Robust Contact Research Articles

Machine learning enabled orthogonal camera goniometry for accurate and robust contact angle measurements

Characterization of surface wettability plays an integral role in physical, chemical, and biological processes. However, the conventional fitting algorithms are not suitable for accurate estimation of wetting properties, especially on hydrophilic surfaces, due to optical distortions triggered by changes in the focal length of the moving drops. Therefore, here we present an original setup coupled with Convolutional Neural Networks (CNN) for estimation of Contact Angle (CA). The developed algorithm is trained on 3375 ground truth images (at different front-lit illuminations), less sensitive to the edges of the drops, and retains its stability for images that are synthetically blurred with higher Gaussian Blurring (GB) values (GB: 0–22) if compared to existing goniometers (GB: 0–12). Besides, the proposed technique can precisely analyze drops of various colors and chemistries on different surfaces. Finally, our automated orthogonal camera goniometer has a significantly lower average standard deviation (6.7° vs. 14.6°) and coefficient of variation (14.9 vs. 29.2%) than the existing techniques and enables wettability assessment of non-spherical drops on heterogeneous surfaces.

Robust Carbon Nitride Homojunction Photoelectrode for Solar-Driven Water Splitting.

Achieving intimate particle-to-particle and particle-to-substrate contacts is the first priority for fabricating high-quality photoelectrodes to ensure sufficient visible light absorption and efficient charge separation/transport. To achieve this goal, a seeding strategy is designed to construct a robust carbon nitride (CN) homojunction photoelectrode, in which vaporized precursors are condensed into a compact seeding layer at low temperatures, inducing the further deposition of the top layer. This optimized photoelectrode displays an excellent photocurrent density of 320 μA cm-2 in 0.1 M NaOH electrolyte at 1.23 VRHE (V vs reversible hydrogen electrode) under AM 1.5G illumination, with H2 and O2 evolution rates of 2.98 and 1.47 μmol h-1 cm-2, respectively. Characterizations show that both the robust contact and the homojunction of the double-layered CN film contribute to enhanced photoelectrochemical performance. This work may provide a new strategy for the design of high-performing CN photoelectrodes.

Enhanced Organic Thin-Film Transistor Stability by Preventing MoO3 Diffusion with Metal/MoO3/Organic Multilayered Interface Source-Drain Contact.

The source-drain electrode with a MoO3 interfacial modification layer (IML) is considered the most promising method to solve electrical contact issues impeding organic thin-film transistors (OTFTs) from commercialization. However, this method raises many concerns because MoO3 might diffuse into organic materials, which causes device instability. In this work, we observed a significant device stability degradation by damaging on/off switching performance caused by MoO3 diffusion. To prevent the MoO3 diffusion, a source-drain electrode with a multilayered interface contact (MIC) consisting of a top-down stack of metal, MoO3 IML, and organic buffer layer (OBL) is proposed. In the MIC device, the MoO3 IML serves well for its intended functions of reducing contact resistance and suppressing minority carrier injection to the OTFT channel. The inclusion of OBL to the MIC helps block MoO3 diffusion and thereby leads to better device stability and an increased on/off ratio. Through combinations with several organic compounds as a buffer layer, the MoO3 diffusion related electrical behaviors of OTFTs are systematically studied. Key parameters related to MoO3 diffusion such as the Fick coefficient and bias-stress stability such as carrier trapping time are extracted from numerical device analysis. Finally, we summarize a general rule of material selection for making robust source-drain contact.

High-capacity Sb2SnO5 with controlled Sb/Sn phase modulation as advanced anode material for sodium-ion batteries

Low cost and considerable theory specific capacity (∼1195 mAh g−1) make Sb2SnO5 (SSO) material becoming a potential candidate for sodium-ions battery anodes. However, the low electronic conductivity and sluggish ions transfer kinetic has inhibited the practical applications. Herein, we demonstrate a novel Sn/Sb@SSO@PCFs composite using simple but effective electrospinning methods, which enable SSO nanoparticles embedded with Sn and Sb nanodomains in situ generation. The SSO was first reported as anode for sodium-ion batteries and in situ generation Sb and Sn nanocrystals domain around the SSO oxides. Different from existing tactics, the unique composite establishes a robust and efficient electrical contact between the SSO and the conductive Sb and Sn phases, enabling fast ions and electrons transfer across the electrochemical active SSO/Sb/Sn. Meanwhile, the composites offer an opportunity to compromise the challenges faced by each entity and enhance the overall performance by circumventing the weakness of individual SSO, Sn and Sb. As evidenced, the as-fabricated composite has unexpected electrochemical properties, including high capacity and long cycle stability with a retention rate of 83% after 450 cycles at 0.5 C. Combined with synergistic Na+ ions storage of SSO/Sb/Sb and a simple and scalable manufacturing process, this study provides a new strategy to modulate material delivering high capacity and cycle stability for the next generation sodium ions batteries (SIBs).

Interfacial Distribution of Nafion Ionomer Thin Films on Nitrogen-Modified Carbon Surfaces.

Chemically modified carbon supports for the cathode catalyst layers of polymer electrolyte fuel cells (PEFCs) show considerable promise for boosting the oxygen reduction reaction. This study evaluated the ionomer distribution of Nafion ionomer thin films on nitrogen (N)-modified carbon surfaces along their depth direction. Neutron reflectivity (NR) measurements performed using the double-contrast technique with H2O and D2O revealed that the introduction of N functional groups to carbon thin films promoted ionomer adsorption onto the surface under wet conditions (22 °C, 85% relative humidity). Molecular dynamics (MD) simulations conducted to verify the origin of the robust contact between the ionomer and N-modified carbon surface revealed an ionomer adsorption mechanism on the N-modified carbon surfaces, which involved Coulomb interactions between the positively charged carbon surface and the ionomer side chains with negatively charged sulfonic acid groups. The positive surface charge, which was determined using the contents of the N functional groups estimated by X-ray photoelectron spectroscopy, was found to be sufficient as an impetus for ionomer adsorption. This strategy involving NR measurements and MD simulations can provide insights into the solid-ionomer interfacial structures in a cathode catalyst layer and can therefore be extensively employed in studies on PEFCs.

Polysaccharide hydrogel electrolytes with robust interfacial contact to electrodes for quasi-solid state flexible aqueous zinc ion batteries with efficient suppressing of dendrite growth

Flexible aqueous zinc-ion batteries (AZIBs) require high conductive and adhesive hydrogel electrolytes. However, high adhesion tends to hinder ion conduction rate. Herein, we designed a water/glycerol binary solvent coordinating the hydrophilic polymers to reconstruct the water molecules' environment in the hydrogel. As a consequence, the interface adhesion strength between Zn and the hydrogel reached 3.0 kPa and the ionic conductivity was up to 16.8 mS cm−1. In addition, inspired by the slurry electrode preparation method, we developed a simple blade coating technique using a non-Newtonian polysaccharide liquid solution to construct an ultra-thin hydrogel electrolyte in situ on the cathode. The thickness of the obtained hydrogel reached 70 μm, and the ultrathin flexible AZIBs were easily constructed by pasting a Zn anode directly on the adhesive hydrogel, showing the potential of flexible AZIBs scalable assembly. In addition, the Zn//Zn symmetrical cells with the hydrogel electrolyte provided stable cycling performance for over 400 h at 0.1 mA cm−2 with suppressed dendrite growth. The assembled Zn//Polyaniline battery and Zn//V2O5 battery also exhibited excellent capacity retention after cycles. This work has realized the hydrogel electrolyte with high adhesion and conductivity, which has good adaptability to metal electrodes and opened up a new practical way for large-scale assembly of flexible energy storage devices.

A fully implicit method for robust frictional contact handling in elastic rods

Accurate frictional contact is critical in simulating the assembly of rod-like structures in the practical world, such as knots, hairs, flagella, and more. Due to their high geometric nonlinearity and elasticity, rod-on-rod contact remains a challenging problem tackled by researchers in both computational mechanics and computer graphics. Typically, frictional contact is regarded as constraints for the equations of motions of a system. Such constraints are often computed independently at every time step in a dynamic simulation, thus slowing down the simulation and possibly introducing numerical convergence issues. This paper proposes a fully implicit penalty-based frictional contact method, Implicit Contact Model (IMC), that efficiently and robustly captures accurate frictional contact responses. We showcase our algorithm’s performance in achieving visually realistic results for the challenging and novel contact scenario of flagella bundling in fluid medium, a significant phenomenon in biology that motivates novel engineering applications in soft robotics. In addition to this, we offer a side-by-side comparison with Incremental Potential Contact (IPC), a state-of-the-art contact handling algorithm. We show that IMC possesses comparable performance to IPC while converging at a faster rate.

Achieving exceptional wear resistance in cemented carbides using B2 intermetallic binders

Conventional strategy for designing wear-resistant composites relies on the immersion of a carbide skeleton into ductile binders to impart necessary strength and deformability but sometimes overlooks the deformation compatibility, rendering the composites vulnerable to premature wear failures. In this work, extensive binder extrusion was specifically noted on traditional cemented carbides during sliding in absence of oxides protection. To alleviate this situation, we designed the WC-CoFeAl composites with a novel B2_CoFe binder phase structure, as per the calculated phase diagrams, in comparison to the WC-CoAl and WC-Co composites that respectively incorporate a single α-Co phase and a mixture of α-Co and ε-Co phases. The WC-CoFeAl reveals an exceptional binder extrusion resistance and realizes a ≥50% wear reduction within a temperature range of 25–400 °C. Originating from the intrinsically high strength and the dynamically generated gradient nano-structures, consisting of a nano-grained surface tribolayer and an ultra-fine grained subsurface layer, the B2 intermetallic binders promote an improved deformation compatibility with the WC skeleton, which contributes to the maintenance of robust contact surfaces. The current work thus highlights the important role of deformation compatibility on the durability of cemented carbides, which offers a new thread to future development of wear-resistant composite materials.

P-Type Ohmic Contact to Monolayer WSe2 Field-Effect Transistors Using High-Electron Affinity Amorphous MoO3

Monolayer tungsten diselenide (1L-WSe2) has been widely used for studying emergent physics due to the unique properties of its valence bands. However, electrical transport studies have been impeded by the lack of a reliable method to realize Ohmic hole-conducting contacts to 1L-WSe2 especially at low carrier densities and low temperatures. Here, we report low-temperature p-type Ohmic contact to 1L-WSe2 field-effect transistors at carrier densities (n) below n = 1 × 1012 cm–2 with negligible temperature dependence down to the lowest measured temperature (10 K). The non-rectifying barrier is achieved between 1L-WSe2 and molybdenum trioxide (MoO3), where 1L-WSe2 underneath MoO3 is heavily hole-doped through surface transfer doping. Electrical transport measurements reveal linear current–voltage relations at a temperature of 10 K and carrier densities from n = 7.7 × 1011 cm–2 to below the threshold. The finding is also supported by nearly temperature-independent output curves up to room temperature and a negligible contact barrier down to the subthreshold regime. Furthermore, the contact resistivity of MoO3-contacted 1L-WSe2 FET is 30.2–64.8 kΩ μm at n = 1.5 × 1012 cm–2, which is the lowest reported for 1L-WSe2 FETs at such low carrier density. Realizing robust p-type Ohmic contact to a 2D transition metal dichalcogenide semiconductor will enable direct electronic measurements of quantum transport in correlated phases in the valence bands of monolayer semiconductors.

PH-Responsive Polyelectrolyte Coatings that Enable Catheter-Mediated Transfer of DNA to the Arterial Wall in Short and Clinically Relevant Inflation Times.

We report the design and characterization of pH-responsive polymer coatings that enable catheter balloon-mediated transfer of DNA to arterial tissue in short, clinically relevant inflation times. Our approach exploits the pH-dependent ionization of poly(acrylic acid) (PAA) to promote disassembly and release of plasmid DNA from polyelectrolyte multilayers. We characterized the contact transfer of multilayers composed of PAA, plasmid DNA, and linear poly(ethyleneimine) (LPEI) identified as promising in prior studies on the delivery of DNA to arterial tissue. In contrast to thinner films evaluated previously, we found thicker coatings composed of 32 repeating (LPEI/PAA/LPEI/DNA)x tetralayers to swell substantially in physiologically relevant media (in PBS; pH = 7.4). In some cases, these coatings also disintegrated or delaminated rapidly from their underlying substrates, suggesting the potential for enhanced balloon-mediated transfer. We developed a technically straightforward agarose gel-based hole-insertion model to characterize factors (inflation time, lumen size, etc.) that influence contact transfer of DNA when film-coated balloons are inflated into contact with soft surfaces. Those studies and the results of in vivo experiments using small animal (rat) and large animal (pig) models of peripheral arterial injury revealed catheters coated with these materials to promote robust contact transfer of DNA to soft hydrogel surfaces and the luminal surfaces of arterial tissue using inflation times as short as 30 s. These short inflation times are relevant in the context of clinical vascular interventions in peripheral arteries. Additional studies demonstrated that contact transfer of DNA using these short times can promote subsequent dissemination and transport of DNA to the medial tissue layer, suggesting the potential for use in therapeutically relevant applications of balloon-mediated gene transfer.

Heterogeneous FeNi2S4/Ni3S4 nanoparticles embedded CNT networks for efficient and stable water oxidation

Development of efficient and reliable transition metal-based oxygen evolution reaction (OER) catalysts has profound implications to achieve carbon-neutral economy in the future. Herein, a novel hybrid OER catalyst of heterogeneous FeNi 2 S 4 /Ni 3 S 4 nanoparticles embedded CNT networks (FeNi 2 S 4 /Ni 3 S 4 @CNT) was prepared by a facile one-step hydrothermal reaction. The ultrafine heterogeneous nanoparticles of FeNi 2 S 4 and Ni 3 S 4 embedded CNT can expose abundant active sites and enhance the electrochemically active area; the electronic structure modulated by the bi-metallization of FeNi 2 S 4 via partial substitution of Ni with Fe; the robust contact between conductive FeNi 2 S 4 and Ni 3 S 4 nanoparticles with abundant active sites on the surface and the CNT network with high conductivity can effectively promote the electron transfer; the 3D network with rich nanopores is beneficial to electrolyte penetration and gas release. These above merits and synergistic effects of FeNi 2 S 4 and Ni 3 S 4 endow the catalyst superior OER performances with an ultralow overpotential of 247 mV for the current density of 10 mA cm −2 , a low Tafel slope of 53.7 mV dec −1 and remarkable durability over 20 h, surpassing those of commercial OER catalyst RuO 2 . This work provides a synergistic OER boosting strategy via bi-metallization, heterogeneous nanoparticle distribution and conductive skeleton to develop non-precious-based electrocatalyst by a facile one-pot synthesis method. • FeNi2S4/Ni3S4 embedded CNT networks were synthesized by solvothermal reaction. • FeNi2S4/Ni3S4@CNT exhibits superior OER performance and long-term stability. • Good OER activity is due to the unique nanoarchitecture and synergistic effect.

Drug-Resistant Tuberculosis Types and Their Treatment Regimens Using First-Line, Second-Line Injectable, Third-Line, Fluoroquinolones, Aminoglycosides, Cyclic Polypeptides, Novel and Repurposed Anti-Tuberculosis Drugs

Drug-Resistant Tuberculosis (DR-TB) causes high mortality and morbidity rates globally. DR-TB and COVID-19 pandemic are posing a major risk to global public health and economic security, and are jeopardizing efforts in the control, prevention and elimination of TB globally. Mycobacterium tuberculosis (MTB) has continued to evolve resistance to anti-TB drugs. Different types of DR-TB have been defined and they include; mono drug-resistant TB, Multi Drug-Resistant TB (MDR-TB), poly drug-resistant TB, pre-Extensively Drug-Resistant TB (pre-XDR TB), Extensively Drug-Resistant TB (XDR-TB), Extremely Drug-Resistant TB (XXDR-TB), and Totally Drug-Resistant TB (TDR-TB). DR-TB is caused by several factors which include: non-adherence, poor compliance, low efficacy anti-TB drugs, delayed diagnosis, interrupted supply, stock-outs, inadequate infection control, HIV co-infection, spontaneous mutations, and chromosomal replication errors. Global TB targets have gone off-track and years of progress reversed due to DR-TB and the COVID-19 pandemic. Treatment failure, death and costs incurred are higher among patients suffering from DR-TB than among those with susceptible TB. For this reason, susceptible TB needs to be diagnosed quickly and treated effectively to prevent its progression to DR-TB. Treatment for susceptible TB requires the use of first-line anti-TB drugs; rifampicin, isoniazid, pyrazinamide, and ethambutol. While DR-TB is treated using the second- and third-line anti-TB drugs. Effective treatment of TB is dependent on: prompt and accurate diagnosis of TB and recognition of drug-resistance; adherence to treatment; robust contact tracing and prophylactic treatment of TB contacts; and screening for TB infection in high-risk groups.

Hybrid continuum–discrete simulation of granular impact dynamics

Granular impact—the dynamic intrusion of solid objects into granular media—is widespread across scientific and engineering applications including geotechnics. Existing approaches to the simulation of granular impact dynamics have relied on either a purely discrete method or a purely continuum method. Neither of these methods, however, is deemed optimal from the computational perspective. Here, we introduce a hybrid continuum–discrete approach, built on the coupled material-point and discrete-element method (MP–DEM), for simulation of granular impact dynamics with unparalleled efficiency. To accommodate highly complex solid–granular interactions, we enhance the existing MP–DEM formulation with three new ingredients: (i) a robust contact algorithm that couples the continuum and discrete parts without any interpenetration under extreme impact loads, (ii) large deformation kinematics employing multiplicative elastoplasticity, and (iii) a trans-phase constitutive relation capturing gasification of granular media. For validation, we also generate experimental data through laboratory measurement of the impact dynamics of solid spheres dropped onto dry sand. Simulation of the experiments shows that the proposed approach can well reproduce granular impact dynamics in terms of impact forces, intrusion depths, and splash patterns. Furthermore, through parameter studies on material properties, model formulations, and numerical schemes, we identify key factors for successful continuum–discrete simulation of granular impact dynamics.

Coupling surfactants with 3D hollow raspberry-like NiS/carbon microsphere with S vacancies for enhanced sensitivity monitoring of serotonin and L-tryptophan

Serotonin (ST) is a monoamine neurotransmitter synthesized from L-tryptophan (L-Try). Solving their simultaneous detection problem is necessary for assisting in diagnostics diseases. In this work, we designed NiS/carbon hybrids with NiS nanoparticles embedded on 3D hollow porous carbon microspheres (NiS/CS) via successive carbonization and sulfidation Ni-MOF for constructing electrocatalysts for the simultaneous electrooxidation of ST and L-Try. The formation of robust contact with surface S vacancies in NiS/CS nanointerfaces demonstrated a remarkably enhanced electrocatalytic activity towards ST and L-Try and the corresponding electrochemical signals appeared as two well resolved oxidation peaks with the significant peak-to-peak separation. Importantly, the dual amplification effect of the high electrocatalytic performance function of NiS/CS and the hydrophobic properties of surfactant CTAB coupling made CTAB/NiS/CS/GCE exhibit high sensitivity recognition to ST and L-Try, effectively shielding other coexisting interference. The developed sensor provided a 0.01–200.0 μmol/L linear response range and the low detection limit of 3.35 and 2.94 nmol/L for ST and L-Try, respectively. Finally, this sensing methodology enabled accurate determination of ST and L-Try amount in serum, urine and injection samples and with successful recovery outcomes.

Multi-Faceted Approach to COVID-19 Surveillance at a Large University Campus in the Southeastern United States.

The coronavirus disease 2019 (COVID-19) pandemic continues to present unique public health challenges both within the United States and across the globe. Institutions of higher learning are tasked with preventing and responding to COVID-19 on campus while also considering implications for the surrounding communities. The process of re-opening campus, whether at full or partial capacity, has tasked these institutions with overcoming complex challenges associated with balancing the resumption of campus operations while simultaneously protecting university affiliates and surrounding community members from COVID-19 through robust surveillance, contact tracing, and testing efforts. Here, we provide a concise outline related to the development and implementation of the comprehensive and sustainable COVID-19 surveillance program at the University of Florida. We also critically discuss the successes and pitfalls of this program while also providing recommendations for the development of similar programs in the future.

An efficient and robust GPGPU-parallelized contact algorithm for the combined finite-discrete element method

In this study, an efficient and robust GPGPU (general purpose graphic processing unit)-parallelized algorithm is proposed for contact force calculation for the three-dimensional combined finite-discrete element method (3D FDEM). The contact force model is energy-conserving and avoids the issues that the mesh-dependence of contact force in the original contact algorithm proposed by Munjiza. The contact force calculation is based on the determination of the geometrical features of the overlapped region between two particles, which can be easily obtained by performing the face–particle intersection calculations consecutively. The contact damping and contact friction are also implemented. Based on Compute Unified Device Architecture (CUDA), the proposed contact algorithm can be parallelized with much less thread unbalance and register usage than the existing energy-conserving contact algorithms due to the simplified computational process. Several numerical tests are performed to validate the efficiency and effectiveness of the proposed contact algorithm. The contact friction model is validated against theoretical solutions with a block sliding test, and the results show that the proposed contact algorithm outperforms the original contact algorithm in both normal and friction force evaluation. For both quasi-static and dynamic scenarios, the simulated results are in good agreement with those generated by the original contact algorithm, as well as the experimental measurements. The computational efficiency tests show that the computation time is linearly proportional to the number of potential contact pairs, and the speedup ratio of the parallelized version of proposed contact algorithm relative to the serial version of original contact algorithm can reach up to 565.1 (Nvidia Quadro GP100), which indicates the proposed contact algorithm is capable to be employed in the simulation of large-scale problems. Besides, the proposed contact algorithm can be applied to the cases where the polyhedrons with more than four vertexes are employed.

Metaphosphate-Bridged Interface Boosts High-Performance Lithium Storage.

Carbon materials with well-dispersed SnOx particles exhibit excellent lithium-storage performance. However, the volume change of SnOx and the weak interaction between SnOx and carbon induce an unsteady SnOx-C interface during the lithiation/delithiation process. This phenomenon results in enhanced charge transfer resistance and reduced electrical contact of active materials, which leads to low reversibility of tin oxidation, restricted capacity, sluggish kinetics, structural deterioration, and rapid capacity decay. Herein, tin oxide/carbon composites with a metaphosphate-bridged interface are synthesized to construct a robust interfacial contact between tin oxides and carbon. The metaphosphate group functions as a bridge between SnOx and carbon and results in excellent electrochemical stability during the charge/discharge process, which is favorable for electrode structural integrity. The formation of the metaphosphate-bridged interface provides a steady transport channel for e-/Li+ and thus improves the reversibility of the conversion reaction. The enhanced charge transfer and interaction can also boost the charge transfer between SnOx and carbon, which leads to higher SnOx utilization. Thus, the prepared P-SnOx/C anode exhibits enhanced lithium-storage performance in terms of specific capacity, cycling stability, and rate performance.

Epidemiological analysis of SARS-COV-2 B.1.617.2 (delta variant) transmission in an educational institute

BackgroundDespite having an effective COVID-19 vaccine, the COVID-19 pandemic is far from over and the delta variant continues to cause havoc across several continents. The present study was conducted to analyze and describe the occurrence of COVID-19 cases among completely vaccinated individuals. MethodsIn an educational institute in Western Maharashtra, we analyzed a cluster of RTPCR positive COVID-19 cases among fully vaccinated students which occurred in 12 days. The cases were linked to a series of curricular and co-curricular events in the institute. A detailed epidemiological investigation and genome sequencing of cases were conducted. IgG antibodies against S1 protein of novel SARS-CoV-2 were estimated for cases and age, sex, and vaccination status matched controls. ResultsAll 37 identified cases were mild COVID. 188 high risk (HR) contacts of the cases were identified. The overall secondary attack was 9.5%. Out of 31 cases and 50 controls, 09 (29%) cases and 08 (16%) controls were found to have IgG antibodies against S1 protein of novel SARS-CoV-2 titer of more than 60 U/ml. Whole-genome sequencing of 15 samples of the cluster showed the presence of the Delta variant of SARS-CoV-2. No correlation was observed between Ct value and IgG S1 antibody titers. ConclusionThe study provides significant evidence that only vaccination alone does not completely protect against SARS-CoV-2 B.1.617.2 (Delta) variant infection. An all-encompassing multicomponent strategy involving implementation of NPIs, robust contact tracing, early identification and isolation of cases, and high vaccination coverage is the way forward for the prevention of COVID-19.

An Isogeometric analysis based method for frictional elastic contact problems with randomly rough surfaces

The problem addressed in this paper concerns the frictional contact between an elastomer and a rigid body with randomly rough surfaces. The work is accomplished on the basis of two crucial elements: a framework for generating random geometries and a robust frictional contact algorithm, both of which are realised in the approach of Isogeometric analysis (IGA) for its high accuracy and robustness. For the former, a new Isogeometric framework for random geometry modelling is proposed, which combines the random field generation based on Karhunen–Loève expansion theory with Non-Uniform Rational B-Spline (NURBS) interpolation method. For the latter, a mortar-based frictional contact algorithm in 2D large deformation regime is adopted incorporating a modified closest point projection method for detection of contact. Numerical experiments are conducted with several settings such as ‘rough–smooth’, ‘smooth–rough’ and ‘rough–rough’ contact, depending on which side of the contact pair the randomly rough surface belongs to. The ratio of the global coefficient of friction to the prescribed local one and the ratio of true contact area to the nominal contact area are characterised under these settings, and factors like the root mean square roughness and correlation length of the random surface and the external traction are discovered to have a significant influence on the two ratios.

Contact State Estimation for Peg-in-Hole Assembly Using Gaussian Mixture Model

Recently, the robotic assembly has been expanded into an unstructured environment. This environment includes uncertainties that may cause unexpected situations such as a failure of the assembly. Such problems can be prevented or monitored by a robust contact state (CS) estimation method. In that sense, the paper suggests a CS estimation method that contains a torque indicator, a position/velocity indicator, and a CS discriminator. Using joint torque of manipulators and position/velocity of the end-effector, a Gaussian Mixture Model (GMM) builds each indicator by reflecting on two properties of measured data, i.e., non-stationary behavior and correlation among the data. The indicators play a role to indicate the corresponding sensor state. The discriminator is defined by rules which combine the results of the indicators, allowing a robust CS estimation to be achieved. In this respect, the proposed method has a distinct advantage over existing distance-based clustering methods which ignore probabilistic properties or correlation among measured data. The performance of the estimation is demonstrated through experiments with torque-controlled manipulators and commercial prefabricated furniture.