Guillaume Racineux

A squeezing experiment showing binder migration in concentrated suspensions

This paper deals with concentrated suspensions (pastes) of TiO2 particles at a solid concentration of 60% per weight in an acidic binder. This paste is used to manufacture petrochemical catalysts. First we show that in a squeezing experiment binder migration occurs in the suspension as long as the velocity at which the test is carried out does not exceed a critical value. Next, we develop a mathematical model of the test and a complete methodology to identify the rheological parameters of this model. We give an analytical expression of the critical velocity, which is related to the physical characteristics of the suspension. The exact identification of the rheological parameters requires the use of a numerical program which was developed for this application.

Friction stir diffusion bonding of dissimilar metals

Abstract This paper reports on a new method based on the friction stir welding process to join dissimilar metals in butt joint configuration. Two different systems were considered: AA1050 H16 aluminium/ASTM A284 steel and AA1050 H16/UNS C12200 H01 copper. The unthreaded steel tool pin was positioned in the aluminium plate so that it was tangential to the opposing metal. Bonding was accompanied by interfacial chemical reactions with no significant mechanical mixing. This new solid state welding process is called friction stir diffusion bonding. Room temperature cross-weld tensile strengths up to 82 MPa were obtained for both metal combinations. Microstructure characterisation suggested that higher joint strengths were associated with thinner, <1 μm thick intermetallic reaction layers at joint interfaces.

Identification and measurement of pastes rheological properties

Sewage sludges exhibit in most cases rheological properties which do not allow us to classify them either as simple fluids or as solids. On one hand, they are not simple fluids because of their non-Newtonian, shear-thinning and time-dependent (thixotropic or rheopectic) behaviour and because of the possibility for some of them of showing a yield stress. On the other hand, they can hardly be considered as solids, mostly because of their high sensitivity to velocity and because they are practically very often pumped as if they were fluids. This intermediate state sometimes referred to as paste state is in fact very common and is extensively studied, from a manufacturing point of view in areas like ceramics, food or polymer processing and from a civil engineering point of view in soil mechanics for the determination of clay rheology. Many experimental tests have already been designed for their characterisation. The aim of this presentation is to compare some of them and try to make a synthesis between the engineering rheology and soil mechanics approaches. For this purpose we show experimental results on the same material with different rheometric devices: viz (i) a tube (or capillary) ROSAND rheometer, (ii) a triaxial soil mechanics cell, (iii) an oscillatory, stress driven, plane and plane STRESSTECH rheometer, and (iv) a specific squeezing device which has been designed here following an idea introduced by Laun for polymers. The triaxial cell and the plane and plane rheometers are similar in the sense that they are supposed to allow for an homogeneous state of stress and strain (or rate of strain). In contrast, the tube or squeezing test does not allow for a homogeneous mechanical state. This means that the first two tests enable a real measure of the constitutive relation but in limited conditions while the two others provide a way to identify rheological parameters in flow conditions which are close to the process conditions. The main originalities of this presentation are (i) the balanced point of view between the fluid and the solid mechanics approach and (ii) the method by which the contact properties of the paste is measured with the tube and the squeezing rheometer, giving evidence of a water migration inside the paste.

On the Forming of Metallic Parts through Electromagnetic and Electrohydraulic Processing

Forming of metallic parts by the application of high intensity transitory magnetic pulses or shock waves is a challenge task from industrial perspectives as this offers extended scope of forming highly precise parts that result from material behavior at high deformation rates. Electromagnetic forming requires that the part must be intrinsically very conducting. The electrohydraulic forming is exempt from this material constraint as the deformation is generated by a shock wave in a fluid through electric discharge in between the electrodes. The application of a static pressure during forming is used to reduce the discharge energy for a given deformation. Work has been conducted to form different parts through these two techniques involving aluminum, copper and steels. The paper presents the technical obstacles still facing the electromagnetic techniques and gives examples of formed parts and joints in relation with microstructures.

Dissimilar Welding Using Spot Magnetic Pulse Welding

Magnetic Pulse Welding (MPW) is a solid state joining technique which have increased development in the past few years due to the industrial need in joining dissimilar materials and difficult-to-weld ones. It is an impact welding technique, such as explosive welding (EXW) and laser impact welding (LIW), which share the same basic joining principle, impact-driven solid state welding, but applied to different scales: EXW for larger parts and LIW for smaller. Defined as a fast, reliable and cost-effective technique, MPW struggles with the lack of knowledge about the welding process despite of the extensive existing literature. The work conducted aimed at joining Al to steel in spot welding configuration widely used in automotive industry. Welds were characterized in order to understand and improve the process.

Measurement and Comparison of Force Effort During Friction Stir Welding in a Parallel Kinematic 5-Axis Milling Machine

Friction stir welding (FSW) is so quite promising that leads it to one of the preferred joining process for a wide range of applications especially for Aluminum. FSW machines are very expensive. The objective is to develop a simple and low cost technique to measure and control the force during FSW in a milling machine. Measurement of forces during welding is a difficult task. Many dynamic measuring devices such as dynamometers are available but each have their own advantages and disadvantages. A new approach to measure force while performing weld is discussed. First, incorporation of FSW in PKM 5-axes milling machine is done. The head of the machine is modified to support higher force levels that are generated during FSW. With the help of the NC-Controller, the force values are retrieved from the axes of the machine while performing weld through actuators. Forces were also measured from load cell and compared to estimate the quality of measurement.Copyright