Relief | EPFL Graph Search

Relief is a sculptural method in which the sculpted pieces remain attached to a solid background of the same material. The term relief is from the Latin verb relevo, to raise. To create a sculpture in relief is to give the impression that the sculpted material has been raised above the background plane. When a relief is carved into a flat surface of stone (relief sculpture) or wood (relief carving), the field is actually lowered, leaving the unsculpted areas seeming higher. The approach requires a lot of chiselling away of the background, which takes a long time. On the other hand, a relief saves forming the rear of a subject, and is less fragile and more securely fixed than a sculpture in the round, especially one of a standing figure where the ankles are a potential weak point, particularly in stone. In other materials such as metal, clay, plaster stucco, ceramics or papier-mâché the form can be simply added to or raised up from the background. Monumental bronze reliefs are made b

Cutting Force Modelling for Drilling of Fiber-Reinforced Composites

Mihai-Bogdan Lazar

Although used in a very large variety of applications, drilling is one of the most complex and least understood manufacturing processes. Most of the research on drilling was done in the field of metal cutting for mechanical parts since, in this case, high precision and quality are needed. The use of composite materials in engineering applications has increased in recent years, and in many of these applications drilling is one of the most critical stages in the manufacturing process. This is because it is among the last operations in the manufacturing plan of composite parts. Delamination and extensive tool wear are among the problems which drilling of composite materials are currently facing. A major difference between metallic and composite plates is their structure: isotropic for metals and anisotropic for composite materials; meaning that while for metallic materials all the structure will respond in a similar manner under the machining loads, the composite structure will have localized responses from the same loads, leading to defects in the internal structure of the remaining work-piece material (i.e. delamination). Delamination can lead to failure in use and parts with such defects are usually discarded. Delamination is not usually visually detectable and special testing is necessary, affecting the costs of the final parts. Delamination during drilling was found to occur at tool entry (peel-up) or tool exit (push-out) and depends on the loads at inter-laminar level. The work presented in the current thesis focuses in providing reliable information about the thrust and torque distribution along the drill radius (and work-piece thickness) during drilling for varying cutting parameters, drill geometry and work-piece material. Such data should assist in the development of delamination models capable of capturing the influence of the drill geometry and cutting parameters on delamination onset and propagation during both exit and entry of the drill in the work-piece. A cutting force model is proposed to obtain the elementary cutting force distribution along the drill radius which is able to account for changes in axial feed rate and drill geometry. Based on oblique cutting, forces are considered on both rake and relief faces. A generic relationship in the form of a transformation matrix is developed to relate oblique cutting to drilling, valid for any drill geometry. The mathematical description of the drill geometry in the scope of cutting force modeling has been revised. The kinematics of the drilling process is now taken into account for (i) all geometrical parameters of the drill and for (ii) the elementary cutting forces decomposition. Additionally, a new drill type and its geometric features have been described mathematically and the definition of the geometrical parameters has been generalized so that other drills types or variations could be easily implemented into the model. It proved therefore possible to adopt simpler expressions for the empirical force coefficients of the cutting force model. Up to four empirical coefficients are used, which are calculated from experiments for each work-piece material and drill type. Most experimental investigations on drilling fiber reinforced composites analyze only the total thrust and torque generated during drilling or separately the forces caused by the chisel edge and cutting lips by drilling with or without a pilot hole. The later type of analysis suggested that is possible to obtain more detailed information about the distribution of the loads in drilling from the analysis of the forces variation during tool entry into the work-piece. Pursuing this direction, an experimental analysis method is proposed to obtain the axial and tangential elementary cutting force distribution along the tool radius or work-piece thickness. The cutting force distribution obtained experimentally was used to calibrate the cutting force model, rather than the total thrust and torque. The experimentally obtained cutting force distribution can also be used alone for analyzing the drilling process (i.e. the loads distribution among the plies of the composite laminate and how this load is influenced by changes in the drill geometry and the cutting conditions).

EPFL2012

Expérience d'un bas-relief de la modernité. Urbanité territoriale

Aurélie Dupuis, Catherine Seiler

Les espaces de fabrication de la ville, de véritables coulisses, ne sont aujourd'hui fréquentés pratiquement que par les hommes qui y travaillent. Ainsi, à la manière d'un théâtre, la découverte des gravières, des zones industrielles ou de production d'énergie, se fait encore bien souvent par delà les plans des aménagements paysagers; lignes d'arbres, rideaux de forêt, murets ou autres talus. Ces derniers dévoilent pour le promeneur attentif de vifs contrastes entre un paysage naturel, construit tel un décor témoin des matières d'alors, et un autre, plus rugueux, remué, agrandi, traduisant une image de nos modes de vie. La distance entre ces lieux infrastructurels immenses et ceux d'une urbanité plus traditionnelle s'amenuise à mesure que le sol se voit consommé, et pose la question de leur interaction à long terme. Ces espaces déjà construits aux caractéristiques différenciées, entrant pour certains dans la désuétude, détiennent un potentiel de réappropriation et offrent une occasion d'assurer la porosité par une mobilité favorable à tout acteur du territoire, tout en ménageant l'espace des champs: les espaces d'infrastructure pourraient alors prendre part aux projets d'une ville-territoire suisse. En ce sens, le territoire du Chablais propose un dispositif conceptuel unique: une large plaine alluviale et une raffinerie en déclin. A la manière d'un bas-relief, signé par un groupe d'hommes et de machines, il présente un répertoire dense et intense des ouvrages et mouvements de terre colossaux de la modernité. Quelles prises nous ont-ils laissées? Dans quelle mesure peut-on s'approprier ces vastes échelles que nous méconnaissons? Pourraient-elles devenir le support d'une nouvelle esthétique? Une urbanité territoriale est-elle envisageable? "

2015

Mechanical load distribution along the main cutting edges in drilling

Mihai-Bogdan Lazar, Paul Xirouchakis

Used in a very large variety of applications, drilling is one of the most complex manufacturing processes. Most of the research on drilling was done in the field of metal cutting since, in this case, high precision and quality are needed. The use of composite materials in engineering applications has increased in recent years, and in many of these applications drilling is one of the most critical stages in the manufacturing process. Delamination and extensive tool wear, affecting the quality and the costs, are among the problems which drilling of composite materials are currently facing. Understanding and predicting the cutting forces occurring during drilling of such materials would allow extending the currently used optimization methods and proposing new tool geometries and tool materials. The current paper introduces a new mechanistic model for predicting the cutting force distribution along the cutting edges of a drill. A simple, generic and effective method is proposed to relate drilling to oblique cutting using a direction cosine transformation matrix valid for any drill geometry. The oblique cutting model used considers forces on both rake and relief faces, and a simple system of empirical coefficients (their number is significantly less than other similar models). The empirical coefficients are calculated assuming the work-piece material is isotropic. The model is validated on experiments carried out on carbon-fiber and glass-fiber reinforced composites using two different drill types (tapered drill reamer and 2-facet twist drill), which are described in more detail in a previous published paper. The mathematical expression of the drill geometry is also reviewed; removing certain assumption, generalizing some definitions and introducing new drill geometry and features.

Elsevier2013

Cutting Force Modelling for Drilling of Fiber-Reinforced Composites

Mihai-Bogdan Lazar

EPFL2012