Alexandre Brosse

A numerical study of phase transformation during grinding

Since grinding is often the last process of a manufactured part, caution has to be taken in order to ensure the integrity of the ground surface. Many authors have shown that in a few cases temperature can be very high and therefore can induce phase transformations. Thus, the best way to ensure the quality of the ground surfaces is to predict the apparition of these phases. This paper shows that numerical simulations of phases during grinding are possible and they gives good predictions of phases. An example using AISI 52100 bearing steel material for the workpiece and a triangular heat flux model is presented. The model of simulation is explained and results are detailed.

Emissivity calibration for temperature measurement using infrared thermography in orthogonal cutting of 316L and 100Cr6 grinding

Material removal operations such as turning or grinding are prone to generate very high temperatures at the tool/chip and tool/workpiece interfaces. These phenomena are involved in studies concerning tools or workpieces, and their estimation is a key point for predicting damages. Temperature elevation is the main cause in workpieces worsening because it generates residual stresses and metallurgical modifications. It is also linked to the tools wear because of the thermal fatigue phenomena and the thermally activated diffusion process. In this paper, a first attempt to measure the temperature fields during 316L orthogonal cutting and 100Cr6 grinding is presented and can be divided in three parts. In the first part the physics of temperature measurement using infrared thermography are presented. Then, the calibration of the infrared camera is realized and allows to obtain of the emissivity curves of 316L and 100Cr6 steels. To do so, an experimental device has been set up to reproduce the luminance recording conditions encountered during the machining operations. The last step is the computation of all the experimental data to obtain the temperature fields from the recorded luminance and the 316L and 100Cr6 emissivity curve. At last, temperature level measured is compared to those presented in the bibliography.

Influence of the Metallurgical Transformation Induced by Grinding on the Residual Stresses Computation

Grinding is one of the important metal cutting processes used extensively in the finishing operation to get components of desired shape, size and accuracy. A perfect control of this process is thus necessary to ensure correct final part and limit damage. Lifetime of machined part depends on the surface integrity especially in terms of microstructure changes and residual stresses. The best way to control those factors is to study the way they appear. Thus, it is important to set up experimentation to get the maximum informations during the grinding process, with in situ measurements and after, on the final surface. On one side, forces and power were measured, on the other side temperature measurements were conducted using an infrared digital video camera. In fact the grinding temperature and the temperature gradients are the major factors which influence surface integrity. Experimentations show white layers in the near ground surface and the measured temperature is higher than the austenitizing temperature. The workpiece subsurface was then characterized by observing and measuring microstructural changes of surface layer. Numerical simulations, using SYSWELD software are performed to formalize what is modeled. Metallurgical transformation is then taken into account in the grinding FE model. The comparison showed that numerical model is capable to accurately predict the white layer thickness and residual stresses values.

SIMULATION OF DUCTILE TEARING IN A DISSIMILAR MATERIAL WELD UP TO PIPE WALL BREAK-THROUGH

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Modelling of Ultrasonic Shot Peening

Component manufacturing may induce cold work, residual stresses, microstructure changes and even surface defects. This initial condition is usually ignored in component integrity assessments, but can strongly affect its lifetime. For instance, it is well-known that a rough surface finish associated to the presence of tensile residual stresses may favor fatigue damage. In the same manner, cold work and tensile residual stress will assist initiation of Stress Corrosion Cracking (SCC) for susceptible materials. As the manufacturing process can affect the lifetime of the structure, mitigation treatments such as precompressive loadings, chemical treatments, film deposits or coatings may be applied to sensitive areas. The objectives of these complementary operations are to avoid or compensate negative effects of manufacturing consequences. In the industry surface mechanical treatments such as Ultrasonic Shot Peening (USP) are then used in order to improve surface integrity. Even if these mitigation treatments are well known to increase component lifetime regarding corrosion and fatigue damages, a good understanding of their consequences is required to assess their efficiency and perpetuity under operating conditions. Numerical modelling of USP is one solution to simulate the motion of beads in the peening chamber and to predict the level of stresses in the peened part as shown in this paper. This model which gives a better understanding of the effect on surfaces should help the manufacturers to select the best process parameters.Copyright

Process Optimization of Ultrasonic Shot Peening by Realistic Modeling of Beads Motion

In the nuclear industry surface mechanical treatments are used in order to improve the surface integrity of the component, which increases their lifetime regarding corrosion and fatigue damages. A good understanding of these processes and their consequences is required to ensure the efficiency and perpetuity of such mitigation treatment.This study focuses on the ultrasonic shot peening process. It consists in shooting at high speed small steel beads on the part to be treated by using a high frequency vibration device. Parameters such as the number and the size of beads, the input frequency and the dimensions of the chamber can induce large ranges of impact velocity and coverage. In order to help manufacturers to control the treatment applied on their components, a numerical model has been developed. It accounts for the shocks of the beads against the walls of the chamber, the peening head and between beads, describing their motions accurately.In this paper, we will introduce the numerical model developed to simulate the motions of beads in the peening chamber. Special attention will be taken to the determination of the restitution rates related to the different materials. Results of the model will be shown for different process parameter (e.g. the number of beads), and a thorough analysis of their effects on the workpiece will be presented, including a comparison with some experimental results.Copyright

Chained Welding and Finish Turning Simulations of Austenitic Stainless Steel Components

The chaining of manufacturing processes is a major issue for industrials who want to understand and control the quality of their products in order to ensure their in-service integrity (surface integrity, residual stresses, microstructure, metallurgical changes, distortions,…). Historically, welding and machining are among the most studied processes and dedicated approaches of simulation have been developed to provide reliable and relevant results in a industrial context with safety requirements. As the simulation of these two processes seems to be at an operational level, the virtual chaining of both must now be applied with a lifetime prediction prospect. This paper will first present a robust method to simulate multipass welding processes that has been validated through an international round robin. Then the dedicated “hybrid method”, specifically set up to simulate finish turning, will be subsequently applied to the welding simulation so as to reproduce the final state of the pipe manufacturing and its interaction with previous operations. Final residual stress fields will be presented and compared to intermediary results obtained after welding. The influence of each step on the final results will be highlighted regarding surface integrity and finally ongoing validation works and numerical modeling enhancements will be discussed.Copyright

LARGE DUCTILE TEARING IN DISSIMILAR MATERIAL WELDS AND TRANSFERABILITY ISSUES

Dissimilar Metal Welds (DMW) are required in nuclear reactors to join low alloy steel components and stainless piping. The thermal and mechanical mismatch between the dissimilar material characteristics favors the stress concentration in the weld along the austenitic/ferritic interface. Assessing the ductile tearing resistance of DMWs is an issue even for crack initiation. But predicting large crack extensions is even more difficult for several reasons: crack path deviation, J-R curve determination, transferability from specimen to structures. This paper presents an approach to determine the resistance curve of a DMW on the basis of a ductile tearing simulation using a cavity growth model.Copyright