Advanced Materials Research Vol. 112

Abstract: The objective of this paper is to present the solution developed to model the chem- ical and thermal coupling occurring in an intensied heat exchanger reactor. The results of this modeling are all the properties of the chemical uid along the conduit, and the temperature distribution in the structure. This will be used to manage a thermal and mechanical reliability study of the heat exchanger reactor.

Abstract: As a complement to classic characterization in the identification of elastomers, full-field measurement methods such as image stereo correlation can undeniably contribute to the validation of elastomeric connection behaviour. Indeed, these measurements enable three-dimensional displacement and strains fields over the totality of the studied surface to be finely reached. Characterization tests in shearing on an elastomer were followed by image stereocorrelation up to high strain levels. The experimental results could thus be confronted with theoretical results using an Alexander hyperelastic behaviour law, which enabled the relevance of this law to be validated locally.

Abstract: This paper presents a Finite Elements Modelling (FEM) based methodology dedicated to the evaluation of the lifetime and the reliability of assemblies involving brittle materials under cyclic loading. It focuses on the particular case of metal bonded Aluminium Nitride (AlN) substrates used in power electronic switch modules. The ceramic fracture criterion was formulated according to the weakest link concept, under Weibull's approach. The material's parameters were determined by running three points bending tests. In order to check the relevancy of the proposed methodology, a non linear thermomechanical Finite Elements Model allowed computing the number of thermal cycles before substrate brittle fracture within a test vehicle, which was then compared to experimental results. Once validated, the methodology was applied to two different configurations of a power switch module, designed for harsh environment aeronautic applications. The corresponding external loading profile was considered to compute and monitor the evolution of the maximal principal stresses within the ceramic substrates whole volumes. Their lifetimes and reliabilities was finally assessed and compared to the applications requirements.

Abstract: Previous works have shown that ceramic matrix composites are sensitive to delayed failure during fatigue in oxidizing environments. The phenomenon of slow crack growth has been deeply investigated on single fibers and multifilament tows in previous papers. The present paper proposes a multiscale model of failure driven by slow crack growth in fibers, for 2D woven composites under a constant load. The model is based on the delayed failure of longitudinal tows. Additional phenomena involved in the failure of tows have been identified using fractographic examination of 2D woven SiC/SiC composite testspecimens after fatigue tests at high temperatures. Stochastic features including random load sharing, fiber overloading, fiber characteristics and fiber arrangement within the tows have been introduced using appropriate density functions. Rupture time predictions are compared to experimental data.

Abstract: The aim of this study is to develop an effective on-line ANN-based approach for quality estimation in resistance spot welding. The proposed approach examines the welding parameters and conditions known to have an influence on weld quality, and builds a quality estimation model step by step. The modeling procedure begins by establishing relationships between welding parameters (welding time, welding current, electrode force and sheet metal thickness), welding conditions represented by typical characteristics of the dynamic resistance curve and welding quality indices (nugget diameter, nugget penetration, and indentation depth), and the sensitivity of these elements to the variation of the process conditions. Using these results and various statistical tools, three estimation models are developed. The first one is based exclusively on welding parameters. The second model is based on characteristics of the dynamic resistance curve. The third estimation model combines welding parameters and characteristics of dynamic resistance curves. In order to carry out the models building procedure, an extensive number of welding experiments are required. For this purpose, Taguchi’s efficient method of experimental planning is adopted. The results demonstrate that the developed models can provide an accurate on-line estimate of the weld quality, under different welding conditions.

Abstract: Chatter is the most classical problem in machining. It is prone to occur in low rigidity structures generating poor surface quality and harmful vibrations which could damage any part of the machine-tool system. In finishing operations, the effect of the tool nose radius should be taken into account in order to obtain safe and reliable cutting conditions. The present paper uses a simple SDOF model to study the stability during finishing operations.

Abstract: Today, Parallel Kinematic Machine tools (PKMs) appear in automotive and aeronautic industry. These machines propose high kinematic performances allowing a higher productivity than Serial Kinematic Machine tools (SKMs). However, this kinematic behaviour is anisotropic and a particular study is then necessary to locate the part in a workspace where the kinematic performances are well exploited. The study presented in this article deals with the determination of geometric and kinematic models of a new PKM : the Tripteor X7 designed by PCI. The inverse kinematic model expresses the joint coordinates with regard to the cartesian coordinates. The kinematic model which takes into account velocity, acceleration and jerk limits axis, allows computing the displacement time between two tool positions. Finally, this model can be used to determine the workspace where Non Effective cutting Times (TNE) are minimum. The method is applied for an automotive part machining

Abstract: In aerospace industry, the manufacturing of critical parts (high energy components) requires an important validation process to guarantee the quality of the produced parts, and thus their fatigue lifecycle. Globally, this validation consists in freezing the cutting conditions using metallurgical analysis or fatigue trials, and a test on the first article. This process is extremely complex and expensive. In this way establishing the correlation between the cutting conditions and the surface integrity will help us to optimize the manufacture of those parts. In this article, by the means of an experimental method, we define a domain of validation by combining the cutting conditions according to the classic criteria established by AFNOR E66-520 norm (Couple-Tool-Material) and the criteria of surface integrity for the drilling of a Nickel-base superalloy. The experimental device consists in drilling a Ø15.5 mm hole on a 3-axis milling centre instrumented by a 4 components Kistler dynamometer (Fx, Fy, Fz and Mz), a spindle power sensor “Watt-pilote” and three accelerometers placed following the directions X, Y and Z. Scanning Electron Microscopy (SEM) observations, micro-hardness tests and topographic measurements with an optical profilometer, are carried out to characterize the metallurgical state of the holes manufactured. Finally, correlations were respectively made between the cutting conditions, the recorded signals and the metallurgical state of the holes.

Abstract: High-speed milling operations are often limited by regenerative vibrations. The aim of this paper is to analyze the effect of spindle speed variation on machine tool chatter in high-speed milling. The stability analysis of triangular and sinusoidal shape variations is made numerically with the semi-discretization method. Parametric studies show also the influence of the frequency and amplitude variation parameters. This modeling is validated experimentally by variable spindle speed cutting tests with a triangular shape. Stable and unstable tests are analyzed in term of amplitude vibration and surface roughness degradation. This work reveals that stability must be considered at period variation scale. It is also shown that spindle speed variation can be efficiently used to suppress chatter in the flip lobe area.