Papers by Dimitrios Manolakos
Machines, 2022
This paper recommends an alternative designing process for a superior road racing bicycle frame m... more This paper recommends an alternative designing process for a superior road racing bicycle frame manufactured from composite materials that is much faster than typically used design processes. The main design goal is for the rider to be faster under the same riding conditions and with the same effort made. This performance gain is the result of a combined structural and aerodynamic optimization process used during the design process along with the selection of the materials. As the needs of the rider are the focus of this design proposal, the optimization can be carried out only after they are understood. The main difference in this approach compared to the typically used methodology is that, instead of analyzing the frame as a whole from the beginning of the design process and the CFD and CAE iterations, we examine each candidate part of the frame separately. After evaluating the parts’ performances, we select those that performed better to create a single frame. This final frame de...
Precision Engineering, 2011
Electrical discharge phenomena in EDM occur in a very short time period and in a very narrow spac... more Electrical discharge phenomena in EDM occur in a very short time period and in a very narrow space, thus making both observation and theoretical analysis extremely difficult. For this reason, the material removal mechanism in EDM has yet to be understood clearly. In this paper, the forming process of discharge craters in three dimensions was simulated, and material removal mechanism in EDM was analyzed using Molecular Dynamics (MD). It was found that material removal mechanism in EDM can be explained in two ways; one by vaporization and the other by the bubble explosion of superheated metals. It was also found that the metal removal efficiency is 0.02-0.05, leaving most of the melted pool resolidified. In addition, the influence of power density on the removal process was investigated, and the results showed that as the power density increases, the diameter and depth of the melted area increase, as does the metal removal efficiency. In this study, the forming mechanism of the bulge around discharge craters was also analyzed, and it was found that bulge is formed due to two mechanisms. The first is the shearing flow of the molten material caused by the extremely high pressure in the superheated material, and the second is the accumulation of the ejected material on the bulge formed by the first forming mechanism. It was also found that existence of micro pores in the workpiece material increases the depth of the discharge crater and melted area, thereby increasing the machining surface roughness. Simulation of the distribution of removed materials in the gap showed that some part of the removed material becomes debris ejected from the gap, while another part settles on the surface of the opposite electrode, and the last part returns to the surface of the electrode from which it was ejected.
Materials Science Forum, 2016
In this study the influence of natural aging in energy absorbance capacity of 6xxx series extrude... more In this study the influence of natural aging in energy absorbance capacity of 6xxx series extruded profiles after artificial aging is examined by means of optical and scanning electron microscopy, quasi-static compression and tensile tests. Mobile quenched-in vacancies are found to play an important role in aging kinetics and formation of precipitate free zones (PFZs) which govern both the observed fracture modes and the resulting strength of the material signifying their important effect when maximum energy absorbance is desired. It is shown that fracture toughness of naturally aged samples is equivalent or higher compared to that of directly aged samples due to restriction of intergranular cracking.
International Journal of Manufacturing, Materials, and Mechanical Engineering, 2016
In order to manufacture parts with dimensions of nanometres, high–technology equipment is require... more In order to manufacture parts with dimensions of nanometres, high–technology equipment is required. There is a demand to study nano-metric cutting mechanisms and phenomena appearing in this level. However, experiments are difficult to be realized, so computational methods are employed. Nano-scale cutting involves workpiece deformation in only a few atomic layers from the workpiece surface; at this scale the continuum theory cannot be used, so methods like finite elements are not sufficient. Molecular Dynamics is a method increasingly used for the simulation of nano-cutting. However, the computational cost required is quite high. In an effort to reduce the time of the analysis, high or extremely high cutting speeds are used in the models. In this paper an analysis is presented where cutting speed is studied and its influence on the chip morphology and workpiece surface is investigated, for nano-cutting modelling of Cu with diamond tools. The results indicate that cutting speed influe...
International Journal of Crashworthiness, 2008
International Journal of Crashworthiness, 2009
ABSTRACT During a crash event, significant energy must be absorbed by kinetic energy-dissipating ... more ABSTRACT During a crash event, significant energy must be absorbed by kinetic energy-dissipating systems through material plastic deformation. Such systems are thin-walled steel tubes installed in specific places of the vehicle body to reduce the amount of forces transferred to occupants to a required safety limit and to minimise the cargo damage. The present paper deals with the improvement of the response characteristics of structural components by embodying geometrical discontinuities in the form of circular holes. These discontinuities play the role of crash initiators, which can affect the axial collapse mode, by ensuring a stable collapse process and decreasing the initial peak load. Results of both experimental and finite element (FE) simulation of square steel tubes with circular discontinuities subjected to quasi-static axial loadings are reported. The tubular test specimens were manufactured from commercially mild steel S355 tubes and were tested under various schemes of discontinuities (hole diameter, location, etc.). The proposed numerical model using the LS-DYNA explicit FE code was validated employing testing results from the axial loading and was found to be in good agreement with the experimental data.
Conventional programming of Numerically Controlled machine tools is normally based on ISO 6983. I... more Conventional programming of Numerically Controlled machine tools is normally based on ISO 6983. In conventional CNC machining, a part is designed using a CAD system, and that is read into a CAM system. The standard assumes informa- tion flow is from CAD to the shop floor, and doesn't enable feedback of experience from the shop-floor to the designer. In this paper, we introduce STEP-NC, a STEP- compliant data interface for Numerical Control that aims to overcome the problems of ISO 6983 and take advantage of advances in computing and controllers. The new STEP-compliant programming interface is based on an object-oriented data model to ensure that information remains in its context and is not reduced to primi- tive instructions such as G-Codes. Machine tools have ingressive developed in the last years. Nowadays numerical control ma- chines and robots are the main productive power for the modern industry. The pursuit for auto- mated manufacturing process control started in 1950s wi...
Special Issue of the International MultiConference of Engineers and Computer Scientists 2013 and World Congress on Engineering 2013, 2014
Volume 4: Fatigue and Fracture, Heat Transfer, Internal Combustion Engines, Manufacturing, and Technology and Society, 2006
ABSTRACT Electro-Discharge machining (EDM) is a thermal process with a complex metal removal mech... more ABSTRACT Electro-Discharge machining (EDM) is a thermal process with a complex metal removal mechanism that involves the formation of a plasma channel between the tool and the workpiece electrodes and the melting and evaporation of material resulted thus in the generation of a rough surface consisting of a large number of randomly overlapping craters and no preferential direction. EDM is considered especially suitable for machining complex contours, with high accuracy and for materials that are not amenable to conventional removal methods. However, certain phenomena negatively affecting the surface integrity of EDMed workpieces, constrain the expanded application of the technology. Accordingly, it has been difficult to establish models that correlate accurately the operational variables and the performance towards the optimization of the process. In recent years, artificial neural networks (ANN) have emerged as a novel modeling technique that is able to provide reliable results and it can be integrated into a great number of technological areas including various aspects of manufacturing. In this paper ANN models for the prediction of the surface roughness of electro-discharge machined surfaces are presented. A feed-forward artificial ANN trained with the Levenberg-Marquardt algorithm was finally selected. The proposed neural network takes into consideration the pulse current and the pulse-on time as EDM process variables, for three different tool steels in order to determine the center-line average (R a) and the maximum height of the profile (R t) surface roughness parameters.
Applied …, 2009
Page 1. 20 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 19, NO. 1, FEBRUARY 2009 Explosiv... more Page 1. 20 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 19, NO. 1, FEBRUARY 2009 Explosively Consolidated Powder-In-Tube MgB2 Superconductor Aided by Post-Thermal Treatment Athanasios G ...
Abstract: In order to accurately assess the safety of ductile structures, it is necessary to find... more Abstract: In order to accurately assess the safety of ductile structures, it is necessary to find the limit load causing collapse. The advantages of lower-bound solutions for simply supported or fully clamped plates have been reported in several references. The purpose ...
Lecture Notes in Mechanical Engineering, 2017
Metal matrix composites (MMCs) represent a new generation of engineering materials in which a str... more Metal matrix composites (MMCs) represent a new generation of engineering materials in which a strong reinforcement is incorporated into a metal matrix to improve its properties including specific strength, specific stiffness, wear resistance, corrosion resistance and elastic modulus. Aluminum matrix composites (AMCs), a specific type of MMCs, are rapidly replacing conventional materials in various engineering applications, especially in the aerospace and automobile industries due to their attractive properties. From the literature already published it is evident that the machining of AMCs is an important area of research, but only very few if any studies have been carried out using metal particles reinforced AMCs. A multi-parameter analysis of surface finish imparted by turning to a new L316 stainless steel flake-reinforced aluminum matrix composite is presented. Surface finish is investigated by examining a number of surface texture parameters. Spindle speed as well as feed rate was treated as the independent variables under a constant depth of cut whilst roughness parameters were considered as the responses under an L9 orthogonal array experimental design. ANOVA analysis was also conducted to study the effect of the two cutting variables on the surface texture responses.
Wind turbine (W/T) installation in coastal regions is highly beneficial for green electricity pro... more Wind turbine (W/T) installation in coastal regions is highly beneficial for green electricity production. Even though the high velocity of air flow in these areas is a crucial factor, there are also issues in the design and construction of the W/T that have to be examined in order to obtain a high level of energy efficiency. Two major issues are: a) the erosion of the W/T's construction material due to the moisture content and salinity and b) the high and volatile loads at the rotor blades caused by the high velocity of air flow. The purpose of this paper is first to assess the durability of Vertical Axis Wind Turbines (VAWTs) and secondly to calculate and evaluate, with the use of numerical and analytical models, the renewable energy produced. The materials used in the modeling of the rotor blades and the tower of the VAWT are fiberglass-reinforced polyester (GFRP) and anodized aluminum respectively. These materials have been selected due to their resistance in erosion and thei...
In this paper, orthogonal cutting finite elements models are built for the investigation of the i... more In this paper, orthogonal cutting finite elements models are built for the investigation of the impact of large negative rake angles on the friction coefficient in the tool-chip interface in machining. The simulation results give an insight on the mechanism of chip formation in processes with large negative active rake angle, such as machining with chamfered tools, grinding and micromachining. For the present analysis, cutting conditions resembling the qualitative and quantitative characteristics of the aforementioned processes were selected. More specifically, tool rake angles varying from -10o to -55o and Coulomb friction with constant friction coefficient were considered. The results indicate that friction coefficient is greatly affected by the negative tool rake angle, exhibiting values well above 1 for the high extreme of the examined rake angle spectrum. © 2016 Published by Faculty of Engineering Corresponding author: Angelos P. Markopoulos Section of Manufacturing Technology,...
Mechanics of Materials, 2016
In order to perform an in-depth analysis of the failure mechanism of woven para-aramid fabrics, t... more In order to perform an in-depth analysis of the failure mechanism of woven para-aramid fabrics, the width of the specimens in this study is expressed in terms of the so-called "transverse inter-yarn nodal number". This is the number of unit cell nodes on the transverse direction, which determine the width of the specimen. This paper reveals that the latter number is closely correlated with the weaving strength and the failure mechanism mode of the afore-mentioned fabrics under tensile loading. It was found that there are two possible failure mechanisms for woven para-aramid fabrics, an inter-yarn debonding (break of the unit cell nodal bonds and abruption of the fibers) and a fracture (break of the fibers) mode, whose presence in the failure mode depends on the transverse inter-yarn nodal number. In practice, there is a critical inter-yarn nodal number for each fabric, after which a transition from debonding to fracture mechanism occurs. The afore-mentioned critical inter-yarn nodal number plays an important role on the strength of the fabric.
Uploads
Papers by Dimitrios Manolakos