Fatigue Damage Research Papers - Academia.edu (original) (raw)

2025, Frattura ed Integrità Strutturale

Bearings, considered crucial components in rotating machinery, are widely used in the industry. Bearing status monitoring has become an essential step in the deployment of preventive maintenance policy. This work is part of the diagnosis and classification of bearing defects by vibration analysis of signals from defective bearings using time domain and frequency analysis and wavelet packet transformations (Wavelet Packet Transform WPT) with Artificial Neural Networks (ANN). WPT is used for extracting defect indicators to train the neural classifier. The main goal is the determination of the wavelet generating the most representative indicators of the state of the bearings for better detection and classification of defects. Using the WPT-based neural classifier, the obtained simulation results showed that the db6 wavelet with level 3 decomposition is best suited for diagnosing and classifying bearing defects.

2025

Dans ce travail, le modèle « Rate Process Method RPM » est calibré pour donner le meilleur ajustement avec des données expérimentales. Il est ainsi nécessaire d'expliquer les incertitudes du modèle dans la prédiction de la durée de vie de la canalisation. Ensuite, une évaluation de la durée vie du tube basée sur la fiabilité est effectuée après avoir intégré deux paramètres d'incertitude  1 et  2 dans le modèle RPM. L'analyse de la fiabilité est effectuée pour un tube en considérant toutes les incertitudes : chargement et géométrie aussi bien que les incertitudes sur les paramètres de RPM .Il ressort que l'influence des incertitudes relatives à la température et au modèle RPM est beaucoup plus importante que les fluctuations de la pression du gaz et la précision de la géométrie. Un des principaux résultats de cette étude réside dans l'utilisation des outils probabilistes pour la qualification des modèles de durée de vie et pour l'évaluation de la sûreté du ...

2025, International Journal of Science and Engineering Applications

Corrosion fatigue crack growth experiment was conducted on ESE(T) (Eccentrically-loaded Single Edge notch Tension) specimen made of IS 2062 steel in salt water environment. The specimen was placed in a transparent chamber made of perspex sheet containing 3.5% NaCl solution which acted as corrosion environment. The corrosion process was accelerated by applying constant direct current of 0.2 A which was supplied by means of a regulated power supply. The test was conducted using a ±250 kN capacity computer controlled servo-hydraulic fatigue rated Universal Testing Machine. The maximum and minimum load values were 15 kN and 1.5 kN. The test frequency was 0.375 Hz and the stress ratio was 0.1. Number of cycles to crack initiation was determined. Crack growth data were recorded at regular intervals. Crack growth curves were plotted and material constants C and m were found. Analytical studies were carried out and the results were compared with experimental results. Details of the analytical and experimental studies and the results are presented in this paper.

2025

En France, l’assurance automobile est un marché mature avec un faible taux de croissance. De plus, s’agissant d’un secteur convoité, de nouveaux intervenants (banques-assurances, les acteurs de la grande distribution . . .) viennent rejoindre les acteurs traditionnels. Confrontés à une forte concurrence exacerbée par la quasi-stabilité du parc automobile assurable, et face aux mutations importantes de leur référentiel comptable et réglementaire, les assureurs sont désormais incités, plus qu’avant, à développer des modèles optimaux de surveillance et de gestion de leur portefeuille afin, entre autres, de fidéliser les clients les plus rentables et éventuellement de résilier certains contrats. Les analyses d’ordre qualitatif s’avèrent rapidement très insuffisantes, et les assureurs ont recours, de plus en plus, à des techniques statistiques plus élaborées. Des techniques de classification, des modèles de prévisions permettent de réaliser la tarification et d’élaborer des modèles prédi...

2025, International Journal of Innovation and Scientific Research

Structural components are the least studied in the literature because of their properties that vary from one design to another, which explains the scarcity of statistical data on them. The objective of this work is to determine the Weibull parameters of the reliability laws of the structural components of a spillway using the Condition Index method. To this end, the partial Top-Down Structural Analysis of a spillway was presented. A structural fault tree served as a starting point for the determination of the Weibull parameters of the corresponding component reliability laws. Then, the state condition tables associated with each element were drawn from the analyses carried out by the experts during the dam inspections. The determination of the Condition Indices was carried out by following a succession of steps developed in detail in this paper. After a variable change and a linear regression on the empirical data, a first approximation of the Weibull parameters of each component was performed. Then, the parameters obtained were optimized using the generalized gradient reduction nonlinear solver of the Excel software, on points of distinct reliability, and starting from the previous approximations. The resulting reliability models are very close to discrete data, and generally conservative. Finally, the Kolmogorov-Smirnov conformity test performed in each case validates the law and the determined parameters with a confidence interval greater than 95%. They can be used as a basis for determining the structural reliability of spillways.

2025

Généralement, le stade II de la propagation de fissure de fatigue (FCP) est décrit par le modèle de Paris- Erdogan. L'approche phénoménologique de la propagation de fissure de fatigue à travers ce modèle suggère l'existence d'une relation linéaire entre ces deux paramètres. Le but général de ce travail est d'étudier les effets des paramètres de chargement sur la propagation de fissure de fatigue dans le cas d'un acier 12NC6 soumis à un traitement thermique pour obtenir des valeurs de limites d'élasticité différentes. La corrélation entre les paramètres C et m a été examinée et comparée avec les résultats donnés par la littérature. La variabilité de ces deux paramètres a été analysée pour prédire la durée de vie des structures.

2025, HAL (Le Centre pour la Communication Scientifique Directe)

A Bayesian method for regression with free knots B-splines under shape restrictions and smoothness conditions is proposed. The shape constraints are taken into account thanks to the prior distribution. To propose statistical inference on the number and position of knots, we use a Multinomial-Dirichlet model. After specifying priors on all unknown parameters, we derive to a constant the posterior distribution. It is shown that in the case of Bayesian regression under shape constraints and with free knots, Bayesian analysis becomes complex. To handle the difficulties, we propose original simulation scheme which allows to simulate from the truncated posterior distribution with free dimension. To estimate the regression function, the posterior mode and the posterior expectation are calculated thanks to a Reversible Jump Metropolis-Hastings within Gibbs algorithm.

2025, Proceedings of the 2nd International Conference on Uncertainty Quantification in Computational Sciences and Engineering (UNCECOMP 2017)

The evaluation of fatigue damage accumulation on wind turbine support structures under operational conditions is heavily influenced by a number of uncertainties. These uncertainties may, firstly, be attributed to the highly variable and complex environmental loads, and secondly, to the unavoidable modelling errors which mainly originate from the inherent randomness in both material properties and fatigue resistance of structural components. It is therefore essential that assessment of fatigue life is carried out within a probabilistic framework; one that accounts for the stochastic nature of the phenomenon. The present study proposes a strategy for real-time reliability prediction of accumulated fatigue damage on wind turbine support structures by taking into account the above-mentioned uncertainties. To this end, the availability of structural monitoring information for the identification of the global response on wind-turbine support structures is exploited in order to address the discrepancies between actual and predicted damage accumulation. This is carried through utilization of an augmented version of the Kalman filter, which is capable of jointly estimating the response and the unknown inputs of the structure while relying on a limited number of noisy observations and a presumably uncertain model of the real system. A fixed-lag smoother is further deployed for the attenuation of the estimation error in an on-line mode and the smoothed stochastic estimates of the response are propagated over the model at the level of stresses. The accumulated damage along with the corresponding reliability level is finally predicted using a stochastic nonstationary fatigue damage model. The proposed scheme is demonstrated via implementation on the NREL 5.0 MW wind turbine under different operational conditions, on the basis of dummy vibration data generated via the FAST software. 76

2025, Proceedings of the 2nd International Conference on Uncertainty Quantification in Computational Sciences and Engineering (UNCECOMP 2017)

2025

Cette these traite des methodes d'estimation non-parametrique du cout medical et des incidences des evenements cliniques qui le gererent. De telles methodes d'analyse statistique existent deja mais elles sont parfois mal employees a cause du biais introduit par les donnees quand on est en presence de censure, de recurrence des evenements d'interet et de risques competitifs. Le choix d'une methode statistique d'estimation correcte pose souvent probleme dans ce contexte. Dans un premier temps, nous avons etudie les methodes statistiques habituellement utilisees. Aucune de ces methodes ne presentait le niveau de generalite pour prendre en compte simultanement toutes les situations souvent rencontrees. Dans un second temps, nous avons developpe dans un cadre " multi-etats " des approches non parametriques permettant a la fois d'estimer le cout medical et les incidences d'evenements qui le generent en presence de toutes ces situations. Les proprietes...

2025

Mechanical systems reliability depends on design, use, physical environment… Moreover, failure mechanisms as fatigue or stress yield systems ageing. The reliability databases are not allowed to deal with these particularities because of generic and constant failure rates. Many uncertainties in reliability predictions can be due to the use of these databases. A failure rate modelling is introduced in this article, and aims at tacking into account both time and influencing factors. An example describes the methodology and is used for assessing the model accuracy. MOTS-CLÉS : taux de défaillance, système mécanique, facteur d'influence, modèle de Cox, distribution de Weibull

2025, … 2007; Proc., Mons, …

La fiabilité des matériels mécaniques est largement conditionnée par les caractéristiques propres à chaque système, à ses conditions d'utilisation, son environnement… De plus, les mécanismes de dégradations comme la fatigue et le stress créent des phénomènes de vieillissement. Les bases de données de fiabilité, en fournissant des taux de défaillance génériques et constants, ne permettent pas de prendre en considération ces particularités. L'utilisation de telles bases entraîne par conséquent de grandes incertitudes quant aux résultats des évaluations fiabilistes. Nous proposons dans cet article une modélisation des taux de défaillance, fonction du temps, qui prend en compte les facteurs d'influence. Une application permet de valider le modèle. Moreover, failure mechanisms as fatigue or stress yield systems ageing. The reliability databases are not allowed to deal with these particularities because of generic and constant failure rates. Many uncertainties in reliability predictions can be due to the use of these databases. A failure rate modelling is introduced in this article, and aims at tacking into account both time and influencing factors. An example describes the methodology and is used for assessing the model accuracy.

2024

L'objectif principal de cette thèse est l'étude de la fiabilité des cartes électroniques. Ces cartes sont utilisées dans plusieurs domaines, tels que l’industrie automobile, l’aéronautique, les télécommunications, le secteur médical, ..., etc. Elles assurent toutes les fonctions nécessaires au bon fonctionnement d’un système électronique. Les cartes électroniques subissent diverses sollicitations (mécaniques, électriques et thermiques) durant la manipulation et la mise en service. Ces sollicitations sont dues aux chutes, aux vibrations et aux variations de température. Elles peuvent causer la rupture des joints de brasage des composants électroniques. Cette rupture entraine la défaillance du système électronique complet. Les objectifs de ce travail sont: - Développer un modèle numérique pour la simulation du drop-test d’une carte électronique ; - Prédire la durée de vie en fatigue des joints de brasure en tenant compte des incertitudes des diverses variables ; - Développer u...

2024

The aim of this work is to investigate changes in material surface microhardness during the different stages of fatigue life. Samples of API 5LX65 grade steel were submitted to high cycle fatigue tests in which different stages of... more

2024, Tribology International

This paper presents a computational methodology for frictional contact mechanics of the pressure armour layer in flexible risers. This will allow, for the first time, quantification of key fretting variables, such as contact pressure, relative slip and sub-surface stresses in this complex geometry, under representative loading conditions. Fatigue lives are calculated using the 3-dimensional critical plane Smith-Watson-Topper multiaxial fatigue parameter. It is shown that COF has a significant effect on predicted trailing-edge tensile stresses in the pressure armour layer and, hence on fretting crack initiation in risers. It is also shown that operating pressure and bending-induced axial displacement significantly affect predicted crack initiation. These results will facilitate representative fretting wear and fretting fatigue testing of pressure armour layer material.

2024

Author manuscript, published in " " Essais accélérés de fatigue pour la validation des objectifs de fiabilité d’un ressort de bouton-poussoir d’ouverture de portes de métro

2024, HAL (Le Centre pour la Communication Scientifique Directe)

Dans un contexte de conception intégrée et afin d'optimiser la durée de vie en fatigue de composants mécaniques nous proposons d'aider au choix de traitement de surface à partir d'une cartographie de durée de vie s'appuyant sur le génie de pré-contrainte, un calcul par éléments finis et les caractéristiques du matériau employé. Cette aide à la décision utilise une architecture d'intégration de connaissances métier qui vise à capitaliser et à restituer les savoir-faire liés aux différents procédés de traitement de surface, leurs cas d'emploi et leurs paramètres techniques de mise en oeuvre.

2024, HAL (Le Centre pour la Communication Scientifique Directe)

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2024, HAL (Le Centre pour la Communication Scientifique Directe)

De plus en plus d'industriels développent des lignes de produits adoptant le concept de ligne de produits afin de rationaliser leur conception. Sans outil d'analyse adéquat, mener une étude de sûreté de fonctionnement d'une ligne de produits conduit à réaliser des études de sûreté de fonctionnement pour chaque produit. Ce qui nous amène à nous interroger sur la nécessité de refaire les analyses de parties déjà traitées, et donc sur la nécessité de développer une ligne de produits sûrs. Notre objectif est de fournir un support d'analyse de type AMDEC paramétrique permettant de conduire une analyse au niveau de la ligne de produits. Cette AMDEC paramétrique permettra la déclinaison rapide des analyses pour chaque produit.

2024

The present work is a contribution to the phenomenological modelling of fatigue damage in short glass fibre reinforced thermoplastic matrix composites. It is a first part of a continuing work which intends to develop a new damage model into the framework of continuum damage mechanics. The developed model is implemented into the finite element implicit code ABAQUS through user defined material subroutine UMAT. The latter is aimed at predicting the fatigue damage accumulation and the subsequent stiffness reduction in short fibre reinforced thermoplastic composites. The developed model is intended to improve the fatigue life predictions and hence the numerical simulations of structures durability. The developed damage modelling will be used to optimize composite parts in automotive industry. Several simulations have been conducted upon a glass (E) /thermoplastics matrix to emphasize and to understand the effect of material parameters on the damage kinetic and accumulation under cyclic loading.

2024, International Journal of Fatigue

The compatibility of the properties of elastomer with conventional diesel fuel has made it favourable in many engineering applications. However, due to global energy insecurity issues, there is an urgent need to find alternative renewable sources of energy as replacements to conventional diesel. In this respect, biodiesel appears to be a promising candidate. Hence, research into the compatibility and fatigue characteristics of elastomers exposed to biodiesel becomes essential. The present paper introduces the first attempt to investigate the effect of different solvents on the fatigue of swollen elastomers. The filled nitrile rubbers are immersed in the palm biodiesel and conventional diesel to obtain the same degree of swelling prior to the application of uniaxial fatigue loading. Field Emission Scanning Electron Microscopy (FESEM) analysis is carried out to observe the fracture surfaces. Stretch-N curves are plotted to illustrate the fatigue life duration. These curves showed that the fatigue lifetime of rubber is the longest for dry rubber and the least for rubber swollen in biodiesel. FESEM micrographs reveal that the loading conditions have no effect on the crack initiation and propagation patterns regardless of the swelling state.

2024, International Journal of Fatigue

This paper deals with fatigue damage in carbon black filled natural rubber under uni-and multiaxial loading conditions. Fatigue damage is described at both the macroscopic (mechanical) scale and the microscopic (material) scale. The different fatigue damages observed at the macroscopic scale are presented accordin g to the prescribed loading conditions. At this scale, five element ary fatigue dama ge patterns are defined, three corresp ond to external macroscop ic cracks and two corresp ond to internal macroscop ic cracks. These elementary fatigue damage patterns are investigated at the microscopic scale by distinguishing crack initiation and crack growt h. Results show that the cracks initiate from microstructural defects, whose mean diameter does not exceed 400 lm and that crack initiation at the macroscopic scale corresp onds to crack growth at the microscopic scale, which validates recent energetic approache s adopted to predict fatigue crack initiation in rubbers. The morphology of fracture surfaces exhib its two types of features: wrenchings and fatigue striations. In particular, results highlight that several shapes of fatigue striations can form, depending on the loadin g conditions, and that several mechanisms of fatigue striation formation could come into play.

2024, HAL (Le Centre pour la Communication Scientifique Directe)

Si les méthodes de démonstration d'un niveau de fiabilité par essai sont bien connues, les récentes normes AFNOR XA50-144-5 et 144-6, abordent la méthode CG-FE pour un faible nombre d'essais en proposant une stratégie d'essai, et en rappelant les hypothèses souvent implicites. Cette méthode propose un calcul du facteur d'essai FE sur la base des essais censurés, avec une possibilité de réexploitation des essais dans le cas d'échec. Elle a par ailleurs la capacité d'intégrer la variabilité du niveau d'essai au risque de démonstration expérimentale. Cette note rappelle les marges supplémentaires nécessaires en conception pour qualifier un système expérimentalement, par rapport à celles suffisantes pour une garantie de défaillance par calcul.

2024, MATEC web of conferences

The paper deals with the implementation of the chosen fatigue damage criterions into FE analysis. Our study considers a shell finite element structural analysis in conjunction with the multiaxial rainflow counting and the fatigue damage prediction. The computational analysis considers stochastic response under random excitation in time domain and damage calculation based on so called critical plane approach (CPA).

2024, MATEC Web of Conferences

2024

The mechanical properties of composite materials are dependent on many factors. During loading the material response becomes nonlinear. The reason for this is microdamage in the material. In multidirectional laminates, microdamage is primarily due to transverse cracks in the off-axis layers. This implies that the thermomechanical properties change. The cracks are formed in the manufacturing step, or develops during loading. Weak fiber-matrix interface leads to debonding, whereafter the debond cracks coalesce and form macrocracks. One of the factors that affect the properties of composite materials is the manufacturing step. For example, Resin Transfer Molding (RTM) is a widely used fabrication method. One problem with this method is that it may produce composite laminates with a high void content. The voids are formed in the matrix due to mechanically entrapped air from moisture, solvents, or by products from the curing reaction. Most studies of the effect of voids aim for determination of a relationship between void content and the fracture property of interest. Paper A consists of an investigation of the effect of voids on the mechanisms of transverse failure in I sincerely thank my supervisor Professor Lars Berglund for his guidance, patience and understanding. I also want to thank all the members of Division of Polymer Engineering for their kind attitude that gives rise to the wonderful atmosphere at the division.

2024

L’évolution des techniques de construction, l’innovation et la prise en compte des normes environnementales poussent les acteurs du domaine de la construction à proposer des matériaux performants et innovants pour la construction des bâtiments et des différentes infrastructures dans le monde. Le matériau béton reste de nos jours le plus utilisé dans le domaine de la construction. La normalisation de la formulation des bétons se base généralement sur des règles prescriptives tenant compte du rapport Eau/Ciment,de la classe de résistance minimale, de la teneur minimale en ciment, teneur minimal en air, etc.Cette méthode prescriptive reste satisfaisante mais doit être complétée par une autre alternative permettant de prendre en compte l’utilisation de composition de béton non mentionnée dans la norme. Ainsi, l’approche performancielle de la durabilité du béton a été proposée.Le principe est de permettre la fabrication d’un béton avec une formule différente de celle de la norme tout en ...

2024

An accelerated flexural fatigue test rig was developed in which imposed displacements are mechanically controlled. For bending tests, frequencies up to 20 Hz and large strains are simultaneously possible. The innovative feature of the test is the design of a five-point bending (5PB) setup with rotating supports, which allows applying bidirectional deformation with boundary conditions similar to a clamped one allowing to apply high strain values with small displacements of the load points. Test rig description and the control program which permits changing the load rate and the speed are presented. Geometrical corrections in bending test setups are presented taking into account the specific boundary conditions of the aforementioned supports. The test rig is validated by comparison with a universal fatigue testing machine. The application of a fatigue statistical model is presented to correlate different fatigue tests, reducing the required amount of tests to obtain the material fatigue properties. Finally, composite T700 fatigue properties are presented applying the proposed test setup and statistical model.

2024, Procedia Engineering

Steel monopiles are support structures mostly applied for offshore wind turbines. Their installation is straightforward, in particular, in shallow and medium waters. While the wind turbine tower is primarily affected by wind, the wave loads are dominant for the monopile, as it is submerged to a large extent. This study deals with the influence of uncertainties in material and load parameters on the behaviour of those structures. It is investigated how the scattering of material properties (namely Young's modulus of elasticity) affect the structural response. In addition, loads with different characteristics are applied, and it is examined how the changes in loads influence the structural response. The analysed output data of interest are the extreme stresses leading to the accumulation of fatigue damage. In order for a realistic modelling, wave loads are considered with irregular sea states with different wave characteristics (significant wave heights and wave peak periods). The final aim of the analysis is to classify the effects of specific wave characteristics on the stresses by means of a sensitivity analysis. The analysis shows that variations in the wave peak period have the strongest influence on stress outputs. This effect results from the strong sensitivity of the structural dynamical response to the decrease of the difference between the values of the wave peak frequency and the natural frequencies of the structure.

2024

In this paper a new model for random loads-the Laplace driven moving average-is presented. The model is second order, non-Gaussian, and strictly stationary. It shares with its Gaussian counterpart the ability to model any spectrum but has additional flexibility to model the skewness and kurtosis of the marginal distribution. Unlike most other non-Gaussian models proposed in the literature, such as the transformed Gaussian or Volterra series models, the new model is no longer derivable from Gaussian processes. In the paper a summary of the properties of the new model is given and its upcrossing intensities are evaluated. Then it is used to estimate fatigue damage both from simulations and in terms of an upper bound that is of particular use for narrowband spectra.

2024, HAL (Le Centre pour la Communication Scientifique Directe)

L'objectif de cette étude est l'estimation d'un quantile extrême dans le cas de données dichotomiques de dépassement de seuil. La problématique est issue d'un cas industriel : l'étude de la résistance d'un matériau pour des probabilités de rupture cibles très faibles. La méthode proposée est séquentielle et consiste à décomposer la probabilité de l'évènement rare en un produit d'évènements conditionnels. Elle se fonde sur l'utilisation de résultats sur les lois limites de dépassements de seuil.

2024, Applied Sciences

Springing occurs more frequently to ultra large ships, as their natural frequencies are relatively low and approaches the spectral peak of the wave energy spectrum in certain sea states. Springing is a resonance phenomenon between the waves and the ship hull, and this high frequency vibration has a significant influence on the fatigue damage of hull structures. This paper deals with the influence of springing on the fatigue damage of ultra large ore carriers. The springing responses of ultra large ore carriers are calculated by a three-dimensional linear hydroelasticity method in the frequency domain. A fatigue damage calculation method accounting for the springing effect is applied that is based on the fatigue spectrum analysis method and the approximation method of joint narrowband. The fatigue damage of the deck and bottom longitudinals in the deck and bottom of ultra large ore carriers of various sizes has been calculated by this method. The influences of ship size, structural damping, sea state, wave heading, navigational speed, and loading condition on the structure fatigue damage ratio of ultra large ore carrier are analyzed.

2024, Periodica Polytechnica Mechanical Engineering

The aim of the present paper is to study and model the fatigue behavior of short glass fibers reinforced polyamide-66. The effect of fiber content on the fatigue and static behavior of this composite is investigated. In such composites fatigue damage growth exhibits three stages. A continuum damage based model is presented to predict damage evolution during these three stages. Experimental results show that increasing the fiber content increases the elastic modulus and the tensile strength of the studied materials under tensile tests. However, the rupture behavior changes from ductile to brittle. Moreover increasing the fiber percentage changes the S-N curves slope and decreases the fatigue life. Analytical results predicted by the proposed model, compared to experimental ones shows good agreement and the developed model predicted fatigue damage growth in its three stages of evolution with good performance.

2024, Reliability, Safety and Hazard Assessment for Risk-Based Technologies

The carbon fiber-reinforced polymeric (CFRP) composite materials are the material of choice for the aircraft structures as the designers require lightweight structures with enhanced mechanical properties. These materials are susceptible to accidental impacts during service and maintenance, and the damage will progress under varying static or dynamic service load conditions leading to the ultimate failure of the component. Recent advancement in non-destructive techniques such as X-ray computed tomography provide excellent details about the presence of damages in 3-Dimension in a component, which is an useful input for failure prediction and remaining life estimation. However, the quality of X-ray CT imaging is dependent on the equipment used, its calibration and image settings which, in turn, may affect the reliability and repeatability of damage quantification, if damage analysis is done in a routine way using binarization algorithms. In this study, the defects as well as the damage present in the low-velocity impacted CFRP laminates subjected to fatigue loading conditions are quantified and analyzed by the analysis of CT scan images obtained from two different CT systems with images of different resolution and contrast. The results of the comparative study show that the damage analysis of polymer composites using X-ray CT depends largely on the image quality and the choice of right threshold level is important for accurate damage estimation.

2024, Fracture and Structural Integrity

A computational simulation of low-cycle fatigue behaviour of lotus-type porous material, subjected to biaxial in-phase loading cycles is presented in this paper. Fatigue properties of porous materials are less frequently published in the literature. This paper evaluates computational analyses, where different pore distribution and biaxial loading conditions in relation to the pore orientations is considered in each simulation. The fatigue analysis is performed by using a damage initiation and evolution law based on the inelastic strain energy. The computational results are subjected to the appropriate statistical analysis, because of different pore topology a different fatigue lives are obtained on the same loading level. Results of computational simulations show also a qualitative understanding of porosity influence on low-cycle fatigue failures of lotus-type porous material under biaxial loading conditions.

2024, HAL (Le Centre pour la Communication Scientifique Directe)

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Modèle paramétrique pour estimer la dégradation de la fiabilité de démarrage d'une turbine à gaz à partir de données d'essais

2024

In this paper, a recursive Bayesian-filtering technique is presented for the joint estimation of the state and input forces. By introducing new prior distributions for the input forces, the direct transmission of the input into the state is eliminated, which allows removing low-frequency error components from the predictions and estimations. Eliminating such errors is of practical significance to the emerging fatigue monitoring methodologies. Furthermore, this new technique does not require a priori knowledge of the input covariance matrix and provides a powerful method to update the noise covariance matrices in a real-time manner. The performance of this algorithm is demonstrated using one numerical example and compared it with the state-of-the-art algorithms. Contrary to the present methods which often produce unreliable and inaccurate estimations, the proposed method provides remarkably accurate estimations for both the state and input.

2024, Composite Structures

In this paper, glass fiber-reinforced polypropylene (GF50-PP) composite composed of long fibers was prepared by the thermo-compression process for the very first time. This composite presents high mechanical strength and is used in infrastructures, which demand resistance against severe conditions. Mechanical strength and multi-scale damage analysis of GF50-PP composite at ambient and cryogenic temperatures have been investigated in this study using a special sampling procedure according to the microscopy observation, X-ray microtomography, ultrasonic measurement, and pyrolysis. The results demonstrated the exceptional behavior of the GF50-PP at the cryogenic temperature of − 70 • C mainly due to the employment of a novel processing method (thermocompression) for composites with long fibers, which have been previously prepared by traditional injection molding process. Tensile results presented no difference in failure strain at 20 • C and − 70 • C and the fatigue lifetime for different fiber orientations was similar in 3-points bending fatigue tests for different orientations of fibers or in samples taken from different regions of the composite plate, indicating the efficinecy of this processing method. Moreover, the results of damage analysis through monotonic loading presented that by decreasing the temperature from 20 • C to − 70 • C, the plasticity threshold didn't change notably. Overall, the proposed preparation method provided outstanding uniformity and excellent mechanical properties in GF50-PP composite even at temperatures as low as − 70 • C, which has not been investigated at this cryogenic temperature before.

2024, International Journal on Interactive Design and Manufacturing (IJIDeM)

Many structural elements are exposed to conditions of load that are difficult to consider during the design stage, such as environment uncertainties, random impacts, overloads and inherent material idealization amongst others, hence, miss-estimating its lifetime cycle. One way to test those designs is to construct a representative full-scale specimen and test it under the most critical load conditions in a controlled laboratory. Herein, we present a case of study of the fatigue test performed over a bolster beam redesigned in Universidad EAFIT belonging to a railway vehicle. The test was composed by three stages, each one testing a different load hypothesis. The bolster beam was instrumented at the most critical locations, following the results of a FEM analysis previously computed. As results, the most critical welds were identified and the total damage computed for an equivalent operation of eighteen-years, and also the behaviour of the specimen in presence of extreme longitudinal loads.

2024, Scientia Iranica

In this article, transverse vibration of an Euler-Bernoulli beam carrying a series of traveling masses is analyzed. A semi-analytical approach based on eigenfunction expansion method is employed to achieve the dynamic response of the beam. The inertia of the traveling masses changes the fundamental period of the base beam. Therefore, a comprehensive parametric survey is required to reveal the resonance velocity of the traversing inertial loads. In order to facilitate resonance detection for engineering practitioners, a new simpli ed formula is proposed to approximate the resonance velocity.

2024, HAL (Le Centre pour la Communication Scientifique Directe)

L'identification des principaux mécanismes d'endommagement et des niveaux de sollicitations est l'un des points clés pour l'élaboration des modèles de fiabilité dans un contexte d'essais accélérés. La méthode proposée est une extension de méthodes existantes permettant un calcul intermédiaire de la probabilité d'occurrence pour chaque défaillance en estimant les effets d'intégration système et ainsi les dépendances mutuelles de chacun des composants.

2024, Incertitudes et fiabilité des systèmes multiphysiques =

Les systèmes mécatroniques sont à la fois hybrides, dynamiques, interactifs et reconfigurables, ce qui entraîne des difficultés dans la modélisation dysfonctionnelle. Les potentielles interactions multi-physiques entre les composants peuvent avoir des impacts sur les dégradations ou sur les dysfonctionnements du système. Tous ces éléments à prendre en compte rendent incertain le modèle d'évaluation de la fiabilité. Le travail de recherche présenté dans cet article a pour but d'améliorer la prise en compte des interactions multi-domaines dans l'évaluation de la fiabilité des systèmes mécatroniques. A partir d'un état de l'art des méthodes d'évaluation de la fiabilité des systèmes mécatroniques, nous proposons des améliorations permettant une prise en compte quantitative des interactions par l'intégration de facteurs d'influence représentant des interactions multi domaines. Cette intégration est effectuée de manière générale à partir d'un modèle à hasards proportionnels et, dans le cas d'une interaction avec pour facteur de stress la température, en utilisant la loi d'Arrhenius. ABSTRACT. The mechatronic systems are hybrid, dynamic, interactive and reconfigurable. Therefore their dysfunctional modeling is very difficult. Multi-physical interactions between components have impacts on the degradation or on system failures, leading thus to more uncertainty in reliability evaluation. The work presented in this paper aims to improve the integration of multi-domain interactions in the reliability assessment of mechatronic systems. After a presentation of the state of the art of mechatronic systems reliability estimation methods, we propose to represent multi domain interactions by influential factors in the dysfunctional model. We generally use proportional hazard models ; in the case of an interaction represented by a temperature stress, Arrhenius model is used. MOTS-CLÉS. Fiabilité, Modélisation fonctionnelle, Modélisation dysfonctionnelle, RdP (Réseaux de Pétri), Interactions multi-domaines, facteur d'influence, modèle de Cox, loi d'Arrhenius.

2024

2024, International Journal of Fatigue

Understanding fatigue damage mechanisms in short fiber reinforced thermoplastics is a key issue in order to optimize material processing and propose physically based multiscale fatigue damage models. The present work aims at further understanding observations of fatigue damage in the polyamide 6.6 matrix with respect to its semi-crystalline structure. In this paper the polymer and associated composite are tested in their ductile regime i.e. above the glass transition temperature. Tomographic and SEM observations are used in order to establish a damage scenario at the spherulitic scale. These observations prove that fatigue damage progresses by intra-spherulitic failure in their equatorial plane. Observations of the spherulite nuclei also evidence the oriented structure of the semi-crystalline polymer induced by the injection-molding manufacturing process.

2024, Engineering Fracture Mechanics

This work investigates the effect of finite size and evolution of fracture process zone on b-value of acoustic emission in concrete beams. It is shown that the AE b-value determined using the Gutenberg-Richter (GR) law varies with beam size and invalidates universality. Since GR law fits the frequency-magnitude curve partially, a recently proposed Maslov's generalized logistic equation (GLE) is used for b-value analysis. The existence of cutoff magnitude and nonlinearity of frequency-magnitude distribution is explained through crack interaction mechanisms occurring within the FPZ. The growth of micro and macro cracking in concrete is observed to follow logistic or sigmoid growth law rather than the power law. The b-values obtained from GR and GLE are compared and it is found that the b-value of GLE correlates well with the effective crack length during damage process of plain concrete thereby exhibiting damage compliant behavior which could be used in health monitoring of structures.

2024, International Journal of Fatigue

A linearized stress intensity factor (SIF) is derived for concrete through a multiscale approach by considering the predominant process zone mechanisms such as aggregate bridging and microcracking. This is achieved by considering a bridging zone and a microcrack at the macrocrack tip. The bridging zone resists the crack growth through aggregate bridging mechanism. The SIF thus derived is further used in developing an analytical model which predicts the entire crack growth curve for plain concrete by making use of the concepts of dimensional analysis and self similarity in conjunction with the human population growth model. This model is validated using experimental data reported on normal strength, high strength and self consolidating concrete. Through sensitivity analyses it is shown that the specimen size plays an important role in the fatigue crack growth process of concrete.