«
- Título de la tesis: A mesoscopic study of plasticity and fracture in disordered materials
- Autor: Clara Beatriz Picallo González
- Universidad: Cantabria
- Fecha de lectura de la tesis: 20/12/2010
Dirección y tribunal
- Director de la tesis
- Juan Manuel López Martín
- Tribunal
- Presidente del tribunal: luís Pesquera gonzález
- horacio sergio Wio beitelmajer (vocal)
- mario Castro ponce (vocal)
- ángel Garcimartín montero (vocal)