Monitoring of dry sliding wear using fractal analysis

Reliable online monitoring of wear remains a challenge to tribology research as well as to the industry. This\ud paper presents a new method for monitoring of dry sliding wear using digital imaging and fractal analysis.\ud Fractal values, namely fractal dimension and intercept, computed from the power spectrum of the images of a\ud wearing surface, are adopted as indicators of the dynamic wear process. Experimental results show that\ud progressive changes of fractal values might reveal the wear status of the surface

Tool Condition Monitoring and Surface Topography Analysis During the Machining of CFRP Composites

RÉSUMÉ Les composites polymères notamment FRP (fibre reinforced plastics) sont de plus en plus employés dans l’industrie manufacturière (aéronautique et automobile notamment) pour la confection de leurs produits. L’emploi de carbone dans les FRP est en particulier prisé pour ses caractéristiques mécaniques. Depuis quelques décennies, le mélange de matériaux composites et métalliques au sein de structures de produits apporte des défis supplémentaires lors de leur assemblage. Face à ces nouveaux matériaux, les scientifiques et industriels réemploient les techniques qui ont été bâties et fait leurs preuves pour des matériaux métalliques relativement homogènes. Cependant, de par les propriétés intrinsèques des composites FRP, l’état de surface est fondamentalement hétérogène et la caractérisation de l’état de surface en devient complexe. Un autre point, de par ces spécificités, usiner un tel matériau provoque des petites vibrations additionnelles que l’on pourrait qualifier de bruit sur des signaux vibratoires, en comparaison avec l’usinage de métaux. Cette thèse vise à répondre aux problèmes de caractérisation de surface mais aussi au développement d’une technique novatrice de suivi de la qualité de coupe. La technique développée se base sur la théorie fractale et l’analyse fractale pour répondre aux besoins de la quantification du bruit sur les signaux de forces de coupe ou de vibration. L’analyse fractale permet de mettre en évidence le niveau de complexité et de rugosité d’objets. Pour bâtir et valider cette méthode, plusieurs tests ont été réalisés : détourage, perçage axial et orbital. Malgré le niveau élémentaire du développement de cette technique, les premiers résultats sont prometteurs. Mise en place sur une cellule de fabrication, cette méthode permet d’évaluer, en un temps très court, le niveau d’usure d’outil (en vue de son possible remplacement) ainsi que la qualité de coupe générée. Pour la caractérisation de surface de composites laminés, l’étude s’est premièrement basée sur des relevés de profils de surface et de rugosité. Dans chacune des deux directions principales (dans le sens du pli et dans le sens de l’empilement), des problèmes spécifiques ont été mis en évidence. Et pour chacune des directions, un plan correctif des méthodes de caractérisation actuelles a été proposé. Le résultat de ces optimisations proposées permet de mieux évaluer l’état de surface au vue de la qualité de coupe ainsi que de la robustesse du procédé.----------ABSTRACT Polymer composites such as FRPs (fiber reinforced plastics) have been increasingly used by the manufacturing industry (aerospace and automotive in particular) in the making of their products. The carbon selection in FRPs is especially preferred for its mechanical properties. For few decades, the combination of composite and metallic materials within products’ structure has been raising up additional challenges during the assembly. To solve those issues, scientists and industrials often reused techniques that had been built and proved for relatively homogeneous metallic materials. However, due to the intrinsic properties of FRP composites, the surface condition is particularly heterogeneous and such surface condition characterization tend to be more complex. Furthermore, machining a FRP material generates additional short vibrations that could be evaluated as noise in the vibration signals in comparison with the machining of metals. This thesis is a contribution to solutions to surface characterization issues and proposes an innovative technique of machining quality monitoring. The developed technique is based on the fractal theory and fractal analysis to meet the needs of the noise assessment in the cutting forces or vibration signals. Fractal analysis allows to evaluate the complexity and roughness of objects. To build and validate this method, several tests were performed: trimming, drilling axial and orbital. Despite the relatively low level of development of this technique, first results are promising. Set up in a manufacturing cell, this method allows to evaluate, in a very short time, the tool wear (for possible tool replacement) and the machining quality. For laminated composites’ surface characterization, the study is primarily based on surface profiles and roughness observations. For both two main directions (in the ply plane direction and in the direction of the stack sequence), specific problems have been highlighted. And for each direction, a corrective plan of current characterization methods proposed. The result of those proposed enhancements to better evaluate the surface condition in view of the machining quality and process robustness

Aerospace medicine and biology: A continuing bibliography with indexes (supplement 324)

This bibliography lists 200 reports, articles and other documents introduced into the NASA Scientific and Technical Information System during May, 1989. Subject coverage includes: aerospace medicine and psychology, life support systems and controlled environments, safety equipment, exobiology and extraterrestrial life, and flight crew behavior and performance

Assessment of Early Hypertensive Retinopathy using Fractal Analysis of Retinal Fundus Image

Hypertensive retinopathy is characterized by changes in retinal vessels, a change known as tortuosity. Automated analysis of retinal vascular changes will make it easier for clinicians to make an initial diagnosis of the disease. The pattern of blood vessels in the retina of the eye can be approached with a fractal pattern. This study proposes a method for the early detection of disease hypertensive retinopathy using the fractal analysis approach fundus retinal image. Variable fractal used is the fractal dimension and lacunarity, whereas for the classification algorithm using ensemble Random Forest and validation using the k-fold cross-validation. Performance measurement using the parameters of accuracy, positive prediction value (PPV), negative prediction value (NPV), sensitivity, specificity and area under the curve (AUC). The test results using 10-fold cross-validation values obtained accuracy 88.0%, PPV 84.0%, NPV 92.0%, sensitivity 91.3%, specificity 85.19%, and 88.25% AUC. The performance is produced when using lacunarity the box size 22. Based on the research results, it can be concluded that early detection of hypertensive retinopathy with fractal analysis approaches have a performance based on AUC produced included in good categories

Surface profile and acoustic emission as diagnostics of tool wear in face milling

This thesis examines the relationship between progressive wear of cutting inserts during a face milling operation and the acoustic emission and surface profile generated by that process. Milling experiments were performed on a range of workpiece materials using both eight point and single point inseý arrangements contained in two cutters of different geometries. Surface profile measurements were made using a stylus profilometer at intervals during the experiments. Correlations between the wear state as measured by the length of the flank wear land (Vb) and the spatial frequency content of the surface profiles were established. Investigations into the variation of fractal dimension of a milled surface with Vb demonstrated that no correlation was observable between these quantities. Acoustic emission (AE) measurements were made using a non-contacting fibre-optic interferometer which allowed the rms of the AE signal and its mean frequency to be determined. Correlations between these parameters and Vb were established for a range of workpiece materials and cutter geometries. It was shown that neither AE measurements nor surface profile measurements in isolation could predict tool wear state in all situations. The advantages of fusing data from surface profile and AE sources via an artificial neural network in tool wear monitoring were demonstrate

Virtual reality as an educational tool in interior architecture

Ankara : The Department of Interior Architecture and Environmental Design and the Institute of Fine Arts of Bilkent Univ., 1997.Thesis (Master's) -- Bilkent University, 1997.Includes bibliographical references.This thesis discusses the use of virtual reality technology as an educational tool in interior architectural design. As a result of this discussion, it is proposed that virtual reality can be of use in aiding three-dimensional design and visualization, and may speed up the design process. It may also be of help in getting the designers/students more involved in their design projects. Virtual reality can enhance the capacity of designers to design in three dimensions. The virtual reality environment used in designing should be capable of aiding both the design and the presentation process. The tradeoffs of the technology, newly emerging trends and future directions in virtual reality are discussed.Aktaş, OrkunM.S

Making Tactile Textures with Predefined Affective Properties

A process for the design and manufacture of 3D tactile textures with predefined affective properties was developed. Twenty four tactile textures were manufactured. Texture measures from the domain of machine vision were used to characterize the digital representations of the tactile textures. To obtain affective ratings, the textures were touched, unseen, by 107 participants who scored them against natural, warm, elegant, rough, simple, and like, on a semantic differential scale. The texture measures were correlated with the participants' affective ratings using a novel feature subset evaluation method and a partial least squares genetic algorithm. Six measures were identified that are significantly correlated with human responses and are unlikely to have occurred by chance. Regression equations were used to select 48 new tactile textures that had been synthesized using mixing algorithms and which were likely to score highly against the six adjectives when touched by participants. The new textures were manufactured and rated by participants. It was found that the regression equations gave excellent predictive ability. The principal contribution of the work is the demonstration of a process, using machine vision methods and rapid prototyping, which can be used to make new tactile textures with predefined affective properties