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Fundamentals of Machine Component Design / R.C. Juvinall, K.M. Marshek.
Abstract
Contenido: Parte I Fundamentos: 1) Perspectiva general del diseño en ingeniería mecánica; 2) Análisis de cargas; 3) Materiales; 4) Esfuerzos en los cuerpos elásticos; 5) Deformación elástica, deflexión y estabilidad; 6) Teorías de las fallas, factores de seguridad y confiabilidad; 7) Impacto; 8) Fatiga; 9) Daño a la superficie. -- Parte II Aplicaciones: 10) Sujetadores roscados y tornillos de potencia; 11) Remaches, soldadura y unión con adhesivos; 12) Resortes; 13) Lubricación y cojinetes deslizables; 14) Rodamientos; 15) Engranes rectos; 16) Engranes helicoidales, cónicos y tornillos sinfín; 17) Ejes de transmisión y partes asociadas; 18) Embragues y frenos; 19) Miscelánea de componentes de maquinaria.
... One of the most important equations governing the pressure in the lubricant film is Reynolds Equation, which represents the simplification of the Reynolds's paper in 1886 [2]. To apply this equation to the lubricant film, many assumptions should be considered [3]–[5]: 1. The lubricant flow between the rotating surfaces should be laminar. ...
... This method stayed convenient till the middle of the last century when the analytical and empirical methods have been found. Journal Bearing and Bearing Notation [4], : Load (lbf) L: JB length (in) D: JB Diameter (in) By using the charts below, journal bearing performance parameters can be evaluated: Relationship between Sommerfeld No. and the Minimum Film Thickness [3], [4], [6] Relationship between Sommerfeld No. and the coefficient of friction [3], [4], [6] Relationship between Sommerfeld No. and the minimum film pressure ratio [3], Relationship between Sommerfeld No. and the position of minimum film thickness [3], [4], [6] Relationship between the position of maximum film pressure and the film terminating [3], [4], [6] Relationship between the Sommerfeld No. and the flow variable [3], [4], [6] Relationship between the Sommerfeld No. and the flow ratio [3], [4], [6] The results which evaluated by using the Raimondi and Boyd Charts have an error percentage. Moreover, using charts for calculating the journal bearings performances required many interpolations and extrapolations process which makes this method very tedious. ...
... This method stayed convenient till the middle of the last century when the analytical and empirical methods have been found. Journal Bearing and Bearing Notation [4], : Load (lbf) L: JB length (in) D: JB Diameter (in) By using the charts below, journal bearing performance parameters can be evaluated: Relationship between Sommerfeld No. and the Minimum Film Thickness [3], [4], [6] Relationship between Sommerfeld No. and the coefficient of friction [3], [4], [6] Relationship between Sommerfeld No. and the minimum film pressure ratio [3], Relationship between Sommerfeld No. and the position of minimum film thickness [3], [4], [6] Relationship between the position of maximum film pressure and the film terminating [3], [4], [6] Relationship between the Sommerfeld No. and the flow variable [3], [4], [6] Relationship between the Sommerfeld No. and the flow ratio [3], [4], [6] The results which evaluated by using the Raimondi and Boyd Charts have an error percentage. Moreover, using charts for calculating the journal bearings performances required many interpolations and extrapolations process which makes this method very tedious. ...
This paper illustrates evaluating performance parameters for the journal bearing design by using three different methods. In the first approach, Raimondi and Boyd Charts (Graphical) method will be used. The second approach represents the first analytical method called Reynold equations tables, which can be used by utilizing familiar equations connected by other values. The second analytical method by Reason and Narang (Combined Solution Method) requires using the empirical equation and tables. Finally, the error percentage for all performance parameters for the analytical methods will be compared with the graphical to show which method is more precise. The main goal of obtaining the precise procedure for the journal bearing performance parameters evaluation is to determine the exact temperature rise in journal bearing and the average temperature of the oil film inside the journal bearing. By knowing these temperatures, the designers can select the best type of lubricant oil and bearing material to avoid bearing failure
... Nomenclatures for the rectangular bar of the seat structure using the Euler's Formula[10,11] Nomenclatures for the circular bent rod of the seat structure using the Secant Formula[10,11] ...
... Nomenclatures for the rectangular bar of the seat structure using the Euler's Formula[10,11] Nomenclatures for the circular bent rod of the seat structure using the Secant Formula[10,11] ...
... In the number of machine elements design textbooks, the stress concentration factors (SCFs) for the shaft with shoulder fillet radius are fully explained and sets of stress concentration factor (SCF) graphs were presented by Norton, Shigley and Robert [1,3]. SCF is higher for larger D/d ratio and smaller fillet radius (r) which can be clearly observed from figure 2. Due to mechanical restrictions like space limits or the presence of neighboring parts, it is often challenging to take higher fillet radius [3]. ...
... In the number of machine elements design textbooks, the stress concentration factors (SCFs) for the shaft with shoulder fillet radius are fully explained and sets of stress concentration factor (SCF) graphs were presented by Norton, Shigley and Robert [1,3]. SCF is higher for larger D/d ratio and smaller fillet radius (r) which can be clearly observed from figure 2. Due to mechanical restrictions like space limits or the presence of neighboring parts, it is often challenging to take higher fillet radius [3]. [4]. ...
: In industries, many unexpected failures of machine components occurs due to lack of proper design, sudden changes that happen during working conditions and pre-existing geometrical irregularities. The geometric discontinuities cannot be avoided as they fulfill functional requirements. The shaft or round bar with shoulder fillet is one of the machine components working under different loading conditions. In the present work, shoulder filleted shaft/round bar working under bending loading conditions is taken for study and the stress concentration factor was evaluated. Finite element analysis (FEA) is performed for a total of seven different geometries with different D/d ratios and analyzed them using ANSYS 19.0 workbench software. Based on the equivalent (Von Mises) stresses obtained from the FEA, stress concentration factor (SCF) for the shoulder filleted shaft is calculated and compared with the theoretical results obtained from derived modified Pilkey's equations, Roark's equations, and S. M. Tipton equations. The outcome of results shows that for lower D/d ratios both results were identical in nature but for higher D/d ratios, the results found deviated. The SCFs are decreased with increasing D/d ratios. The results of SCFs are presented in the form of graphs for comparison purpose as well as one can refer it for his/her applications.
... (number ot strips t0r layer 1) n~ = 1 (number of strips for layer 3) al = -87.5 deg (laying angle evaluated for layer 1) E~ = 190 GPa (elastic modulus for stainless steel according to Juvinall and Marshek (1983)) E3 = Es = E7 = 207 GPa (elastic modulus for carbon or alloy steel, according to Juvinall and Marshek (1983)) E~ = 300 MPa (elastic modulus assumed for layer 8) ...
... (number ot strips t0r layer 1) n~ = 1 (number of strips for layer 3) al = -87.5 deg (laying angle evaluated for layer 1) E~ = 190 GPa (elastic modulus for stainless steel according to Juvinall and Marshek (1983)) E3 = Es = E7 = 207 GPa (elastic modulus for carbon or alloy steel, according to Juvinall and Marshek (1983)) E~ = 300 MPa (elastic modulus assumed for layer 8) ...
This paper shows the derivation of an analytical model for the local analysis of unbonded flexible pipes, which can be used as risers in offshore applications. All of the loads considered are axisymmetric, which include: axial force, twisting moment as well internal or external pressures. Prescribed displacements on the pipe's extremities, such as those producing an elongation and/or an axial rotation of the pipe, can alternatively be considered in the model, instead of the axial force and twisting moment. The possibility of gap formation between any two adjacent layers of the pipe is taken into account, rendering the obtained system of equations non-linear. This non-linear system is then solved numerically for all the unknown of the problem, stresses or displacements. In order to verify the consistency of the proposed analytical model, results are compared with a finite element based model analysis, which, for its turn, takes some guidelines from the analytical one. The results shown in the paper concentrate mainly on the analysis of axial stresses of armour steel layers. Additionally, the adequacy of the analytical model is verified by comparing calculated values of axial and torsional stiffness with corresponding experimental data, previously published in the literature. The agreement is found to be very satisfactory in all comparative analyses, either analytical x FEM result or analytical x experimental data.
... The classical analysis presented e.g. in the machine design treatise of Juvinall and Marshek [7] was adopted for the fatigue study. This involves the Basquin law and Goodman diagram, and the relationship between ultimate tensile strength and fatigue limit. ...
A durability design case study concerning a U spring is presented. For a given geometry of the component, the question was to predict the maximum permissible displacement per cycle whilst ensuring a service life of at least 260 kcycles. The stiffness of the spring was evaluated using the finite elements software SolidWorks. As an approximation a linear model was used in the finite elements analysis, which was also compared with an analytical treatment based on Castigliano’s theorem. Using a given safety factor, a high cycle fatigue analysis was performed assuming the use of a steel with 650 MPa ultimate tensile strength. The spring is either loaded by an imposed displacement, or it is load free, i.e. load ratio (minimum load / maximum load per cycle), is R = -1. An algorithm based on finite fatigue life prediction techniques, the Basquin and Goodman diagrams, and the relationship between ultimate tensile strength and fatigue limit was used and will be briefly presented and discussed. Also, the stress analysis helped to highlight the need for some minor geometry changes. The outcome of the study was the evaluation of the maximum permissible displacement per cycle, as required in the real life case addressed.
... This is a traditional approach [6,7] for teaching the DME course. The justification for this approach was that mechanical design is based on design theory, so students must have solid understanding theoretical calculation of the stress/strain. ...
... Taking into account the allowable tensile strength of M6 bolt and the yielding strength of the aluminum beam, 10 N m is selected to be the normal torque value in this work. The famous torque-tension relationship is used to convert the bolt torque T to contact pressure P , defined as [35], where k is the nut factor and k = 0.2 is often used, D is the nominal diameter of the bolt and S is the washer covered area. ...
Loss of preload in pretensioned bolts is inevitable. Reliable monitoring of bolt preload is significant to ensure structural reliability and safety. This paper proposes a modified time reversal method for bolt loosening monitoring. In this method, both phase shift and signal amplitude of the focalized wave packet in the reconstructed signal are extracted as tightness indices. To this end, the conventional time reversal method is modified. Initially, for a nominal healthy structure, the conventional time reversal method is performed. The reemitted signal used in this step is recorded as a ‘standard’ reemitted signal. Then, the ‘standard’ reemitted signal is inputted back to the structure for detecting damage. If the structure is damaged, the focalized wave packet in the reconstructed response signal due to the ‘standard’ remitted signal can have both phase shift and peak amplitude difference compared to the focalized wave packet at the healthy state. The main difference between the modified time reversal method and the conventional method is that for all damage cases the proposed method uses the same remitted signal which is recorded for a nominal healthy structure. Numerical and experimental studies are performed to validate the effectiveness of the proposed method for quantitative monitoring of bolt preload in a lap-jointed specimen. The experimental results of the proposed method are compared with those the wave energy dissipation based and the conventional time reversal methods. It is found that the proposed method outperforms the other methods in terms of accuracy and the sensitive range for bolt loosening detection.
... MECH 4003 was delivered via FCI using assigned textbook readings [13]. The textbook is mandatory and has been used for many years within the course and a prerequisite course. ...
Flipped classroom instruction places the transfer of information outside of the class and focuses on the application of the information in the class. Applying flipped classroom instruction to engineering design courses is challenging because design is open-ended.Three approaches were tested for second year and fourth year students taught by the same instructor in six course offerings. All course offerings used case studies. Three offerings were taught using traditional methods such as blackboard notes or PowerPoint presentations. The other course offerings used flipped classroom instruction that applied assigned textbook readings or assigned, instructor-created YouTube videos. A statistical assessment of the final exam scores show that flipped classroom instruction using assigned textbook readings result has a negative impact on final exam performance. YouTube videos and case studies have positive impacts on final exam performance.
... Design a pair of spur gear to transmit 20kW at pinion speed is 1400 rpm, transmission ratio is 4. Assume suitable material and stresses34567. Calculated center distance is greater than the early calculated one. ...
Power or energy production is improbable everywhere due to various factors. For assorted applications, people depending source of power.This shows the need of transmission of power. Considering power transmission of mechanical drives, mesh type of drives are largely used to maintain the velocity ratio. Among mesh type, gears transmitting the power by means of successive engagement of their teeth. Design of gears either by manually or using computers has become a highly convoluted and comprehensive subject. Therefore, this study present a new method of how the gears can be designed and detailed with computer, previously, highlighting the design process which involves prolong time. A reliable software package developed with a help of Visual Basic 6.0 (VB) provides significant saving time reduces its convolution.
... В Україні вимоги до виготовлення МК кранів взагалі та КБ зокрема регламентуються галузевими стандартами, де представлено ряд конструктивних і технологічних ре комендацій та вказано, що зварювання МК виконується за технологічними документами, в яких повинні бути передбачені порядок накладання швів та режими зварю вання. Технологія і режими зварювання оказують значний вплив на міцність конструкції [2][3][4][5], при цьому науково обґрунтованих рекомендацій щодо режимів накладання поясних швів кранових КБ на цей час не існує. Цим обґрунтовується актуальність проведеного дослідження. ...
The residual stress-strain state of welded joints of cranes’ steel structures is understudied scientific and technical issue. Finite-element analysis of the post-weld residual stresses in longitudinal T-joints of overhead cranes’ box girders was applied to this study. Goldak’s moving heat source model based on double-ellipsoid heat flux distribution was used. Thermal and mechanical tasks were sequentially solved, wherein the phase transformation processes were taken into consideration. The effects of such factors as box girder geometry, welding speed, pre-heating technology on the residual stresses and phase distribution in longitudinal welds were further investigated.
The post-weld stress-strain state of the box girders’ T-joints was detailed. The recommendations to streamline the overhead cranes girders’ production technology intended to improve their quality and overall technological level were formulated. The necessity of taking into account the phase and structural transformations in the simulation is proved. The requirements for the finite-element modeling of longitudinal T-joints were established.
... The design of a shaft is generally done based on the application and uses of the shaft [3]. Here in this case the design was made keeping the fact that it will be used in a rear axle transmission system. ...
This paper describes the failure analysis of an intermediate shaft used in a prototype, which had been failed during the trial run of the prototype. The shaft was found to be bending. The investigation was carried out in order to establish whether the failure was the cause or a consequence of the accident. A study of the bend shaft shows how vulnerable such a rotating component can be to failure by fatigue, even when operating under steady conditions, if basic preventative design actions are not taken. The analysis considers the effects of both transmission torque and weight (thus bending) upon stress levels and assesses their individual affect on the breakage and upon any subsequent modifications needed to improve the design. Results indicate that the axle shaft bends due to fatigue as a result of improper design. The drive shaft arrangement is compared with the feasible alternative of using a driven wheel arrangement rotating on a stationary axle. Findings confirm the importance of recognizing in advance the salient factors leading to fatigue and the necessity in paying adequate attention to detail during design and manufacture if long service life is to be achieved.
... Such observations offered a basis for procedures to construct the notched member S–N curve if the material fatigue limit or even the material tensile strength only is known, e.g. [9,10]. These types of predictions are, however, not adequate for the present coupons because for the axial loadings, the notched specimen fatigue test data exhibit a slope (exponent n in Basquin equation) very close to that of the corresponding smooth specimen test data, whilst for bending, the un-notched S–N curve (n = À0.45) is even steeper than the notched curve (n = À0.32). ...
... An important example is the analysis of the REXIS baseplate bolted joints that mount the spectrometer to the spacecraft deck. Further detail on joint analysis and design can be found in additional sources [33] [36]. ...
Engineers of space flight programs face unique technical challenges created by the space environment in which these systems operate. High costs and increasing complexity of space programs create a greater demand for mission reliability. This demand further drives up development costs and project time lines. The result is that few missions are flown and few organization are able to participate in space program development. Project budget and schedule overruns are in part a result of a risk-averse culture and the desire the create fail-proof systems. Resource constrained programs will have difficulty developing successful space systems if they attempt to fully address every risk. Rather, by taking a risk-tolerant posture, resource-constrained programs can more efficiently allocate resources to the most important areas of a system's development. By focusing effort and resources on high-risk areas, successful space programs can still be developed with lower budgets and smaller schedules than has traditionally been done. Recent attempts to lower the time and budgets necessary to develop space systems have focused on developing smaller, less complex, and more numerous space system to replace traditionally larger, more expensive systems. The benefits of small space systems range from distributing risk across multiple systems and thereby lowering the cost of failure, to providing smaller organizations and universities the capabilities to develop their own space systems. Though these programs are cheaper, many organizations of small space systems are faced with limited resources that must be intelligently allocated to develop successful space programs. This thesis presents the structural design, analysis, and testing of the REgolith Xray Imaging Spectrometer (REXIS), a student-led instrument on board the National Aeronautics and Space Administration (NASA) Origins Spectral Interpretation Resource Identification and Security-Regolith Explorer (OSIRIS-REx) asteroid sample return mission. As part a student experiment, the REXIS team must develop its system under tight resource constraints. The limited funding, personnel, equipment, and facilities available to the REXIS team all have important implications on how design, analysis, and testing decisions are made on REXIS. This thesis provides a discussion of key areas of the REXIS structural development and lessons learned from a structural engineering point of view. Chapter 1 opens the discussion by talking about the motivation behind this thesis. It provides background information to the REXIS instrument and the context for the rest of the instrument discussion. The REXIS flight structural design and how this design facilitates the accomplishment of REXIS goals is presented in Chapter 2. Next, the analysis and testing of the Radiation Cover, one of REXIS's most critical elements, is described in Chapter 3. The key efforts taken on the REXIS structural development is discussed in Chapter 4. This particular section, through the discussion of the chronological development of the REXIS flight structural design, will highlight important areas of where efforts was focused on REXIS within the project constraints. Lastly, Chapter 5 provides lessons learned from a structural engineering point of view from the experiences on REXIS. Although the discussion focuses on the REXIS structural development, the examples and discussions described are relevant to other programs. This thesis is meant to provide insight into the REXIS development from which engineers of future small space programs can learn.
Generally, the fatigue strength of a welded structure is characterized by certain factors, which are incorporated in the detail categories and S-N curves as a statistical variation. However, digitized welding production enables the precise control and evaluation of the fatigue-related design and manufacturing parameters at different levels; this can be utilized when applying modern fatigue assessment methods. The fatigue strength of a weldment is usually evaluated based on idealized and standardized factors, but the availability of measured parameters can improve the accuracy of fatigue analysis. In this study, the validity of general design simplifications is compared with actual measurable parameters. Different factors, such as loading, global structure, structural detail, local weld geometry, initial defects and residual stresses, are identified, and their effect on the total fatigue life is evaluated. To exemplify the outcomes of different factors, the fatigue strength of a mobile working machine is evaluated using idealized and measured parameters. The results indicate that the idealized model can produce distinguishing features compared to the real structure, whereby the scatters of individual factors have an essential effect on the deviation in the fatigue assessment results. However, the case study reveals that when the fatigue analysis is conducted using the effective notch stress (ENS) method, the actual weld shape has a minor effect on the results compared to the idealized geometry. Thus, the analysis and efforts must be focused on those factors that have a considerable impact on the reliability of theoretical results in practice and a substantial effect on the quality of weldments.KeywordsFatigue lifeWelded structuresDesign and fabricationDigitized productionWeld qualityQuality parameters
The direct dynamics of a body in planar motion is studied. The equations of motion are developed with symbolic MATLAB. At a certain moment an external elastic force acts on the body. MATLAB ODE solver is employed to integrate the equations taking into consideration different events. The impact of a free kinematic link with a surface is also studied. The results are obtained with Newton-Euler and Lagrange methods.
A planar R-RRT-RTR mechanism with two dyads is considered. There are two independent closed contours for the velocity and acceleration fields. For dynamic analysis D’Alembert principle is employed to calculate individual joint forces.
Main components of the gears are defined. The angular velocities of epicyclic gear trains are calculated using the classical method and the closed contour method.
The planar motion of a mechanism with three moving links is analyzed. Symbolical and numerical MATLAB are used for the kinematics and dynamics of the system. The classical vectorial equations for velocity and acceleration of the rigid body are used. The joint reaction forces and the moment applied to the driver link are calculated for a given position with Newton-Euler equations for inverse dynamics.
A cam and follower mechanism is analyzed. Same kinematic results are obtained with an equivalent mechanism. The differential method is used for velocity analysis.KeywordsCam and follower mechanismEquivalent linkagesDifferential method
The Mechanical Engineering essence is the understanding of all the available resources, their effective utilization, and making use of the law of nature to help, gain and benefit the entire humanity. Mechanical Engineering is the applied science using scientific knowledge and procedures as the means to accomplish a specific practical and useful results. It is related to the sense that involves a proper understanding of all the scientific principles and effectively applying them to attain the designated goal. The machine design in mechanical engineering is the most crucial section of engineering, and it deals with the design, conception, refinement, development of machines and component application together with the mechanical apparatus of every kind.
In the professional engineering, the main concern is to obtain the requisite solutions to all the practical problems in the machinery production. The solutions should reflect the knowledge, understanding and application of the underlying technology and science. However, normally the mere understanding is not sufficient. The related empirical knowledge together with engineering judgment become the most prerequisite. For instance, no scientist can entirely understand electricity. However, it does not prevent any electrical engineer from creating highly useful and functional electrical devices. Likewise, no scientist can fully understand metal fatigues and combustion procedures, yet, the mechanical engineers utilize the knowledge and insight available to generate highly useful and functional combustion engines. When more scientific solutions are accessible, engineers can devise better explanations and clarifications to practical problems. This study tries to analyze and evaluate the perception and usefulness of AM- additive manufacturing systems and technologies to understand machine elements, product design and its development.
The Mechanical Engineering essence is the understanding of all the available resources, their effective utilization, and making use of the law of nature to help, gain and benefit the entire humanity. Mechanical Engineering is the applied science using scientific knowledge and procedures as the means to accomplish a specific practical and useful results. It is related to the sense that involves a proper understanding of all the scientific principles and effectively applying them to attain the designated goal. The machine design in mechanical engineering is the most crucial section of engineering, and it deals with the design, conception, refinement, development of machines and component application together with the mechanical apparatus of every kind.
In the professional engineering, the main concern is to obtain the requisite solutions to all the practical problems in the machinery production. The solutions should reflect the knowledge, understanding and application of the underlying technology and science. However, normally the mere understanding is not sufficient. The related empirical knowledge together with engineering judgment become the most prerequisite. For instance, no scientist can entirely understand electricity. However, it does not prevent any electrical engineer from creating highly useful and functional electrical devices. Likewise, no scientist can fully understand metal fatigues and combustion procedures, yet, the mechanical engineers utilize the knowledge and insight available to generate highly useful and functional combustion engines. When more scientific solutions are accessible, engineers can devise better explanations and clarifications to practical problems. This study tries to analyze and evaluate the perception and usefulness of AM- additive manufacturing systems and technologies to understand machine elements, product design and its development.
Additive manufacturing (AM) has the ability to design ankle–foot orthosis (AFO) using different materials, shapes, and sizes with characteristics for functional and reliable clinical applications. Nowadays, for custom-AFOs for the patients, the designers are looking for optimization of weight, shape, structures, thickness and functional characteristics using AM. The objective of this study is to manufacture a customized AFO using AM with fused deposition modeling (FDM) and also compare it with traditional manufacturing route. Dimensions were measured using a 3D scanner, followed by CAD modeling and manufacture with AM using FDM. The model fit was then tested for mechanical properties, vibration analysis and flexibility of the AFO. A clinical case study methodology was applied to a 22-year-old patient suffering from drop-foot and the patient showed improved gait performance. The study showed that FDM based framework is best suited for the application of designer/customized AFO being more flexible, light in weight and took lesser manufacturing time compared to traditional manufacturing.
The suspension assembly of a vehicle is a vital component in its ability to function safely and effectively. This paper details the design and simulation of the James Cook University Motorsports 2nd generation vehicle for the Formula Society of Automotive Engineers competition. After in-depth research it was decided that a pull-rod suspension system would be the most effective assembly for the Gen 2 car. Contrary to the current push-rod suspension on the Gen 1 car, the pull-rods allow the centre of gravity to be lowered, which is ideal. Working closely with the rear drive train, cockpit and upright teams, a design was conceived and developed. After several redesigns a final model was able to be created. SolidWorks was the tool used to generate the components created in the design phase. This is an extremely powerful program that allows the user to not only produce a three-dimensional component but also allow future modifications to be made to the component to change its dimensions. It was decided this was a vitally important ability, as future modifications will be needed when less conservative loading cases are discovered and then applied. The SolidWorks models where then transported to a computational simulation program, ANSYS. ANSYS, like SolidWorks, was an important tool in verifying design assumptions and concepts. With this program loading cases where able to be applied to the system to understand how they would react and if they would fail under the stresses applied.
Script MC carbides are easily formed in the welding of Ni-base superalloys. In this study, the effect of script MC carbides on the tensile behavior of laser-welded DZ125L/IN718 joints in the fusion zone was investigated. The phase size, phase distribution and element distribution of script MC carbides, and the orientation relationship between script MC carbides and γ matrix were carefully analyzed using SEM, EDS, TEM and HRTEM. The breaking behavior of script MC carbides was investigated through interrupted tensile testing at 650 °C. The results demonstrate that the script MC carbides are distributed in the interdendrites with an average size of 3.5 \(\pm\) 1.6 μm. They are (Ta, Nb, W, Ti and Mo)C and incoherent with the γ matrix. The fine script MC carbides are beneficial for improving both the strength and ductility of the fusion zone by improving coordinated deformation with γ matrix. However, the script MC carbides are found broken very early. About 9% script MC carbides have been broken after welding. The number of broken carbides increases with the increasing plastic strain. The majority of the cracks are found at the necks of the script MC carbides. The breaking mechanism of script MC carbides reveals that the high breaking tendency of the neck is attributed to the relatively long arm length and, more importantly, to the minimum section width size. Modifying the carbide morphology into a sphere is suggested for lowering the breaking tendency of MC carbides.
Cast Al alloys are widely employed for engine components, structural parts, gear box, chassis, etc. and subjected to mechanical cyclic load during operation. The accurate fatigue life prediction of these alloys is essential for normal operation as fatigue cracks initiated during operation induce the lubrication oil leak and serious safety hazard. Microstructural heterogeneity, including shrinkage/gaspores and secondary phase particles, is the most detrimental factor that affects fatigue life of cast Al alloys. The approximate fatigue life cycles could be estimated based on the size distribution and locations of shrinkage pores/defects. The relationship between crack population and stress was reported by statistical distributions and the cumulative probability for cast Al alloys fail at a certain stress could be predicted by combination of Paris law and pore size distribution. Pore depth was found to dominate the stress field around the pore on the surface and the maximum stress increases sharply when the pore intercepted with the surface at its top. The microstructure of cast Al alloys usually is composed of primary Al dendrites, eutectic silicon, Fe-rich particles and other intermetallic particles are dependent upon alloy composition and heat treatment. The coalescence of microcracks initiated from the fractured secondary phases was clearly found and can accelerate the initiation and propagation of the fatigue cracks. A link between defect features and the fatigue strength needs to be established through a good understanding of the fatigue damage mechanisms associated with the microstructural features under specific loading conditions. This paper reviews the influences of shrinkage/gaspores and secondary phase particles, formed during casting process, on the fatigue life of Al-Si-Mg cast Al alloys.
Margin occurs where a design is overspecified with respect to the minimum required. Margin may be desirable to mitigate risk and absorb future changes, but at the same time, may be undesirable if the overspecification deteriorates the design’s performance. In this article, the margin value method (MVM) is introduced to analyse an engineering design, localise the excess margin, and quantify it considering change absorption potential in relation to design performance deterioration. The method provides guidance for improving a design by prioritising excess margin that provides relatively little advantage at high cost, and that could, therefore, be eliminated to improve design performance. It shows how the value of excess margin depends on its localisation in the design parameter network, the importance of design performance parameters, and the importance of absorbing potential future changes. The method is applied to a belt conveyor design. This case indicates that the method is practicable, reveals implications, and suggests opportunities for further work.
In this chapter, a general survey is first done on the tooth bending strength of spur and helical gears, also focusing attention on fatigue tooth root breakage and safety factor to be used for their design. The theoretical bases of calculation of tooth bending strength are then discussed, with particular reference to the constant strength parabola introduced by Lewis and 30° tangent lines proposed and used subsequently. Stress state at the tooth root is then analyzed, considering the load application at the outer point of single pair gear tooth contact as well as the local stress concentrations, also due to combined local notch effects. Finally, the procedure for calculating the tooth bending strength of these types of gears in accordance with the ISO standards is described, highlighting when deemed necessary as the relationships used by the same ISO are founded on the theoretical bases previously discussed.
Os objetivos centrais desta monografia, intitulada “Análise e Síntese de Trens de Engrenagens”, passam por (i) apresentar alguns dos principais tipos de trens de engrenagens comummente utilizados em máquinas e mecanismos, (ii) descrever os métodos frequentemente usados na análise cinemática de trens de engrenagens simples e complexos, bem como (iii) estabelecer procedimentos gerais que permitem efetuar a síntese de trens de engrenagens.
Nowadays, electric vehicles are becoming more popular day by day. Prototypes of such vehicles are being built extensively; however, cost of them is usually very high. This study presents novel approaches for design and manufacturing of an electric vehicle chassis and its fixtures with very low cost. The chassis is tub type and its original structure is formed regarding manufacturing simplicity, lightness, robustness, and low cost. This novel chassis is formed by planar and simple aluminum profiles that are readily available in stocks of producers. The design philosophy of the chassis is discussed in detail. Finite element analyses of the chassis are adopted for various crash impact loading scenarios and torsional rigidity. Also, original fixture designs for low-cost manufacturing are introduced in this study. Manufacturing cost of the chassis, fixtures, and the vehicle is presented. After road tests, the results are presented and discussed. It is evidenced that a lightweight and low-cost chassis built from simple planar parts may perform very well. Electric vehicles possessing such simple and robust chassis may be popular due to the manufacturing advantages against today’s extremely complex designs.
This paper numerically models the behavior of double-shear, single-bolted joints in wood-steel structures when subjected to very large deformations and compares results with test information. A three-dimensional finite-element model is developed of the main Douglas-fir wood member, steel side plates, bolt, washers, and nut. The model accounts for friction, bolt clearance, progressive damage in the wood, nonlinear and inelastic behavior in the steel bolts and side plates, and complete (linear and nonlinear) compressive constitutive response parallel to the grain in the wood. Hashin’s 3-D failure criteria are used to predict the onset and type of damage. Once failure is detected, and its mode identified at a particular location, material properties there are degraded to simulate the loss of load carrying capacity. The predicted load versus displacement results correlate with experiment. The present numerically determined displacements exceed by seven times those previously reported for bolted wood joints.
An experimental and numerical investigation of fatigue life and crack propagation in two-dimensional perforated aluminum structures is presented. Specifically, the performance of positive Poisson’s ratio (PPR) geometries using circular holes is compared to that of auxetic stop-hole and straight-groove hole geometries. Mechanical fatigue testing shows that the considered auxetic structures have more than 20% longer life than the porous PPR structure at the same porosity and peak effective maximum stress despite having holes with larger stress concentrations. Digital image correlation is used to detect crack initiation and damage propagation much earlier than can be detected by the unaided eye. Accompanying finite element analyses reveal that auxetic structures have the advantage over their PPR counterparts by delaying crack initiation, spreading damage over a larger area, and having a stress intensity factor that decreases over a significant range of crack lengths. In addition, numerical simulations suggest that auxetic structures maintain their negative Poisson’s ratios in the presence of cracks.
A method of program load spectrum compilation suitable for ALT (accelerated life test) of parabolic leaf spring was presented. In order to shorten the design and test period, road test is conducted on proving ground roads. The displacement spectrum of shock absorber connecting the point of the parabolic leaf spring seat on a commercial vehicle exposed to roads was obtained. The FEA (finite element analysis) method was used to obtain stress spectrum of hot spots on leaf spring by the displacement spectrum, and the fatigue life of the leaf spring is predicted using Palmgren-Miner’s rule. Statistical characteristics of the amplitudes and means of the displacement spectrum is investigated. The amplitudes and means of displacement spectrum found in experiment obey Weibull distribution and normal distribution respectively, and the distributions of amplitudes and means are independent. Based on the Conover principle, the two-dimensional spectrum with eight levels is established by applying the cycle extrapolation method, and then it is converted into one-dimensional spectrum with the variable mean method. Follow the theory of equal damage, the program load spectrum is compiled suitable for bench test of fatigue life of leaf spring. The method of program load spectrum compilation can provide reference for fatigue life test and life prediction of parabolic leaf spring assembly.
The purpose of this study is to identify the causes of the continuous failure of center-link chains for a trolley conveyor system by analyzing their failure characteristics under static and dynamic loading conditions and to propose methods for securing their mechanical integrity. For this purpose, center-link chains were minimally processed to prepare testing specimens with their original surface property and structural dimension maintained. These specimens were used to measure the tensile strength (1172.1 MPa), elongation (8.7%), yield strength (1073.4 MPa), hardness (44.1 HRC), and surface roughness (\(R_{a}\) = 10.5 μm). A three-point bending fatigue test (R = 0.1) resulted in a fatigue limit of 746.7 MPa. The results confirmed that the rough surface of the center-link chain caused a reduction in the elongation and fatigue limit and an increase in the scattering of the surface hardness and fatigue life, which were the direct causes of frequent chain failure in the field. To improve the fatigue life of the center-link chain, two methods were reviewed in this study. The first method was to reduce its surface roughness through surface machining of the center-link chain, and the second was to modify its shape design to allow improved structural integrity, even if the current surface roughness is retained. In the case of the first method, the results of the fatigue test using the specimen with reduced surface roughness (from \(R_{a}\) = 10.5 to 0.9 μm) by surface machining demonstrated reduced scattering and increased fatigue limit (from 746.7 to 920.3 MPa). As for the second method, a stiffener was added and two design variables (slope angle and fillet radius) of the stiffener were selected to propose a new design that can reduce the maximum stress ~ 1.6 times compared to the conventional design. While both methods for improving the structural integrity of the center-link chain were effective enough to improve the fatigue life of the chain, the second method, which requires only the initial mold manufacturing cost for modifying the shape design of the chain, was finally selected, because it exhibited better economic feasibility than the first method that increases the product cost and overall process time due to addition of the surface machining process.
In this paper, we study families of optimal frames of aircraft, as the fuselage cross-section vary, in the preliminary design. A complete closed-form solution of displacements and stresses for a circular arc, already introduced in a previous paper of the authors, is applied to study, in a wide generality, a fuselage cross-section made of tangent circular arcs, connected together in a \({\mathscr {C}}^1\)-class curve. The closed-form solution is used here for two optimization case studies involving such piece-wise tangent cross-sections. First, we obtain minimum weight configurations of frames under pressurization, and also the effect of a small eccentricity with respect to the perfect circular fuselage is investigated; then, the constraints due to the presence of two floor decks are introduced. Second, the analytic solutions are validated by means of a finite element simulation in Abaqus and, to show the generality of the closed-form solution, the case studies are dedicated to non-conventional aircraft. Finally, we investigate the effects of the ellipticity ratio and the presence of a vertical and horizontal truss by means of finite element beam models.
This paper proposes a new design method for predicting the finite lifetime of mechanical assemblies subjected to constant amplitude (CA) fretting fatigue loading. The proposed methodology is based on the use of the Modified Wӧhler Curve Method (MWCM) applied in conjunction with the Theory of Critical Distance (TCD) and the Shear Stress-Maximum Variance Method (τ-MVM). In more detail, this engineering approach uses the τ-MVM to calculate the stress quantities relative to the critical plane, whose orientation is determined numerically by locating the plane containing the direction experiencing the maximum variance of the resolved shear stress. To estimate the fretting fatigue lifetime, the time-variable linear elastic stress quantities are post processed according to the MWCM applied in conjunction with the TCD. The proposed approach was checked against experimental data taken from the literature and generated by testing specimens made of aluminium alloy Al 7075-T6. The extensive validation supports the idea that the MWCM applied in conjunction with both the TCD and τ-MVM can be suitable to predict the finite lifetime of mechanical assemblies subjected to fretting fatigue loading.
Gear size is one of the most important criteria in design optimization of gear set used in automotive, aeronautical and various other applications. Smaller gear size results in requirement of less material and hence reducing manufacturing cost. This paper aims at minimizing center distance of spur gear set to obtain its corresponding optimal design variables. Design variables included in this study are diametrical pitch and number of pinion teeth. Real Coded Genetic Algorithm and simulated annealing are employed for performing design optimization procedure. In this study, along with constraints on bending strength, contact strength, interference and contact ratio, scoring has been added as design constraint in design problem. All the design factors included in design procedure are considered as per AGMA standards. The recommended optimization techniques are implemented on a design example and optimum values of design variables are obtained. The obtained results are compared with those obtained by traditional design procedure to find the better solution as well as better optimization technique. Variations in input power and gear ratio have been done to verify their effect on the objective function and to further investigate a more useful optimization technique for gear design.
Treatment options for limb deformities were delevoped through time and Taylor Spatial Frame was indicated as a Stewart Platform based external fixation system that superior in terms of correction and ease of use. New external fixator (i.e. Ross’s external fixator) was created as solution from Taylor Spatial Frame’s problems. Several changes on Taylor Spatial Frame design were made to create Ross’ external fixator. However, Ross’ frame may have stability issue as consequence from Taylor’s design changes. Comparation of these frames is needed to develop limb deformities treatment. This paper is focused on the design performance of external fixator’s rings based on Stewart Platform. Taylor Spatial Frame’s and Ross Frame’s ring are compared and evaluated in design form. Both ring models are presented using Autodesk Inventor 2016. Numerical Modelling (i.e. Finite Element Analysis) used for compare both rings design performance. The comparation results will be useful for further research in ring fixation product development.
In the early stages of engineering design, numerous concepts may be envisioned and suggested. Considering normal time constraints, a large degree of design freedom may be a major challenge at this stage. Candidate concepts should be reviewed quickly and the final choice should be correct. In this regard, a simplified evaluation criterion based on cost, simplicity, and safety is suggested. Cost is estimated by required level of tolerance. Simplicity is represented by the number of parts, assembly steps, and fasteners. Safety is assessed by the level of potential failure. The proposed criterion is applied to an example swivel structure for a flat panel display stand.
Objective
Mathematical model of an Un-Coiling Idle Coiling (UCIC) process has been used to estimate strip tension T and has combined with a controller to operate the UCIC system because T should be applied to a strip of the UCIC system to coil the strip uniformly. This paper suggests an advanced mathematical model of the UCIC process based on the previous model for winding a web to increase accuracy for estimating T.
Methods
To conduct numerical integration of structural dynamics equations; the suggested model consists of equations of motion and state variable equations. Geometrical variations including radius of the coil r, eccentricity of the coil lecc, and effective strip tension Teff with slip behavior among contact layers are renewed automatically in numerical analysis.
Simulation
The suggested model contains real operating conditions and design variables, and is calculated by Newmark's method to get dynamics responses. Moreover, planar motions are defined in the equations of the motion to check how T and dynamics responses of the un-coiler, the pinch roller, and the coiler affect each other. The planar motions have translational motions by applying spring stiffness k x and k y on the center of the rotor that correspond to elastic deformation of a bearing and a shaft.
Conclusion
Using the suggested model, T and unusual vibrations that are caused by improper coiling conditions are predicted quickly compared to a Finite Element (FE) model. Especially, Teff is similar to real T profile compared to the previous tension model when two tension models are validated with the FE model of the UCIC process.
Students with relatively low affinity and/or weak ability for science and mathematics have been presently acknowledged into Mechanical Engineering (ME) departments around the world. This has resulted in apparent lowering of fully competent graduate engineers, due to insufficient comprehension and its concomitant cognitive issues. Now, the complexity and the demand of ME education have been extremely unbalanced with recruited students. This conflict between the education process and less knowledgeable students has been adequately acknowledged, but remedies for this global issue are not yet available. This is no longer sustainable. The paper gives insight into (individual and combined) plausible reasons for fewer fully competent graduate engineers, taking the specific case study in Turkey. It proposes a generic approach, which can be extended to courses of any university/degree subject. Findings on student learning are provided using a hierarchical decomposition. A proposed remedy for this issue has been thoroughly evaluated, and accountability measures, qualitative data and a survey has been conducted for the ME design course taught in Turkey. The findings indicate that the new recruits are not fully to blame for the conflict, because there have also been other reasons for the issues within teaching. It identified multiple instances of the reasons such as unnecessary complexity of textbooks, unsolved contradictions even between the technical component design standards and etc. If these are considered by educators, this will help to reduce the perceived degree of teaching difficulty, and have a positive effect on the quality of graduates. It may even assist in attracting higher ability students into ME.
Rolling contact testing requires understanding of friction, lubrication transfer, and a common framework from which to calculate contact stress between rolling contact elements. So long as the calculations and assumptions for each of these topics are consistently applied across all experiments, the resulting experimental data is very useful to assess coating performance. Often, data from tests involving friction are fit to an empirical model set of equations. There are numerous references concerning the foundational aspects of friction and wear, “Friction and Wear of Materials,” by Rabinowicz, and “Engineering Tribology,” by Stachowiak and Batchelor to name a few. More recently, textbooks concerning wear and friction of thin film coatings and surface engineering have emerged as well, “Coatings Tribology: Properties, Techniques and Applications in Surface Engineering,” by Holmberg and Matthews, and “Surface Modification and Mechanisms,” by Totten and Liang. A more general approach to friction has been proposed by Nosonovsky and Mortazavi (2014), considering friction and the associated processes of wear as a universal and general phenomenon, independent of how the friction is generated. This approach removes the distinction between wear in rolling contact systems, such as ball bearing sets and sliding contact wear mechanisms in reciprocating machinery, for example, and presents a thermodynamic connection for all types of wear.
Accelerated life testing has major impact on the success of a ground vehicle development program. Accelerated life testing profile should represent the customer usage so that optimum design can be achieved. A novel approach incorporating finite element analysis and vehicle durability test data into single axis accelerated life test profile generation was developed in this study. The proposed approach was successfully applied to the engine mount bracket of a heavy duty truck engine and it is validated by vehicle and rig tests. The accelerated life testing procedure developed in this study is applicable to many components of ground vehicles. It is possible to test components at high confidence level and low cost with this approach.
Implantation and maintenance of a permanent cardiac pacing system in children remains challenging due to small patient size, congenital heart defects and somatic growth. We are developing a novel epicardial micropacemaker for children that can be implanted on the epicardium within the pericardial space via a minimally-invasive technique. The key design configurations include a novel open-coiled lead in which living tissue replaces the usual polymeric support for the coiled conductor. To better understand and be able to predict the behavior of the implanted lead, we performed a radiographic image-based modeling study on a chronic animal test. We report a pilot study in which two mechanical dummy pacemakers with epicardial leads were implanted into an adult pig model via a minimally invasive approach. Fluoroscopy was obtained on the animal on Post-Operative Days #9, #35 and #56 (necropsy). We then constructed an analytic model to estimate the in vivo stress conditions on the open-coil lead based on the analysis of orthogonal biplane radiographic images. We obtained geometric deformation data of the implanted lead including elongation magnitudes and bending radii from sequenced films of cardiac motion cycles. The lead stress distribution was investigated on each film frame and the point of maximum stress (Mean Stress = 531.4 MPa; Alternating Stress = ± 216.4 MPa) was consistently where one of the leads exited the pericardial space, a deployment that we expected to be unfavorable. These results suggest the modeling approach can provide a basis for further design optimization. More animal tests and modeling will be needed to validate whether the novel lead design could meet the requirements to withstand ~200 million cardiac motion cycles over 5 years.
In this paper, a method is described for theoretical and experimental studies of a front and rear stabilizer bars used on vehicle steering and suspension systems. Based on the fatigue experimental tests performed on a special test-bed, a complex actuation mechanism from the test bed structure will be analyzed. This mechanism through his kinematic and dynamic structure assures complete conditions for simulating the dynamic behavior in a complex mode of the rear stabilizer bar used on a vehicle steering and suspension structures.
The aim of this work is to develop an experimental device useful to evaluate the friction coefficient in triangular thread joints (M12) manufactured with rolling and machining processes, and therefore, to relate precisely the clamping force to the tightening torque. Experimental static tests of clamp force during 10 tightening–loosening cycles were applied to specific threaded specimens obtained with the rolling and machining process. To analyze the mechanical and tribological behaviors of the manufactured threads, the torque coefficient (K) (nut factor), the average friction coefficient (μ
m
), and the clamped force (F) have been evaluated during 10 cycles of tightening–loosening. The results of this study showed that the range of the variability of the torque coefficient and friction coefficient is between 0.151 and 0.54 and from 0.19 to 0.69 for the rolled thread, respectively. However, these coefficients are between 0.187 and 0.55 and from 0.25 to 0.72 for the machined thread, respectively. The clamping force preserves a linear relationship with the tightening torque and decreases as the number of tightening increases. The use of the rolling process to manufacture the thread joint can preserve a higher mechanical resistance and ameliorate the tribological behavior of the thread compared to the machining process.
This paper analyzes the possibility to substitute the gray iron, traditionally used for the production of relevant parts in woodworking machines, with ductile iron or vermicular iron. A large experimental campaign to determine the mechanical beavior of ductile and vermicular irons respect to tensile, fatigue, and fracture loads was conducted and the microstructures were also analyzed. Results show that ductile or vermicular cast iron in parts and components of machine tools could provide additional stiffness and resistance for the high precision woodworking respect to Gray Iron. A balanced utilization of these alternative irons would permit to take a full advantage by each specific property (as strength, hardness, weight, etc.).
Lasers are ideal tools for various material processing. Inherent characteristics of light energy allow an easy control over the delivery and thus provide high-quality results. Due to the recent technological advances, transformation hardening with laser have seen a growing interest. Each part to be heat treated by laser require the development of recipes in order to achieve desired results. Numerical modeling allows to simulate the process with great accuracy, thus reducing the need of experiments. This study focuses on the modeling and simulation of thermal flow resulting from the interaction between laser beam and workpiece. A numerical function is developed to accurately and automatically model a laser beam traversing complex surfaces, such as the gear tooth.
First, a literature review covers the modeling of laser hardening. It reviews the different technics, factors inherent within the process and the state of current knowledge. A particular interest is done over the laser hardening of AISI 4340 steel and on application of the process on small spur gears. Subsequently, the basic principles of the process are exposed as wells as the parameters and mechanisms that are taking place.
After this overview, the study focuses on numerical modeling using finite-element method. Two modeling approaches are established and used to simulate simple situations with COMSOL software. These approaches are numerically validated by reproducing tests found in literature.
The numerical function is developed in MATLAB based on one of these approaches. It is developed to model the passage of the laser on the surface of a 3D component while including deformations of the laser beam and the variations of the absorption coefficient according to the conditions of interaction laser / surface.
The function is validated by a series of experiments using a fiber laser and flat specimens made of AISI 4340. We observe the dynamics of the absorption coefficient under different operating conditions (power, speed and incidence angle). The tests are validated based on surface temperatures and the dimensions of the hardened zones. The developed models can predict the size of the treatment with a relative error of 2%. These tests are also an opportunity to verify the self-quenching capabilities of AISI 4340 made possible by the inherent characteristics of the laser process.
In a high-speed press, numerous moving links are interconnected and each link executes a constrained motion at high speed. As a consequence, high-level dynamic unbalance force and unbalance moment are transmitted to the main frame of the press, which results in unwanted vibration and significantly degrades manufacturing accuracy. Dynamic unbalance force and unbalance moment inevitably transmits high-level vibrational force to the foundation on which the press is installed. Minimizing the vibrational force transmitted to the foundation is critical for the protection of both the operators and the surrounding structures. The whole task should be carried out in two steps. The first step is to reduce dynamic unbalance based upon kinematic and dynamic analyses. The second step is to design and build an optimal vibration isolation system minimizing the vibrational force transmitted to the foundation. Firstly, the dynamic design method is presented to reduce dynamic unbalance force and moment. For this a 3D CAD software was utilized and a computer program was written to compute dynamic unbalance force and moment. Secondly, the design method for vibration isolation system is presented. The method for designing coil springs and viscous dampers are explained in detail.
We designed and fabricated suitable vibrational equipment for ultrasonic assisted oblique turning process to enable researchers to perform experimental tests with the operating conditions closest to common assumptions of cutting mechanics theories. Applying ultrasonic vibrations to the tool cutting edge along tangential direction and in the presence of inclination and tool cutting edge angles necessitates a novel design and fabrication of vibrational horn with special oblique geometry. In this vibrational horn, the natural frequency of longitudinal vibration mode is forced to be in a certain frequency range of the ultrasonic power supply. The novel tool-workpiece assembly was designed using modal analysis to provide the most conformity of cutting geometry and process parameters between theory and practice. Three-dimensional cutting forces were measured experimentally in vibrational oblique turning process carried out by the mentioned horn. The most suitable conditions to profit from ultrasonic vibrations in oblique turning process were determined, and these experimental results were in agreement with modal analysis results.
Bolted joints are frequently subjected to self-loosening (gradual loss of clamping force) causing multiple failures, especially leaking and breaking of mechanical systems. Such physical phenomena would occur whatever the considered coating (Ag, MoS2, Zn–Ni and others). To enlighten this phenomenon, which remains rather misunderstood due to the confined nature of bolted joint contacts, a coupled experimental-numerical approach is adopted on a bolted joint with silver coating. Indeed, from tribological expert assessments of disassembled joints without loosening, a local view of nut/screw threads contacts is proposed, using discrete element method. This method becomes essential in tribology since it offers the ability to model the dynamic behavior of a contact interface. The model is based on a Non-Smooth Contacts Dynamics approach. The case of third body formed in contacts during tightening process, which has been ignored so far, is placed at the focus of self-loosening phenomenon.
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