Showing papers by "Vadim V. Silberschmidt published in 2018"

Mechanically robust transparent anti-icing coatings: roles of dispersion status of titanate nanotubes

Abstract: Ice accretion on automobiles, aerospace components, precision instruments, and photovoltaic devices detrimentally affect their performance and increase the maintenance cost. Despite significant efforts devoted to the investigation of anti-icing coatings in the past decades, mechanically robust and transparent anti-icing coatings are rarely reported. In this study, titanate nanotubes are used as filler to prepare mechanically robust anti-icing coatings with a sol-gel method. Specially, the effect of dispersion status of nanotubes on the transmittance, surface roughness, and water repellency is investigated. The optimized smooth, transparent coating exhibits higher water repellency and better anti-icing performance in terms of ice-adhesion strength, icing delay time, and ice-nucleation temperature than the rough one. Much higher hardness and scratch resistance than that of commercially available icephobic or anti-icing coatings is obtained on the smooth, transparent sample; the coating also presents good adhesion to the substrate.

Experimental Study on the Effect of Point Angle on Force and Temperature in Ultrasonically Assisted Bone Drilling

Abstract: Drilling of bone is a common surgical procedure in orthopedics to produce holes for screw insertion. The force and temperature rise in bone drilling are two important factors affecting the outcome of the process. The present work attempts to investigate the effect of drill point angle on the level of force and temperature in bone in the presence of ultrasonic vibrations imposed on the drill along the drilling direction. The effect of drill speed on the drilling force and bone temperature was studied using two types of drills with different point angles. The influence of a range of ultrasonic frequencies and amplitudes of vibrations on drilling force, torque and surface temperature of bone was also investigated. The drilling force and bone temperature were found to be strongly influenced by the drill point angle in the presence of ultrasonic vibrations. The drill with larger point angle caused more force and temperature compared to the drill with smaller point angle. Ultrasonic frequency above 15 kHz was observed to produce more temperature in bone for both types of drill geometries. This study found drill with smaller point angle favorable for safe and efficient drilling in bone.

Hybrid machining process: experimental and numerical analysis of hot ultrasonically assisted turning

Abstract: © 2018 Springer-Verlag London Ltd., part of Springer Nature A hybrid turning is presented for turning of Ti-15V-3 Al-3 Cr-3 Sn alloy. In this technique, cutting insert is vibrated in velocity direction with the help of ultrasonic transducer and external heat is provided to the machined workpiece to gain collective benefits of both arrangements in cutting of hard-to-cut alloys. The studied alloy was investigated numerically and experimentally using hybrid turning process to determine its rewards in decline of measured cutting forces and enhancement in quality of machined surface. The assessment for thermal evolution in the cutting process was carried out both numerically and experimentally, and an accurate prediction of process zone temperatures is achieved. A significant improvement in dry turning of the studied alloy was achieved in terms of substantial decline in cutting forces and no substantial alterations in the metallurgy of the tested material. An elastoplastic thermo-mechanically coupled finite-element model for oblique-turning process is established to investigate the effect of heat and vibration on output parameters numerically. The developed model was used to explore the influence of selected machining parameters (depth-of-cut, feed rate, cutting speed, and tool nose radius) on three components of forces, stresses, and process zone temperature. Comparative case studies were executed with the developed models of conventional-turning, hot-conventional-turning, and hybrid turning and were confirmed by the outputs from tests carried out on the in house prototype available at Loughborough University, United Kingdom. The model was used for two-dimensional ultrasonic vibration in all three axis and resulted no significant drop in the cutting forces when compared to the studied hybrid turning process.

Microstructural evolution of 96.5Sn–3Ag–0.5Cu lead free solder reinforced with nickel-coated graphene reinforcements under large temperature gradient

Abstract: In this study, 96.5Sn–3Ag–0.5Cu (SAC305) lead-free composite solder containing graphene nanosheets (GNS) decorated with Ni nanoparticles (Ni-GNS) was prepared using a powder metallurgy method. A lab-made set-up and a corresponding Cu/solder/Cu sample design for assessing thermo-migration (TM) was established. The feasibility of this setup for TM stressing using an infrared thermal imaging method was verified; a temperature gradient in a solder joint was observed at 1240 K/cm. Microstructural evolution and diffusion of Cu in both plain and composite solder joints were then studied under TM stressing conditions. Compared to unreinforced SAC305 solder, the process of diffusion of Cu atoms in the composite solder joint was significantly reduced. The interfacial intermetallic compounds (IMCs) present in the composite solder joint also provide a more stable morphology after the TM test for 600 h. Furthermore, during the TM test, the Ni-GNS reinforcement affects the formation, migration and distribution of Ni–Cu–Sn and Cu–Sn IMCs by influencing the dissolution rate of Cu atoms.

Experimental studies of shear bands in Zr-Cu metallic glass

Abstract: Shear bands are the key feature that control deformation in bulk metallic glasses (BMGs). This study provides a comprehensive analysis of plastic deformation of a Zr-Cu-based BMG at room temperature. Experiments were conducted to observe the evolution of shear bands in the material. It was shown that shear bands formed discretely in the material which allows for material deformation to occur across it. Additionally, individual shear bands were characterised to obtain a better understanding of shear-band-induced plasticity. Assessment of mechanical properties, such as hardness and elastic modulus, indicate the deformed regions of the material were weaker than undeformed regions. No compositional or structural changes were found in shear-band of the studied BMG suggesting generation of local free volume in the deformed region.

3D DDD modelling of dislocation-precipitate interaction in a nickel-based single crystal superalloy under cyclic deformation

Abstract: Strain-controlled cyclic deformation of a nickel-based single crystal superalloy has been modelled using three-dimensional (3D) discrete dislocation dynamics (DDD) for both [0 0 1] and [1 1 1] orie...

Interfacial fracture of 3D-printed bioresorbable polymers

Abstract: A micro specimen for tensile testing was designed with two primary aims: (i) to characterise interface fracture behaviour between fused 3D-printed polymer filaments; and (ii) to minimise material use of high-cost medical-grade polymer since a high number of specimens are required for time-series studies (e.g. polymer degradation). Polylactide specimens were fabricated on an extrusion 3D-printer as a single-filament-wide wall. The widths of filaments were set individually, with a custom machine-control code, to achieve a higher width in the grip sections of specimens and a narrower width in their gauge section. On average, the interface between filaments was 114 µm narrower than the widest point of the filaments. Each specimen was tested in the build direction to determine the interfacial strength between 3D-printed layers. Optical microscopy was employed to characterise geometry of specimens and fracture surfaces. Samples fractured in the gauge section and the fracture surface demonstrated brittle characteristics. The specimens utilised an order of magnitude less material than ASTM D638 samples, whilst maintaining repeatability for tensile strength similar to that in other studies. The average strength was 49.4 MPa, which is comparable to data in the literature. Further optimisation of the specimen design and 3D printing strategy could realise greater reductions in material use.

Dynamic interfacial fracture of a thin-layered structure

Abstract: To calculate the dynamic energy release rate of a crack is important for understanding a structure’s fracture behavior under transient or varying loads, such as impact and cyclic loads, when the inertial effect can be significant. In this work, a method is proposed to derive an analytic expression for the dynamic energy release rate of a stationary crack under general applied displacement. An asymmetric double cantilever beam with one very thin layer is considered as a special case, with vibration superimposed onto a constant displacement rate applied to the free end. The resulting expression for dynamic energy release rate is verified using the finite-element method (FEM) in conjunction with the virtual crack closure technique. The mode-mixity of the dynamic energy release rate is also calculated. The predicted total dynamic energy release rate and its components, GI and GII, are both in close agreement with results from FEM simulations

A diffusion-based approach for modelling crack tip behaviour under fatigue-oxidation conditions

Abstract: Modelling of crack tip behaviour was carried out for a nickel-based superalloy subjected to high temperature fatigue in a vacuum and air In a vacuum, crack growth was entirely due to mechanical deformation and thus it was sufficient to use accumulated plastic strain as a criterion To study the strong effect of oxidation in air, a diffusion-based approach was applied to investigate the full interaction between fatigue and oxygen penetration at a crack tip Penetration of oxygen into the crack tip induced a local compressive stress due to dilatation effect An increase in stress intensity factor range or dwell times imposed at peak loads resulted in enhanced accumulation of oxygen at the crack tip A crack growth criterion based on accumulated levels of oxygen and plastic strain at the crack tip was subsequently developed to predict the crack growth rate under fatigue-oxidation conditions The predicted crack-growth behaviour compared well with experimental results

8.14 Composites Under Dynamic Loads at High Velocities

Abstract: The use of fiber-reinforced polymer composites (FRPs) in aerospace, automotive, and military applications as well as in energy and naval structures is ever expanding, mainly, due to the weight-saving benefits. To manufacture durable composites parts, understanding their structural behavior under severe loading conditions is critical to designers and end-users. FRPs usually demonstrate a multiplicity of damage mechanisms under varying impact conditions due to their heterogeneous microstructure. A wealth of knowledge is available on a low-velocity impact response of composites, though with continuously emerging advanced materials and structures, established structure–property–performance relationships that could provide guidelines on dynamic impact behavior of composites are rare. A compulsory compliance with extensive testing standards and affirmation to the personnel health and safety makes real-time dynamic impact experiments rather expensive. Repeatability and reliability of their results may also suffer due to the rapid time frame in the absence of a suitable data-acquisition system. Finite-element (FE) models, in such cases, can be used as a virtual simulation tool to help engineers improving design of composite structures exposed to dynamic loading.

Finite Element Modeling and Analysis of Ultrasonically-Assisted Drilling of Bone

Abstract: Drilling in bone is a common surgical procedure in orthopedics for fixation and reconstructive surgeries. Research in this area is largely focused on investigating alternate drilling techniques for minimal destruction to the bone tissue. This study measured temperature and force generated during conventional drilling (CD) and ultrasonically-assisted drilling (UAD) using Finite Element (FE) simulations. Three-dimensional FE model of bone drilling was developed and analyzed to simulate the dynamic processes involved in the process. Numerical simulation predicted lower drilling force and temperature in UAD compared to CD using controlled ultrasonic parameters (frequency -- 20kHz, amplitude = 10 micrometers). Drilling tests are performed on fresh bovine femur using surgical drills in the presence of ultrasonic vibrations imposed on the drill in the cutting direction. Force and temperature generation at various depths are calculated and compared for the prescribed drilling techniques. The results obtained from numerical simulations are compared with bone drilling experiments.

Experimental and morphological investigations of fracture behavior of PBT/TPEE

Abstract: Short-fiber-reinforced polymers are widely used in industry. They are light-weight, have excellent mechanical properties and can be processed via injection molding. This allows the mass production of high-quality components with high geometric accuracy. Their superior electrical isolation properties make them a good choice for electrical housings in the automotive sector. Due to the importance and precise nature of applications, in which such products are employed, many studies have investigated the properties of these materials. Polybutylenterephthalat (PBT) with thermoplastic polyester elastomer (TPEE), an impact-enhancing additive, is a typical example. Still, there is a lack of knowledge regarding the effect of TPEE on mechanical and fracture behaviors of short-fiber-reinforced PBT and the effect of its microstructure on the dynamic performance. To study the characteristics of modified short-fiber-reinforced PBT and to assess the effect of the filament, two types of polymers - standard PBT-GF10 and PBT-GF10 blended with 10% TPEE - were compared. Morphological investigation of fracture surfaces produced in tensile tests at different loading rates was undertaken with scanning electron microscopy (SEM). Further two-dimensional image analysis was completed with the image processing software ImageJ. The morphological analysis showed that TPE-E generally affected the microstructure of the material. Micrographs of fracture surfaces demonstrated a decrease in the size of area of ductility with increasing loading rate. These results will support the development and design of optimized parts and their processing methods.

Computational Evaluation of Artery Damage in Stent Deployment

Abstract: This paper aims to evaluate damage in an arterial wall and plaque caused by percutaneous coronary intervention using a finite-element (FE) method. Hyperelastic damage models, verified against experimental results, were used to describe stress-stretch responses of arterial layers and plaque in the lumen; these models are capable to simulate softening behaviour of the tissue due to damage. Abaqus CAE was employed to create the FE models for an artery wall with two constituent layers (media and adventitia), a symmetric uniform plaque, a bioresorbable polymeric stent and a tri-folded expansion balloon. The effect of percutaneous coronary intervention on vessel damage was investigated by simulating the processes of vessel pre-dilation, stent deployment and post-stenting dilation. Energy dissipation density was used to assess the extent of damage in the tissue. Overall, the plaque experienced the most severe damage due to its direct contact with the stent, followed by the media and adventitia layers. Softening of the plaque and the artery due to the pre-dilation-induced damage can facilitate the subsequent stent-deployment process. The plaque and artery experienced heterogeneous damage behaviour after the stent deployment, caused by non-uniform deformation. The post-stenting dilation was effective to achieve a full expansion of the stent but caused additional damage to the artery. The computational evaluation of artery damage can be also potentially used to assess the risk of in-stent restenosis after percutaneous coronary intervention.

Ultrasonically assisted drilling of rocks

Abstract: Conventional drilling of rocks can generate significant damage in the drilled material; a material layer is often split off a back surface of a sample during drilling, negatively affecting its strength. To improve finish quality, ultrasonically assisted drilling (UAD) was employed in two rocks - sandstone and marble. Damage areas in both materials were reduced in UAD when compared to conventional drilling. Reductions in a thrust force and a torque reduction were observed only for UAD in marble; ultrasonic assistance in sandstone drilling did not result in improvements in this regard.

Ultrasonic Assisted Turning: A Comparative Study of Surface Integrity

Abstract: The surface integrity of machined sample has detrimental effects on the product’s life. The machining parameters have been found to significantly affect the surface integrity during the turning operation. Surface roughness, residual stresses and microhardness are the most commonly used parameters to study the surface integrity. In this chapter, an attempt has been made to present a comparative analysis of conventional turning (CT) and ultrasonically assisted turning (UAT) processes with plain and textured cutting tools. The effect of ultrasonic power (measured in terms of amplitude) on surface roughness has been studied during UAT process. An increase in the amplitude improved the surface finish of the machined specimen, significantly. The surface residual stresses generated in the machined part during UAT have been compared for plain and self-lubricating cutting inserts using XRD analysis. An attempt has been made to evaluate the residual stresses generated during the process by using commercially available finite element method package, ANSYS. The generation of a large compressive residual stresses during UAT process with self-lubricating cutting inserts signifies better fatigue life of the component. The microhardness measurements are used to demarcate the Machine Affected Zone (MAZ) for UAT and CT process. A comparative analysis between CT and UAT has also been presented in terms of surface integrity to demonstrate better machining regime found in UAT using self-lubricating cutting inserts.

Numerical and analytical model of long tubular bones with anisotropic distribution of elastic properties

Abstract: Elastic parameters of a cortical bone tissue at the macrolevel can vary for various bones, as well as in different parts or anatomical quadrants, of the same bone. In this paper, an approach to finite-element modelling of the nonlinear anisotropic and isotropic distribution of elastic properties of tubular bones is proposed. Dependences of the Young’s moduli, shear moduli and the Poisson’s ratios on the spatial coordinates determining the position of the element in the bone model are used. They were obtained on the basis of experimental data on anisotropic elastic properties of tubular bone. A comparative finite-element analysis of the principal stresses and deformations caused by the action of own weight on the human femur was carried out for nonlinear anisotropic and isotropic distributions of elastic properties. Differences between the levels of maximum principal stresses and deformations for the three cases of elastic properties can reach approximately 10% and 30%, respectively.

Relations between Parameters of Fracture Processes on Different Scale Levels

Abstract: The processes of ultrasonically-assisted drilling (UAD) and the dynamic tests on split Hopkinson pressure bar (SHPB), fracture in which is implemented at various structural-scale levels, are considered. The simulation of UAD based on the Hertz contact problem and the structural−time criterion is presented. The problem of using the value of the fracture incubation time and its linear size obtained from the tests on SHPB in the simulation is considered. A principle of equal power is used for converting the strength parameters into another structural−scale level. The theoretical curve obtained in the simulation is compared with the results of experiments on conventional drilling (CD) and UAD.