scholarly journals Friction coefficient of solid lubricating coating as a function of contact pressure: experimental results and microscale modeling

2021 ◽  
Author(s):  
Marcin Białas ◽  
Jan Maciejewski ◽  
Stanisław Kucharski
Keyword(s):  
Friction Coefficient ◽  
Contact Pressure ◽  
The Novel ◽  
Temperature Relation ◽  
Actual Surface ◽  
Sliding Motion ◽  
Friction Temperature ◽  
Micro Level ◽  
Microscale Modeling ◽  
Selection Of

AbstractThe paper presents experimental analysis of relation between friction coefficient and contact pressure of $$\hbox {MoS}_2$$ MoS 2 film deposited on $$\hbox {Ti}_6\hbox {Al}_4\hbox {V}$$ Ti 6 Al 4 V substrate in contact with sapphire ball during reciprocating sliding motion. It is shown that the value of friction coefficient decreases with increasing contact pressure. A microscale modeling approach is next developed to mimic the experimental observations. Representative volume element is defined based on the actual topography of outer surface of $$\hbox {MoS}_2$$ MoS 2 film. Assuming thermo-elastic material properties, the calculations on the asperity level are performed in two steps. Firstly, the mechanical contact between two surfaces is calculated. As a result, the relation between the global load and micro-stress distribution is obtained. Secondly, for a given stress load, thermal analysis is performed providing temperature fluctuation within simplified conical asperity. By assuming relation between friction coefficient and temperature on the microscale, it is possible to obtain macroscopic friction coefficient as a function of contact pressure. In the end, model results are compared with experimental data. The novel aspects of presented approach lie in the selection of three main factors on a micro-level defining macroscopic friction. They are actual surface topography, microscopic temperature and microscopic friction-temperature relation.

scholarly journals Zero-Width Quasi-Sliding Mode Band in the Presence of Non-Matched Uncertainties

Energies ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3011
Author(s):  
Paweł Latosiński ◽  
Andrzej Bartoszewicz
Keyword(s):  
Sliding Mode Control ◽  
Discrete Time ◽  
Sliding Mode ◽  
Control Strategies ◽  
Relative Degree ◽  
Band Width ◽  
Representative Point ◽  
Mode Control ◽  
Sliding Motion ◽  
Selection Of

Sliding mode control strategies are well known for ensuring robustness of the system with respect to disturbance and model uncertainties. For continuous-time plants, they achieve this property by confining the system state to a particular hyperplane in the state space. Contrary to this, discrete-time sliding mode control (DSMC) strategies only drive the system representative point to a certain vicinity of that hyperplane. In established literature on DSMC, the width of this vicinity has always been strictly greater than zero in the presence of uncertainties. Thus, ideal sliding motion was considered impossible for discrete-time systems. In this paper, a new approach to DSMC design is presented with the aim of driving the system representative point exactly onto the sliding hyperplane even in the presence of uncertainties. As a result, the quasi-sliding mode band width is effectively reduced to zero and ideal discrete-time sliding motion is ensured. This is achieved with the proper selection of the sliding hyperplane, using the unique properties of relative degree two sliding variables. It is further demonstrated that, even in cases where selection of a relative degree two sliding variable is impossible, one can use the proposed technique to significantly reduce the quasi-sliding mode band width.

Influence of the contact with friction on the deformation behavior of advanced high strength steels in the Nakajima test

2021 ◽  
pp. 030932472110212
Author(s):  
Mohammad Mehdi Kasaei ◽  
Marta C Oliveira
Keyword(s):  
Finite Element ◽  
Friction Coefficient ◽  
Strain Rate ◽  
Contact Pressure ◽  
Deformation Behaviour ◽  
High Strength Steels ◽  
High Strength ◽  
Advanced High Strength Steels ◽  
Deformation Mechanics ◽  
Nakajima Test

This work presents a new understanding on the deformation mechanics involved in the Nakajima test, which is commonly used to determine the forming limit curve of sheet metals, and is focused on the interaction between the friction conditions and the deformation behaviour of a dual phase steel. The methodology is based on the finite element analysis of the Nakajima test, considering different values of the classic Coulomb friction coefficient, including a pressure-dependent model. The validity of the finite element model is examined through a comparison with experimental data. The results show that friction affects the location and strain path of the necking point by changing the strain rate distribution in the specimen. The strain localization alters the contact status from slip to stick at a portion of the contact area from the pole to the necking zone. This leads to the sharp increase of the strain rate at the necking point, as the punch rises further. The influence of the pressure-dependent friction coefficient on the deformation behaviour is very small, due to the uniform distribution of the contact pressure in the Nakajima test. Moreover, the low contact pressure range attained cannot properly replicate real contact condition in sheet metal forming processes of advanced high strength steels.

Stabilization of networked switched affine systems with event-triggered strategy

2021 ◽  
pp. 014233122110213
Author(s):  
Dandan Li ◽  
Zhiqiang Zuo ◽  
Yijing Wang
Keyword(s):  
Affine Systems ◽  
Switching Law ◽  
Event Time ◽  
Sliding Motion ◽  
State Dependent ◽  
Event Triggering ◽  
Stability Issue ◽  
The Stability ◽  
Event Based ◽  
Selection Of

Using an event-based switching law, we address the stability issue for continuous-time switched affine systems in the network environment. The state-dependent switching law in terms of the region function is firstly developed. We combine the region function with the event-triggering mechanism to construct the switching law. This can provide more candidates for the selection of the next activated subsystem at each switching instant. As a result, it is possible for us to activate the appropriate subsystem to avoid the sliding motion. The Zeno behavior for the switched affine system can be naturally ruled out by guaranteeing a positive minimum inter-event time between two consecutive executions of the event-triggering threshold. Finally, two numerical examples are given to demonstrate the effectiveness of the proposed method.

Study of the Size Effects and Friction Conditions in Microextrusion—Part II: Size Effect in Dynamic Friction for Brass-Steel Pairs

2007 ◽  
Vol 129 (4) ◽  
pp. 677-689 ◽  
Author(s):  
Lapo F. Mori ◽  
Neil Krishnan ◽  
Jian Cao ◽  
Horacio D. Espinosa
Keyword(s):  
Grain Size ◽  
Friction Coefficient ◽  
Size Effect ◽  
Contact Pressure ◽  
Size Effects ◽  
Numerical Models ◽  
Kolsky Bar ◽  
Experimental Results ◽  
Material Response ◽  
Dynamic Coefficients

In this paper, the results of experiments conducted to investigate the friction coefficient existing at a brass-steel interface are presented. The research discussed here is the second of a two-part study on the size effects in friction conditions that exist during microextrusion. In the regime of dimensions of the order of a few hundred microns, these size effects tend to play a significant role in affecting the characteristics of microforming processes. Experimental results presented in the previous companion paper have already shown that the friction conditions obtained from comparisons of experimental results and numerical models show a size effect related to the overall dimensions of the extruded part, assuming material response is homogeneous. Another interesting observation was made when extrusion experiments were performed to produce submillimeter sized pins. It was noted that pins fabricated from large grain-size material (211μm) showed a tendency to curve, whereas those fabricated from billets having a small grain size (32μm), did not show this tendency. In order to further investigate these phenomena, it was necessary to segregate the individual influences of material response and interfacial behavior on the microextrusion process, and therefore, a series of frictional experiments was conducted using a stored-energy Kolsky bar. The advantage of the Kolsky bar method is that it provides a direct measurement of the existing interfacial conditions and does not depend on material deformation behavior like other methods to measure friction. The method also provides both static and dynamic coefficients of friction, and these values could prove relevant for microextrusion tests performed at high strain rates. Tests were conducted using brass samples of a small grain size (32μm) and a large grain size (211μm) at low contact pressure (22MPa) and high contact pressure (250MPa) to see whether there was any change in the friction conditions due to these parameters. Another parameter that was varied was the area of contact. Static and dynamic coefficients of friction are reported for all the cases. The main conclusion of these experiments was that the friction coefficient did not show any significant dependence on the material grain size, interface pressure, or area of contact.

PRELIMINARY STUDY ON NOVEL BEAM-TO-COLUMN CONNECTION BASED ON SMA PLATE

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Michael CH Yam ◽  
Ke Ke ◽  
Ping Zhang ◽  
Qingyang Zhao
Keyword(s):  
Friction Coefficient ◽  
Energy Dissipation ◽  
Numerical Study ◽  
Numerical Models ◽  
Numerical Technique ◽  
The Self ◽  
Hysteretic Behavior ◽  
The Novel ◽  
Energy Dissipation Capacity ◽  
Preliminary Study

A novel beam-to-column connection equipped with shape memory alloy (SMA) plates has been proposed to realize resilient performance under low-to-medium seismic actions. In this conference paper, the detailed 3D numerical technique calibrated by the previous paper is adopted to examine the hysteretic behavior of the novel connection. A parametric study covering a reasonable range of parameters including the thickness of the SMA plate, friction coefficient between SMA plate and beam flange and pre-load of the bolt was carried out and the influence of the parameters was characterized. In addition, the effect of the SMA Belleville washer on the connection performance was also studied. The results of the numerical study showed that the initial connection stiffness and the energy-dissipation capacity of the novel connection can be enhanced with the increase of the thickness of the SMA plate. In addition, the initial connection stiffness and energy-dissipation behavior of the novel connection can be improved by increasing the friction coefficient or pre-load of bolts, whereas the increased friction level could compromise the self-centering behavior of the connection. The hysteretic curves of the numerical models of the connection also implied that the SMA washers may contribute to optimizing the connection behavior by increasing the connection stiffness and energy-dissipation capacity without sacrificing the self-centering behavior.

The logic of formatting: A case study on transnational television production

2021 ◽  
Vol 9 (3) ◽  
pp. 391-408
Author(s):  
Jolien van Keulen ◽  
Tonny Krijnen ◽  
Joke Bauwens
Keyword(s):  
Business Models ◽  
Daily Work ◽  
Ownership Structures ◽  
Television Production ◽  
Media Companies ◽  
Content Development ◽  
Micro Level ◽  
Production Company ◽  
Selection Of

The transnationalization of television production has been examined by studies on formats and multinational media companies, which have often highlighted the resilience of the local in the global. This article investigates transnationalization on the micro level of television production, drawing on participant observations in a Dutch production company that is partly owned by an American conglomerate. It explores the deep entanglement of the local with the global in different facets of production – including legal, organizational and market aspects – as manifested in daily practices and decision-making in television production. Our analysis reveals an industrial logic of formatting that is not only induced by transnational ownership structures and business models but also deeply ingrained in production routines and programme conventions. Through this logic, transnationalization shapes media professionals’ daily work, the selection of programme ideas and the process of content development.

A Self-Actuating Traction-Drive Speed Reducer

2004 ◽  
Vol 127 (4) ◽  
pp. 631-636 ◽  
Author(s):  
Donald R. Flugrad ◽  
Abir Z. Qamhiyah
Keyword(s):  
Friction Coefficient ◽  
Normal Force ◽  
Drive System ◽  
Traction Drive ◽  
Sliding Motion ◽  
Output Torque ◽  
Speed Reducer ◽  
Rolling Elements ◽  
Drive Speed ◽  
High Output

Traction-drive speed reducers offer certain advantages over geared speed reducers. In particular, they generally run quieter than geared units and provide an opportunity for higher efficiency by eliminating sliding motion between contacting elements. In order to generate a sufficiently high output torque, some means must be provided to create a normal force between the rolling elements. This normal force, along with the friction coefficient, enables the device to transmit torque from one rolling member to the next. The speed reducer proposed here is designed so that the configuration of the rolling elements creates the needed normal force in response to the torque exerted back on the system by the downstream loading. Thus the device is self-actuating. Since the normal force is only present when needed, the rolling elements of the device can readily be disengaged, thus eliminating the need for a separate clutch in the drive system. This feature can be exploited to design a transmission with several distinct speed ratios that can be engaged and disengaged in response to changing speed requirements.

scholarly journals Indestructible Pasts and Paranoid Presents: John Franzen against Active Forgetting in Purity

2019 ◽  
pp. 21-34
Author(s):  
Cristina Garrigós
Keyword(s):  
Traumatic Event ◽  
The Novel ◽  
Contemporary Society ◽  
The Public ◽  
The Past ◽  
Personal Archives ◽  
Conscious Process ◽  
Unconscious Desire ◽  
Selection Of

Forgetting and remembering are as inevitably linked as lifeand death. Sometimes, forgetting is motivated by a biological disorder, brain damage, or it is the product of an unconscious desire derived from a traumatic event (psychological repression). But in some cases, we can motivate forgetting consciously (thought suppression). It is through the conscious repression of memories that we can find self-preservation and move forward, although this means that we create a fable of our lives, as Nietzsche says in his essay “On the Uses and Disadvantages of History for Life” (1997). In Jonathan Franzen’s novel, Purity (2015), forgetting is an active and conscious process by which the characters choose to forget certain episodes of their lives to be able to construct new identities. The erased memories include murder, economical privileges derived from illegal or unethical commercial processes, or dark sexual episodes. The obsession with forgetting the past links the lives of the main characters, and structures the narrative of the novel. The motivated erasure of memories becomes, thus, a way that the characters have to survive and face the present according to a (fake) narrative that they have constructed. But is motivated forgetting possible? Can one completely suppress facts in an active way? This paper analyses the role of forgetting in Franzen’s novel in relation to the need in our contemporary society to deny, hide, or erase uncomfortable data from our historical or personal archives; the need to make disappear stories which we do not want to accept, recognize, and much less make known to the public. This is related to how we manage information in the age of technology, the “selection” of what is to be the official story, and how we rewrite our own history

scholarly journals Effect of COVID-19 on Students Studying in the Secondary and Higher Secondary Level

2021 ◽  
Vol 8 (4) ◽  
pp. 134-146
Author(s):  
Sudarshina Sinha
Keyword(s):  
Mental Health ◽  
Human Life ◽  
Secondary Level ◽  
Likert Scale ◽  
The Novel ◽  
School Students ◽  
Corona Virus ◽  
Micro Level ◽  
Future Plans

The novel Corona virus has been declared a pandemic due to its high transmissibility rate, influencing human life to its heights. It has affected the psychological and mental health of all people, including the functioning of various sectors. This study is based on a micro-level survey that discusses the pandemic's effect on 600 students pursuing education in secondary and higher secondary levels in Kolkata. The school students’ effect was analysed based on four parameters— school, home, a shift in the medium of education from offline to online, and the effect on the students’ future plans, aims, and ambition. The survey was conducted using a questionnaire, which was comprised of structured and semi-structured questions circulated online among the respondents. The respondents were asked to initially rank the indicators and the variables they considered the most critical cause affecting their studies. The respondents were then asked to rate the indicators on a five-point Likert scale to judge the degree of impact of the variables on the respondents.

scholarly journals Hope and equilibrium in the dystopian world of The Hunger Games

2021 ◽  
Vol 85 ◽  
pp. 227-244
Author(s):  
María Sandra Peña-Cervel ◽  
Andreea Rosca
Keyword(s):  
Critical Discourse Analysis ◽  
Cognitive Linguistics ◽  
Social Inequalities ◽  
The Novel ◽  
Hunger Games ◽  
Accurate Picture ◽  
The Social ◽  
The Hunger Games ◽  
The Status ◽  
Selection Of

This paper provides evidence of the fruitfulness of combining analytical categories from Cognitive Linguistics and Critical Discourse Analysis for the analysis of complex literary characterizations. It does so through a detailed study of the “tributes”, i.e. the randomly selected children who have to fight to death in a nationally televised show, in The Hunger Games. The study proves the effectiveness of such categories to provide an analytically accurate picture of the dystopian world depicted in the novel, which is revealed to include a paradoxical element of hope. The type of dehumanization that characterizes the dystopian society of Panem is portrayed through an internally consistent set of ontological metaphors which project negative aspects of lower forms of existence onto people. This selection of metaphors promotes a biased perspective on the poor inhabitants of Panem, while legitimizing the social inequalities the wealthy Capitol works hard to immortalize. However, Katniss undergoes a metamorphosis through her discovery of her own identity, which hints at an emerging female empowerment. This transformation, together with her identification with the Mockingjay, a supernatural being that voices her beliefs and emotions, contributes to disrupting the status quo imposed by the almighty Gamemakers and to purveying a message of optimism.

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