Karl Debray

Effect of cascade methods on vibration defects detection

Within the framework of monitoring rotating machines, vibration analysis remains an effective tool for fault detection. This analysis generally consists of measuring acceleration signals from critical and judiciously chosen points of a machine with the help of piezoelectric sensors. However, relevant information concerning the machine health can be masked by disturbances such as noise. The detection reliability will then be conditioned directly by the quality of the collected signal. Signal preprocessing methods, in particular denoising methods, can significantly improve the detection quality in terms of reliability. In this paper we aim to compare two methods of denoising based on signal spectral content analysis: discrete wavelet transform and empirical mode decomposition. A first study is carried out in order to optimize specific parameters related to each of the two methods, starting from experimental data obtained on degraded bearings. In fact for each parameter, one has to define conditions which allow the best detection of periodic pulses in vibration signals thanks to indicators such as kurtosis and crest factor. The second study consists of assessing the effectiveness of each denoising method on a vibration signal measured on a failed bearing. This signal is then disturbed by various noises simulated with variable levels. This study aims to show the effectiveness of each of these two methods on the early detection of impulse defects.

Determination of sensor positions for predictive maintenance of revolving machines

Abstract The monitoring by measurement and analysis of vibration is largely used to detect the defects in revolving machines. The determination of the best sensor positions is one of the main research goals in the field of predictive maintenance. This paper proposes a numerical methodology based on a finite element model and a spectral analysis in order to find optimum sensor positions. The bearing is a key component for the vibration propagation from the moving parts to static ones. An analytical bearing model and its numerical implementation in a finite element code are presented. The tangent stiffness matrix of the bearing element is obtained by the Newton–Raphson method and then used for the modal and spectral analyses. Several techniques are used to find the most sensitive zones to common defects. The proposed numerical approach correlate well with the experimental results. The numerical modeling of a grinder shows the interests in industrial applications.

Design and Optimization of Addendum Surfaces in Sheet Metal Forming Process

In the sheet forming process, addendum surfaces have an important influence on the formability of the workpiece. If the design of addendum surfaces is done manually with a CAD software, many corrections should be made according to the experimental or/and numerical results. This study proposes an automatic procedure for the design and optimization of addendum surfaces by using our fast Inverse Approach and two optimization algorithms. The present optimization procedure is applied to the Renault Twingo dashpot. The results show that the optimization calculation converges rapidly towards an optimal solution. The future work is to automatically (or semi-automatically) create the addendum surfaces with G1 continuity for the industrial workpiece with complex geometry.

Finite element modeling of TMJ joint disc behavior

INTRODUCTION On account of its specific biodynamics, the disc joint located at the very heart of the joint can impact every constituent of the manducatory system. The disc is deformed when subjected to stresses exerted by the muscles of mastication which it partly absorbs and partly redistributes. MATERIALS AND METHODS CT-scan slices and MRI images of a subject were made in order to create a finite element anatomical model of the TMJ. The forces applied to the subjects joint model were obtained by performing vector decomposition of the maximum muscle forces produced by this individual. The resultant force in this study was subjected to different frequencies approximating those observed in mastication. RESULTS The reaction force at the glenoid fossa can reach up to 1035 N depending on the frequency of the indentation. Generally, during the different exercises, the areas of maximum stress were located at the lateral portion of the disc and on the posterior band. They reached forces up to 13.2 MPa following a 32 s exercise at a frequency of 0.5 Hz. DISCUSSION Even if the behavior law needs to be improved, joint resiliency was demonstrated in this study. The areas of maximum stress were equivalent in the different exercises on account of the anatomy of the different parts and the axis of the forces applied. This study offers food for thought regarding joint disorders and opens the way for further research to complement the current investigation.

An efficient algorithm of plastic integration for damage modelling in sheet forming process

An efficient method called “Inverse Approach” (I.A.) for sheet forming modelling is based on the assumptions of the proportional loading and simplified tool actions. To improve the stress estimation for damage modelling, the Pseudo‐Inverse Approach (P.I.A.) has been recently developed taking into account the loading history: 1) some realistic intermediate configurations are determined without contact treatment to consider the deformation paths; 2) a new efficient algorithm of plastic integration is proposed to consider the bending‐unbending effects. In this algorithm, the equations of unknown stress vectors are transformed into scalar equations using the notion of the equivalent stress, thus the plastic multiplier λ can be directly obtained without iterative resolution scheme. The numerical experience has shown that this direct algorithm allows to largely reduce the CPU time of plastic integration and to avoid convergence problems for the damage modelling in the sheet forming process.

Analysis of a horse simulator’s locomotion by inertial sensors

To determine the imbalance of each, horse or rider, the balance’s quality of the rider will be expertise and improve by an adjusted simulator, without the unpredictable reactions of a real horse. The use of an equestrian simulator enables the rider to improve his technique without the different risks linked to the practice on a real horse. These simulators are sold without any specification regarding the operation, validity and regularity. Such a device has to be however controlled in terms of movement stability (Mager-Maury et al. 2012). This study aims to verify this aspect on a mechanical horse by using an inertial measurement unit (IMU), in order to improve the rider’s training programs by adapting the different protocols to the inter-individual differences between the riders. This will allow us to be relevant to the session’s repeatability and riders monitoring. The unpredictable reactions of a real horse prevent the accuracy and secure rider’s balance studies. The weight and rider’s experience has an effect on the horse’s behaviour (Clayton 1997; Eckardt et al. 2014).

Finite element model and ergonomic pertinent choice for stirrup sensors location

The scope of this paper is to export our results to create a device able to quantify the forces applied on the stirrups. The subject is to determine the ergonomic and pertinent choice for sensor location. French research in equine sports performance publishes articles that present significant results, such as the 43rd Equine Research Days organized by IFCE in partnership with ‘The French Equine School’. We haven’t found any scientific paper that has validated the proposed experimental methodology. Some experimental results only used sensor to determine the specificity of the stirrup sensor without any valid test (Cosson 2012; Van Beek et al. 2012; Martin et al. 2016; Biau 2017). The difficult is to discover the strain and the real frictions applied on the different parts of the stirrups fasteners.