Half-apex Angle Research Articles

An optical study on the enhanced light trapping performance of the perovskite solar cell using nanocone structure

Photon management strategies are crucial to improve the efficiency of perovskite thin film (PTF) solar cell. In this work, a nano-cone (NC) based 2D photonic nanostructure is designed and simulated aiming at achieve superior light trapping performance by introducing strong light scattering and interferences within perovskite active layer. Compared to the planar PTF solar cell, the NC nanostructured device with 45 degrees half apex angle obtains highest short-circuit current density, which improved over 20% from 15.00 mA/cm2 to 18.09 mA/cm2. This work offers an alternative design towards effective light trapping performance using 2D photonic nanostructure for PTF solar cell and could potentially be adopted as the nano-structuring strategy for the future perovskite solar cell industry.

Cracking behavior during scratching brittle materials with different-shaped indenters

The cracking behavior greatly influences the material removal and surface integrity during the abrasive machining of brittle materials. The abrasive machining can be simplified as a series of scratching by different-shaped indenters. In this paper, a scratch-induced stress field model is built to analyze the cracking behavior during scratching brittle materials. The model considers conical, pyramidal, and spherical (CPS) indenters and correlates the scratch-induced principal stress with workpiece material properties, indenter geometries, and scratch behavior parameters (e.g., scratch normal load, tangential load, friction coefficient, scratch depth). With the model, the effects of scratch depth and indenter geometries on the scratch behavior and cracking behavior are investigated. The results show that the scratch load decreases when a sharper indenter or a spherical indenter with a smaller radius is used. The larger the scratch depth, the easier it is for radial, median, and lateral (RML) cracks to initiate. There is an optimal indenter half-apex angle at which it is most difficult to initiate radial and median cracks. The lateral crack easily initiates when the indenter becomes sharp. The initiation position of radial crack changes from being in front of the indenter to being behind it as the scratch depth increases or the half-apex angle decreases. The propagation angle of radial crack decreases, while that of median crack increases with an increase in scratch depth. The sizes of RML cracks increase with an increasing scratch depth or half-apex angle. Finally, the model is validated through scratching experiments on fused silica using CPS indenters and by referencing previous research. It demonstrates that the model can accurately determine the sizes of RML cracks, with an average relative error of less than 11%. This research provides guidance on selecting suitable process parameters or indenter geometries to increase the material removal rate and mitigate the crack damage during the abrasive machining of brittle materials.

Effect of cone rotation on the nonlinear evolution of Mack modes in supersonic boundary layers

In this paper, we present a systematic study of the nonlinear evolution of the travelling Mack modes in a Mach 3 supersonic boundary layer over a rotating cone with a $7^{\circ }$ half-apex angle using the nonlinear parabolic stability equation (NPSE). To quantify the effect of cone rotation, six cases with different rotation rates are considered, and from the same streamwise position, a pair of oblique Mack modes with the same frequency but opposite circumferential wavenumbers are introduced as the initial perturbations for NPSE calculations. As the angular rotation rate $\varOmega$ increases such that $\bar \varOmega$ (defined as the ratio of the rotation speed of the cone to the streamwise velocity at the boundary-layer edge) varies from 0 to $O(1)$ , three distinguished nonlinear regimes appear, namely the oblique-mode breakdown, the generalised fundamental resonance and the centrifugal-instability-induced transition. For each regime, the mechanisms for the amplifications of the streak mode and the harmonic travelling waves are explained in detail, and the dominant role of the streak mode in triggering the breakdown of the laminar flow is particularly highlighted. Additionally, from the linear stability theory, the dominant travelling mode undergoes the greatest amplification for a moderate $\varOmega$ , which, according to the $e^N$ transition-prediction method, indicates premature transition to turbulence. However, this is in contrast to the NPSE results, in which a delay of the transition onset is observed for a moderate $\varOmega$ . Such a disagreement is attributed to the different nonlinear regimes appearing for different rotation rates. Therefore, the traditional transition-prediction method based on the linear instability should be carefully employed if multiple nonlinear regimes may appear.

Dynamic Analysis of Flexoelectric Actuated Truncated Conical Shells

Conical shells are widely used in aerospace engineering, such as for rocket fairings, satellite-rocket joints, load-bearing structures of solid rocket motor cases, and so on. In this study, the truncated conical shell with a flexoelectric actuator was discussed, and the precision flexoelectric actuation and control effectiveness were evaluated. A flexoelectric patch covered with an electrode layer was attached to the external surface of an elastic truncated conical shell, and a line electrode was longitudinally attached to the external surface of the patch. When a control voltage was applied to the line electrode and the electrode layer, an inhomogeneous electric field was generated; consequently, the stresses were induced in the flexoelectric patch due to the converse flexoelectric effect, thus regulating the vibration of the conical shell. The dynamic model of the truncated conical shell with a flexoelectric actuator was established. Then, the actuation effects of the flexoelectric actuator on the conical shell were investigated in terms of the microscopic behaviors, that is, flexoelectric-induced stresses, membrane control forces, bending control moments, and modal forces. Furthermore, the influences of several design parameters (that is, the line-electrode radius, conical shell thickness, flexoelectric patch thickness, and conical shell half-apex angle) on the flexoelectric actuation behaviors were also investigated.

Instabilities of the natural convection around a cone in thermally stratified medium.

In this paper, we provide a mathematical description of the onset of instability for buoyancy-driven flow around a cone. The self-similar solutions of the basic flow are derived, where the ambient fluid and the cone have independent temperature gradients. The linear instability properties are investigated by utilizing the Chebyshev collocation method. It is demonstrated that the neutral curves have a two-lobed structure and that changing the Grashof number has only quantitative influence on stability. The critical streamwise location increases when the half-apex angle is increased, and the unstable range of the wave number diminishes. According to the examination of eigenfunction profiles and the progression of the two spatial branches in the (α_{i},α_{r}) planes, the primary instabilities on the surface of cone are identified as type-I mode and type-II mode. The energy analysis is investigated for a typical situation to gain a physical insight, where it is demonstrated that besides the viscous dissipation, the streamline curvature and buoyancy-driven effects are dominant for the type-I mode while inviscid effect plays an essential role in type II. These encouraging results are expected to be conducive to understanding buoyancy-driven systems.

ICAE 2021 - Preface

One of the applicable shell structures related to underwater systems, covering riser pipes, ice-breaking equipment, underwear noise migrations, ballast water components, and gliders, can be considered Linked Hemispherical-Conical Shell (LHCS) structures. Accordingly, the ensuing investigation is provided to compute the Natural Frequency Values (NFVs) of the LHCS, with the opening angle at starting part of the hemispherical structure (which will be studied for the first time) enhanced by graphene-based nanocomposite materials containing Graphene Nano-Platelet (GNP) and Graphene Oxide-Powder (GOP) nanocomposites. For this reason, the Halpin-Tsai approach and the rule of the mixture are engrossed in determining the productive functionally graded mechanical criteria of the graphene-based nanocomposite materials. To obtain the main formulations of the LHCS, Donnell's assumptions and First-Order Shear Deformation Theory (FOSDT) are also engaged. Additionally, Hamilton's technique is involved in finding the kinetic equations coupled with the hemispherical and the conical parts of the LHCS. Next, the distinguished approach, Generalized Differential Quadrature (GDQ) program, is applied to discrete the kinetic equations. Subsequently, the standard eigenvalue problem determines the NFVs related to the GNP and GOP nanocomposites LHCSs. At termination, the exactness of the suggested scheme is confirmed by comparing the provided outputs with the NFVs of the submitted work (which can be used as the benchmark) with responses determined by FEM commercial software and the only benchmark study that exists in the literature. Furthermore, some novel cases are solved to estimate the effects of different geometric criteria of the LHCS, such as the opening angle of the hemispherical, the Half-Apex (HA) angle of the conical segment, the thickness related to the structure, and also the effect of GNP and GOP scattering models spread in conjunction with the thickness of the LHCS on the NFVs coupled with the GNP and GNP nanocomposites LHCS.

Wave frequency responses estimate of the nanocomposite linked hemispherical-conical shell underwater-like bodies with the impacts of two types of graphene-based nanofillers

One of the applicable shell structures related to underwater systems, covering riser pipes, ice-breaking equipment, underwear noise migrations, ballast water components, and gliders, can be considered Linked Hemispherical-Conical Shell (LHCS) structures. Accordingly, the ensuing investigation is provided to compute the Natural Frequency Values (NFVs) of the LHCS, with the opening angle at starting part of the hemispherical structure (which will be studied for the first time) enhanced by graphene-based nanocomposite materials containing Graphene Nano-Platelet (GNP) and Graphene Oxide-Powder (GOP) nanocomposites. For this reason, the Halpin-Tsai approach and the rule of the mixture are engrossed in determining the productive functionally graded mechanical criteria of the graphene-based nanocomposite materials. To obtain the main formulations of the LHCS, Donnell's assumptions and First-Order Shear Deformation Theory (FOSDT) are also engaged. Additionally, Hamilton's technique is involved in finding the kinetic equations coupled with the hemispherical and the conical parts of the LHCS. Next, the distinguished approach, Generalized Differential Quadrature (GDQ) program, is applied to discrete the kinetic equations. Subsequently, the standard eigenvalue problem determines the NFVs related to the GNP and GOP nanocomposites LHCSs. At termination, the exactness of the suggested scheme is confirmed by comparing the provided outputs with the NFVs of the submitted work (which can be used as the benchmark) with responses determined by FEM commercial software and the only benchmark study that exists in the literature. Furthermore, some novel cases are solved to estimate the effects of different geometric criteria of the LHCS, such as the opening angle of the hemispherical, the Half-Apex (HA) angle of the conical segment, the thickness related to the structure, and also the effect of GNP and GOP scattering models spread in conjunction with the thickness of the LHCS on the NFVs coupled with the GNP and GNP nanocomposites LHCS.

Theory of adhesive contact on multi-ferroic composite materials: Conical indenter

There is still a challenge to realize controllable attachment and detachment in the adhesive devices. New approaches of the controllable or reversible adhesion need to be developed in a wider area. In order to study the influence of the electric and magnetic quantities on the reversible adhesion, the adhesive contact problem between a half-space of the multi-ferroic composite material and a rigid conical indenter is investigated. The classical Johnson–Kendall–Roberts (JKR) and Maugis–Dugdale (MD) models are extended to the framework of magneto-electro-elasticity. The corresponding physical fields are analytically obtained. With the help of the Griffith energy balance relations, the stable equilibrium states of the adhesive contact are established. The corresponding indentation forces and the penetration depths for the JKR and MD models are derived in the closed-form. It is found that the pull-out forces associated with the JKR model depend on the electric potential and magnetic potential in certain cases. The validity is discussed by comparing the obtained solutions with the experimental data in the context of the elasticity. Numerical results show that the adhesive contact behaviors may be adjusted and controlled by changing the electric potential, the magnetic potential and the half apex angle of the rigid conical indenter. The present analytical results not only are the theoretical fundament for the forthcoming indentation experiments at the micro/nanoscopic scale, surface force microscopy (SFM) and atomic force microscopy (AFM), but also serve as guiding bionic design of the robots and grippers with reverse adhesion.

Bioconvection in a Convectional Nanofluid Flow Containing Gyrotactic Microorganisms over an Isothermal Vertical Cone Embedded in a Porous Surface with Chemical Reactive Species

In this examination, a mathematical model is developed for Darcy free convection with reference to an isothermal vertical cone along with fixed apex half angle, pointing downward in a nanofluid-saturated porous medium. The aim of this methodology is to offer another sort of primary fluid containing nanoparticles and gyrotactic microorganism’s consistence of permeable medium, chemical reaction alongside convective boundary circumstance. The model presents design rules for improvement of imperative fabrication of fertilizer and polymer substance. The present model includes the gyrotactic microorganisms alongside nanoparticles, and cone is dependent on concentration of nanoparticles as well as density of motile microorganisms. Two important impacts Brownian motion as well as thermophoresis are also included in the present model for nanofluids. Reduced system of nonlinear differential equations is derived from governing partial differential of the present flow by using usual transformations along with Oberbeck–Boussinesq approximation. After that, this reduced system is solved numerically with the use of fifth-order Runge–Kutta method in conjunction with the shooting technique. Relevant outcomes are exhibited graphically and talked about quantitatively as for variety in the flow controlling parameters related to the present analysis. Mainly, the observations are bioconvection parameters will in general improve the concentration of the rescaled density of microorganisms and nanoparticles volume fraction and dimensionless motile microorganisms reduce with strong chemical reactions.

Electro Winning from Dilute Solutions at Enhanced Rates using Three-Phase Flow Reactor

Enhancement of mass transfer coefficient is highly desirable for economic design of process equipment. The present study is essentially carried out to know the effect of flow variables such as gas and liquid velocities and geometric parameters of the internal on mass transfer coefficients in a three phase fluidized bed. The mass transfer coefficient data were obtained using a string of cones internal in a three-phase fluidized bed electrochemical reactor. The flow system investigated was nitrogen, a fluid electrolyte and spherical glass beads as gas, liquid and solid phases respectively. Limiting current technique was employed to obtain mass transfer data. The internal comprises of a string of cones arranged concentrically on a central rod which is placed coaxially in a three phase fluidized bed. The presence of internal in three phase fluidized beds augmented the mass transfer coefficient significantly. In the present investigation it was found that the effect of gas velocity, liquid velocity, rod diameter and cone diameter was only marginal. However, the influence of pitch, half apex angle of cone and particle diameter was found to be significant. Correlations were developed based on least squares regression analysis for the prediction of mass transfer coefficient in terms of pertinent variables.

GYROTACTIC MICROORGANISMS FREE CONVECTION BOUNDARY LAYER FLOW ABOUT A VERTICAL TRUNCATED CONE IN NANOFLUID POROUS MEDIA

A non-similar boundary layer analysis is presented to examine the natural convection flow over a truncated cone with fixed apex half angle; pointing downwards in a nanofluid saturated porous medium contains gyrotactic microorganisms. A suitable coordinate transformation is performed, and the obtained non-similar equations are solved by fourth order Runge–Kutta method technique coupled with shooting scheme. The effects of the thermophoresis parameter, Brownian parameter, Lewis number, bioconvection Peclet number, bioconvection Lewis number, bioconvection Rayleigh number and buoyancy ratio on the reduced Nusselt, Sherwood and density of motile microorganisms numbers have been studied. A comprehensive numerical computation is carried out for various values of the parameters that describe the flow characteristics.

Effect of pineapple leaf (PALF), napier, and hemp fibres as filler on the scratch resistance of epoxy composites

This article presents the effects of pineapple leaf (PALF), napier, and hemp fibres as filler on the scratch resistance of epoxy composites. In particular, it explores the effect of these natural fillers on the horizontal load, coefficient of friction (COF), penetration depth, fracture toughness, scratch hardness, brittleness index and scratch observation. The mixing method using magnetic stirrer was used to produce the natural fibre-filled epoxy composites with different wt%, namely, 5, 7.5, and 10wt%. The test was performed using a CSM Revetest Xpress, which consisted of a cone of the half-apex angle of 60° ending with a sphere having a tip radius of 200μm. The indenter scratch distance and speed were 7mm and 1.5mm/min, respectively. The results show that the napier fibre-filled epoxy composites have the highest peak load and COF. It was also noted that the napier fibre-filled epoxy composites have the lowest penetration depth for each wt% of filler. Lastly, the fracture toughness (Kc) for the napier fibre-filled epoxy composites with 10wt% of filler yielded the highest value of 4.33MPa.m1/2. It can also be seen that using a scanning electron microscope (SEM), the amount of debris increased with higher of wt% of the natural fibre fillers in the composites. Hence it was demonstrated that the napier fibre-filled epoxy composites have higher scratch resistance compared to the PALF and hemp fibre-filled epoxy composites.

Theoretical analysis on transition from interface defeat to penetration in the impact of conical-nosed long rods onto ceramic targets

Based on related investigations, theoretical analysis on the transition from interface defeat to penetration in the impact of conical-nosed long rods onto ceramic targets is conducted systematically in the present manuscript, and comparison with the case of the flat-nosed long rod is carried out. Considering that the radius of rod-target contact face is variable during the dwell process of the conical nose, an effective impact pressure on the target surface is introduced to represent its total effect, and the corresponding formulae of the critical impact velocity range are deduced out. Furthermore, the influences of the half apex angle and the initial radius of nose tip on the lower and upper bounds of critical impact velocity range are discussed in detail, and the decay of critical impact velocity derived from the conical nose is predicted reasonably. Besides, by considering the damage and failure characteristics within the ceramic target, the critical transition time from interface defeat to penetration is analyzed, and the corresponding analytical formula is provided. Related analysis is of great significance for the design of nose shape of long rods which are directed against ceramic targets.

Corrections to the stiffness relationship in 3-sided and conical indentation problems

One key relationship in the depth-sensing indentation technique is the proportionality between the contact stiffness and the contact size, as can be proved from the Sneddon's solution of axisymmetric frictionless contact. However, Sneddon's solution is only accurate when the indenter approaches a half-space (e.g., for conical indenter, the half-apex angle approaches 90º) and the interface is frictionless. As Hay et al. (J. Mater. Res., 1999) pointed out, sharp indenters lead to a radial inward displacement on the sample surface, thus leading to extra indentation force needed to push the surface back to conform with the conical indenter. In this paper, we argue that the physical origin arises from the incorrect use of reference and deformed coordinates in the boundary conditions that define Sneddon's problem. This yields two correction factors for both load and depth solutions, which are needed for sharp pyramidal indenters and frictional contact. Approximate solutions are derived which compare favorably well with the finite element simulations. We also find that the stiffness correction factor of three-sided indenter is about 11∼15% times higher than that of conical indenter, and this multiplicative factor is only a weak function of the indenter angle but does not depend on the friction coefficient and Poisson's ratio.

Experimental study of the influence of small angles of attack and cone nose bluntness on the stabilization of hypersonic boundary layer with passive porous coating

The present work was devoted to an experimental study of small angles of attack and cone nose bluntness on the efficiency of stabilization of high-frequency disturbances in hypersonic boundary layer with a passive porous coating. The experiments were carried out on a cone with an apex half-angle 7° and nose bluntness radii R = 0.03, 0.5 and 1 mm installed under angles of attack α = 0–1° at the freestream Mach number M∞ = 5.8. High-frequency pressure fluctuations on the sides of the cone with the solid and porous surfaces were measured. It is shown that at all angles of attack and cone bluntness, the passive porous coating permits an efficient suppression of disturbances in hypersonic boundary layer both on the windward and leeward sides of the cone.

Numerical and experimental investigation on the deformation mechanism of micro single point incremental forming process

Single-point Incremental Sheet Forming (ISF) is a die-less forming process with advantages of high-flexibility, low-cost and short lead time. Recently, micro components have been employed in many applications, especially in medical industry using as implant components, surgical tool and tooth caring accessories etc. Therefore, the reduction of component size to micro-domain has becoming one of the key elements for the development of ISF technique, which will encounter many challenges, such as reduction of formability, tool wear, inaccuracies in tooling fabrication, etc. This work combined numerical and experimental approaches to study the deformation mechanisms in micro ISF process. Aluminum 1145 soft-temper foils with thickness of 38.1 μm and 50.8 μm were employed. A truncated pyramid with variable half-apex angle was employed here as the standard geometry for measuring the maximum forming angle that could be achieved in micro-ISF process. The result shows that forming angle has direct link with material formability. A full tool path micro-ISF finite element model has been developed using incompatible mode eight-node brick element C3D8I, which is capable to capture the shape and thickness distribution of the formed parts with most accuracy and least computational time. The thickness distribution of the workpiece was compared with the Sine Law to unveil the additional stretch region appearing at the top edge of the formed feature in the micro ISF as compared to macro ISF.

Mean flow generation by an intermittently unstable boundary layer over a sloping wall

Direct numerical simulations (DNS) of the flow in various rotating annular confinements have been conducted to investigate the effects of wall inclination on secondary fluid motions due to an unstable boundary layer. The inner wall resembles a truncated cone (frustum) whose apex half-angle is varied from$18^{\circ }$to$0^{\circ }$(straight cylinder). The large inner radius$r_{1}$, the mean rotation rate$\unicode[STIX]{x1D6FA}_{0}$and the kinematic viscosity$\unicode[STIX]{x1D708}$were kept constant resulting in the constant Ekman number$E=\unicode[STIX]{x1D708}/(\unicode[STIX]{x1D6FA}_{0}r_{1}^{2})=4\times 10^{-5}$. Flows were excited by time-harmonic modulation of the inner wall’s rotation rate (so-called longitudinal libration) by prescribing the amplitude$\unicode[STIX]{x1D700}\unicode[STIX]{x1D6FA}_{0}$and the forcing frequency$\unicode[STIX]{x1D714}=\unicode[STIX]{x1D6FA}_{0}$. By steepening the inner wall and hence reducing the effect of the local Coriolis force in the boundary layer three different flow regimes can be realized: a rotation-dominated, a libration-dominated and an intermediate regime. In the present study we focus on the libration-dominated regime. For small libration amplitudes (here$\unicode[STIX]{x1D700}=0.2$), a laminar Ekman–Stokes boundary layer (ESBL) is realized at the librating wall. With the aid of laminar boundary layer theory and DNS we show that the ESBL exhibits an oscillatory mass flux along the librating wall (Ekman property) and an oscillatory azimuthal velocity, which resembles a radially damped wave (Stokes property). For large libration amplitudes (here$\unicode[STIX]{x1D700}=0.8$), the DNS results exhibit an intermittently unstable ESBL, which turns centrifugally unstable during the prograde (faster) part of a libration period. This instability is due to the Stokes property and gives rise to Görtler vortices, which are found to be tilted with respect to the azimuth when the librating wall is at a finite angle relative to the axis of rotation. We show that this tilt is related to the Ekman property of the ESBL. This suggests that linear and nonlinear dynamics are equally important for this intermittent instability. Our DNS results indicate further that the Görtler vortices propagate into the fluid bulk where they generate an azimuthal mean flow. This mean flow is notably different from the mean flow driven in the case of the stable ESBL. A diagnostic analysis of the Reynolds-averaged Navier–Stokes (RANS) equations in the unstable flow regime hints at a competition between the radial and axial turbulent transport terms which act as generating and destructing agents for the azimuthal mean flow, respectively. We show that the balance of both terms depends on the wall inclination, that is, on the wall-tangential component of the Coriolis force.

A study of continuous rotation modes of detonation in an annular chamber with constant or increasing section

The detonation regime is an alternative to the conventional constant-pressure combustion mode typically used for propulsive systems because of its higher thermal efficiency and temperature and pressure of products, and shorter characteristic combustion time and length. The classic implementation is the rotating detonation engine, with the combustion chamber consisting of the annular space between a center-body and an outer cylindrical wall. This experimental study focuses on the effects of the chamber inner geometry, the total mass flow rate, and the detonation cell width on the conditions for detonation rotation. Cylindrical and conical center-bodies with several lengths and half-apex angles are considered to approach the hollow configuration of the RDE chamber. The cell width is varied by testing with mixtures of ethylene and enriched air, with several equivalence ratios and nitrogen dilutions. The combustion modes and the detonation velocities and pressures are characterized by analyzing pressure signals and high-speed camera visualizations. Three detonation regimes are identified, characterized by one or two fronts propagating in the same or opposite directions. Decreasing the center-body length and increasing the half-apex angle increases the measured detonation velocity and pressure. Velocities range between 53 and 89% of the Chapman–Jouguet value, and the pressure reaches about 11 bar. For the conditions tested, higher detonation velocity and pressure are obtained for the conical center-body configuration. Our interpretation is that center-bodies that are too long, or channels that are too narrow, hinder the exhaust of the burned gas. As a result, the proportion of products in the unburned gas mixture ahead of the detonation wave (consisting of fresh and burned gas) increases, resulting in a decrease in the magnitude of the detonation properties.

Analysis of disturbances in a hypersonic boundary layer on a cone with heating/cooling of the nose tip

Experimental results of the influence of local heating/cooling on the development of hypersonic boundary layer disturbances are reported. Local heating/cooling is applied at the cone nose tip. The experiments are carried out at the Mach number M = 5.95, stagnation temperature T0 = 360–418 K, and stagnation pressure P0 = 3.7–45 atm. The unit Reynolds number is varied in the interval Re1 = (4.5–63) × 106 m−1. The investigations are conducted in the boundary layer on a cone with an apex half-angle of 7° and varied bluntness radius of the nose tip [R = 0.03 (sharp nose), 0.75, and 1.5 mm] for different values of the local temperature factor. The nose tip is heated by an ohmic heater. Cooling is performed by supplying liquid nitrogen into the internal cavity of the model nose. A comparative analysis of pressure pulsation spectra on the cone surface is performed. It is demonstrated that heating/cooling in the case of a sharp cone leads to flow destabilization/stabilization. The opposite effect is observed for blunted cones: heating/cooling stabilizes/destabilizes the second-mode disturbances. This effect is enhanced by increasing the nose tip bluntness. All the observed effects vanish with distance downstream from the nose tip.

Molecular dynamics simulation of subsurface damage mechanism during nanoscratching of single crystal silicon

Three-dimension molecular dynamics (MD) simulation is employed to investigate the nanoscratching process of monocrystalline silicon with diamond tools. The effects of tool geometry on subsurface damage and scratching surface integrity are investigated by analyzing phase transformation, chip, defect atoms, hydrostatic stress, von Mises stress and workpiece deformation. In addition, a theoretical analytical model to study the subsurface damage mechanism by analyzing the zone size of phase transformation and normal force with diamond tools at different half-apex angles on silicon surfaces is established. The results show that a bigger half apex angle causes a higher hydrostatic stress, a larger chip volume, a higher temperature and a higher potential energy, and increases subsurface damage. The results also reveal that the evolution of crystalline phases is consistent with the distribution of hydrostatic stress and temperature. In addition, tip scratching with a bigger half-apex angle would result in a larger scratching force and a bigger phase transformation zone, which is in good agreement with the results of the theoretical analytical model.