Fabien Bogard

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.

Numerical Modeling of Fatigue Damage and Fissure Propagation under Cyclic Loadings

The purpose of this work is to develop a numerical simulation procedure in order to predict the evolution of the fatigue damage and rupture in mechanical parts (such as rolling bearings and gears) under cyclic loadings. The study of the fatigue damage evolution, from the first defect appearance until the parts failure, is primordial in view of the preventive maintenance. The numerical procedure is based on the continuum damage mechanics and the thermodynamics of irreversible processes. The damage effects are fully coupled with the elasto-plastic constitutive laws on a macroscopic point of view. The Sines fatigue criterion for multiaxial stress states is used to estimate the lifetime of mechanical parts in terms of number of cycles. This numerical model is implemented into Abaqus/Explicit using an users subroutine (Vumat). A cycle jumping algorithm allows to largely reduce the computation time. Some remeshing techniques are used to follow up the damage and rupture evolutions. The birth and the growth of the damage and rupture can be visualized via the element deleting and remeshing. These numerical tools are applied to a 2D specimen under a cyclic stretching.

Damage and Rupture Simulation for Mechanical Parts Under Cyclic Loadings

The purpose of this study is to develop a numerical methodology to simulate the fatigue damage of revolving mechanical parts under cyclic loadings (such as rolling bearings). The methodology is based on the continuum damage mechanics and on a fatigue damage model. The fatigue damage can be caused by numerous loading cycles, even in an elastic state; the damage will then influence the elastoplastic behaviors. The coupling effect of both enfeebles the material strength and leads to the rupture. An important improvement on the Sines fatigue criterion is proposed, which allows the coupling behaviors of damage and plasticity to be described better. This paper deals with the following aspects: (i) the fatigue damage model and the identification of fatigue parameters using S-N curves; (ii) the elastoplastic constitutive behaviors coupled with the fatigue damage; (iii) a cycle jumping algorithm to reduce the computation time; and (iv) an adaptative remeshing to follow the rupture propagation. These mechanical and numerical models are implemented in the framework of ABAQUS software. Two applications are presented in this paper: the fatigue lifetime prediction for a cyclic tension specimen and the fatigue spalling (or chipping) initiation and growth in a thrust roller bearing under a cyclic loading. The present approach is very efficient and helpful for the lifetime prediction of revolving mechanical components.

Numerical determination of the mechanical stiffness of a force measurement device based on capacitive probes: Application to roller bearings

Abstract Bearings allow external loadings to be transferred from one raceway to the other through rolling elements, which induces strains in the bearing constituents. In order to measure the radial component of these forces, the fixed ring is inserted within a housing equipped with capacitive probes able to measure displacements with very high sensitivity. This work mainly focuses on determining the optimal housing shape using FE simulations and their influence on the global stress state undergone by the structure. Finally, an averaged global stiffness is computed, allowing proper calculation of the contact forces involved in the bearing.

Numerical simulation and experimental comparison of flaw evolution on a bearing raceway: Case of thrust ball bearing

Abstract Bearings are essential elements in the design of rotating machines. In an industrial context, bearing failure can have costly consequences. This paper presents a study of the rolling contact fatigue damage applied to thrust ball bearings. It consists in building a dynamic three-dimensional numerical model of the cyclic shift of a ball on an indented rolling surface, using finite element analysis (FEA). Assessment of the evolution in size of a surface spall as a function of loading cycles is also performed using FEM coupled with fatigue laws. Results are in good agreement with laboratory tests carried out under the same conditions using a fatigue test cell dedicated to ball bearings. This study may improve knowledge about estimating the lifetime of rolling components after onset of a spall using FEA and accounting for structural damage state.

Optimization and Ergonomics of Novel Modular Wheelchair Design

The Manual Wheelchair (MW) is an important device which provides technical assistance to people affected by mobility impairments. This mode of displacement is neither natural nor easy and the environments, whether natural or built, can present various obstacles, which will restrict mobility and the social participation of MW users. Users complete autonomy depends on their capacity to cope with the many obstacles of their daily life, such as pavements or unleveled grounds. Ever since its invention the MW as an economical mobility solution, it has gone through many improvements, yet its technological innovation slowed down during the recent years. In this study, we present a novel design of MW. Its conception includes innovative kinematics with genuine lifting and folding systems. A lever system mounted on hubless-wheels is dedicated to the propulsion mechanism. The objective of this new concept is the optimization of MW mechanism to be more user friendly and to take into account the ergonomics considerations in an attempt to improve the user’s daily life.

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.

Experimental Investigations and Finite Element Modelling of the Vibratory Comportment of a Manual Wheelchair

This paper presents the comparison between the numerical results provided by the finite element model of a manual wheelchair and the vibration experiments performed on the same actual wheelchair. Two patients having different corpulence participated in this study while sitting on different types of cushions. The tests were carried out using a vibrating table with white noise as the input, in an attempt to simulate the entire vibration spectrum that the user of the chair could undergo. A numerical approach based on the finite element method has made it possible to create a numerical model of the wheelchair that can then anticipate structural problems resulting from these vibratory constraints. The objective of this work is to characterize the structure of the wheelchair as well as the vibration disturbances suffered by the user according to the daily life tasks. This first study will later allow the development of a design strategy oriented towards patient’s comfort with regard to vibrations and also to develop a new type of wheelchair using an adapted structure guaranteeing a longer material life.

EMG Comparison of Sport Manual Wheelchair Propelled by Lever Drive and Push Rims and Possible Consequences for Rehabilitation: A Case Study

The goal of this paper is to demonstrate a comparison of EMG muscle activity of a subject who conducted two 4 min long rides on a manual wheelchair using push rims and lever drive. The tests were carried out on a mechanical treadmill which allowed for maintaining constant ride conditions regarding slope and velocity of the wheelchair. The resulting muscle activity is presented in % MVC as a function of elbow joint position in deg. From this case study we conclude that it is possible that using lever drive for wheelchair propulsion activates muscles of a subject differently from push rims thus enabling a different way of muscle rehabilitation.

The Musculoskeletal Contribution in Wheelchair Propulsion Systems: Numerical Analysis

Although many improvements are still being investigated in the Manual Wheelchair (MWC), a number of criticisms are formulated by a vast majority of daily users. One of the most significant concerns are related to the handrim propulsion system, which is responsible for micro-traumas. The numerical study described in this paper compares two types of propulsion systems: the classical handrim and the lever propulsion. The purpose is to assess the force required for propulsion and the related consequences on involved muscles in the case of a paraplegic patient. Numerical results on lever propulsion demonstrates improved force distribution and reduced muscle activity compared to the classic handrim propulsion. In our view, these results constitute a promising initial step for demonstrating the superiority of lever propulsion from an ergonomics viewpoint.