MECHANICAL PROPERTIES MEASUREMENT

Author: BRIS CABRERA JORGE LUIS.
Year: 2006.
University: POLITÉCNICA DE CATALUÑA.
Place of defense: ETSEIB.
Place of preparation: ETSEIB, PAVELLÓ E PORTA 19-31 SD.

Summary: In recent years, manufacturing of sintered components has shown an important growth. Competitiveness of powder metallurgy demands to produce higher performance components at low costs. Reducing internal porosity is a well known method to improve the mechanical properties of sintered steels. In this doctoral thesis, the mechanical behaviour of a high-density sintered steel (Fe-4,0Ni-1,5Cu-0,5Mo-0,5C) is studied. Several processing routes have been used in order to attain different density levels (from 7,2 to 7,5 g/cm3), including: cold compaction, warm compaction, single and double pressing, sintering at low- and high-temperatures, and secondary operations. The results achieved shows that density of a PM part can be controlled by processing conditions. Highest density levels are obtained combining warm compaction with double pressing-double sintering. The mechanical properties evaluated increased linearly with sintered density, regardless of the processing route followed for achieving a given density level. This correlation can be rationalized taking into account that the mechanical resistance in PM steels is influenced not only by the reduction in load-bearing area produced by the presence of pores, but also by stress concentration and localized plastic deformation at sintering necks. In this context, it is found that smaller and rounder pores and larger pore-spacing improve the mechanical performance. The localized plastic deformation observed on the fracture surfaces of the materials investigated explain the positive correlation between yield stress and fracture toughness; opposite to the relationship exhibited by wrought materials. This performance may be highlighted as a structural advantage once the accompanying improvement in tensile properties by density is accounted. The study of the mechanical behaviour under cyclic loading allows to state that fatigue failure starts with nucleation of microcracks at larger and more irregular pores, where stress concentration is higher. Then, localized plastic deformation promotes propagation of such microcracks through microstructural interfaces. The heterogeneity of the microstructure, resulting from concentration gradients of the alloying elements after sintering, induces continuous changes along the crack growth trajectory, which represents an important issue for fatigue resistance enhancement of the PM steels here investigated. Fatigue crack growth rate increases with porosity while the threshold for propagation of long cracks remains almost constant along the density range evaluated. However, crack extension has been observed even in cracks smaller than the critical size calculated by threshold long-crack growth data. Consequently, it is concluded that any calculations based on growth data under fatigue for long cracks have low reliability. Finally, the study of the fatigue behaviour indicates that notch sensitivity in PM steels does not change with density and their value is significantly lower than the one exhibited by wrought materials with similar tensile properties. From a mechanical viewpoint, this behaviour is highly beneficial for optimizing the design of high-density PM components intended to be used under fatigue loading.

Author: TSANTINI EVANTHIA.
Year: 2006.
University: BARCELONA.
Place of defense: FACULTAD DE HISTORIA I GEOGRAFÍA.
Place of preparation: UNVIERSITAT DE BARCELONA.

Summary: Our doctoral thesis aims to tackle the study profunditat of them Iberian amphorae from several sites located primarily in the area Ne coast of the Iberian peninsula, from the application of techniques arqueométricas, identifying the reference groups and units reference compositional pasta. Additionally, studies of source, the project is also designed to explore the technological characteristics and mechanical properties of these packages. Our work focuses primarily on the study of amphorae dating Iberian environment centuries IV-II AC and from the area today serial coastline and pre-litoral area Catalan (Laietánia and Cosetánia), in some locations off the Ribera d'Ebre, Alt Emporá and Osona of them Balearic Islands, and some parts of the northern coast of the country valenciá (Edetania and Contestania). To do the job arqueométrioc properly and be able to obtain information on the possible origin and dissemination of these containers have included in the study material from different types of deposits: possible manufacturing centers and potential host schools. Specifically, the sites selected for the area layetana include the necropolis of turó dels two pins (cabrera Mar, Barcelona), can Bartomeu (Cabrerade Mar, Barcelona), abogador sight cheerful (Mataró), the furnace of the Iberian riera de sant simó (Mataró), and the village of Iberian puig castellar (Sta. Coloma de Gramenet). The area Cosetana is filed by individuals from deposit alorda park (Calafell, Tarragona), hortes lime ponts, which is a workshop Iberian important area penedés. It has also been included in the study for the area cossetana, the field of silos of Iberian Vinya in pau d'or vinya of torelletes and the site's fonts dels iglos or font over pollina. In our view have also been studied amphorae from Castellet in Banyoles (Tivissa) Camp of them Llloses (Tona), the Balearic Islands (Trepucó, Menorca) and Sa Punta des Padró (Sta. Margalida, Mallorca) and the price the Binissafúler. In the same way we have included some deposits Iberian country's major Valencian.