Tip Geometry Research Articles

Amorphous Si critical dimension structures with direct Si lattice calibration**Project supported by the National Key Scientific Instrument and Equipment Development Projects of China (Grant No. 2014YQ090709), the National Key Research and Development Program of China (Grant No. 2016YFA0200902), and Major Projects of Science and Technology Commission of Shanghai, China (Grant No. 17JC1400800).

Developing highly accurate critical dimension standards is a significant task for nanoscale metrology. In this paper, we put forward an alternative approach to fabricate amorphous Si critical dimension structures with direct Si lattice calibration in the same frame scanning transmission electron microscopy image. Based on the traceable measurement analysis, the optimized method can provide the same calibration accuracy and increase the fabrication throughput and lower the cost simultaneously, which benefits the application needs in atomic force microscopy (AFM) tip geometry characterization, benchmarking measurement tools, and conducting comparison measurements between different approaches.

Aerothermal Optimization of Fully Cooled Turbine Blade Tips

Optimal turbine blade tip designs have the potential to enhance aerodynamic performance while reducing the thermal loads on one of the most vulnerable parts of the gas turbine. This paper describes a novel strategy to perform a multi-objective optimization of the tip geometry of a cooled turbine blade. The parameterization strategy generates arbitrary rim shapes around the coolant holes on the blade tip. The tip geometry performance is assessed using steady Reynolds-averaged Navier–Stokes simulations with the k–ω shear stress transport (SST) model for the turbulence closure. The fluid domain is discretized with hexahedral elements, and the entire optimization is performed using identical mesh characteristics in all simulations. This is done to ensure an adequate comparison among all investigated designs. Isothermal walls were imposed at engine-representative levels to compute the convective heat flux for each case. The optimization objectives were a reduction in heat load and an increase in turbine row efficiency. The multi-objective optimization is performed using a differential evolution strategy. Improvements were achieved in both the aerodynamic efficiency and heat load reduction, relative to a conventional squealer tip arrangement. Furthermore, this work demonstrates that the inclusion of over-tip coolant flows impacts the over-tip flow field, and that the rim–coolant interaction can be used to create a synergistic performance enhancement.

The improvement of the accuracy of electromagnetic actuator based atomic force microscope operating in contact mode and the development of a new methodology for the estimation of control parameters and the achievement of superior image quality

The dynamics of atomic force microscope (AFM) acting in contact mode is crucial for correct interpretation of AFM images and especially for the identification of artefacts and the determination of their sources. This paper presents a methodology for the interpretation and improvement of the AFM image quality. The developed AFM dynamic model has been applied for the control of scanning parameters to achieve superior image quality. The model provides possibility to tune AFM parameters, such as tip-surface interaction force and scanning speed in respect of the sample’s material and cantilever’s tip geometry. This methodology allows us to ensure the ideal imaging conditions, to evaluate AFM images and to produce a superior picture quality. Using this model, we can also analyze experimental data and simulate the experimental results.

Investigation of the effect of load distribution along the face width and load sharing between the pairs in contact on the fracture parameters of the spur gear tooth with root crack

Abstract The magnitude and location of stress intensity factor (SIF) in mode I (KI), mode II (KII), mode III (KIII) relies mainly on the geometry and location of the crack tip, variation in magnitude of load due to multiple pair contact along the active profile and the distribution of the load along the face width of a spur gear drive. Mostly, in literature the calculation of SIF in gear were carried out either by using a two dimensional (2D) Finite element model (FEM) with point load for unit width or a three dimensional (3D) FEM with uniform / parabolic load distribution along the face width without considering load sharing effect between the multiple pairs in contact. In the present study, an attempt has been made to explore the significance of the load distribution along the face width and the load sharing between the pairs when the contact moves from the highest point of tooth contact (HPTC) to the lowest point of tooth contact (LPTC) on the SIF calculation. A comparative study has been made by using a validated 3D single tooth spur gear FEM with four different load cases such as case 1: Uniform load distribution along face width without considering load sharing between the pairs, case 2: Uniform load distribution along face width by including the effect of load sharing between the pairs, case 3: Actual load distribution along the face width without considering load sharing between the pairs, case 4: Actual load distribution along the face width by including the effect of load sharing between the pairs. The stiffness based approach was used to calculate the load distribution ratio (LDR) of a contact point along the contact line and the load sharing ratio (LSR) between the pairs in contact. The detailed analysis showed that case 1, case 2 and case 3 load cases overestimate the SIFs comparing to the case 4. The first three load cases overestimate the KI by 39%, 2.5%, and 45% and KII by 390%, 36%, and 129% and KIII by 282%, 47%, and 132% respectively when compared to load case 4. The results of this study provide valuable guidelines for the crack propagation as well as life prediction calculations for spur gear drives.

Uncertainty Considerations for Nonlinear Dynamics of a Class of MEMS Switches Undergoing Tip Contact Bouncing

Batch fabrication processes used to produce micro-electro-mechanical systems (MEMS) are prone to uncertainties in the system geometrical and contact parameters as well as material properties. However, since the common design method for these systems is typically based on precise deterministic assumptions, it is necessary to get more insight into their variations. To this end, understanding the influences of uncertainties accompanied by these processes on the system performance and reliability is warranted. The present paper focuses on predictions of uncertainty measures for MEMS switches based on the transient dynamic response, in particular, the bouncing behavior. To understand and quantify the influence of pertinent parameters on the bouncing effects, suitable mathematical model that captures the bouncing dynamics as well as the forces that are dominant at this micron scale are employed. Measure of performance in terms of second-order statistics is performed, particularly for the beam as well as beam tip parameters since excessive tip bounce is known to degrade switch performance. Thus, the present study focusses on the influence of uncertainties in the beam tip geometry parameters such as beam tip length/width as well as contact asperity variables such as the area asperity density and the radius of asperities. In addition to beam tip parameters, this study quantifies the effects of uncertainties in Young's modulus, beam thickness as well as actuation voltage. These influences on significant switch performance parameters such as initial contact time and maximum bounce height have been quantified in the presence of interactive system nonlinearities.

Ultra-sharp and surfactant-free silver nanowire for scanning tunneling microscopy and tip-enhanced Raman spectroscopy.

Chemically-synthesized single-crystalline silver nanowire (AgNW) probes can combine the scanning tunneling microscopy (STM) technique with tip-enhanced Raman scattering spectroscopy (TERS) for complementary morphological and chemical information with nanoscale spatial resolution. However, its performance has been limited by the blunt nanowire tip geometry, the insulating surfactant layer coating AgNW surfaces, and the thermal-induced mechanical vibrations. Here, we report a reproducible fabrication method for the preparation of sharp-tip AgNW-based TERS probes. By removing the polyvinylpyrrolidone (PVP) surfactant molecules from the AgNW surfaces for stable electrical conductivity and controlling the protruding length with μm-level accuracy for improved mechanical stability, we demonstrate atomic-resolution STM imaging with the sharp-tip AgNW probe. Furthermore, the sharp-tip AgNW has an excellent TER enhancement (∼1.1 × 106), which is about 66 folds of that achieved by regular AgNWs. Our experiments demonstrate that AgNWs with clean interfaces and the proper tip geometry can provide reliable and reproducible STM and TER characterizations, which remove the hurdles preventing the implementation of AgNW in STM-based near-field optical applications for a broad community.

Couple effects of mixed mode biaxial loading and crack tip configuration on plastic stress intensity factor behavior at small and large scale yielding

In this paper the plastic stress intensity factor (SIF) approach is used to study the coupling effects of loading biaxiality, material properties and crack tip configuration in both the small- and large-scale yielding ranges. For comparison between small-scale and large-scale yielding solutions, a rectangular plate with a centered line crack subjected to biaxial loading and three types of test specimens under mixed mode loading were analysed by using a finite element method. Numerical analysis was performed for two types of steel and titanium and aluminum alloys with different elastic–plastic properties. Both the mathematical notch type crack tip and the crack tip with finite radius of curvature were considered. The governing parameter of the elastic–plastic crack-tip stress field In-integral, J-integral, and the plastic SIF were calculated as functions of loading biaxiality and applied stress levels. Special emphasis was put on an ambivalent J-integral and the plastic SIF behavior for specified the crack tip geometries. Contrary trends of biaxiality effects on J-integral behavior were established depending on crack tip configuration. Nonlinear fracture resistance parameters in the form of J-integral, In-integral and the plastic SIF were calculated as a function of the material properties and mode mixity for specified test specimen geometries. Finally, the applicability of the plastic stress intensity factor approach to large-scale yielding analysis of mixed mode crack tip stress fields was demonstrated.

Experimental and Numerical Investigation of Optimized Blade Tip Shapes—Part I: Turbine Rainbow Rotor Testing and Numerical Methods

Blade tip design and tip leakage flows are crucial aspects for the development of modern aero-engines. The inevitable clearance between stationary and rotating parts in turbine stages generates high-enthalpy unsteady leakage flows that strongly reduce the engine efficiency and can cause thermally induced blade failures. An improved understanding of the tip flow physics is essential to refine the current design strategies and achieve increased turbine aerothermal performance. However, while past studies have mainly focused on conventional tip shapes (flat tip or squealer geometries), the open literature suffers from a shortage of experimental and numerical data on advanced blade tip configurations of unshrouded rotors. This work presents a complete numerical and experimental investigation on the unsteady flow field of a high-pressure turbine, adopting three different blade tip profiles. The aerothermal characteristics of two novel high-performance tip geometries, one with a fully contoured shape and the other presenting a multicavity squealer-like tip with partially open external rims, are compared against the baseline performance of a regular squealer geometry. The turbine stage is tested at engine-representative conditions in the high-speed turbine facility of the von Karman Institute. A rainbow rotor is mounted for simultaneous aerothermal testing of multiple blade tip geometries. On the rotor disk, the blades are arranged in sectors operating at two different clearance levels. A numerical campaign of full-stage simulations was also conducted on all the investigated tip designs to model the secondary flows development and identify the tip loss and heat transfer mechanisms. In the first part of this work, we describe the experimental setup, instrumentation, and data processing techniques used to measure the unsteady aerothermal field of multiple blade tip geometries using the rainbow rotor approach. We report the time-average and time-resolved static pressure and heat transfer measured on the shroud of the turbine rotor. The experimental data are compared against numerical predictions. These numerical results are then used in the second part of the paper to analyze the tip flow physics, model the tip loss mechanisms, and quantify the aero-thermal performance of each tip geometry.

Scratching of silicon surfaces

Nanoscale scratching of silicon surfaces is the elementary abrasive event for various machining techniques including fixed abrasive wire saw slicing, grinding, elliptical ultrasonic cutting and single-point diamond turning. The understanding of this process is essential for improving the surface quality and reducing sub-surface damage. Nanoscratching experiments are performed using a well characterized diamond tip geometry. The finite element method is employed in order to simulate the scratching process with a continuum constitutive model developed for phase transformation in silicon (Budnitzki, M., Kuna, M., 2016. Stress induced phase transitions in silicon. JMPS 95, 64–91). The required material parameters were determined from indentation experiments in a (111) single crystal Si wafer. The simulation results agree very well with data from scratch experiments without requiring additional calibration.

Modifications of Surgical Suction Tip Geometry for Flow Optimisation: Influence on Suction-Induced Noise Pollution.

Introduction Suction devices for clearing the surgical field are among the most commonly used tools of every surgeon because a better view of the surgical field is essential. Forced suction may produce disturbingly loud noise, which acts as a nonnegligible stressor. Especially, in emergency situations with heavy bleeding, this loud noise has been described as an impeding factor in the medical decision-making process. In addition, there are reports of inner ear damage in patients due to suction noises during operations in the head area. These problems have not been solved yet. The purpose of this study was to analyse flow-dependent suction noise effects of different surgical suction tips. Furthermore, we developed design improvements to these devices. Methods We compared five different geometries of suction tips using an in vitro standardised setup. Two commercially available standard suction tips were compared to three adapted new devices regarding their flow-dependent (10–2000 mL/min) noise emission (dB, weighting filter (A), distance 10 cm) and acoustic quality of resulting noises (Hamilton fast Fourier analysis) during active suction at the liquid-air boundary. Noise maps at different flow rates were created for all five suction devices, and the proportion of extracted air was measured. The geometries of the three custom-made suction tips (new models 1, 2, and 3) were designed considering the insights after determining the key characteristics of the two standard suction models. Results The geometry of a suction device tip has significant impact on its noise emission. For the standard models, the frequency spectrum at higher flow rates significantly changes to high-frequency noise patterns (>3 kHz). A number of small side holes designed to prevent tissue adhesion lead to increased levels of high-frequency noise. Due to modifications of the tip geometry in our new models, we are able to achieve a highly significant reduction of noise level at low flow rates (new model 2 vs. standard models p < 0.001) and also the acoustic quality improved. Additionally, we attain a highly significant reduction of secondary air intake (new model 2 vs. the other models p < 0.001). Conclusion Improving flow-relevant features of the geometry of suction heads is a suitable way to reduce noise emissions. Optimized suction tips are significantly quieter. This may help us to reduce noise-induced hearing damage in patients as well as stress of medical staff during surgery and should lead to quieter operation theatres overall. Furthermore, the turbulence reduction and reduced secondary air intake during the suction process are expected to result in protective effects on the collected blood and thus could improve the quality of autologous blood retransfusions. We are on the way to evaluate potential benefits.

Investigation of Microstructure and Mechanical Properties of Welded Joints of Aluminum Alloys Welded with Titanium Based Powder Material by High Velocity Oxygen Fuel Spray Method (HVOF) Combined with Friction Stir Welding Method

In this study, spectral analyzes were performed to determine the chemical composition of the samples at 2x40x40 mm taken from aluminum alloy sheet materials. Plates to be combined with friction stir welding were mechanically cut with guillotine scissors at 2x100x300mm. The welded joints of the aluminum plates to be friction-mixed are coated with titanium-based powder material with a thickness of 40&amp;amp;micro;m by high velocity oxygen fuel spraying (HVOF) method. A friction stir tool with a cone tip geometry with machining, 20mm shoulder diameter and 1.8mm pin height was produced for use in the friction stir welding process. In addition, the aluminum alloy sheets prepared were machined according to ASTM E8M-04 standard with dimensions of 2x100x300mm so that they could be joined with friction stir welding on the milling bench. Waterjet drawing and metallographic samples were cut from welded aluminum plates formed with parameters of 2000 rpm rotation speed and 140 mm / min welding speed and 2 degree head angle in accordance with ASTM E8M-04 standard. Tensile specimens were measured on the universal drafting table at a pulling speed of 2 mm / min along with the maximum tensile breaking values ??as well as percent elongation. In order to determine the microstructure and mechanical properties of the weld inserts, hot stamping of the samples, which were not affected by heat, was followed by coarse and fine sanding followed by final polishing with 1&amp;amp;micro;m diamond paste. The hardness values of the samples were determined by Vickers hardness measurement along an axis to characterize the welded zone upper, middle and lower zones to cover all weld zones and the main material.

Multi-Disciplinary Design Optimisation of the Cooled Squealer Tip for High Pressure Turbines

The turbine tip geometry can significantly alter the performance of the turbine stage; its design represents a challenge for a variety of reasons. Multiple disciplines are involved in its design and their requirements limit the creativity of the designer. Multi-Disciplinary Design Optimisation (MDO) offers the capability to improve the performance whilst satisfying all the design constraints. This paper presents a novel design of a turbine tip achieved via MDO techniques. A fully parametrised Computer-Aided Design (CAD) model of the turbine rotor is used to create the squealer geometry and to control the location of the cooling and dust holes. A Conjugate Heat Transfer Computational Fluid Dynamics (CFD) analysis is performed for evaluating the aerothermal performance of the component and the temperature the turbine operates at. A Finite Element (FE) analysis is then performed to find the stress level that the turbine has to withstand. A bi-objective optimisation reduces simultaneously the aerodynamic loss and the stress level. The Multipoint Approximation Method (MAM) recently enhanced for multi-objective problems is chosen to solve this optimisation problem. The paper presents its logic in detail. The novel geometry offers a significant improvement in the aerodynamic performance whilst reducing the maximum stress. The flow associated with the new geometry is analysed in detail to understand the source of the improvement.

The Effect of Pick Profile on the Cutting Performance of Point Attack Picks

Tungsten carbide tipped pointed attack picks is widely used in mechanical machinerysuch as roadheaders, continuous miners and longwall shearers. Great efforts have been made toinvestigate the interaction between point attack pick and rock. However, the research on theinvestigation of pick profile on the cutting performance is still a subject little investigated by thescientific community. In this study, the rock fragmentation process is simulated using a 2D discreteelement code, PFC2D. In the simulations, four types of pick tip geometries (mushroom insert, bulletinsert, conical insert, and cap) were employed to investigate the effect of pick profile on the cuttingperformance of point attack picks. The forces acting on the pick and crack propagation process werecontinuously monitored during the simulations. The preliminary results of cutting performance ofthe picks under different cutting scenarios were analyzed.

Effective stress regime around a jacked steel pile during installation ageing and load testing in chalk

This paper reports experiments with 102 mm diameter closed-ended instrumented Imperial College piles (ICPs) jacked into low- to medium-density chalk at a well-characterized UK test site. The “ICP” instruments allowed the effective stress regime surrounding the pile shaft to be tracked during pile installation, equalization periods of up to 2.5 months, and load testing under static tension and one-way axial cyclic loading. Installation resistances are shown to be dominated by the pile tip loads. Low installation shaft stresses and radial effective stresses were measured that correlated with local cone penetration test (CPT) tip resistances. Marked shaft total stress reductions and steep stress gradients are demonstrated in the vicinity of the pile tip. The local interface shaft effective stress paths developed during static and cyclic loading displayed trends that resemble those seen in comparable tests in sands. Shaft failure followed the Coulomb law and constrained interface dilation was apparent as the pile experienced drained loading to failure, although with a lesser degree of radial expansion than with sands. Radial effective stresses were also found to fall with time after installation, leading to reductions in shaft capacity as proven by subsequent static tension testing. The jacked, closed-ended, piles’ ageing trends contrast sharply with those found with open piles driven at the same site, indicating that ageing is affected by pile tip geometry and (or) installation method.

Effects of Hob Tip Radius and Addendum Modification Coefficients on Tooth Bending Stress of Spur Gears under Dynamic Conditions

The paper presents a bending stress analysis of spur gear pairs in order to enhance the effects of the tooth root influence factors in relation to the hob tip geometry and addendum modification coefficients. These factors are evaluated in accordance with ISO 6336 for the basic rack profiles. In order to improve the accuracy of this analysis, a dynamic model is considered to analyse the shared dynamic load for a meshing cycle. All these influence factors are included in a global factor Yd. A comparative study has been performed to investigate the effects of the hob tip radius, addendum modification coefficients and pinion speed on the variation of the factor Yd on the meshing cycle. The approach makes for improved in predicting the tooth bending stress at the design stage.

Experimental and Numerical Investigation of Optimized Blade Tip Shapes—Part II: Tip Flow Analysis and Loss Mechanisms

The leakage flows within the gap between the tips of unshrouded rotor blades and the stationary casing of high-speed turbines are the source of significant aerodynamic losses and thermal stresses. In the pursuit for higher component performance and reliability, shaping the tip geometry offers a considerable potential to modulate the rotor tip flows and to weaken the heat transfer onto the blade and casing. Nevertheless, a critical shortage of combined experimental and numerical studies addressing the flow and loss generation mechanisms of advanced tip profiles persists in the open literature. A comprehensive study is presented in this two-part paper that investigates the influence of blade tip geometry on the aerothermodynamics of a high-speed turbine. An experimental and numerical campaign has been performed on a high-pressure turbine stage adopting three different blade tip profiles. The aerothermal performance of two optimized tip geometries (one with a full three-dimensional contoured shape and the other featuring a multicavity squealer-like tip) is compared against that of a regular squealer geometry. In the second part of this paper, we report a detailed analysis on the aerodynamics of the turbine as a function of the blade tip geometry. Reynolds-averaged Navier-Stokes (RANS) simulations, adopting the Spalart–Allmaras turbulence model and experimental boundary conditions, were run on high-density unstructured meshes using the numecafine/open solver. The simulations were validated against time-averaged and time-resolved experimental data collected in an instrumented turbine stage specifically setup for the simultaneous testing of multiple blade tips at scaled engine-representative conditions. The tip flow physics is explored to explain variations in turbine performance as a function of the tip geometry. Denton's mixing loss model is applied to the predicted tip gap aerodynamic field to identify and quantify the loss reduction mechanisms of the alternative tip designs. An advanced method based on the local triple decomposition of relative motion is used to track the location, size and intensity of the vortical flow structures arising from the interaction between the tip leakage flow and the main gas path. Ultimately, the comparison between the unconventional tip profiles and the baseline squealer tip highlights distinct aerodynamic features in the associated gap flow field. The flow analysis provides guidelines for the designer to assess the impact of specific tip design strategies on the turbine aerodynamics and rotor heat transfer.

Transitions in nutation trajectory geometry in peppermint (Mentha x piperita L.) with respect to lunisolar acceleration.

Nutations of plant organs are significantly affected by the circatidal modulation in the gravitational force exerted by the Moon and Sun (lunisolar tidal acceleration, Etide). In a previous study on nutational rotations of stem apices, we observed abrupt alterations in their direction and irregularities of the recorded trajectories. Such transitions have not yet been analysed in detail. Peppermint plants were continuously recorded with time-lapse photography and aligned with contemporaneous time courses of the Etide estimates. Each nutational stem tip movement path was assigned to one of two groups, depending on its geometry, as: (i) regular elliptical movements and (ii) irregular movements (with a random type of trajectory). Analyses of the correlation between the plant nutation trajectory parameters and Etide, as well as of the trajectory geometry of the individual plants were performed. The trajectory geometry of young mint stem apices was related to the velocity of the apex rotation and significantly affected by the gravitational force estimated from the Etide. A low velocity of nutational movement, associated with the random character of the trajectory, usually occurred simultaneously with local minima or maxima of Etide. As the mint plant ages, the transitions in the stem tip trajectory were limited; no correspondence with Etide dynamics was observed. The results indicate that the plant tip geometry path transitions with respect to the changing gradient of lunisolar tidal acceleration could be interpreted as manifestation of a continuous accommodation of the shoot apical part to the state of minimum energy dissipation.

Flow-induced oscillations of low-aspect-ratio flexible plates with various tip geometries

The distinctive oscillations and induced wake of wall-mounted thin plates with flat, elliptic, and aristate tips were experimentally studied under nearly uniform flows for various Cauchy numbers, Ca. Particle tracking velocimetry and planar particle image velocimetry were used to characterize the dynamics of the plates and surrounding flow. The results show that the oscillations of the plates were dominated by their natural frequency across Ca. The structures underwent distinctive reconfigurations which led to asymmetric distributions of the tip fluctuations with respect to the equilibrium position. Interestingly, the oscillation intensity of the plates reached a local maximum at a critical Cauchy number Cacri, which increased with narrower tip. This is explained with a basic model that accounts for the nonlinear structure bending and the flow fluctuations in the vicinity of the structures. The very near wake was characterized by two recirculation regions at sufficiently low Ca, one at the base of the plates and another right above it extending up to the tip. However, the recirculation region near the tip eventually vanished under large structure bending at sufficiently high Ca, which led to increased mean shear. Also, the turbulence levels were dominated by the streamwise component of the velocity fluctuations around the tips, where the aristate tip induced the lowest levels.

Wiarygodność pomiaru mikroskopowego geometrii frezu kulistego oraz jej wpływ na nierówności powierzchni po frezowaniu kopiowym

New ball end mills in various lighting conditions were examined and detailed 3D models were obtained. Differences in the geometry of the tool tip resulted in a surface with drastically different parameters. The effect of the edge break was observed. The obtained 3D models were used to create a map of the material loss on the cutting edge of cutting tool.

Analysis of indentation measured mechanical properties on Multilayer Ceramic Capacitors (MLCCs)

Most failures of Multilayer Ceramic Capacitors (MLCCs) are mechanical (e.g., cracking) in nature. Therefore, reliability assessment of these parts depends heavily on the available mechanical properties in the literature. As indentation offers advantages such as minimal sample preparation and access to small areas, more mechanical properties on MLCCs based on measurement by indentation are being published in literature. However, indentation measured properties are known to vary with different factors such as measuring loads, geometry of indenter tip, and residual stresses. In this article, indentations are performed on commercial MLCCs at different loads and locations with different indenter tips. By identifying the causes of variations and understanding the limitations and implications of the indentation measured properties, the use of indentation for reliability assessment of MLCCs, and other electronic components can be facilitated.