Constant Force Mode Research Articles

A study of rotary cutting machine (RCM) performance on Korean granite

PurposeDespite the many advantages this type of equipment offers, there are still some major drawbacks. Linear cutting machine (LCM) cannot accurately simulate the true rock-cutting process as 1. it does not account for the circular path along which tunnel boring machine (TBM) disk cutters cut the tunnel face, 2. it does not accurately model the position of a disk cutter on the cutterhead, 3. it cannot perfectly replicate the rotational speed of a TBM. To enhance the knowledge of these issues and in order to mimic the real rock-cutting process, a new lab testing equipment was developed by Hyundai Engineering and Construction.Design/methodology/approachA new testing machine called rotary cutting machine (RCM) is designed to simulate the excavation process of hard-rock TBMs and includes features such as TBM cutterhead, RPM simulation, constant normal force mode and constant penetration rate mode. Two sets of tests were conducted on Hwandeung granite using different disk cutter sizes to analyze the cutting forces in various excavation modes. The results are analyzed using statistical analysis and dimensional analysis. A new model is generated using dimensional analysis, and its results are compared against the results of actual cases.FindingsThe effectiveness of the new RCM test was demonstrated in its ability to apply various modes of excavation. Initial analysis of chip size revealed that the thickness of the chips is largely dependent on the cutter spacing. Tests with varying RPM showed that an increase in RPM results in an increase in the normal force and rolling force. The cutting coefficient (CC) demonstrated a linear correlation with penetration. The optimal specific energy is achieved at an S/p ratio of around 15. However, a slightly lower S/p ratio can also be used in the design if the cutter specifications permit. A dimensional analysis was utilized to develop a new RCM model based on the results from approximately 1200 tests. The model's applicability was demonstrated through a comparison of TBM penetration data from 26 tunnel projects globally. Results indicated that the predicted penetration rates by the RCM test model were in good agreement with actual rates for the majority of cases. However, further investigation is necessary for softer rock types, which will be conducted in the future using concrete blocks.Originality/valueThe originality of the research lies in the development of Hyundai Engineering and Construction’s advanced full-scale laboratory rotary cutting machine (RCM), which accurately replicates the excavation process of hard-rock tunnel boring machines (TBMs). The study provides valuable insights into cutting forces, chip size, specific energy, RPM and excavation modes, enhancing understanding and decision-making in hard-rock excavation processes. The research also presents a new RCM model validated against TBM penetration data, demonstrating its practical applicability and predictive accuracy.

Ductile deformation and subsurface damage evolution mechanism of silicon wafer induced by ultra-precision grinding process

In the field of advanced packaging, large-size silicon wafers are usually thinned by ultra-precision grinding technology relying on the process of workpiece self-rotation. However, the damage caused by mechanical material removal deteriorates the wafer surface flatness and die strength, while its atomic-scale formation principle has yet to be revealed. This work explores the ductile deformation and subsurface damage evolution mechanism of silicon wafer during the ultra-precision grinding process. Some grinding tests are first conducted using different diamond wheels. The surface topography and energy dispersive spectroscopy (EDS) mapping of ground wafers are measured by scanning electron microscope (SEM). The phase transition properties of the ground silicon wafer are confirmed via Raman spectrum. Next, the specimen of groove cross-section is fabricated and its morphology is examined via transmission electron microscopy (TEM) to analyze the subsurface damage characteristics. The subsurface defects at the atomic scale, involving amorphous layer, dislocations, stacking faults and lattice distortions, are observed. Due to its controllable load and similarity of the cutting motion, nanoscratch is utilized for investigating the influence of abrasive interactions on subsurface deformation during the grinding process. Thus, a series of multiple nanoscratch tests are performed in both varied and constant force modes. The material removal behaviors under different scratching conditions are illustrated. This work provides a fundamental understanding of developing a high-efficiency and low-damage thinning method for 12-inch silicon wafers.

Shape stability of 3D printable concrete with river and manufactured sand characterized by squeeze flow

Without formwork support, shape stability is one of the most critical properties of 3D printable concrete. This study evaluated the influence of the substitution of river sand by manufactured sand (0%, 15%, 25%, 35%, 50%, 75%, and 100% by volume) on the shape stability of freshly printed concrete. Shape stability was measured by squeeze flow tests with two different loading modes including an increasing force mode and a constant force mode. In the increasing force squeeze flow test, the elastic and plastic behaviors of mixtures were analyzed, while in the constant force squeeze flow test, modified yield stress was derived, with the consideration of the strength correction factor. Furthermore, two series of square wall layouts were printed and the failure patterns (either plastic collapse or elastic buckling) were well predicted by the squeeze flow. In addition, results demonstrated that the substitution of river sand by manufactured sand enhanced the shape stability of the 3D printable concrete, which closely related to the packing fraction of aggregate.

Numerical Analysis of Mechanical Characteristics of Constant-Resistance, Energy-Absorbing and Anti-Scour Bolts.

In order to improve the impact resistance mechanical properties of bolt, the requirements of rock burst roadway support must be met. Based on the requirements that the anchor should have a reasonable deformation load threshold, high stroke efficiency, constant reaction force and stable repeatable deformation damage mode. A constant resistance anti-impact device was designed, and a new constant resistance energy-absorbing impact anchor rod was designed in combination with a conventional anchor rod, and the working principle of a constant resistance energy-absorbing impact anchor rod was given. ABAQUS finite element software was used to analyze the mechanical properties of bolt and the results showed that the constant resistance energy-absorbing anti-shock anchor has a stable and repeatable deformation damage mode under both static and impact loads, and the three indexes of the constant resistance energy-absorbing anti-shock anchor, such as yield distance, impact resistance time and energy absorption, are significantly better than those of the conventional anchor. The impact energy and impact velocity have less influence on the load-bearing capacity and stroke efficiency of the impact device. The impact velocity has less influence on the indices of the rod yield load, breaking load, absorbed energy and the yield distance of a conventional anchor and constant resistance energy-absorbing anti-stroke anchor, and the impact resistance time decreases non-linearly with the increase in the impact velocity.

Electro-lubrication in Janus transition metal dichalcogenide bilayers

Lubrication induced by a vertical electric field or bias voltage is typically not applicable to two-dimensional (2D) van der Waals (vdW) crystals. By performing extensive first-principles calculations, we reveal that the interlayer friction and shear resistance of Janus transition metal dichalcogenide (TMD) MoXY (X/Y = S, Se, or Te, and X ≠ Y) bilayers under a constant normal force mode can be reduced by applying vertical electric fields. The maximum interlayer sliding energy barriers between AA and AB stacking of bilayers MoSTe, MoSeTe, and MoSSe decrease as the positive electric field increases because of the more significant counteracting effect from the electric field energy and the more significant enhancement in interlayer charge transfer in AA stacking. Meanwhile, the presence of negative electric fields decreases the interlayer friction of bilayer MoSTe, because the electronegativity difference between Te and S atoms reduces the interfacial atom charge differences between AA and AB stacking. These results reveal an electro-lubrication mechanism for the heterogeneous interfaces of 2D Janus TMDs.

Interfacial Friction Anisotropy in Few-Layer Van der Waals Crystals.

Friction anisotropy is one of the important friction behaviors for two-dimensional (2D) van der Waals (vdW) crystals. The effects of normal pressure and thickness on the interfacial friction anisotropy in few-layer graphene, h-BN, and MoSe2 under constant normal force mode have been extensively investigated by first-principle calculations. The increase of normal pressure and layer number enhances the interfacial friction anisotropy for graphene and h-BN but weakens that for MoSe2. Such significant deviations in the interfacial friction anisotropy of few-layer graphene, h-BN and MoSe2 can be mainly attributed to the opposite contributions of electron kinetic energies and electrostatic energies to the sliding energy barriers and different interlayer charge exchanges. Our results deepen the understanding of the influence of external loading and thickness on the friction properties of 2D vdW crystals.

Atomic Force Microscopy Breaking Through the Vertical Range-Bandwidth Tradeoff

This article proposes a mechatronic system design for atomic force microscopes (AFMs) in order to realize a large range and high control bandwidth of the vertical probe motion by a flexure-guided voice coil actuator. The first mechanical resonant frequency of the actuator is decreased to 67 Hz for a large motion, whereas the second resonant frequency is maximized to 1.15 kHz. The frequency band between the resonances enables twodegree-of-freedom control with a position sensor to realize a control bandwidth of 881 Hz, which is 13 times higher than the first resonance that is the limitation of conventional AFMs. The closed-loop actuator achieves a positioning resolution of 1.7 nm and a nonlinearity of 0.02% for a motion range of 700 μm. Consequently, the actuator realizes a range-bandwidth product of 617 kHz·μm, breaking through a theoretical limit of piezoelectric actuators (567 kHz·μm). The high performance of the actuator is further confirmed by 400 μm topography measurement in the constant force mode with a bandwidth of 197 Hz. The achieved resolution of the topography measurement is 2.9 nm, and it is demonstrated by successfully imaging nanostructures on a CD-ROM disk.

WiFi-controlled portable atomic force microscope.

This article proposes to develop a WiFi-controlled portable atomic force microscope (AFM). The AFM consists of a horizontal probe, controlling circuits, digital to analog (D/A) and analog to digital (A/D) interfaces, a microcomputer (Raspberry Pi, RPi), and a laptop. The proposed AFM uses a pocket-size power supply to drive the controlling circuits, the D/A and A/D interfaces, as well as the RPi that constructs network hotspots and generates scanning signals. With special design and integration of the whole system, both of the AFM probe and electronic controlling system are portable. At a distance of 50 m from the proposed AFM, experiments in the constant height mode and the constant force mode are conducted to evaluate its performance. The results show that this WiFi-controlled AFM has a maximum scan range of 3.6 × 3.6 μm2 with nanometer order resolution. Meanwhile, it achieves satisfactory image contrast, stability, and repeatability. Compared with conventional AFMs, the AFM proposed in this paper no longer relies on commercial AC mains supply or high-voltage DC power supply, and realizes WiFi-controlled AFM scanning and imaging in 50 m or farther without wire or network cable connection to a laptop or a desktop computer. Given credits to these features, WiFi-controlled AFMs are expected to own a wider range of application, especially in isolated environments, outdoor researches, or even fieldwork investigations.

Electrostatic Force Microscopy Measurement System for Micro-topography of Non-conductive Devices

AbstractA home-made electrostatic force microscopy (EFM) system is described which is directed toward assessment of the microscopic geometry of the surface of specimens made of non-conductive material with a large thickness. This system is based on the variation in the electrostatic force between the conductive probe and the non-conductive specimen in order to get its surface morphology. First, based on the principle of dielectric polarization, the variation rules of the electrostatic force between the charged probe and the non-conductive specimen were studied. Later, a special tuning fork resonant probe unit made of quartz crystal was fabricated for measurement of the electrostatic force, and the scanning probe microscopic system in the constant force mode was constructed to characterize the three-dimensional micro-topography of the surface of the specimen. Finally, this system was used to perform scanning measurement experiments on the indented surface of the specimen made of the polyvinyl chloride (PVC) material with thickness 3 mm. In the present experimental system, when the external voltage was 100 V and the distance from the probe tip to the specimen surface approximately 100 nm, the variance in the resonant frequency of the probe unit was around 0.5 Hz. These results indicate that this home-made EFM system can effectively characterize the micro-topography of the non-conductive specimen with very large thickness which is above several millimeters.

Size investigation of silicon nanoclusters deposited on HOPG using noncontact atomic force microscopy

The sizes of silicon nanoparticles produced using two different novel methods are investigated in this report. The method of production used to generate silicon oxide nanoparticles was achieved via gas aggregation codeposition with water on a cold target, and also via a liquid jet method. The nanoparticles were drop-cast on a highly oriented pyrolytic graphite (HOPG) substrate and assessed using ultrahigh vacuum atomic force microscopy (AFM). Noncontact constant force mode was used in the AFM investigations. The silicon nanoparticles produced using the gas aggregation and water codeposition method were found to be smaller than 2 nm. A degree of deviation in the measured sizes of the silicon nanoparticles in different layers was detected. The size deviation was attributed to surface-nanoparticle, surface-tip, and nanoparticle-tip interactions. Silicon nanoparticles produced in alcohol using the liquid jet method were also found to be smaller than 2 nm. The solvent used for the silicon nanoparticles was varied in our investigations. When water was used as a solvent, a size deviation for silicon nanoparticles in different layers was also observed.

Force feedback effects on single molecule hopping and pulling experiments.

Single-molecule experiments with optical tweezers have become an important tool to study the properties and mechanisms of biological systems, such as cells and nucleic acids. In particular, force unzipping experiments have been used to extract the thermodynamics and kinetics of folding and unfolding reactions. In hopping experiments, a molecule executes transitions between the unfolded and folded states at a preset value of the force [constant force mode (CFM) under force feedback] or trap position [passive mode (PM) without feedback] and the force-dependent kinetic rates extracted from the lifetime of each state (CFM) and the rupture force distributions (PM) using the Bell-Evans model. However, hopping experiments in the CFM are known to overestimate molecular distances and folding free energies for fast transitions compared to the response time of the feedback. In contrast, kinetic rate measurements from pulling experiments have been mostly done in the PM while the CFM is seldom implemented in pulling protocols. Here, we carry out hopping and pulling experiments in a short DNA hairpin in the PM and CFM at three different temperatures (6 °C, 25 °C, and 45 °C) exhibiting largely varying kinetic rates. As expected, we find that equilibrium hopping experiments in the CFM and PM perform well at 6 °C (where kinetics are slow), whereas the CFM overestimates molecular parameters at 45 °C (where kinetics are fast). In contrast, nonequilibrium pulling experiments perform well in both modes at all temperatures. This demonstrates that the same kind of feedback algorithm in the CFM leads to more reliable determination of the folding reaction parameters in irreversible pulling experiments.

Steered Molecular Dynamics Simulation Study of Quantified Effects of Point Mutation Induced by Breast Cancer on Mechanical Behavior of E-Cadherin

E-cadherin is a member of the cadherin family that plays a key role in the formation of cell-cell adhesion among epithelial tissues. Point mutations are one of the structural abnormalities of E-cadherin in human carcinomas. Such abnormalities can alter mechanical properties of proteins that play an important role in their biological activities. To determine the impact of point mutations on protein mechanical properties, the second fragment of extracellular domain of E-cadherin was modeled using steered molecular dynamics simulations. The molecular dynamics modeling included application of tensile forces in both constant velocity and constant force modes to examine the effects of Met282 to He and Asn315 to Ser mutations on mechanical behavior of protein structure. The stabilities of the wild type and mutant structures were also obtained by the protein design foldX algorithm. Results confirmed the lower stability of the mutant domains compared to the wild type. The mutated proteins displayed softer behavior than the reference protein and their stiffness decreased by up to 34%. Our findings suggest that local changes in molecular structure due to mutations may lead to noticeable alterations in mechanical properties within the entire domain. Since the function of protein is related to its structure, these changes may influence the function of the protein.

Optical Beam Deflection Based AFM with Integrated Hardware and Software Platform for an Undergraduate Engineering Laboratory

Atomic force microscopy (AFM) has been used extensively in nanoscience research since its invention. Recently, many teaching laboratories in colleges, undergraduate institutions, and even high schools incorporate AFM as an effective teaching tool for nanoscience education. This paper presents an optical beam deflection (OBD) based atomic force microscope, designed specifically for the undergraduate engineering laboratory as a teaching instrument. An electronic module for signal conditioning was built with components that are commonly available in an undergraduate electronic laboratory. In addition to off-the-shelf mechanical parts and optics, the design of custom-built mechanical parts waskept as simple as possible. Hence, the overall cost for the setup is greatly reduced. The AFM controller was developed using National Instruments Educational Laboratory Virtual Instrumentation Suite (NI ELVIS), an integrated hardware and software platform which can be programmed in LabVIEW. A simple yet effective control algorithm for scanning and feedback control was developed. Despite the use of an educational platform and low-cost components from the undergraduate laboratory, the developed AFM is capable of performing imaging in constant-force mode with submicron resolution and at reasonable scanning speed (approximately 18 min per image). Therefore, the AFM is suitable to be used as an educational tool for nanoscience. Moreover, the construction of the system can be a valuable educational experience for electronic and mechanical engineering students.

Study of uncertainties of height measurements of monoatomic steps on Si 5 × 5 using DFT

The development of nanotechnology gives rise to new demands on standards for dimensional measurements. Monoatomic steps on, e.g. silicon are a suitable length standard with a very low nominal value. The quantum-mechanical nature of objects consisting of only a few atomic layers in one or more dimensions can no longer be neglected and it is necessary to make a transition from the classical picture to a quantum approach in the field of uncertainty analysis. In this contribution, sources of uncertainty for height measurements using atomic force microscopy (AFM) in contact mode are discussed. Results of density functional theory (DFT) modeling of AFM scans on a monoatomic step on silicon are presented. Van der Waals forces for the interaction of a spherical tip and an infinite step are calculated classically. Height measurements in constant force mode at different forces are simulated. In our approach, we model the tip apex and the monoatomic step as systems of individual atoms. As interatomic forces act on the sample and the tip of the microscope, the atoms of both relax in order to reach equilibrium positions. This leads to changes in those quantities that are finally interpreted as the resultant height of the step. The presence of van der Waals forces induces differences between the forces acting on atoms at different distances of the step. The behavior of different tips is studied along with their impact on the resulting AFM scans. Because the shape of the tip apex is usually unknown in real experiments, this variance in the height result due to different tips is interpreted as a source of uncertainty.

Biocompatible and High Stiffness Nanophotonic Trap Array for Precise and Versatile Manipulation.

The advent of nanophotonic evanescent field trapping and transport platforms has permitted increasingly complex single molecule and single cell studies on-chip. Here, we present the next generation of nanophotonic Standing Wave Array Traps (nSWATs) representing a streamlined CMOS fabrication process and compact biocompatible design. These devices utilize silicon nitride (Si3N4) waveguides, operate with a biofriendly 1064 nm laser, allow for several watts of input power with minimal absorption and heating, and are protected by an anticorrosive layer for sustained on-chip microelectronics in aqueous salt buffers. In addition, due to Si3N4's negligible nonlinear effects, these devices can generate high stiffness traps while resolving subnanometer displacements for each trapped particle. In contrast to traditional table-top counterparts, the stiffness of each trap in an nSWAT device scales linearly with input power and is independent of the number of trapping centers. Through a unique integration of microcircuitry and photonics, the nSWAT can robustly trap, and controllably position, a large number of nanoparticles along the waveguide surface, operating in an all-optical, constant-force mode without need for active feedback. By reducing device fabrication cost, minimizing trapping laser specimen heating, increasing trapping force, and implementing commonly used trapping techniques, this new generation of nSWATs significantly advances the development of a high performance, low cost optical tweezers array laboratory on-chip.

High-speed vertical positioning stage with integrated dual-sensor arrangement

This article presents a novel vertical positioning stage with a dual-sensor arrangement suitable for scanning probe microscopy. The stage has a travel range of 8.4μm and a first resonance frequency of 24kHz in the direction of travel. The sensor arrangement consists of an integrated piezoelectric force sensor and laminated piezoresistive strain sensor. The piezoelectric force sensor exhibits extremely low noise and introduces a zero into the dynamics which allows the use of integral force feedback. This control method provides excellent damping performance and guaranteed stability. The piezoresistive sensor is used for tracking control with an analog PI controller which is shown to be an approximate inverse of the damped system. The resulting closed-loop system has a bandwidth is 11.4kHz and 6σ-resolution of 3.6nm, which is ideal for nanopositioning and atomic force microscopy (AFM) applications. The proposed vertical stage is used to replace the vertical axis of a commercial AFM. Scans are performed in constant-force contact mode with a tip velocity of 0.2mm/s, 1mm/s and 2mm/s. The recorded images contain negligible artefacts due to insufficient vertical bandwidth.

Collocated Z-Axis Control of a High-Speed Nanopositioner for Video-Rate Atomic Force Microscopy

A key hurdle to achieve video-rate atomic force microscopy (AFM) in constant-force contact mode is the inadequate bandwidth of the vertical feedback control loop. This paper describes techniques used to increase the vertical tracking bandwidth of a nanopositioner to a level that is sufficient for video-rate AFM. These techniques involve the combination of: a high-speed XYZ nanopositioner; a passive damping technique that cancels the inertial forces of the Z actuator which in turns eliminates the low 20-kHz vertical resonant mode of the nanopositioner; an active control technique that is used to augment damping to high vertical resonant modes at 60 kHz and above. The implementation of these techniques allows a tenfold increase in the vertical tracking bandwidth, from 2.3 (without damping) to 28.1 kHz. This allows high-quality, video-rate AFM images to be captured at 10 frames/s without noticeable artifacts associated with vibrations and insufficient vertical tracking bandwidth.

On the operating stability of a scanning force microscope with a nanowhisker at the top of the probe

The functioning of the scanning probe microscope cantilever with a metal-carbon whisker at the top is studied. Metal-carbon whiskers grown by focused ion beam deposition in the presence of precursor gases have an aspect ratio in the range α = 10−200 and hold shape upon multiple scanning in the constant force mode. The advantage of probes with whiskers at the top in examining rough surfaces with vertical walls and narrow grooves is demonstrated experimentally. At high α, the scanning probe microscope is found to operate unstably, because the lateral surface of the whisker interacts with the specimen. It is shown that the axis of the whisker should be set normally to the specimen’s surface for the microscope to operate reliably at high aspect ratios.

Design of an Inertially Counterbalanced $Z$ -Nanopositioner for High-Speed Atomic Force Microscopy

In many conventional atomic force microscopes (AFMs), one of the key hurdles to high-speed scanning in constant-force contact mode is the low-feedback control bandwidth of the -axis loop. This paper presents the design of a fast -nanoposi-tioner to overcome this limitation. The -nanopositioner has its first resonant mode at 60 kHz and a travel range of 5 m. It consists of a piezoelectric stack actuator and a diaphragm flexure. The flexure serves as a linear spring to preload the actuator and to prevent it from getting damaged during high-speed operations. The -nanopositioner is mounted to an XY-nanopositioner. To avoid exciting the resonance of the XY -nanopositioner, an inertial counterbalance configuration was incorporated in the design of the -nanopositioner. With this configuration, the resonances of the XY-nanopositioner were not triggered. A closed-loop vertical control bandwidth of 6.5 kHz is achieved. High-speed constant-force contact-mode images were recorded at a resolution of 200 200 pixels at 10, 100, and 200 Hz line rates without noticeable image artifacts due to insufficient control bandwidth and vibrations. Images were also recorded at 312- and 400-Hz line rates. These images do not show significant artifacts. These line rates are much higher than the closed-loop bandwidth of a conventional AFM in which this nanopositioner was tested.

Microstructure and Local Charge Distribution in Hydrogenated Nanocrystalline Silicon under Illumination Studied by Electrostatic Force Microscopy.

ABSTRACTHydrogenated nanocrystalline silicon (nc-Si:H) is a promising absorber material for photovoltaic applications. Nanoscale electrical conductivity and overall electronic quality of this material are significantly affected by film microstructure, specifically the density and dimension of grains and grain-boundaries (GB). Local charge distribution at grains and grain/GB interfaces of nc-Si:H was studied by Electrostatic Force Microscopy (EFM) in constant force mode under illumination of white LED. Bias voltage from -3V to +3V was applied on the tip. Scanning Kelvin Force (KFM) images were taken before and after illumination to study the change in surface photovoltage (SP). EFM and KFM analysis were combined with film topography to draw a correlation between surface morphology and nanoscale charge distribution in this material. After illumination, small blister like structures were observed whose size and density increase with time. Raman spectroscopy confirmed these new structures as nanocrystalline silicon. This change was assumed due to relaxation of strained Si-Si bonds as an effect of photo response. Nanocrystalline grain interiors were at lower potential and amorphous grain boundaries were at higher potential for negative bias; it was opposite for positive bias. Change in polarity in bias voltage reversed the polarity of the potential in grains and GBs indicating the dominance of negative type of defects. Further study with current sensing AFM in dark and illumination with variable bias voltages will be able to identify the type and density of defects in grains and grain/GB interfaces.