Normal Force Research Articles

Modeling of the unsteady aerodynamic characteristics of the NACA 0015 airfoil from the data of numerical calculations of the flow

The possible application of the results of numerical modeling in developing an approximate phenomenological mathematical aerodynamic model applicable in solving the problems of dynamics is studied with reference to the example of the unsteady flow past the NACA 0015 airfoil oscillating in the angle of attackat different frequencies, amplitudes, and mean angles of attack. For this purpose, the Reynolds equations are solved in both steady and unsteady formulations, together with thek–ω-SST turbulence model. The results of the calculations are validated by means of comparing them with the experimental data. The model of the normal force and the longitudinal moment formulated within the frameworkof an approach introducing an internal dynamic variable is identified according to the data of calculations. The results of the modeling are compared with the numerical and experimental data. The comparison with the conventional approach to the modeling based on the linear unsteady model with the use of dynamic derivatives is also carried out.

On the Aptness of Material Constitutive Models for Simulating Nano-Scratching Processes.

The simulation of nano-scratching on metallic substrates using smooth particle hydrodynamics (SPH) has been attempted by researchers in recent years. From a review of the existing SPH simulations of nano-scratching processes, it was found that mainly two different material constitutive models (i.e., the Johnson-Cook model and the elasto-plastic model) were employed to describe the material flow. In the majority of these investigations, the Johnson-Cook model was employed to characterise the stress flow of the material subjected to scratching. A natural question remains as to which material constitutive model is preferable for the SPH modelling of nano-scratching when quantitatively predicting the process outcomes. In this paper, a quantitative comparison of material responses during the nano-scratching of copper is reported when the process is simulated using SPH with two different constitutive material models, namely the Johnson-Cook and the elasto-plastic models. In particular, the simulated cutting and normal forces as well as the machined topography using both approaches are compared with the experimental work reported in the literature. The SPH-based simulation results in this paper are investigated based on the following three aspects: (a) cutting and normal forces with different material models and depths of the cut, (b) the effect of the cutting speed on forces and its dependence on adopted material models, and (c) the effect of adopted material models on the surface topography of machined nano-grooves. The SPH simulation results showed that using the Johnson-Cook material model, cutting and normal forces were closer to the experimental data compared to the results obtained with the elasto-plastic model. The results also showed that the cross-sectional profile of simulated nano-grooves using the Johnson-Cook model was closer to the experimental results. Overall, this paper shows that the selection of the Johnson-Cook model is preferable for the SPH modelling of the nano-scratching process.

Analysis of BGA Lead-Free solder joints failure behavior based on thermal shock testing

The interconnected solder joints within automotive electronic components are the most vulnerable parts of the structure, and their reliability is crucial for the development of new energy vehicles. This study focuses on automotive ADAS (Advanced Driver Assistance System) devices, analyzing the failure behavior of internal BGA (Ball Grid Array) lead-free solder joints under thermal shock conditions.Through thermal shock testing from −40℃ to 95℃, it was observed that microcracks first appeared in the upper intermetallic compound (IMC) layer of corner solder joints after 1600 cycles. As the number of thermal shock cycles increased, the net-like β-Sn phase in the solder joints gradually transformed into block and dot-like structures. Due to the relatively weak strength between the IMC layer and the Ag-Sn compound region, cracks typically propagated along the boundaries of these areas. Recrystallization occurred in the interface between the solder joint and the upper pad, with the proportion of high-angle grain boundaries increasing from 10.74% to 72.43%. The crack propagation mode changed from initial intergranular to transgranular fracture. Throughout the thermal shock test, the upper IMC layer remained thicker than the lower one, with the lower IMC layer thickness showing a minimum point at 750 cycles.The average thrust force between the solder joints and the substrate decreased more rapidly with thermal shock cycles, indicating that non-solder mask defined pads are more effective in improving structural strength.

Potential-dependent superlubricity of stainless steel and Au(1 1 1) using a water-in-surface-active ionic liquid mixture

HypothesisThe friction and interfacial nanostructure of a water-in-surface-active ionic liquid mixture, 1.6 M 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate ([BMIm][AOT]), can be tuned by applying potential on Au(111) and stainless steel. ExperimentalAtomic force microscopy (AFM) was used to examine the friction and interfacial nanostructure of 1.6 M [BMIm][AOT] on Au(111) and stainless steel at different potentials. FindingsSuperlubricity (vanishing friction) is observed for both surfaces at OCP+1.0 V up to a surface-dependent critical normal force due to [AOT]− bilayers adsorbing strongly to the positively charged surface thus allowing AFM tip to slide over solution-facing hydrated anion charged groups. High-resolution AFM imaging reveals ripple-like features within near-surface layers, with the smallest amplitudes at OCP+1 V, indicating the highest structural stability and resistance to thermal fluctuations due to highly ordered boundary [AOT]− bilayers templating robust near-surface layers. Exceeding the critical normal force at OCP+1.0 V causes the AFM tip to penetrate the hydrated [AOT]− layer and slide over alkyl chains, increasing friction. At OCP and OCP-1.0 V, higher friction correlates with more pronounced ripples, attributed to the rougher templating [BMIm]+ boundary layer. Kinetic experiments show that switching from OCP-1.0 V to OCP+1.0 V achieves superlubricity within 15 s, enabling real-time friction control.

Measurements and predictions of seedling emergence forces

Quantifying seedling emergence pressure or forces (soil impedance to seedling) during the process of plant emergence is difficult in a practical setting. In this study, a mechanical seedling testing device was designed and calibrated to measure seedling emergence pressures experienced by conical or spherical mechanical seedling in soil with varying compaction levels. The data were analysed to generate regression models for predicting seedling emergence forces. Results showed a high correlation between the seedling emergence pressure and soil resistance. The resultant regression model produced a coefficient of determination (R2) of 0.99. After incorporating the morphological characteristics of soybean cotyledon and maize coleoptile into the model, the predicted seedling emergence forces increased with the soil compaction level. During the emergence process, average emergence force of the soybean seedlings was 11.8 N for the lowest compaction level and 28.5 N for the highest compaction level, and the corresponding values of the maize seedlings were 0.2 N and 0.6 N. In a non-compacted field plot, maize crop had a 95.4% emergence rate and soybean crop had 97.2%, whereas for a compacted plot, the corresponding emergence rates were decreased to 19.1% and 60.5%. Inferences made from the study provide information on the dynamics of soil-seedling interaction, which have important implications for managing soil compaction in crop production.

Healthy older adults generate transverse-plane momenta required for 90° turns while walking during the same phases of gait as used in straight-line gait

BackgroundGeneration and regulation (control) of linear and angular momentum is a challenge during turning while walking which may be exacerbated by age-related changes. In healthy older adults, little is known about how momentum is controlled during turns, especially within each phase of gait. Each phase of gait affords unique mechanical contexts to control momenta and regulate balance. In healthy young adults, we found that the transverse-plane linear and angular momenta generation strategies observed within specific phases of gait during straight-line gait were also used during turns. Therefore, in this study, we investigated whether healthy older adults shared similar momentum control strategies specific to each gait phase during straight-line gait and turns.MethodsNine healthy older adults completed straight-line gait and 90° leftward walking turns. We compared the change in transverse-plane whole-body linear and angular momentum across gait phases (left and right single and double support). We also compared the average leftward force and transverse-plane moment across gait phases.ResultsWe found that leftward linear momentum was generated most during right single support in straight-line gait and leftward turns. However, in contrast to straight-line gait, during leftward turns, average leftward force was applied across gait phases, with left single support generating significantly less leftward average force than other gait phases. Leftward angular momentum generation and average moment were greatest during left double support in both tasks. We observed some within-participant results that diverged from the group statistical findings, illustrating that although they are common, these momenta control strategies are not necessary.ConclusionsOlder adults generated transverse-plane linear and angular momentum during consistent phases of gait during straight-line gait and 90° turns, potentially indicating a shared control strategy. Understanding momentum control within each phase of gait can help design more specific targets in gait and balance training interventions.

Energy required to cut the soil with No.4 circumferential knives of the large rotor of the straight-through rotary ripper

Introduction. To solve the problem of the fast and high-quality road construction, when economic facilities and settlements are located at a considerable distance from each other, cannot be solved without the use of a complex of continuous units. The continuous ditch forming unit and the tunneling unit contain straight-through rotary rippers. Insufficient theoretical studies in this area do not enable to calculate the interaction of the elements of a direct-flow rotary ripper with the soil. Therefore, there is a need for theoretical studies to determine the energy parameters of the large rotor, in particular, that which is necessary for cutting the soil with the No.4 circumferential knives of the large rotor.The research method. The methods for calculating the required energy inputs: to separate the reservoir from the soil mass; separation of the reservoir into fragments; creating a gap in the soil mass; deformation of a part of the soil mass; overcoming the friction of the ground on the edge of the blade; overcoming the soil pressure on the front surface; movement of the soil by the front surface; overcoming the friction of the ground on the front surface have been developed.Results. On the basis of the developed methods, the parameter calculations were made. From the plane models and the spatial model of the forces of interaction with the soil of the circumferential knives No.4 of the large rotor, resultant forces, their components, normal forces were revealed. The force of friction of the soil on the edge of the blade and the front surface of No4 circumferential knives was calculated. The volumetric energy required for cutting with No.4 circumferential knives when mining one cubic meter of soil with a straight-through rotary ripper is calculated.Conclusion. The energy required to drive the circumferential knife includes separating the seam from the soil mass; separation of the reservoir into fragments; creating a gap in the soil mass; deformation of a part of the soil mass; overcoming the friction of the ground on the edge of the blade; overcoming the soil pressure on the front surface; movement of the soil by the front surface; overcoming the friction of the ground on the front surface. As a result of the calculations, the total energy required for cutting with No.4 circumferential knives, when mining one cubic meter of soil with a straight-through rotary ripper, was 9110 joules.

On the application of RHT model and SPG algorithm for the analysis of rock cutting process

The linear cutting process in rock poses challenges for verification in field experiments, laboratory investigations, or numerical simulations. This study aims to analyze the rock cutting process and disc cutter force estimation when using linear cutting mode. Three-dimensional numerical simulations using the explicit dynamic finite element method (LS-DYNA software) are conducted to characterize the cutting process. In this regard, two computational algorithms (Lagrangian and Smoothed Particle Hydrodynamics (SPH)) and two material models (Johnson-Holmquist Concrete (JHC) and Riedel-Hiermaier-Thoma (RHT)) are compared, with SPH and RHT identified as more suitable for rock cutting simulation. The results of comparative analyses show that the Lagrangian computational algorithm is highly dependent on the erosion value, hence this method is not suitable for the simulation of the rock-cutting process. Comparing to the RHT material constitutive model, the Johnson-Holmquist model does not well model the post-failure softening strain behavior, which leads to a reduction in the width of the failure area. The comparative analyses also show that the normal and rolling forces predicted by the JHC model are well over 30% higher than the actual experimental results, while the RHT model shows a good agreement between the predictions and the actual results. Overall, the RHT material model with the use of the SPH computational algorithm shows a very good combination in rock cutting process simulation.

How to identify earth pressures on in-service tunnel linings: Insights from Bayesian inversion to address non-uniqueness

Identifying earth pressures on in-service transportation tunnel linings is essential for their health monitoring and performance prediction, particularly in structures that exhibit poor performance. Due to the high costs associated with pressure gauges, pressure inversion based on easily observed structural responses, such as deformations, is preferred. A significant challenge lies in the non-uniqueness of inversion results, where various pressures can yield similar structural responses. Existing approaches often overlook detailed discussions on this critical issue. In addressing this gap, this study introduces a Bayesian approach. The proposed statistical framework effectively quantifies the uncertainty induced by non-uniqueness. Further analysis identifies the uniform component in distributed pressures as the primary source of non-uniqueness. Insights into mitigation strategies are provided, including increasing the quantity of deformation data or incorporating an observation of internal normal force within the tunnel lining — the latter proving to be notably more effective. A practical application in a numerical case study demonstrates the effectiveness of this approach. In addition, our investigation recommends maintaining deformation measurement accuracy within the range of [–1, 1] mm to ensure satisfactory outcomes. Finally, deficiencies and potential future extensions of this approach are discussed.

Research on the migration law of aggregate particles in the compaction process of asphalt mixture based on discrete element method

Asphalt mixture compaction is among the key technologies in asphalt pavement construction, but the effect of asphalt mixture mixing quality on mixture compaction performance is still unclear. This research aimed to develop an asphalt mixture compaction model by discrete element simulation and verify it by compaction degree. Asphalt mixture compaction process was simulated and the effect of asphalt mixture workability on the stress, migration law and void distribution properties of aggregate particles during compaction process was investigated. The obtained results showed that the developed asphalt mixture compaction model was reasonable and correct. The more uniform the asphalt mixture is mixed, the smaller the average force on the aggregates, the aggregate particle migration velocity, and the aggregate particle displacement during the compaction of the asphalt mixture. Under the same conditions, increasing the mixing temperature from 140℃ to 180℃ increased the average velocity of the aggregates in the asphalt mixture by 92 %. It also decreased the voids in the compacted mixture specimens. At the same time, under the action of edge effect, void distribution at the center of compacted specimen was small, void distribution around the specimen was high, and void distribution along specimen compaction force direction was also high.

Early Bolt Loosening Detection Method Based on Digital Image Correlation.

Bolt loosening can significantly impact the accuracy, stability, and safety of equipment. The detection of bolt loosening in a timely manner is crucial for ensuring the safety, reliability, performance, and service life of equipment, structures, and systems. Various methods exist for detecting bolt loosening, such as strain gauges and ultrasonic waves. However, these technologies have some limitations that impede their widespread application. In this paper, for the high-pressure pipe manifolds that may experience leakage accidents due to the loosening of bolts, an early bolt loosening detection method based on digital image correlation is proposed. Initially, a model is established through tensile tests to relate the average strain on the side of the bolt head to the axial force. Subsequently, an industrial camera captures images of bolts with random speckles under operational conditions. Using digital image correlation technology, the average strain in a specific region on the side of the bolt head is calculated. By integrating the average strain into the established relationship model between the average strain and axial force, the axial force of the bolt under operational conditions can be predicted, enabling the early assessment of bolt loosening. The findings show that the average strain on the side of the bolt head increases proportionally with the axial force, indicating a strong linear relationship. This method enables accurate prediction of the bolt's axial force, offering a new approach for identifying the early loosening of bolts in high-pressure manifolds and monitoring structural health.

Atomistic simulations of the thinning process of tantalum/copper heterostructure in wafer containing through silicon via

Through silicon via (TSV) interconnect structure plays an essential role in high-density 3-D integration. The tantalum (Ta)/copper (Cu) heterointerface is one of the significant interfaces in the wafer containing TSV. Molecular dynamics simulations are utilized to study the interface evolution and thinning mechanism of Ta/Cu heterostructure at different grinding depths during the thinning process. It is found that atomic diffusion, amorphization, phase transition, and micro-defects are typical characteristics of interfacial evolution, which become more pronounced at deeper grinding depths. The extrusion of the hard Ta layer on the soft Cu layer leads to an early appearance of interface defects, including dislocations and stacking faults. It is revealed that the large lattice mismatch of the constituent layers and obstruction of the heterointerface result in obvious stress concentration. The reduced tangential and normal forces at the interface are ascribed to atomic structure evolution and intrinsic properties of the heterostructure. Additionally, the heterointerface can hinder heat conduction between the Ta and Cu layers. These findings can provide valuable guidance for the manufacture of the wafer containing TSV.

Molecular dynamics study of the groove-forming mechanism of mechanically scratched grating multilayer aluminum films

For a long time, the forming quality of large area diffraction gratings is restricted by the one-time coating quality and uniformity of large thickness and large area aluminum films. Large thickness coatings, low accuracy of large depth grooves and diamond tool wear problems were the main reasons for the failure of the test to inscribe large area diffraction gratings. Therefore, the use of layered coating process can effectively ensure the uniformity and consistency of large-area and large-thickness grating blanks coated with aluminum film, and improve the high precision of large depth diffraction grating slot type. In order to reveal the mechanism of the groove-forming process of multilayer aluminum films, the microstructure and mechanical properties of different aluminum films were observed. In this article, the removal behavior and mechanism of nanomechanically scratched multilayer aluminum film materials are investigated using a molecular dynamics approach, and the characteristics of multilayer aluminum films scratched into grooves are analyzed in terms of surface morphology, scratching force, structural evolution, dislocation distribution, von Mises stress and shear strain. The results indicate that in the scratching simulation process, multilayer aluminum film has a higher number of removed atoms and a larger atomic displacement compared to single layer aluminum film, which is conducive to precise shape control of the groove. The average tangential force and normal force of multilayer aluminum film show a decreasing trend compared to single layer aluminum film, which helps to scratch grooves and reduce tool wear. The total length of the dislocation lines of the multilayer aluminum film is large, and the distribution area is large, which improves the precision of scratching the grooves. Therefore, an appropriate increase in the number of aluminum film layers has a precise control effect on the groove shape. This study has certain reference significance for analyzing the complex grooving deformation law of grating aluminum film, improving the diffraction efficiency of grating aluminum film, and further improving the manufacturing process of grating aluminum film.

Development and application of magnetic tentacles array for sensing tiny forces

Modeled after rodent whiskers, we fabricated magnetic tentacles sensing array that can sense tiny force. The magnetic tentacles sensing array consists of three parts: magnetic tentacles that sense stimuli from the external environment, a silicone substrate that covers the magnetic sensing elements and holds the magnetic tentacles in place, and magnetic sensing elements that collect signals from changes in the magnetic field. The performance test of the magnetic tentacles sensing unit shows that the unit can realize tiny normal force detection at the mN level, with the force measurement range of 0–55 mN and the maximum sensitivity of 14.8 mV/mN. Dynamic test results show that the magnetic tentacle sensor has good stability over 2000 cycles. Nine tentacles sensing units are assembled into a tentacles sensing array which has 12 magnetic tentacles, and the total size of the array is 29 mm × 29 mm × 6 mm. The sensing array can sensitively sense the change of tiny force. This magnetic tentacles sensing array enables the recognition of objects for grasping and the tracking of the center of gravity of a ping pong ball.

Estimation of Normal Ground Reaction Forces in Multiple Treadmill Skiing Movements Using IMU Sensors With Optimized Locations

Estimation of Normal Ground Reaction Forces in Multiple Treadmill Skiing Movements Using IMU Sensors With Optimized Locations

Vibration suppression of series elastic actuator used for robotic grinding based on reconstructed hybrid optimized input shaper

Vibration suppression of the series elastic actuator (SEA) used for robotic compliant grinding is significant for guaranteeing force control accuracy and stability, which is important for material removal accuracy and surface quality improvement. This paper establishes a multi-feedforward control system to achieve vibration suppression for the SEA. The hybrid optimized input shaper (HOIS), instruction reconstructor, and nonlinear friction compensation model are seamlessly integrated into the multi-feedforward control method. Combination optimization principles are employed to formulate the HOIS, ensuring selectable performances on vibration suppression, response speed, and model stability when addressing the residual vibration caused by elastic elements. Base on the inherent delay characteristics of the shaper, a head/tail compression and intermediate shift instruction reconstruction (CSIR) method is introduced to address the tracking error induced by the time-delay of the shaper. Additionally, the friction compensator is established based on the Stribeck model and integrated into the feedforward control system to mitigate the vibration caused by the low-speed viscous friction. The effectiveness of the proposed method is verified by experimental tests. Results show that the HOIS has rich optional performance and can effectively suppress vibration. The tracking error caused by the shaper is effectively mitigated through the reconstruction of instructions. Grinding tests on curved parts are conducted on the robotic grinding system with SEA used as the force-control system. Compared with the benchmark method, the developed reconstructed hybrid optimized input shaper reduces the average force tracking error, the average absolute grinding depth error, and average roughness by 26.6 %, 22.5 %, and 21.5 % respectively. At the natural frequency of the grinding system, the amplitude of the frequency spectrum with the developed multi-feedforward method decreases by 48.13 %.

Design optimization of a snowboard performing an ollie

The ollie, a fundamental manoeuver in snowboarding, serves as a basis for various tricks requiring high altitude and extended airtime. The maximum ollie height depends on the snowboard’s geometry and structural characteristics. In this study, the influence of these properties is investigated with a flexible multibody dynamics simulation, where the snowboard is modeled by geometrically non-linear finite elements, snow contact is considered by a penetration depth and velocity proportional normal force and ollie motion is achieved by imposing measured loads to the bindings. To maximize the height, a genetic optimization procedure is presented, which yields substantial improvements. Optimizing the camber line and the bending stiffness distribution yields enhanced performance. Less damping as well as lighter boards lead to higher jumps, no noteworthy correlation between axial stiffness and damping distribution and jump height was found, and the strain energy stored in the board during takeoff is a useful indicator for estimating ollie heights. Nevertheless, further investigations should take a more advanced and realistic rider interaction into account.

Vibration-induced wall–bubble interactions under zero-gravity conditions

This work is devoted to a theoretical and numerical study of the dynamics of a two-phase system vapour bubble in equilibrium with its liquid phase under translational vibrations in the absence of gravity. The bubble is initially located in the container centre. The liquid and vapour phases are considered as viscous and incompressible. Analysis focuses on the vibrational conditions used in experiments with the two-phase system SF $_6$ in the MIR space station and with the two-phase system para-Hydrogen (p-H $_2$ ) under magnetic compensation of Earth's gravity. These conditions correspond to small-amplitude high-frequency vibrations. Under vibrations, additionally to the forced oscillations, an average displacement of the bubble to the wall is observed due to an average vibrational attraction force related to the Bernoulli effect. Vibrational conditions for SF $_6$ correspond to much smaller average vibrational force (weak vibrations) than for p-H $_2$ (strong vibrations). For weak vibrations, the role of the initial vibration phase is crucial. The difference in the behaviour at different initial phases is explained using a simple mechanical model. For strong vibrations, the average displacement to the wall stops when the bubble reaches a quasi-equilibrium position where the resulting average force is zero. At large vibration velocity amplitudes this position is near the wall where the bubble performs only forced oscillations. At moderate vibration velocity amplitudes the bubble average displacement stops at a finite distance from the wall, then large-scale damped oscillations around this position accompanied by forced oscillations are observed. Bubble shape oscillations and the parametric resonance of forced oscillations are also studied.

Multiphysics simulation and design framework for developing a vision-based tactile sensor with force estimation and slip detection capabilities

Recent achievements in the field of tactile sensing has enhanced the dexterity of robots interacting with their environments. Superior to other transduction mechanisms, vision-based tactile sensing enables high-resolution sensing of the contact surface. Accordingly, many vision-based tactile sensors have been introduced in recent years, all of which are designed and fabricated based on a trial-and-error approach with limited prior system modeling and simulation. In this study, we introduce a detailed framework for the development of a vision-based tactile sensor with markers motion mechanism. We start with the design and coupled simulation of the mechanical and optical subsystems followed by fabrication, testing, and validation of the proposed sensor. An uncertainty analysis is carried out during the design stage where various errors are propagated to determine the expected sensor accuracy. The simulated sensor showed a maximum error of 0.15 newtons with the error for the camera distance to the rigid membrane having the highest contribution. After fabrication of the sensor, it is observed that there is a very good agreement between simulation and experimental results. The sensor was tested for sensing tangential forces (up to slip) along two directions and normal force (up to 5 newtons) at 30 Hz rate with measurement errors (95 % confidence interval) of 0.39 newton, 0.11 newton, and 0.12 newton, respectively. The sensor detected the slip in 97 % of the tests with an average latency of 10 frames.

Modeling of the Particle Abrasion Process and a Discrete Element Method Study of Its Shape Effect.

This study introduces a novel method for particle abrasion derived from fundamental natural phenomena and mechanical principles, allowing precise control over the degree of abrasion and more accurately mimicking natural processes. The method's validity is confirmed using a specific shape index. Through conventional triaxial tests, the mechanical behavior of granular aggregates with varying degrees of abrasion was analyzed. The findings indicate that increased particle abrasion leads to a decrease in the average coordination number and sliding amount, while the rotation amount increases. This suggests an inverse relationship between the degree of abrasion and the structural stability and interlocking of the particle aggregate. The fabric anisotropy of the system is mainly attributed to the anisotropy of the contact normal force, which decreases as particle abrasion increases. The partial stress ratio of the particle system is influenced by fabric anisotropy and remains independent of particle shape. Additionally, the internal friction angle may be overestimated in conventional triaxial tests.