Defect and Diffusion Forum Vol. 428

Abstract: We present our recent study on adhesive contacts of viscoelastic materials sliding against rigid substrates. Ultimately, the theory addresses the combined effect of viscoelasticity and adhesion in sliding contacts, with specific focus on the sliding frictional behavior. Compared to the adhesiveless case, we show that a significant enhancement of hysteretic friction occurs in the presence of adhesion, in agreement with long-standing experimental evidence. The presented formulation allows to investigate the effect of sliding velocities ranging from extremely slow to very high, thus taking into for local viscoelasticity, occurring at the edges of the contacts (crack tips), and bulk viscoelasticity, occurring in the bulk deformable material.

Abstract: A mode I, centre crack, in ductile steel plate of finite dimensions is modeled in ANSYS software. Non-linear stress-strain data of steel are used. Plane strain case is adopted. A suitable value of far field tensile stress (pressure) is chosen such that EPFM condition prevails at the crack tip. Process and plastic zones are obtained at the crack tip. Desired values are noted. Areas of high stress and high strain are identified. Validation of void nucleation taking place ahead of crack tip and not exactly at the crack tip and coalescence of voids happening at the crack tip are confirmed from the results. Plots between the distance of desired location from the crack tip and load line stresses and strains are drawn. The plots are in accordance with the expectations.

Abstract: Usually, contact mechanics focus on semi-infinite solids, so that any interaction between normal and in-plane deformation is commonly disregarded. However, when dealing with layers of finite thickness, this assumption is no longer valid, and the specific geometry of the contact pair plays a key role in determining the normal-tangential coupling. In this study, we focus on the exemplar case of a thin deformable layer in frictional sliding contact with a rough profile, where the interplay between tangential friction and normal pressure may lead to significantly different contact behavior compared to the uncoupled case, both in terms of contact area size and frictional response.

Abstract: The article analyzes and develops an algorithm for the operation of the powder backfill process using vibration oscillations. The results of the study make it possible to predict the main properties of particles of any shape. The developed computer simulation model also provides for the superposition of horizontal and vertical oscillations. It should be noted that the difference between them is that the main one for the implementation of horizontal oscillations is the X - coordinate, and for vertical ones – the Y - coordinate. It is also important that the model algorithm provides for simultaneous application of vibration oscillations, which makes it possible to study the influence of the history of the backfill process. It should also be noted that in this scientific study, a number of experiments were conducted, the change in porosity during the imposition of oscillations was studied, and graphs of the obtained experimental dependences were constructed. Porosity from the main parameters of the bunker, in particular: width and height, is also studied. The obtained results made it possible to record the optimal porosity of the backfill with a reliable deviation error (± 1%).

Abstract: The article substantiates the main possibilities of filling with irregular bodies, and provides a visual analysis of the parameters formed as a result of structures. It was found out that the form factor acts as the main indicator of the characteristic parameter of changes in the structure and all other parameters of an inhomogeneous medium. It was also found out that when filling a container with irregular ellipsoid elements, the conditions for non-opening (one-way contact) must be met. The obtained calculations of the form factor show the minimum value of the average coordination number of an inhomogeneous medium. This allows us to assert and predict reliable modelling results (± 2-3%). It is also important that the developed simulation model for modelling an inhomogeneous medium using an irregular (ellipsoid) shape of elements can significantly reduce the time spent on conducting field experiments, as well as simulate irregular elements with different shape factors.

Abstract: The article describes in detail the process of modelling an inhomogeneous environment. It should be noted that the modelling of a rectangular plate is justified by the Kirchhoff – Love methods. A special feature of this simulation with the intervention of the Abaqus software package was the setting of different steps at different points in time. We also constructed H-adaptive schemes of finite element methods and their triangulation with different steps and with pre-guaranteed accuracy. When adapting the grid at the places of the greatest errors, a local thickening of the Triangle grid was observed, which ultimately determines that the structure of the desired solutions contains features in the edges of the vertices of the fixed edge. We also found that the proximity to linear growth of the number of nodes and finite elements in the initial stages of adaptation slows down their growth in the final stages. It should also be noted that the proposed H-adaptive schemes of ITU using the Abaqus software package with pre-guaranteed accuracy of calculating approximations showed satisfactory results, since they obtained a final deviation error of 2%. Also, a detailed description of the step-by-step adaptation results allowed us to generate the reliability of the proposed schemes with different steps.

Abstract: The article presents modelling of spherical elements based on the developed computer model. We recorded the main combinations of spherical particles during filling, which are formed in the hopper. It was found that the most likely combination that occurs when modelling spherical elements consists of three balls. It should be noted that in the cross-section of such a combination passing through the center of the balls, an equilateral triangle is formed. And in the cross-section of the structure, which consists of four spherical balls, a rhombus is formed, if you connect the centers of these spherical elements. It is worth noting that from this formed combination of spherical elements, it can be seen that the rhombus forms two smaller equilateral triangles that fix the process of pushing the spherical balls apart. In turn, the process of pushing spherical elements apart made it possible to fix the contact between spherical elements, as well as to state the stable position of each (individual) particle. This paper also presents the main fragments of encoding the source text of a 3D computer model for modelling spherical elements, which made it possible to optimize the model parameters. It was found that from the obtained data on the distribution of coordination numbers for different volume fillings of spherical elements, it follows that the largest filling was 72 %, which corresponds to the state when 112 lobules have an average coordination number of 3,92.

Abstract: SiO₂ were successfully synthesized by sol–gel process via in-situ modification. The SiO₂ consists of two kinds of co-precursor namely raw material from quartz sand and methyltrimethoxysilane (MTMS) as main SiO₂ source. By introducing SiO₂ with different sizes of particle micro-submicron scale, it was suggested to construct hierarchical structure. The sample was characterized by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), and Atomic Force Microscope (AFM) to analyze crystal structure, morphology of particles, and surface roughness of the samples. In this research, SiO₂ co-precursor from quartz sand were extraction and synthesis to be SiO₂ quartz (SQ) phase and SiO₂ amorphous (SA) phase respectively which is combine with SiO₂ based MTMS by sol–gel process via in-situ modification. Based on the results, it can be concluded that SiO₂ with high purity levels maintains its crystal structure even after in-situ modification, resulting in an increase in particle size to approximately 12-20 μm. SEM images showed that particle was irregular shape due to agglomeration which is SiO₂ based quartz sand stick by SiO₂ based MTMS. AFM showed the surface roughness of MTMS/SQ have a larger roughness than MTMS/SA with Sa 3.3 ± 0.8 nm and Sq 5.0 ± 1.0 nm. The formation of hierarchical structure layers based on SiO₂ has a promising potential for wide applications in various fields such as hydrophobic surface.

Abstract: In this research, a hydrophobic surface has been successfully created using a mixture of silica sand and methyltrimethoxysilane (MTMS) precursor. This research aims to determine the effect of varying the volume of MTMS on the hydrophobic surface. The MTMS as silica precursor was synthesized with Stöber method. The variation used is the volume of the MTMS precursor, while the silica from silica sand is made constant. The volume variation of the MTMS precursor is 9.5 ml, 19 ml, 28.5 ml and 38 ml. The MTMS/SiO2 composite which has been synthesized then get mixed with steel ship paint and coated on the steel plate surface as a topcoat. The MTMS/SiO2 composite was further characterized by X-ray Powder Diffraction (XRD), Scanning Electron Microscopy (SEM), Water Contact Angle (WCA), and Atomic Force Microscope (AFM) which were employed to investigate crystal structure, morphology of particle, hydrophobicity on a surface, and topography of the three-dimensional surface layer respectively. The type of liquid used in the WCA characterization is seawater. XRD characterization results show that silica sand has a quartz phase, MTMS has an amorphous phase and MTMS/SiO2 composite tends to have an amorphous phase. SEM characterization show that the particle size of silica sand that has been mixed with MTMS is around 8 – 20 μm. WCA characterization show that the addition of silica powder on the topcoat increase surface roughness and WCA, so that the steel plate surface has good hydrophobic properties. The highest water contact angle obtained in this research was 109o by seawater.