Contact Theory Research Articles

An improved energy wear model of three-dimensional ball-plane contact structure and its fretting wear dynamic behaviors study

This paper proposes a method that combines the finite element method with an improved energy wear model to establish a three-dimensional (3D) ball-plane contact structures fretting wear model. The correctness of the model was verified by Hertz contact theory and fretting wear experiments. Then, the fretting wear dynamic behaviors of 3D ball-plane contact structures were investigated in detail. The results show that when the contact structure is in the partial slip regime (PSR), the cross-sectional wear scar profile changes from the “W” shape to the “U” shape along the fretting direction. When the contact structure is in the gross slip regime (GSR), the cross-sectional wear scar profile always maintains a “U” shape along the fretting direction. In addition, it was also found in the study that when the contact structure is at GSR under a low normal load or PSR under a high normal load, it will help reduce wear. This study can provide significant theoretical guidance for reducing and protecting fretting wear in contact structures.

Theoretical modeling and experimental verification of a broadband microvibrational energy harvesting system

AbstractTo scavenge energy from imperceptible vibrations, this paper investigates the broadband response and output performance of a microvibrational piezoelectric energy harvesting system with mechanical stopper. The energy harvesting system comprises a cantilever beam made of piezoelectric material, which is affixed with a coil at its unbound end and a mechanical stopper. The coil is placed in a magnetic field to provide an ultra‐low level excitation. The electromechanical model is derived according to force integration method (FIM) and Hertz's contact theory, and numerical simulations are undertaken to evaluate the influence of the excitation level, and the gap on the performance. For the linear counterpart without stopper, experimental results indicate the system generates a peak power of 24.12 μW with matched resistance under excitation with a level of 0.003 N and a frequency of 200.3 Hz. When a polydimethylsiloxane (PDMS) stopper is introduced, the vibration of the piezoelectric beam exhibits an obvious nonlinearity with an amplitude of micron scale. Increasing the excitation level and decreasing the gap could efficiently broaden the response bandwidth. Experimental results demonstrate that a copper stopper with larger elastic modulus results in a wider response frequency range, and the half‐power bandwidth could reach 37.1 Hz under excitation with a level of 0.003 N.

Elastic contact between rough surfaces: Bridging the gap between theory and experiment

Friction is generated where solids touch, thus quantitative understanding of the microscopic contact area is crucial to predict macroscopic friction. All surfaces are rough, and typically small-scale roughness rather than macroscopic geometry sets the contact area. Rough contact theories have been developed that predict the contact area, using the surface topography and the mechanical properties of the solids as input. However, the validity of these theories remains under debate. Systematic comparison between theory and experiment has been lacking, due to the experimental difficulty to access the contact area, especially at small length scales where idealised assumptions of contact models may not hold. Here, we use a state-of-the-art fluorescence microscopy technique to directly access the contact area of a glass-glass contact with nanometric out-of-plane resolution. We systematically vary the roughness of the contact and carefully measure the surface topography across length scales. Comparison of high-resolution contact experiments to different contact theories enables us to unambigously conclude that only elastic Persson theory quantitatively describes experimental observations.

Understanding how tourists with disabilities’ perceptions of residents’ emotional solidarity influence their behavioural intention: the mediating role of perceived fairness

Tourists with disabilities face several constraints when travelling, including interpersonal issues. The intergroup contact theory suggests that intergroup contact can diminish social prejudice. This study aims to understand how tourists with disabilities’ perceptions of residents’ emotional solidarity influence their attitude and behavioural intention towards a destination and the mediating role of perceived fairness. A systematic sampling survey was conducted among 359 tourists with disabilities in China. The results revealed that emotional closeness and sympathetic understanding had a positive effect on perceived fairness and attitude towards the destination, but a welcoming nature affected attitude alone. Ultimately, perceived fairness and the attitude towards the destination impacted behavioural intention. Additionally, the results confirmed the mediating role of perceived fairness between emotional solidarity and behavioural intention. The contribution of this study to accessible tourism research is to provide a model that helps to explain how tourists with disabilities’ psychological mechanisms and behavioural patterns are affected by favourable interpersonal relationships with destinations. In short, it promotes the concept of perceived fairness. The study also argues that greater social inclusion contributes to the quest for good health and well-being (SDG #3), equality (SDG #10), and inclusive and sustainable cities (SDG #11).

Generalized Shannon entropy sparse wavelet packet transform for fault detection of traction motor bearings in high-speed trains

An effective structural health monitoring method of traction motor bearings is a powerful guarantee for the safety operation of high-speed trains. However, it is exceptionally difficult to detect bearing fault characteristics from the vibration signals of traction motor bearings operating at high rotational speeds. In this scenario, a generalized Shannon entropy sparse wavelet packet transform (GSWPT) for fault detection of motor bearings is proposed in this paper. Firstly, a generalized Shannon entropy sparse regularization method is proposed to obtain sparse wavelet reconstruction coefficients by extending the definition of the Shannon information entropy, and the non-convex sparse regularization function is minimized by synergistic swarm optimization algorithm. Then, the wavelet node coefficients are weighted according to the second-order cyclostationarity index of the wavelet packet node to further enhance the sparsity of the reconstructed signal. Moreover, the optimal decomposition level of GSWPT is adaptively selected by the maximum sparsity and cyclostationarity criterion. Particularly, in order to verify the bearing fault detection performance of GSWPT in practical engineering, a bearing fault dynamic model of traction motor in high-speed train was established based on Hertz contact theory and the fourth-order Runge-Kutta method to obtain simulated data under strong Gaussian white noise, and a corresponding test platform was constructed to collect experimental data under different operating conditions. Finally, the applications on the simulated and experimental signals of traction motor bearings in high-speed trains demonstrate that GSWPT significantly outperforms the conventional wavelet packet transform, dual-tree complex wavelet packet transform, blind deconvolution, modal decomposition, and Infogram methods to some extent for fault detection.

Numerical Simulation and Modeling of Mechano–Electro–Thermal Behavior of Electrical Contact Using COMSOL Multiphysics

Electrical contacts are important circuit components with diverse industrial applications, and their failure can lead to multiple unwanted effects. Hence, the behavior of electrical contacts is a widely studied topic in the scientific literature based on various approaches, tools, and techniques. The present study proposes a new approach to numerical modeling and simulation based on the Holm contact theory, aiming to study the dependence between the electric potential and the temperature within an electrical contact. Structured in five sections, the research was conducted using COMSOL Multiphysics software and its solid-state mechanics, electric current, and heat transfer modules in order to highlight contact behavior from mechanical, electrical and thermal points of view: the von Mises stress, contact force, electric field amplitude, variation of the electrical potential along the current path, temperature gradient, and dependence of temperature along the contact elements edges were obtained by simulation, and are graphically represented. The results show that the temperature increase follows a parabolic curve, and that for values higher than 4 mV of voltage drop, the temperature of the contact increases to 79.25 degrees (and up to 123.81 degrees for 5 mV) over the ambient temperature, thus the integrity of insulation can be compromised. These values are close (10–12%) to the analytically calculated ones, and also in line with research assessed in the literature review.

Population decline and public attitudes toward multicultural immigration policies in South Korea

AbstractPopulation decline due to low fertility and aging causes socioeconomic challenges such as a shrinking labour force and regional decline. In response to these challenges, there is a growing discussion about accepting immigrants to mitigate the side effects of population decline. This implies the importance of analyzing local peoples' perceptions as a basis of policy and planning in anticipation of demographic transitions toward a multicultural society. While there are many studies on local problems caused by depopulation and perceptions of immigrants based on contact theory and group threat theory, there has been relatively little research on the relationship between depopulation and individual perceptions of immigrants. This study fills this gap by using survey data of Seoul, Korea, the city experiencing both population decline and an increase in immigrants. It employs the multilevel ordered logit model to explore how the decrease in local population associates with individuals' perception on the need for multicultural immigration policies. The results suggest that individuals are more likely to have a positive view of multicultural immigration policies if their region is experiencing a higher population decline. This finding is significant as it demonstrates that a shift to an unfavourable demographic structure can have a positive impact on perceptions of immigrant acceptance, offering a new perspective on the relationship between immigrants and native residents.

Exploring Attitude Change and Experiences of Undergraduate Students in a Goalball and Sitting Volleyball Focused Paralympic Skill Lab

ABSTRACT Rooted in contact theory, the Paralympic Skill Lab (PSL) program is designed to guide participants toward recognizing and understanding the experiences of disabled people to support new pathways of thought and changed attitudes. The purpose of this inquiry was to explore the experiences of college students in a goalball and sitting volleyball focused PSL program and their attitudes and perceptions about disability and disability sport. This study utilized an experiential qualitative approach. Participants were fifty-seven college students who took part in a PSL event. Data were collected via reflective writing responses. Written materials were analyzed inductively using a three-step process: immersion in the data, bracketing the data, and determining emergent themes. Analysis revealed three themes related to the participants’ experiences during the PSL event (a)“I realized that there was no need for having low expectations for Paralympic athletes:” Breaking down bias, ;(b) “It made them real people, with real thoughts and real beliefs:” Humanizing through contact, and (b) “My closed-minded thinking thought they all would have a prosthetic leg or have a mind disease:” Deconstructing assumptions. The findings support the value of PSL as a mechanism for learning and engagement through experience, with clear implications for practice. Future research should explore different types of Paralympic activities offered in the PSL program.

Meta-contact analysis based on contact theory in three-dimensional discontinuous deformation analysis

Accurate contact analysis between nonspherical blocks, such as polyhedral blocks, is crucial for modeling jointed rock masses. The Contact Theory provides a rigorous foundation for contact detection. However, designing a robust and efficient algorithm that conforms to the original Contact Theory remains challenging. This study introduces the meta-contact concept for polyhedral blocks, which corresponds to the contact cover on the entrance block of the Contact Theory. Using the meta-contact concept, contact type identification, determination of contact points and plans, and contact force calculation can be formulated while retaining the advantages of Contact Theory in dealing with irregular blocks with small edges and large penetration.

Is contact theory still valid in acute asymmetrical violent conflict? A case study of Israeli Jewish and Arab students in higher education.

Is contact theory still valid in acute asymmetrical violent conflict? A case study of Israeli Jewish and Arab students in higher education.

Research on axial nonlinear vibration characteristics of ball screw feed system considering segmented restoring force

Taking the ball screw feed system as the research object, the two degree of freedom axial dynamic model of the system is constructed firstly. Based on Hertz contact theory, when the ball screw pair adopts variable lead self-preloading to eliminate the assembly clearance between the ball and raceway, considering the nonlinear segmented axial elastic recovery force generated by the uneven contact deformation between the ball and raceway under the action of external excitation force, further derive the nonlinear dynamic equation group of the system. Next, the fourth-order Runge-Kutta method was used to numerically solve the equation system, obtaining the system’s two and three-dimensional phase diagrams, Poincaré sections, time-domain waveform diagrams, frequency spectra, and bifurcation diagrams. Then, the effects of damping constant, initial contact angle between ball and raceway in ball screw pairs, and number of balls on the system’s response characteristics were analyzed, and the influence of external excitation forces on system stability was further studied. Finally, it was verified through experiments that the axial vibration of the system is indeed nonlinear vibration, providing a theoretical basis for the study of the dynamic characteristics of the ball screw feed system.

Multi-optimization of rod fastened rotor on the distribution of bending stiffness and unbalance

A rod fastened rotor (RFR), which contains serial disks, rods (or a rod), and a torque tube, is the main form of heavy duty gas turbines and light duty aero engines. The roughness of the interface is the main parameter affecting the bending stiffness of RFR, and the jumpiness of the disks is the intuitive representation of the unbalance of the rotor. In this paper, a multi-optimization algorithm, NSGA-Ⅱ, was used to improve the vibration behavior of the RFR-bearing system. First, the quantitative relation between the bending stiffness of the rotor and the roughness of the interface was set up by combining the Persson contact theory and the Greenwood–Williamson model, and the nondimensional bending stiffness (NS) was proposed as the optimization objective of roughness. Then, the optimization objective of the jumpiness of the disk, (A + B), was rendered based on the minimum unbalance force. Finally, the multi-optimization on the roughness and jumpiness of the RFR was carried out, and the vibration behavior was improved greatly. In addition, this multi-optimization method was applied to a practical RFR, and the experimental results showed that the vibration amplitude was reduced by about 82%. The work in this paper can provide the guidance for vibration reduction of the rotor system.

Study of energy dissipation mechanisms and hotspot formation patterns during impact process in octogen explosives with circular cavities

Considerable focus has been given to hotspot generation and ignition phenomena in impact-induced explosives. Hotspot formation in explosives is typically attributed to internal dissipation and heat transfer occurring within them. This study refines the momentum and energy equations to illustrate the entire process of particle collision, temperature-rise evolution, and hotspot formation in octogen explosive bed under impact. By octogen, we mean the substance known as cyclotetramethylene tetranitramine, which is also commonly referred to as HMX. Dense particles are considered to have pseudo-fluid properties. During the impact of the explosive, we captured the propagation of the stress wave and compared its similarities and differences with the shock wave. The collision force model incorporates a combination of Hertz–Mindlin elastic and Thornton elastoplastic contact theories. The temperature-governing equation includes sliding friction, rolling resistance, and plastic dissipations as energy sources, taking into account the heat transfer processes between particles. Temperature evolution is a spatiotemporally correlated phenomenon divided into three processes: high-temperature bands formation, cavity collapse, and particle bed dispersion, all of which lead to hotspot formation near the cavity and near the wall. Plastic dissipation is the primary source for particle temperature-rise and hotspot formation. Furthermore, the effect of cavity size, impact velocity, and particle size on temperature evolution and hotspot formation patterns is analyzed. It was found that higher impact velocities and smaller cavity sizes are associated with increased hotspot temperatures near the wall, but the hotspot temperature near the cavity does not consistently vary with impact velocity and cavity size. This is attributed to the relationship between energy dissipation rate and void collapse time.

Investigating preservice teachers’ attitudes toward lesbian, gay, and bisexual students in Luxembourg

AbstractLesbian, gay, and bisexual (LGB) students face victimization in multiple contexts, including the educational context. Here, teachers can serve as an important resource for LGB students. However, teachers who are prejudiced against students from sexual minorities might not be able to fulfill this role. Accordingly, it is important to find out more about teachers' attitudes and their correlates, as such information can provide starting points for sensitization interventions in teacher education programs, which have the potential to improve the situation of LGB students in the school setting. In the present preregistered questionnaire study, we investigated the attitudes of 138 preservice teachers from the University of Luxembourg toward LGB students and tried to identify predictors of teachers’ attitudes. Results suggested that Luxembourgish preservice teachers hold mostly positive attitudes toward LGB students. Using correlation and multiple regression analyses, we identified the frequency of participants’ contact with LGB people in family or friend networks, hypergendering tendencies, sexual orientation, and religiosity as reliable predictors of attitudes toward LGB students. Age, gender, and right-wing conservatism did not reliably predict preservice teachers’ attitudes in the regression models. Our findings thus offer support for intergroup contact theory and have implications for teacher education in Luxembourg.

Research on the Preparation of Zirconia Coating on Titanium Alloy Surface and Its Tribological Properties

Titanium alloys have been widely used in aerospace and other fields due to their excellent properties such as light weight and high strength. However, the extremely poor tribological properties of titanium alloys limit their applications in certain special working conditions. In order to improve the tribological properties of titanium alloys, the zirconia coatings were prepared on the surface of a TC4 titanium alloy using the discharge plasma sintering method in this article. The influence of sintering parameters on properties such as density, adhesion, hardness, and phase composition, as well as tribological properties (friction coefficient, wear rate) were investigated, and the influence mechanism of the coating structure on its mechanical and frictional properties was analyzed. The results showed that, with the increase in sintering temperature, the density, bonding strength, and hardness of the zirconia coating were significantly improved. The zirconia coating prepared at a sintering temperature of 1500 °C and a sintering time of 20 min had the lowest friction coefficient and wear rate, which are 0.33 and 6.2 × 10−8 cm3·N−1·m−1, respectively. Numerical analysis showed that the increase in temperature and the extension of time contributed to the extension of the diffusion distance between zirconia and titanium, thereby improving the interfacial adhesion. The influence mechanism of different sintering temperatures and sintering times on the wear performance of zirconia coatings was explained through Hertz contact theory.

Effect of Post-Processing Heat Treatment on Micro-Contact Damage of Zirconia-Reinforced Lithium Silicate Dental Materials.

Zirconia-reinforced lithium silicate (ZLS) is utilized as a material for prosthetic tooth crowns, offering enhanced strength compared to other dental glass-ceramics. In this study, we investigate a commercial ZLS material, provided in a fully crystallized form. We examine the effects of an optional post-processing heat treatment on micro-contact damage using controlled indentation tests simulating the primary modes of contact during chewing: axial and sliding. Our findings indicate that the heat treatment does not affect mechanical properties such as the elastic modulus, hardness and indentation fracture toughness. However, it does enhance the resistance to contact damage by fracture and chipping in both axial and sliding modes, as well as the resistance to crack initiation measured from sliding tests. This improvement is attributed to the refinement of the flaw population achieved through the heat treatment. The results are analysed using principles of contact and fracture mechanics theory, discussing their significance in prosthetic dentistry.

Coal falling trajectory and strength analysis of drum of shearer based on a bidirectional coupling method

The cutting and crushing of coal and rock containing gangue is the result of the coupling effect of multiple factors. The geometric parameters of the working mechanism, the kinematic parameters of the shearer, and the physical and mechanical properties of the coal and rock to be cut all affect the cutting and crushing process of the shearer. To study the coal falling trajectory of cutting coal and rock using a spiral drum, optimal cutting parameters were obtained, efficient cutting using a spiral drum was achieved, and analysis of the coal falling trajectory and strength of the drum of a shearer based on bidirectional coupling technology was proposed based on particle discrete element contact theory and virtual prototype technology. The discrete element method multi-flexible body dynamics two-way coupling method was used to obtain cutting and interactive information about the spiral drum for a complex coal seam with gangue. The cutting conditions of the spiral drum under different cutting depths, rotational speeds, and traction speeds were determined. The movement status of coal and rock particles was monitored under different working conditions. Coal falling trajectory equations for the coal and rock particles were compiled under different working conditions, and the coal falling trajectory curve was drawn. The optimal coal loading rate was used as the measurement standard for the coal falling trajectory, and the optimal coal falling trajectory of the drum was obtained through full factor experiments. The load of the drum and pick was extracted, their stress and deformation were analyzed, and fatigue life analysis was performed on the pick with the highest stress. The results indicate that the maximum deformation occurs on the cutting teeth that are cutting hard gangue. The stress of the tooth seat is mainly concentrated at the root of the tooth seat, and its maximum equivalent stress is less than the yield limit value of the selected material. Therefore, the material selection and structural design of the drum are safe and reliable. By building a coal mining machine cutting coal and rock experimental platform and monitoring the working status of the designed spiral drum, it meets the usage requirements. Based on industrial experiments conducted underground, the measured average coal loading rate of the shearer drum was 46.31%, achieving stable operation and verifying that the designed drum of the shearer has an efficient cutting ability.

Investigation of contact behavior on a model of the dual-mobility artificial hip joint for Asians in different inner liner thicknesses.

The four components that make up the current dual-mobility artificial hip joint design are the femoral head, the inner liner, the outer liner as a metal cover to prevent wear, and the acetabular cup. The acetabular cup and the outer liner were constructed of 316L stainless steel. At the same time, the inner liner was made of ultra-high-molecular-weight polyethylene (UHMWPE). As this new dual-mobility artificial hip joint has not been researched extensively, more tribological research is needed to predict wear. The thickness of the inner liner is a significant component to consider when calculating the contact pressure. To make use of finite element analysis to gain a better understanding of the contact behavior in various inner liner thicknesses on a new model of a dual-mobility artificial hip joint, with the ultimate objective of determining the inner liner thickness that was most suitable for this particular type of dual-mobility artificial hip joint. In this study, the size of the femoral head was compared between two diameters (28 mm and 36 mm) and eight inner liner thicknesses ranging from 5 mm to 12 mm. Using the finite element method, the contact parameters, including the maximum contact pressure and contact area, have been evaluated in light of the Hertzian contact theory. The simulation was performed statically with dissipated energy and asymmetric behavior. The types of interaction were surface-to-surface contact and normal contact behavior. The maximum contact pressures in the inner liner (UHMWPE) at a head diameter of 28 mm and 36 mm are between 3.7-13.5 MPa and 2.7-10.4 MPa, respectively. The maximum von Mises of the inner liner, outer liner, and acetabular cup are 2.4-11.4 MPa, 15.7-44.3 MPa, and 3.7-12.6 MPa, respectively, for 28 mm head. Then the maximum von Mises stresses of the 36 mm head are 1.9-8.9 MPa for the inner liner, 9.9-32.8 MPa for the outer liner, and 2.6-9.9 MPa for the acetabular cup. A head with a diameter of 28 mm should have an inner liner with a thickness of 12 mm. Whereas the head diameter was 36 mm, an inner liner thickness of 8 mm was suitable. The contact pressures and von Mises stresses generated during this research can potentially be exploited in estimating the wear of dual-mobility artificial hip joints in general. Contact pressure and von Mises stress reduce with an increasing head diameter and inner liner's thickness. Present findings would become one of the references for orthopedic surgery for choosing suitable bearing geometric parameter of hip implant.

Investigation of the lubrication performance of a marine diesel engine crankshaft using a thermo-electrohydrodynamic model

Abstract This study outlines the development of a three-dimensional model for the crankshaft-bearing and a multi-body dynamics model for a four-stroke marine diesel engine. The models are constructed through a simulation approach that integrates the finite element method and multi-body dynamics method. Additionally, the Greenwood/Tripp asperity contact theory and average flow model are incorporated. The investigation also delves into the dynamic coupling between the crankshaft-bearing multi-body system and the mixed lubrication effects, accounting for lubricating oil as a thermo-electrohydrodynamic model and the journal as an elastomer. The study meticulously examines the lubrication characteristics of main bearings in marine diesel engines during normal operational conditions and scrutinizes the impact of various parameters on crankshaft-bearings. The study concludes by offering recommendations and technical support for innovative optimization design and model enhancement of diesel engine crankshaft-bearings.

A literature review to explore the use of Contact Theory, in exploring integration strategies between students who have defected from North Korea and South Korean students

Objectives The purpose of this research was to explore effective integrated strategies utilizing Contact Theory principles, to reduce prejudice and discrimination and build friendships between North and South Korean students.
 Methods A literature review synthesizing the findings of literature retrieved from searches for integration between North and South Korean students. Especially, Contact Theory was particularly used for the theoretical framework.
 Results Intergroup cooperation: Repeated integrated strategies and high-quality contact strategies should be applied in school curriculums to build friendships based on intergroup cooperative tasks such as discussion or presentations about each other’s culture, and societal issues between the two Koreas’ students. Common goals: Both students groups should discuss and debate the common goal of peace within the Korean Peninsula by allowing students to consider the advantages and disadvantages of inter-Korean unification on their own. Equal status: Schools should provide some programmes via literature or films related to North Korean words which are neglected by South Koreans who will need to change their perception by developing a more objective view of North Korean culture and their way of thinking that can ultimately bring equal status between the two Korean student groups. Support of institutions: The support of authorities of the Korean government is suggested. Especially, the government will need to provide more effective teacher education for integrated education between two Korean students to prepare for future reunification.
 Conclusions The implications and limitation of the study is provided. Suggestions for future studies are also presented.