PSI - Issue 26

A.V. Vakhrushev et al. / Procedia Structural Integrity 26 (2020) 256–262 Vakhrushev / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction One of the modern directions of increasing the durability and reliability of structural materials is the development of self-healing materials of various types and purposes (Kessler (2007), Aıssa et. all (2012), Yang and Ding (2015), Bekas et. all (2016)). Self-healing materials are different substances or systems (Ming and MIn (2011), Sitnikov et. all (2018), Sreenatha et. all (2020)), artificially created for the manufacture of structures and machines that automatically and without special repair operations autonomously restore the initial operational parameters of the materials: elastic modulus, tensile strength, fracture toughness and other characteristics after damage caused by them during loading and operation of manufactured of which are constructions and machines. There are two types of self-healing materials external and internal. Internal mechanisms of self-healing do not require any additional reducing substances. External self-healing mechanisms use regenerative components specially introduced in advance or penetrating into the material during operation: microcapsules with healing substances, nano- and microparticles, consisting of healing materials and other elements (for example - Yang et. all (2019)). One of the main factors determining the durability of machine parts, is the abrasion resistance of the surface of materials from which the parts are made. Increased wear resistance is based on the study of the physics of the phenomena occurring on the surfaces of parts in friction and, above all, the evolution of the structure of the surface layers of the contacting materials. For process control structure formation in the surface layer and reduce the work of friction lubricants are applied, including additives that provide the desired surface modification of the layer structure. At the moment, there are plenty of liquids and plastic lubricants, relating to the type of metal-cladding. As the active ingredient powders of various metals, their oxides and alloys with different dispersion, including nanopowders are often used. It should be noted that despite the significant number of publications devoted to the influence metal lubricants on the friction and wear processes of structural materials, the lubricating mechanism of action of nanopowders is studied insufficiently. In this connection, a computer simulation of complex multi-phase nanosystems (Steinhauser (2008), Weinan (2011), Vakhrushev (2009), Vakhrushev and Fedotov (2020)) will complement experimental studies detailing the processes of interaction in the two-phase medium consisting of components: surface, nanoparticles and a liquid lubricating medium. The paper presents in-depth analysis and modeling of processes of interaction of nanoparticles with micro cracks on a solid surface. The molecular dynamics method was used to simulate the processes of interaction of nanoparticles with a crack. 2. Formulation of the problem Let us consider examples of the use of nanoparticles for healing surface defects and cracks. Fig. 1 shows an example of the nanoparticles utilization for the improvement of the properties of glues and sealants for healing defects in materials. When crack (2) appears in material (1), it is filled with an adhesive composition containing nanoparticles as filler. Doping with the above additives improves the strength of adhesive materials in narrow cracks due to the penetrability of nanopowders and their capability to form additional strong bondings. The doping of fuels and oils with nanoparticles is widely used (for example, boric acid nanoparticles improve lubricating properties of motor oils). Fig.2 demonstrates the use of nanoparticles as additives for oils. In the process of the interaction of the “working” faces of components (1) (in Fig . 5 one of the working contacting faces is shown), nanopowders (4) added into oil (3) fills micro irregularities (2) forming a strong metal-composite surface layer. Friction in the contact diminishes substantially, the wear-resistance of the interacting components increases and the heat losses on the interacting surfaces decrease. As follows and given examples, system modeling of processes of interaction of nanoparticles with micro cracks on a solid surface includes three sequential tasks: the construction of the initial configuration of nanosystems; the relaxation to an equilibrium state nanosystems; loading nanosystems external forces before failure (Fig.3). To simulate this nanosystems using the method of molecular dynamics (MD) and a numerical scheme Verlet for the integration of MD equations (Heerman (1986)). MD equations for the nano systems containing nanoparticles are given in in detail in Vakhrushev (2017). At the initial time nanosystems it is at rest. Initial temperature of the system defines velocities with which the atoms oscillate about the equilibrium position.