Thierry Cutard

Pullout of metallic fibres from a ceramic refractory matrix

The extraction behaviour of stainless steel fibres from a ceramic refractory matrix has been studied by way of pullout tests and scanning electron microscopy observations. The effect of first heating of such composites has been characterised both by room temperature pullout tests and by dilatometric experiments. High temperature pullout tests have been performed too. Mechanical and microstructural evolutions are discussed with the help of analytical models.

Numerical simulation of failure prediction for ceramic tools: comparison with forging test results

A fracture prediction criterion for brittle materials has been introduced in the POLLUX finite-element code in order to predict the risk-of-rupture of ceramic tools during a forging operation. POLLUX is a software dedicated to the simulation of forging operations, initially developed by INSA (Lyon). The chosen probabilistic fracture model is based on the weakest-link theory and the statistical theory of Weibull. A surface approach or a volume approach can be retained on the basis of the type of critical flaws in the ceramic. Two different criteria are available in order to characterise the stress state, considering the tensile normal stresses and neglecting the compressive stresses. An identification procedure of the critical flaw type is presented for a particular ceramic material. Statistical parameters of ceramic fracture have been determined experimentally using bending tests performed under environmental conditions close to those of forging. A constitutive equation of the workpiece material has been proposed, issued from torsion tests. In order to validate the model in the case of ceramic tools subjected to multi-axial stress states, a particular configuration has been defined to compare the simulation predictions with the experimental results. A forging test has then been developed, in which a billet of superalloy is formed in a ceramic tool up to its fracture at the temperature of 1423 K. The experimental distribution of tool fracture, according to the strain of the billet, is in good agreement with fracture predictions computed by the simulation.

Processes and equipment for superplastic forming of metals

The industrial use of materials with superplastic behaviour has required the development of dedicated processes, including all the related tooling equipment. This chapter first describes the various superplastic sheet-forming processes. Then the industrial equipment is detailed along with the technological options that may be used for heating platens. Special focus is given to tools and dies, either metallic, ceramic or refractory concrete-based: their material grades and properties are discussed, as are the methods used for modelling them. Finally, emerging processes are identified.

Modelling of the Swelling of SiC-Based Refractory Lining Used in Waste-to-Energy Plants

This work provides a computational model of the chemo-mechanical behavior of based refractories used in waste to energy plant (WTE) linings. In this application, oxygen gas present in the atmosphere diffuses through the porosity and reacts with the refractory producing silica (SiO2). This new phase clogs gradually the pores and causes swelling of the refractory lining. The proposed thermo-chemo-mechanical model which simulates these phenomena is briefly summarized. The results obtained from the model implemented in a F.E code prove the ability of the model to reproduce qualitatively the swelling of post-mortem bricks taken from WTE linings.Copyright