Predictive Modelling of Tribological Systems using Movable Cellular Automata

In the science of tribology, where there is an enormous degree of uncertainty, mathematical models that convey state-of-the-art scientific knowledge are invaluable tools for unveiling the underlying phenomena. A well-structured modelling framework that guarantees a connection between mathematical representations and experimental observations, can help in the systematic identification of the most realistic hypotheses among a pool of possibilities. This thesis is concerned with identifying the most appropriate computational model for the prediction of friction and wear in tribological applications, and the development of a predictive model and simulation tool based on the identified method. Accordingly, a thorough review of the literature has been conducted to find the most appropriate approach for predicting friction and wear using computer simulations, with the multi-scale approach in mind. It was concluded that the Movable Cellular Automata (MCA) method is the most suitable method for multi-scale modelling of tribological systems. It has been established from the state-of-the-art review in Chapter 2 of this thesis, that it is essential to be able to model continuous as well as discontinuous behaviour of materials on a range of scales from atomistic to micro scales to be able to simulate the first-bodies and third body simultaneously (also known as a multi-body) in a tribological system. This can only be done using a multi-scale particle-based method because continuum methods such as FEM are none-predictive and are not capable of describing the discontinuous nature of materials on the micro scale. The most important and well-known particle-based methods are molecular dynamics (MD) and the discrete element methods (DEM). Although MD has been widely used to simulate elastic and plastic deformation of materials, it is limited to the atomistic and nanoscales and cannot be used to simulate materials on the macro-scale. On the other hand, DEM is capable of simulating materials on the meso/micro scales and has been expanded since the algorithm was first proposed by Cundall and Strack, in 1979 and adopted by a number of scientific and engineering disciplines. However, it is limited to the simulation of granular materials and elastic brittle solid materials due to its contact configurations and laws. Even with the use of bond models to simulate cohesive and plastic materials, it shows major limitations with parametric estimations and validation against experimental results because its contact laws use parameters that cannot be directly obtained from the material properties or from experiments. The MCA method solves these problems using a hybrid technique, combining advantages of the classical cellular automata method and molecular dynamics and forming a model for simulating elasticity, plasticity and fracture in ductile consolidated materials. It covers both the meso and micro scales, and can even “theoretically” be used on the nano scale if the simulation tool is computationally powerful enough. A distinguishing feature of the MCA method is the description of interaction of forces between automata in terms of stress tensor components. This way a direct relationship between the MCA model parameters of particle interactions and tensor parameters of material constitutive law is established. This makes it possible to directly simulate materials and to implement different models and criteria of elasticity, plasticity and fracture, and describe elastic-plastic deformation using the theory of plastic flow. Hence, in MCA there is no need for parametric fitting because all model parameters can be directly obtained from the material mechanical properties. To model surfaces in contact and friction behaviour using MCA, the particle size can be chosen large enough to consider the contacting surface as a rough plane, which is the approach used in all MCA studies of contacting surfaces so far. The other approach is to specify a very small particle size so that it can directly simulate a real surface, which allows for the direct investigation of material behaviour and processes on all three scale levels (atomic, meso and macro) in an explicit form. This has still been proven difficult to do because it is too computationally extensive and only a small area of the contact can be simulated due to the high numbers of particles required to simulate a real solid. Furthermore, until now, no commercial software is available for MCA simulations, only a 2D MCA demo-version which was developed by the Laboratory of CAD of Materials at the Institute of Strength Physics and Materials Science in Tomsk, Russia, in 2005. The developers of the MCA method use their own in-house codes. This thesis presents the successful development of a 3D MCA open-source software for the scientific and tribology communities to use. This was done by implementing the MCA method within the framework of the open-source code LIGGGHTS. It follows the formulations of the 3D elastic-plastic model developed by the authors including Sergey G. Psakhie, Valentin L. Popov, Evgeny V. Shilko, and the external supervisor on this thesis Alexey Yu. Smolin, which has been successfully implemented in the open-source code LIGGGHTS. Details of the mathematical formulations can be found in [1]–[3], and section 3.5 of this thesis. The MCA model has been successfully implemented to simulate ductile consolidated materials. Specifically, new interaction laws were implemented, as well as features related to particle packing, particle interaction forces, bonding of particles, and others. The model has also been successfully verified, validated, and used in simulating indentation. The validation against experimental results showed that using the developed model, correct material mechanical response can be simulated using direct macroscopic mechanical material properties. The implemented code still shows limitations in terms of computational capacity because the parallelization of the code has not been completely implemented yet. Nevertheless, this thesis extends the capabilities of LIGGGHTS software to provide an open-source tool for using the MCA method to simulate solid material deformation behaviour. It also significantly increases the potential of using MCA in an HPC environment, producing results otherwise difficult to obtain

FRICTION BEHAVIOR OF ALUMINUM BRONZE REINFORCED BY BORON CARBIDE PARTICLES

A promising composite material for tribotechnical applications based on aluminum bronze with reinforcing boron carbide particles fabricated by a special electron beam additive deposition technique was studied experimentally and numerically. Tribological experiments showed that reinforcing by carbide particles allowed reducing the coefficient of friction from 0.26 to 0.19 and improving the wear resistance by 2.2 times. Computer modeling reveals two main factors playing a significant role in the friction behavior of the studied metal matrix composite: the mechanical effect of reinforcing ceramic inclusions and effective hardening of the metal matrix due to the peculiarities of the 3D electron beam printing. The mechanical effect of hardening inclusions determines a more rounded shape of wear particles, preventing wedging, and thereby increasing the stability of friction. Strengthening the metal matrix leads to reducing the number of wear particles

Multiscale Biomechanics and Tribology of Inorganic and Organic Systems

This open access book gathers authoritative contributions concerning multiscale problems in biomechanics, geomechanics, materials science and tribology. It is written in memory of Sergey Grigorievich Psakhie to feature various aspects of his multifaceted research interests, ranging from theoretical physics, computer modeling of materials and material characterization at the atomic scale, to applications in space industry, medicine and geotectonics, and including organizational, psychological and philosophical aspects of scientific research and teaching as well. This book covers new advances relating to orthopedic implants, concerning the physiological, tribological and materials aspects of their behavior; medical and geological applications of permeable fluid-saturated materials; earthquake dynamics together with aspects relating to their managed and gentle release; lubrication, wear and material transfer in natural and artificial joints; material research in manufacturing processes; hard-soft matter interaction, including adhesive and capillary effects; using nanostructures for influencing living cells and for cancer treatment; manufacturing of surfaces with desired properties; self-organization of hierarchical structures during plastic deformation and thermal treatment; mechanics of composites and coatings; and many more. Covering established knowledge as well as new models and methods, this book provides readers with a comprehensive overview of the field, yet also with extensive details on each single topic

A study of the influence of soft particle size and concentration on strength and strain properties of ceramic composites

In the paper a theoretical study of the influence of particle distribution of soft inclusions-agglomerates in a ceramic composite sample on its strength and deformation characteristics was carried out. A movable cellular automaton method was used to simulate a uniaxial compression test of two-dimensional rectangle composite samples. It was found that the average size of inclusions agglomerate-while maintaining the volume fraction of the particles of the soft phase has little effect on the strength and deformation properties of the simulated samples. The simulation results can help to understand the mechanical properties of such objects within any generalized model

Dynamic modeling of disc brake contact phenomena

Interakcija između diska kočnice i frikcionog materijala disk kočnice motornih vozila se odlikuje velikim brojem kontaktnih fenomena. Nastanak ovih fenomena je vezan za radne uslove kočnice (pritisak aktiviranja, brzina, temperatura u kontaktu) kao i za karakteristike materijala frikcionog para. Dinamičke i izraženo nelinearne promene, koje se dešavaju u kontaktu frikcionog para, izazivaju teško predvidivu promenu momenta kočenja, kao najvažnije izlazne performanse kočnice. Složena situacija u kontaktu frikcionog para se ne može lako modelirati i predvideti korišćenjem klasičnih matematičkih metoda. Zbog toga su istraživane mogućnosti razvoja metode za predviđanje uticaja radnih režima disk kočnice na pojavu tzv. 'stickslip' fenomena tokom ciklusa kočenja. Korišćenjem dinamičkih neuronskih mreža, razvijen je dinamički model uticaja radnih uslova disk kočnice na pojavu kontaktnih fenomena i način promene momenta kočenja.An interaction between a brake disc and friction material of automotive brake is characterized by a number of braking phenomena. These phenomena are influenced by brake operation conditions (applied pressure, speed, and brake interface temperature) and material characteristics of a friction couple. The dynamic and highly non-linear changes occurred in the contact of the friction pair, provokes hard-to-predict change of braking torque as the most important brake's output performance. Complex disc brake contact situation is causing sudden change of braking torque and could not be easily modeled and predicted using classical mathematical methods. That is why, the possibilities for development of the method for prediction of influence of braking regimes on generation of the stick-slip phenomena during a braking cycle has been investigated in this paper. Dynamic neural networks have been employed for development of the model of influences of the disc brake operation conditions on contact phenomena generation and 'nature' of braking torque change

Dynamic modeling of disc brake contact phenomena

Interakcija između diska kočnice i frikcionog materijala disk kočnice motornih vozila se odlikuje velikim brojem kontaktnih fenomena. Nastanak ovih fenomena je vezan za radne uslove kočnice (pritisak aktiviranja, brzina, temperatura u kontaktu) kao i za karakteristike materijala frikcionog para. Dinamičke i izraženo nelinearne promene, koje se dešavaju u kontaktu frikcionog para, izazivaju teško predvidivu promenu momenta kočenja, kao najvažnije izlazne performanse kočnice. Složena situacija u kontaktu frikcionog para se ne može lako modelirati i predvideti korišćenjem klasičnih matematičkih metoda. Zbog toga su istraživane mogućnosti razvoja metode za predviđanje uticaja radnih režima disk kočnice na pojavu tzv. 'stickslip' fenomena tokom ciklusa kočenja. Korišćenjem dinamičkih neuronskih mreža, razvijen je dinamički model uticaja radnih uslova disk kočnice na pojavu kontaktnih fenomena i način promene momenta kočenja.An interaction between a brake disc and friction material of automotive brake is characterized by a number of braking phenomena. These phenomena are influenced by brake operation conditions (applied pressure, speed, and brake interface temperature) and material characteristics of a friction couple. The dynamic and highly non-linear changes occurred in the contact of the friction pair, provokes hard-to-predict change of braking torque as the most important brake's output performance. Complex disc brake contact situation is causing sudden change of braking torque and could not be easily modeled and predicted using classical mathematical methods. That is why, the possibilities for development of the method for prediction of influence of braking regimes on generation of the stick-slip phenomena during a braking cycle has been investigated in this paper. Dynamic neural networks have been employed for development of the model of influences of the disc brake operation conditions on contact phenomena generation and 'nature' of braking torque change

Survey on modelling and techniques for friction estimation in automotive brakes

The increased use of disc brakes in passenger cars has led the research world to focus on the prediction of brake performance and wear under different working conditions. A proper model of the brake linings’ coefficient of friction (BLCF) is important to monitor the brake operation and increase the performance of control systems such as ABS, TC and ESP by supplying an accurate estimate of the brake torque. The literature of the last decades is replete with semi-empirical and analytical friction models whose derivation comes from significant research that has been conducted into the direction of friction modelling of pin-disc couplings. On the contrary, just a few models have been developed and used for the prediction of the automotive BLCF without obtaining satisfactory results. The present work aims at collecting the current state of art of the estimation techniques for the BLCF, with special attention to the models for automotive brakes. Moreover, the work proposes a classification of the several existing approaches and discusses the relative pro and cons. Finally, based on evidence of the limitations of the model-based approach and the potentialities of the neural networks, the authors propose a new state observer for BLCF estimation as a promising solution among the supporting tools of the control engineering

MULTILEVEL NUMERICAL MODEL OF HIP JOINT ACCOUNTING FOR FRICTION IN THE HIP RESURFACING ENDOPROSTHESIS

Friction between the moving parts of the endoprosthesis has a significant impact on the endoprosthesis operation time. Primarily, it concerns the endoprosthesis of hip and knee joints. To improve the tribological characteristics of the metal endoprosthesis, hardening nanostructured coatings are used. Usually, titanium and titanium alloys are used as metal, and titanium nitride is used as a coating. Herein, we propose an approach to multilevel modeling of the system “bone-endoprosthesis” which is based on the movable cellular automaton method and accounts for friction between the moving parts of the hip resurfacing endoprosthesis. We validated the models of the friction system materials using the instrumented scratch test simulation. Then, we simulated friction at the mesolevel, explicitly considering roughness of the coating. The results obtained at the mesolevel were used as tribological characteristics of the coating in the macroscopic model of the hip resurfacing endoprosthesis