Robust Force Research Articles

Modelling unstable crack propagation in concrete by finite element method with continuous nodal stress

Cracks in concrete will propagate unstably due to excessive shear stress, interactions at the rock-concrete interface, or sudden energy release, significantly compromising structural bearing capacity. To investigate this phenomenon, a nonlinear numerical method for modelling mixed-mode I-II crack propagation has been developed. This approach integrates dynamic equilibrium with a fictitious crack model and an initiation fracture toughness criterion. Key innovations include the incorporation of a finite element method with continuous nodal stress to enhance calculation accuracy, the utilization of kinetic energy to compensate for abrupt losses of strain energy during crack propagation, and the consideration of the deformation of the distributive beam and its interactions with specimens and supports. It was validated by modelling classic benchmarks for the dynamic initiation and propagation of brittle materials under mode I and mixed-mode I-II loading, and applied to analyse unstable crack propagation in concrete for four-point shear (FPS) beam specimens under various ratios of mode I and II stress intensity factors (KI/KII = 0 to 5.32) and loading rates (2 × 10-7 m/s to 2 × 10-3 m/s). Results indicated that the method effectively captures unstable crack propagation, with load-crack mouth shear displacement (CMSD) curves and crack propagation trajectories closely matching the experimental data. Furthermore, it was observed that when the elastic strain energy within the concrete beam exceeds the residual energy stored in the extended cracks, the crack transitions from stability to instability; conversely, if the elastic strain energy is less than or approximately equal to the residual energy, the crack decelerates and returns to stability. Additionally, parametric analyses reveal that lower distributive beam stiffness, shorter preset crack lengths, reduced concrete fracture energy, and a less robust cohesive force–displacement curve increase the likelihood of unstable crack propagation in concrete.

Sensorless contact force estimation and robust impedance control for a quadrotor manipulation system

The research on aerial manipulation systems has been increased rapidly in recent years. These systems are very attractive for a wide range of applications due to their unique features. However, dynamics, control and manipulation tasks of such systems are quite challenging because they are naturally unstable, have very fast dynamics, have strong nonlinearities, are very susceptible to parameters variations due to carrying a payload besides the external disturbances, and have complex inverse kinematics. In addition, the manipulation tasks require estimating (applying) a certain force of (at) the end-effector as well as the accurate positioning of it. Thus, in this article, a robust force estimation and impedance control scheme is proposed to address these issues. The robustness is achieved based on the Disturbance Observer (DOb) technique. Then, a tracking and performance low computational linear controller is used. For teleoperation purpose, the contact force needs to be identified. However, the current developed techniques for force estimation have limitations because they are based on ignoring some dynamics and/or requiring of an indicator of the environment contact. Unlike these techniques, we propose a technique based on linearization capabilities of DOb and a Fast Tracking Recursive Least Squares (FTRLS) algorithm. The complex inverse kinematics problem of such a system is solved by a Jacobin based algorithm. The stability analysis of the proposed scheme is presented. The algorithm is tested to achieve tracking of task space reference trajectories besides the impedance control. The efficiency of the proposed technique is enlightened via numerical simulation.

A robust force identification method based on L1+2-norm approximation theory

Obtaining the real force of the structure is the basic condition for efficient vibration reduction design. However, the uneasiness and instability of the inverse problem make the force identification still challenging. On the basis of L2-norm regularization, we propose a new method for force identification based on L1+2-norm approximation theory. By introducing the L1-norm penalty operator, a joint norm approximation optimization model is constructed to limit the non-zero force and punish the force value which approaching to zero, so that it can adapt to the identification of various types of forces. Then the optimal force solution is obtained by using the Primal-dual interior point method. Finally, the effectiveness and accuracy of the proposed method are verified by numerical simulation and experiment of asymmetric plate and double-layer plate structures. Different from previous studies, the L1+2-norm method in this work has high robustness, considers the characteristics of sparse regularization and L2-norm regularization, and can adapt to the identification of continuous forces and sparse forces at the same time, which has potential engineering application value.

Calving Dynamics and the Potential Impact of Mélange Buttressing at the Western Calving Front of Thwaites Glacier, West Antarctica

AbstractThe western region of the wide Thwaites Glacier terminus is characterized by a near‐vertical calving front. The grounding line at this western calving front (WCF) rests on a relatively high ridge, behind which exists a reverse‐sloping bed; retreat of the grounding line into this over‐deepening basin could therefore expose deep calving faces that may be subject to ice‐cliff failure. Here, we use the 3D Helsinki Discrete Element Model to identify the factors that control the calving dynamics in this location. We then focus on the ability of mélange to influence these dynamics given the wide embayment in which Thwaites Glacier terminates. We find that calving along the WCF is currently influenced by ice flow across the grounding line and consequent longitudinal tensile stress and rift formation. Calving is slowed in simulations that are initiated with a highly constricted mélange, with a thicker mélange suppressing calving entirely. We liken the constrained simulations to a scenario in which mélange piles behind a large grounded iceberg. In a future which may see calving become a more dominant control on the retreat of Thwaites Glacier, this type of blockage will be necessary for robust force chains to develop and transmit resistive forces to the terminus. The ability of the mélange to hinder calving at this location will be determined by the presence and rigidity of binding land‐fast sea ice and iceberg keel depths. Therefore, it is necessary to represent calving, mélange and sea ice in a single framework to predict the fate of Thwaites Glacier.

Sentience and the Issue of Animal Welfare

Abstract In this article, I discuss a precondition of moral consideration that sets the bar lower at sentience. The popular sentience thesis identifies the capacity to feel pain as its condition of consideration. By appealing to the capacity to feel, it is possible to address some fundamental questions about anthropocentrism such as a threat to sentient animals in factory farming and unnecessary experimentation on nonhuman animals. This article interrogates the issue of animal welfare and exposes how discussions on moral considerations focusing on animal sentience exclude non-sentience animals from public welfare policy. While the sentience thesis is a well-established approach in the animal welfare literature, I argue that it lacks robust normative force and, as such, is inadequate for promoting animal welfare since it forces fragmentation of our moral life.

Enhancing Robot End‐Effector Trajectory Tracking Using Virtual Force‐Tracking Impedance Control

This article presents an extended Cartesian space robot control framework that features a virtual force tracking impedance control to enhance the end‐effector trajectory tracking performance. Initially, the concept of a virtual surface is introduced, which is assumed to be at some constant distance from the desired end‐effector trajectory. This virtual surface generates a virtual contact force when interacting with the torque‐controlled robot end‐effector. The interaction is then manipulated using an impedance control model to track a constant desired force. If the robot end‐effector deviates from the desired trajectory, the constant force‐tracking impedance control generates a compliance trajectory that regulates the end‐effector movements, constraining it to the desired trajectory. For robust force tracking, impedance parameters are optimally tuned using a closed‐loop dynamic model incorporating both robot and impedance dynamics. Additionally, super twisting sliding mode control (STSMC) is integrated to overcome uncertainties and the impact of robot dynamics on force‐tracking performance. Experimental validation confirms the theoretical claims of the proposed approach. It demonstrates that force‐tracking impedance control improves the end‐effector trajectory tracking by quickly reacting to the dynamic trajectories compared to position control only and effectively maintains it on the desired trajectories.

DEMAND AND SUPPLY OF LABOR RESOURCES IN THE DEFENSE FORCES UNDER THE INFLUENCE OF THE CONCEPT OF TOTAL DEFENSE

The concept of Total Defense necessitates the mobilization of all national resources, including labor, to ensure comprehensive national security. This study examines the demand and supply dynamics of labor resources within the defense forces under the Total Defense framework. It explores how Total Defense influences recruitment, training, and retention strategies in the defense sector, particularly in the context of the Georgian Defense Forces. The analysis delves into the factors driving the demand for military and civilian personnel, such as heightened security threats and technological advancements, and evaluates the supply side, considering demographics, labor market conditions, and societal attitudes towards military service. Explores examples of total defense concepts developed by various countries, while assessing supply-side demographics, labor market conditions, and public attitudes toward military service. The interplay between these factors is critical in shaping effective human resource strategies to maintain a robust and responsive defense force. This research aims to provide insights into optimizing labor resource management to support Total Defense objectives, thereby enhancing national resilience and security readiness. Keywords: Total Defense, Military Economy, National Security, Georgian Defense Forces, Resources, Recruitment, Deterrence, Resilience.

Study on anti-segregation performance of cement stabilized macadam and its impact on mechanical and shrinkage properties

This study systematically explores the relationship between the mechanical and shrinkage properties of cement-stabilized macadam (CSM) stone base layers and their resistance to segregation to address the issue of segregation in wide and thick base layers. It establishes three cement dosage levels and five aggregate gradation types (GW1, GW2, GW3, GW4, and GW5). This research evaluates the anti-segregation performance of the mixtures by introducing the shape segregation coefficient L and the sieving segregation coefficient Seg and investigates how these properties influence segregation resistance. The findings revealed that mixtures with GW3 and GW4 gradations exhibit superior segregation resistance, with the most concentrated gradation curves in each zone. These mixtures form a robust force chain structure that resists segregation tendencies during descent. With a 5% cement content, the shape segregation coefficient L decreases by an average of 3.1%, and the sieve segregation coefficient Seg reduces by 14.0%. In addition, mixtures with GW3 and GW4 gradations show optimal drying shrinkage properties. Effective segregation-resistant gradations can significantly reduce the dry shrinkage coefficient of the specimens.

Estimating muscle force based on a neuromuscular decoding approach adaptive to fatigue conditions

Electromyography (EMG) has been extensively employed for precise muscle force estimation. Although methods based on motor unit (MU) activities (the smallest functional unit of the neuromuscular control system) have achieved superior performance, their effectiveness in fatiguing conditions remains unknown. This study aims to investigate the performance of existing MU-based muscle force estimation methods in fatiguing conditions, including the representative neuromuscular decoding (NMD) method and firing rate (FR) −based method. Compared to FR-based method, the NMD method specifically accounts for the differences in force contributions among MUs and the force twitch response of muscle fibers. We conducted fatigue induction experiment to collect force and high-density surface EMG data from the abductor pollicis brevis muscles of eight subjects during their performance of thumb abduction. Subsequently, the analysis of myoelectric manifestation of fatigue was performed and four training–testing strategies were designed to examine the effect of fatigue on force estimation methods. Experimental results indicated that the NMD method achieved superior and stable performance (assessed through root mean square difference between estimated and actual force) across four strategies (p >0.05 revealed by ANOVA), with only slight performance decline when fatigue data was involved in training or/and testing phase. Conversely, fatigue caused significant performance degradation when using the FR-based and other five comparative methods (p <0.05). These findings demonstrate that the NMD approach is adaptive to fatiguing MU activities, which can provide precise and robust muscle force estimation against fatigue in motor control and human–machine interfaces.

Nurse Attrition: Content Analysis of Free-Text Responses From Two Military Nursing Practice Environment Surveys.

Staff nurse attrition negatively impacts readiness of the warfighter and the health and wellbeing of all beneficiaries of the Military Health System (MHS). To promote the retention of a robust nursing workforce, a complete understanding of nurses' perceptions regarding their intent to leave is necessary. The purpose of this study was to explore the free-text responses of 1,438 nurses working among military medical treatment facilities for factors influencing their intent to leave, as an indicator of potential turnover, or attrition. This study employed thematic analysis to investigate the qualitative responses from the 2016 and 2018 Military Nursing Practice Environment Surveys. The study was determined to be exempt from Institutional Review Board review through the Womack Army Medical Center's Human Research Protection Program. Findings indicate that leadership and management (n = 647), staffing (n = 353), career opportunities (n = 345), staff outcomes (n = 247), culture (n = 153), quality of care (n = 99), patient care barriers (n = 86), non-patient care activities (n = 79), lack of formal professional development (n = 75), and area or care environment (n = 67) were among the top factors influencing staff nurse intent to leave, respectively. Our findings support the evaluation of retention strategies using implementation science for nurses and nurse resource personnel (e.g., nursing assistants, technicians, medics, and corpsman) to ensure a robust nursing work force throughout the MHS. Staff nurses and resource personnel working among military treatment facilities and embedded in units supporting combat and humanitarian missions ensure access to care and health promotion of the warfighter and all MHS beneficiaries.

Robust Force Control Based on Fuzzy ESO and Hysteresis Compensation for a Pneumatic Actuator-Driven Compliant Mechanism with Full-State Constraints

Robust Force Control Based on Fuzzy ESO and Hysteresis Compensation for a Pneumatic Actuator-Driven Compliant Mechanism with Full-State Constraints

Ab Initio Prediction of Vapor Pressure for Diverse Atomic Layer Deposition Precursors.

Understanding the saturated vapor pressure (Pvap) is vital for evaluating atomic layer deposition (ALD) precursors, as it directly influences the ALD temperature window and, by extension, the processability of compounds. The early estimation of vapor pressure ranges is crucial during the initial stages of novel precursor design, reducing the reliance on empirical synthesis or experimentation. However, predicting vapor pressure through computer simulations is often impeded by the scarcity of suitable empirical force fields for molecular dynamics simulations. This challenge is further compounded by the diverse chemical substances and the introduction of new elements into modern ALD processes, necessitating robust force fields that can accommodate metals, organics, and halides. In response, this study introduces a novel approach utilizing a quantum mechanically derived force field for the prediction of vapor pressure across a wide spectrum of potential ALD precursors. This approach enables the creation of system-specific force fields through parametrization based on ab initio calculations for a single molecule. We develop a comprehensive workflow to simulate both liquid and gaseous equilibrium phases, allowing the calculation of vapor pressure across a wide temperature range. Our methodology has been validated with a diverse set of ALD precursors, demonstrating its robustness in predicting Pvap at specified temperatures. The approach yields a Pearson's correlation coefficient (R2) greater than 0.9 on a logarithmic scale and a root-mean-squared deviation in self-solvation-free energies as low as 1.3 kcal mol-1. This innovative workflow, which does not require any prior experimental data, marks a significant advancement in the computer-aided design of novel ALD precursors, paving the way for accelerating developments in technology.

Nu–Gr correlation for laminar natural convection heat transfer from a sphere submitted to a constant heat flux surface

The work numerically investigated laminar natural convection heat transfer from the single sphere with a constant heat flux surface in air over the wide range of Grashof number (10≤Gr≤107\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10 \\le Gr \\le 10^{7}$$\\end{document}). The more efficient and precise numerical method based on Bejan et al. was employed here, the accuracy of which has been confirmed through validation against a single sphere case. The heat transfer characteristics were systemically analyzed in terms of isothermal contours and streamlines around the sphere, dimensionless temperature and velocity profiles. Additionally, local Nusselt number as well as local pressure and friction drag coefficients were studied with different Grashof number. In comparison to the sphere with uniform heat flux surface, the heat transfer from the isothermal sphere was found to be enhanced attributable to a more robust buoyancy force and a steeper temperature gradient. Moreover, the average Nusselt number for the sphere with a constant heat flux between 60.4 and 98.6% of the isothermal sphere’s value, this range being contingent upon the specific Grashof number. What’s more, the proposed correlation addresses a notable void in the predictive understanding of heat transfer from the sphere with uniform heat flux, which is scenario prevalent in various engineering applications, particularly for the cooling of electrical and nuclear systems, and offer values for academic research.

Force Control of a Haptic Flexible-Link Antenna Based on a Lumped-Mass Model.

Haptic organs are common in nature and help animals to navigate environments where vision is not possible. Insects often use slender, lightweight, and flexible links as sensing antennae. These antennae have a muscle-endowed base that changes their orientation and an organ that senses the applied force and moment, enabling active sensing. Sensing antennae detect obstacles through contact during motion and even recognize objects. They can also push obstacles. In all these tasks, force control of the antenna is crucial. The objective of our research is to develop a haptic robotic system based on a sensing antenna, consisting of a very lightweight and slender flexible rod. In this context, the work presented here focuses on the force control of this device. To achieve this, (a) we develop a dynamic model of the antenna that moves under gravity and maintains point contact with an object, based on lumped-mass discretization of the rod; (b) we prove the robust stability property of the closed-loop system using the Routh stability criterion; and (c) based on this property, we design a robust force control system that performs efficiently regardless of the contact point with the object. We built a mechanical device replicating this sensing organ. It is a flexible link connected at one end to a 3D force-torque sensor, which is attached to a mechanical structure with two DC motors, providing azimuthal and elevation movements to the antenna. Our experiments in contact situations demonstrate the effectiveness of our control method.

Modulation of ion-conducting groups in aqueous terpolymer binders to boost the electrochemical performance of silicon-based anodes

Silicon anodes hold great promise for the next-generation energy dense lithium-ion batteries (LIBs) due to their high specific capacity, yet the capacity of silicon anodes rapidly decays during repeated charge/discharge processes, which can hardly be alleviated via conventional binders due to the poor mechanical properties, insufficient ion/electronic conduction, and weak adhesion force. Herein, a random terpolymer (AMS) with fast ion transport and robust adhesion force was developed via the radical polymerization of acrylic acid (AA), acrylamide (AM) and 2-acrylamide-2-methylpropanesulfonic acid (AMPS), and used as aqueous binder for silicon/graphite (Si/C) anodes. The carboxyl and amide groups from AA and AM can form numerous of hydrogen bonds with the silicon particles, leading to a strong adhesion effect, while the sulfonic acid groups can construct fast channels for the rapid transport of lithium ions. Finally, the Si/C anode using the AMS411 binder delivers a high specific capacity of 322.48 mAh g−1 along with the superior operation stability at 0.5C (high-capacity retention ratio of 80.8 % after 500 cycles). This work provides that the incorporation of specific functional groups effectively enhances the overall electrochemical performance of the silicon-based anodes.

Establishing Effective Reserve Components: Lessons Learned from Russia

This research uses a qualitative approach with a case study method to explore lessons that can be drawn from Russia's experience in building an effective military reserve component. The article discusses the importance of establishing a robust and effective reserve force in Indonesia, drawing lessons from Russia's experiences and strategies employed by other nations. It emphasizes the need for a well-structured organization, clear command structures, efficient hierarchies, and regular training programs. The integration of technology and information systems, as well as the provision of welfare and incentives, is also highlighted as essential components for enhancing the effectiveness and readiness of Indonesia's reserve forces. The document also emphasizes the necessity of clear regulations and policies to provide a strong legal framework, ensuring the operational effectiveness and integrity of Indonesia's reserve forces. Additionally, it underscores the importance of integrating reserve components with regular forces through joint exercises, standardized doctrines, and operational procedures. The document concludes by emphasizing the opportunity for Indonesia to design a resilient reserve force by learning from Russia's challenges and strategies employed by other nations, ensuring the creation of a large, effective, well-trained, and deployable reserve force to balance and strengthen the overall national defense system.

Constrained trajectory optimization and force control for UAVs with universal jamming grippers

This study presents a novel framework that integrates the universal jamming gripper (UG) with unmanned aerial vehicles (UAVs) to enable automated grasping with no human operator in the loop. Grounded in the principles of granular jamming, the UG exhibits remarkable adaptability and proficiency, navigating the complexities of soft aerial grasping with enhanced robustness and versatility. Central to this integration is a uniquely formulated constrained trajectory optimization using model predictive control, coupled with a robust force control strategy, increasing the level of automation and operational reliability in aerial grasping. This control structure, while simple, is a powerful tool for various applications, ranging from material handling to disaster response, and marks an advancement toward genuine autonomy in aerial manipulation tasks. The key contribution of this research is the combination of a UG with a suitable control strategy, that can be kept relatively straightforward thanks to the mechanical intelligence built into the UG. The algorithm is validated through numerical simulations and virtual experiments.

Mn-S chemical bond mediated Z-scheme photocatalyst boosting efficient H2 evolution with apparent quantum yield exceeding 32% under visible light

Developing a highly effective solar-to-H2 conversion system is a promising strategy for carbon neutrality. Here, we report a chemically bonded Z-scheme photocatalyst by specifically linking the conduction band site of ZnIn2S4 with the valence band site of Mn0.3Cd0.7S1-x. Deviates from the typical van der Waals interactions between two semiconductors, the in-built robust binding force (Mn-S bond) and charge transfer channel facilitates the electron mobility, minimizes detrimental deep charge trapping, and prolongs the active charge lifetime from 983 ps to 4250 ps. The sulfur vacancies in Mn0.3Cd0.7S1-x are partially refilled by atoms of the same element in ZnIn2S4 during the in-situ formation of heterojunctions, which promotes and solidates the establishment of interfacial chemical bonds. The optimal photocatalyst achieves a high quantum efficiency of 32.71 % at 420 nm. This study offers a new insight into the development of Z-Scheme heterojunctions via a synergistic approach involving doping, vacancy filling and strong interfacial chemical bonds.

Stretchable rubber composites with lower hysteresis losses, improved magnetic effect, and a robust magnetic sensitivity

The stretchable materials exhibit various challenges such as high hysteresis losses, lower magnetic effect, and less magnetic sensitivity. In this work, we design and fabricate stretchable magnetic-rheological elastomers based on silicone rubber with robust magnetic sensitivity and lower hysteresis losses. The nanofillers used were carbon black (CB), and electrolyte iron particle (EIP). The stretchable materials obtained show an anisotropic effect of up to 165%. Moreover, the hysteresis losses were 0.4 kJ (control), 2.45 kJ (15 phr of CB), 0.58 kJ (60 phr of EIP), and 3.53 kJ (60 phr of hybrid filler system). The compressive modulus was 1.4 MPa (control), 3.76 MPa (15 phr of CB), 2.1 MPa (60 phr of EIP), and 3.9 MPa (60 phr of hybrid filler system). The fracture strain was 164% (control), 160% (15 phr of CB), 100% (60 phr of EIP), and 139% (60 phr of hybrid filler system). To sum up, the CB shows robust mechanical properties with high stretchability. However, the hybrid filler system shows high stiffness with a higher magnetic response. Finally, EIP-filled composites show optimum stiffness and robust magnetic response force.

Enhanced hyaline cartilage formation and continuous osteochondral regeneration via 3D-Printed heterogeneous hydrogel with multi-crosslinking inks

The unique gradient structure and complex composition of osteochondral tissue pose significant challenges in defect regeneration. Restoration of tissue heterogeneity while maintaining hyaline cartilage components has been a difficulty of an osteochondral tissue graft. A novel class of multi-crosslinked polysaccharide-based three-dimensional (3D) printing inks, including decellularized natural cartilage (dNC) and nano-hydroxyapatite, was designed to create a gradient scaffold with a robust interface-binding force. Herein, we report combining a dual-nozzle cross-printing technology and a gradient crosslinking method to create the scaffolds, demonstrating stable mechanical properties and heterogeneous bilayer structures. Biofunctional assessments revealed the remarkable regenerative effects of the scaffold, manifesting three orders of magnitude of mRNA upregulation during chondrogenesis and the formation of pure hyaline cartilage. Transcriptomics of the regeneration site in vivo and scaffold cell interaction tests in vitro showed that printed porous multilayer scaffolds could form the correct tissue structure for cell migration. More importantly, polysaccharides with dNC provided a hydrophilic microenvironment. The microenvironment is crucial in osteochondral regeneration because it could guide the regenerated cartilage to ensure the hyaline phenotype.