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Emmanuel Cailleux (V.2)
Abstract
Development of tools for the superplastic forming of titanium
Emmanuel Cailleux - 11 may 2001.
Compared to metallic materials, refractory concretes used as superplastic forming moulds present some attractive advantages such as a lower material cost and the possible direct casting of the mould to final dimensions. Nevertheless, their brittle behaviour often leads to catastrophic failure of the mould caused by handling and thermal shocks during operating service. The metallic fibers reinforcement which greatly improves the energy absorption capacity of the concrete is a solution to solve this problem. The aim of this study was to optimize the thermomecanical behaviour of a refractory concrete reinforced by metallic fibers in the 20°C-1000°C temperature range.
In a first step, the structural transformations of the concrete during the first heating have been identified. They conduct to the determination of a stabilisation heat treatment which takes into account a sintering mechanism and the presence of a liquid phase.
In a second step, the study presents a thermomechanical model used to optimize the fiber efficiency on a microscopical level and to optimize the distribution of the fiber orientations on a macroscopic level. With this aim, a micromechanical model was developed and is based on the strength of materials theory. This model includes the elementary pullout mechanisms which are the debonding, the bending of the fiber and the spalling effect. These mechanisms were investigated through an experimental program including the study of the thermal heat treatment, the test temperature and the fiber orientation. A macromechanical model was developed too. This model is based on the micromechanical one and on the experimental distribution of the fiber orientations quantified by a stereovision technique. The model prediction present a good agreement with the experimental tension softening curves obtained by a high temperature tensile test. A parametric study was then performed to quantify the effect of the material properties and of the distribution of the fibers.
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