Direction Of Contact Force Research Articles

Investigation on the rheological properties of dense granular inertial flow based on the contact features of four dual-partitioned subnetworks

The rheological properties of shear granular system under inertial flow regimes are investigated by fully considering both strong/weak and sliding/non-sliding contact features of four dual-partitioned subnetworks. Discrete element simulation results reveal that strong non-sliding subnetwork plays a dominant role in bearing external load. For strong sliding and weak non-sliding subnetworks, their anisotropy principal directions of normal contact forces undergo dynamic deflections during evolution, resulting in the lateral support of microstructures being primarily borne by unstable sliding contacts. Although the subnetworks display substantial variations in stability, their strong spatial correlation makes these variations complement each other, forming an intrinsic coupling relationship.

Micro‐mechanism of stress‐dilatancy anisotropy in granular materials: Affine and nonaffine deformation

AbstractThe stress‐induced dilatancy anisotropy is an important kinematic response in granular materials and is very complex due to the stochastic motion of particles. In this study, the local stress‐dilatancy relationship is investigated referring to the local contact force and relative displacement in a certain contact direction. The micromechanism of this anisotropy is investigated from the view of affine and nonaffine approaches based on DEM simulation. Numerical results indicate that the local nonaffine dilatancy/contraction tendency is opposite with that of local affine deformation in macroscopic compression and extension direction, which mainly stems from the counteraction effect between the normal components of affine and nonaffine displacements. The local stress‐dilatancy of affine and nonaffine components is linear and orientation‐dependent, which results in the nonlinear character of macroscopic stress‐dilatancy. By establishing an analytical relation of stress‐dilatancy, the local affine/nonaffine dilatancy is decomposed into the component of stress‐induced dilatancy synchronized with the local stress anisotropy; and the component of stress‐induced dilatancy asynchronized with the local stress anisotropy. The former is related to the unchanged isotropic microstructure, and the latter attributes to the anisotropic microstructure. Besides, the contribution of nonsliding contacts to nonaffine dilatancy is larger than that of sliding contacts even for the case of relatively higher sliding ratio, which indicates that the heterogeneous deformation attributes not only to the friction dissipation, but to the blocked energy at micro contacts in granular materials.

A 2D energy-conserving contact model for the combined finite-discrete element method (FDEM)

The combined finite-discrete element method (FDEM) has been widely used to simulate the progressive fracturing of brittle materials from continua to discontinua. However, due to the relatively simple definition of contact potential, the contact interaction algorithm utilized in the original FDEM is element size-dependent. As a result, a non-smooth and fluctuating contact force direction can occur when a contact point moves from one area of an element to another, and the contact interaction algorithm may fail to accurately evaluate the tangential contact force. To circumvent these limitations, we adopt an energy-conserving model developed recently to calculate the contact force in 2D FDEM, in which the magnitude and direction of contact force can be directly determined by geometrical features. A suite of numerical benchmarks is conducted to validate the effectiveness and robustness of the proposed method for contact interaction processing between discrete bodies, and the advantages of the proposed method are also demonstrated. As an application, two typical examples are performed to systematically explore the potential of the proposed approach for evaluating the stability of rock mass and rock slope. The proposed contact model may help enhance the applicability and accuracy of FDEM for rock fracturing simulation.

Hip Contact Forces During Sprinting in Femoroacetabular Impingement Syndrome.

Sprinting often provokes hip pain in individuals with femoroacetabular impingement syndrome (FAIS). Asphericity of the femoral head-neck junction (cam morphology) characteristic of FAIS can increase the risk of anterior-superior acetabular cartilage damage. This study aimed to 1) compare hip contact forces (magnitude and direction) during sprinting between individuals with FAIS, asymptomatic cam morphology (CAM), and controls without cam morphology, and 2) identify the phases of sprinting with high levels of anteriorly directed hip contact forces. Forty-six recreationally active individuals with comparable levels of physical activity were divided into three groups (FAIS, 14; CAM, 15; control, 17) based on their history of hip/groin pain, results of clinical impingement tests, and presence of cam morphology (alpha angle >55°). Three-dimensional marker trajectories, ground reaction forces, and electromyograms from 12 lower-limb muscles were recorded during 10-m overground sprinting trials. A linearly scaled electromyogram-informed neuromusculoskeletal model was used to calculate hip contact force magnitude (resultant, anterior-posterior, inferior-superior, medio-lateral) and angle (sagittal and frontal planes). Between-group comparisons were made using two-sample t -tests via statistical parametric mapping ( P < 0.05). No significant differences in magnitude or direction of hip contact forces were observed between FAIS and CAM or between FAIS and control groups during any phase of the sprint cycle. The highest anteriorly directed hip contact forces were observed during the initial swing phase of the sprint cycle. Hip contact forces during sprinting do not differentiate recreationally active individuals with FAIS from asymptomatic individuals with and without cam morphology. Hip loading during early swing, where peak anterior loading occurs, may be a potential mechanism for cartilage damage during sprinting-related sports in individuals with FAIS and/or asymptomatic cam morphology.

Robust Multilegged Walking Robots for Interactions With Different Terrains

Abstract This paper explores the kinematic synthesis, design, and pilot experimental testing of a six-legged walking robotic platform able to traverse through different terrains. We aim to develop a structured approach to designing the limb morphology using a relaxed kinematic task with incorporated conditions on foot-environments interaction, specifically contact force direction and curvature constraints, related to maintaining contact. The design approach builds up incrementally starting with studying the basic human leg walking trajectory and then defining a “relaxed” kinematic task. The “relaxed” kinematic task consists only of two contact locations (toe-off and heel-strike) with higher-order motion task specifications compatible with foot-terrain(s) contact and curvature constraints in the vicinity of the two contacts. As the next step, an eight-bar leg image is created based on the “relaxed” kinematic task and incorporated within a six-legged walking robot. Pilot experimental tests explore if the proposed approach results in an adaptable behavior which allows the platform to incorporate different walking foot trajectories and gait styles coupled to each environment. The results suggest that the proposed “relaxed” higher-order motion task combined with the leg morphological properties and feet material allowed the platform to walk stably on the different terrains. Here we would like to note that one of the main advantages of the proposed method in comparison with other existing walking platforms is that the proposed robotic platform has carefully designed limb morphology with incorporated conditions on foot-environment interaction. Additionally, while most of the existing multilegged platforms incorporate one actuator per leg, or per joint, our goal is to explore the possibility of using a single actuator to drive all six legs of the platform. This is a critical step which opens the door for the development of future transformative technology that is largely independent of human control and able to learn about the environment through their own sensory systems.

Study on rock mass failure characteristics of double-hole delayed blasting in interbedding based on particle expansion algorithm

The existence of the interface between soft and hard rock often makes it difficult to control the blasting effect. Studying the influence of structural plane and delayed initiation time on rock blasting characteristics can make the blasting effect more controllable. In this paper, by using the Particle Flow Code (PFC2D) and particle expansion algorithm, the double-hole delayed blasting experiments of soft-hard rock are carried out, and the results are analyzed from the perspectives of fragment gradation, micro contact force and energy field. Results show that: 1) When blasting in hard rock, if the distance between structural plane and blasthole is about two times the radius of crushing area, it will easier to form large area fragments, and the fragments tend to be crushed with the increase of the distance. When the distance is 2–4 times the radius of crushing area, with the increase of delay time, the overall fragment area value increases first and then decreases, and reaches the maximum when the delay time is 4 ms. 2) When the structural plane existing in the rock mass, the delayed initiation will make the contact force become relatively uniform within a certain range. The main direction of contact force will appear in the uneven state of contact force generated by simultaneous or delayed initiation, which is close to the parallel or vertical direction of blasthole connection. 3) When blasting in hard rock, if the distance between the structural plane and the blasthole is greater than about two times the radius of the crushing area, compared with simultaneous blasting, the peak kinetic energy and peak strain energy of delayed blasting will be reduced by about 33% and 46% respectively.

Effect of Alteration in Hip Joint Alignment following Total Hip Arthroplasty on Hip Joint Contact Force during Gait

Purpose Investigation of the relationship between changes in hip-joint center and hip loading pre- and post- total hip arthroplasty (THA) is important in evaluating the effect of surgery on motor function. However, few longitudinal studies comparing pre- and post-THA have been reported. The purpose of this study was to determine the effect of changes in hip-joint center pre- and post-THA on the magnitude and direction of hip-joint contact force during the gait cycle, using a patient-specific musculoskeletal model. Methods The simulation program AnyBody was used to create musculoskeletal models incorporating patient specific hip-joint shape and hip-joint center position for 17 patients. The relationship between the displacement distance of the hip-joint center and the amount of change in hip-joint contact force was examined by correlation analysis. Results A decrease in the medial force (p ≤ 0.049) and an increase in the anterior force (p ≤ 0.001) acting on the hip joint were observed during gait post-THA compared to pre-THA. Mediolateral displacement of the hip-joint center post-THA compared to pre-THA was significantly positively correlated with the difference in anterior hip-joint contact force, and negatively to hip-joint medial contact force. Conclusions Longitudinal observations revealed the effects of change in hip-joint center position induced by THA on the hip-joint contact force during gait. Therefore, the change of hip-joint center position during THA can be an important factor for estimating the improvement of motor function following THA.

Evaluation of asphalt mixture micromechanical behavior evolution in the failure process based on Discrete Element Method

Asphalt mixture was a granular material, and traditional mechanical testing methods were difficult to reveal the failure mechanism. To evaluate the micromechanical behavior of asphalt mixture in the failure process, the DEM (Discrete Element Method) model of the uniaxial compression test was established. The virtual aggregate particle database with real morphology properties was constructed, and the linear parallel bond model was used to simulate the adhesion of asphalt. In the DEM model of the asphalt mixture failure process, the movement of asphalt mortar and coarse aggregate was evaluated, and the Discrete Fracture Network (DFN) was proposed to represent the microcrack. Finally, the three-dimensional spherical coordinate histogram was used to analyze the evolution of magnitude and direction of the coarse aggregate skeleton contact force. It found that the movement of coarse aggregate was less than that of asphalt mortar in the process of the uniaxial compression test, and the coarse aggregate movement was affected by its particle size and location. The result also found that although the adhesive and cohesion failure could occur at the same time, the adhesive failure was less than cohesion failure in the early stage of the uniaxial compression test, and the aggregate with larger particle size could reduce the generation of adhesive failure. Compared with the magnitude of coarse aggregate skeleton contact force, the change of direction was the main reason for a decrease in stress when the asphalt mixture specimen exceeded the peak strength.

A dynamic weaving simulator for filament-level 3D woven fabric modelling

A dynamic textile weaving simulator is established to connect weaving actions to fabric patterns and microstructures. It utilizes the Digital Element Approach (DEA) under the framework of the software package Digital Fabric and Composite Analyser (DFCA). The key components of a Jacquard loom are explicitly modelled utilising the ‘hole/no hole’ principle. Yarn interlacing motion is guided by weaving matrix specified by steps. Shedding, weft insertion, beat-up, and take-up actions are modelled and explained. The inter-fibre contact force, fibre forces (tensile, shear, and bending), and boundary conditions in the weft direction are considered. The weaving process of five cells in the warp direction of a 10-layer 3D orthogonal woven fabric is simulated at the filament level to derive for its microstructure. The results show that the fabric microstructure continues to change after being woven, and the thickness and length of each individual cell decrease with further weaving steps. The microstructures of newly woven cells converge after the weaving of two further cells in the lengthwise direction. The microstructure of the second cell closely matches that of an actual weaved fabric, as evaluated by microscopy images. Penetration occurs between adjacent weft yarns in the same column, which fundamentally changes their microstructure, composition, and material properties. Parametric studies show that the ratio of binder to warp yarn tension determines the fabric thickness. Increases in the take-up length and binder yarn tension lead to a decrease and increase in the reed tension, respectively. This work provides valuable insights into fabric design and manufacture instruction.

GTac: A Biomimetic Tactile Sensor With Skin-Like Heterogeneous Force Feedback for Robots

The tactile sensing capabilities of human hands are essential in daily activities. Simultaneously perceiving normal and shear forces via the mechanoreceptors integrated into the hands allow us humans to achieve daily tasks like grasping delicate objects. In this paper, we design and fabricate a biomimetic tactile sensor with skin-like heterogeneity that perceives normal and shear contact forces simultaneously. It mimics the multilayered structure of mechanoreceptors in human skin by combining an extrinsic layer (piezoresistive sensors) and an intrinsic layer (a Hall sensor) so that it can perform estimation of contact force directions, locations, and joint-level torque. By integrating our sensors, a robotic gripper can obtain contact force feedback at the fingertips; accordingly, robots can perform challenging tasks, such as using tweezers and grasping eggs. This insightful sensor design can be customized and applied in different areas of robotics and provide them with heterogeneous force sensing, potentially supporting robotics in acquiring skin-like tactile feedback.

Electromyography measurements of the deep hip muscles do not improve estimates of hip contact force

The deep hip muscles are often omitted in studies investigating hip contact forces using neuromusculoskeletal modelling methods. However, recent evidence indicates the deep hip muscles have potential to change the direction of hip contact force and could have relevance for hip contact loading estimates. Further, it is not known whether deep hip muscle excitation patterns can be accurately estimated using neuromusculoskeletal modelling or require measurement (through invasive and time-consuming methods) to inform models used to estimate hip contact forces. We calculated hip contact forces during walking, squatting, and squat-jumping for 17 participants using electromyography (EMG)-informed neuromusculoskeletal modelling with (informed) and without (synthesized) intramuscular EMG for the deep hip muscles (piriformis, obturator internus, quadratus femoris). Hip contact force magnitude and direction, calculated as the angle between hip contact force and vector from femoral head to acetabular center, were compared between configurations using a paired t-test deployed through statistical parametric mapping (P < 0.05). Additionally, root mean square error, correlation coefficients (R2), and timing accuracy between measured and modelled deep hip muscle excitation patterns were computed. No significant between-configuration differences in hip contact force magnitude or direction were found for any task. However, the synthesized method poorly predicted (R2-range 0.02–0.3) deep hip muscle excitation patterns for all tasks. Consequently, intramuscular EMG of the deep hip muscles may be unnecessary when estimating hip contact force magnitude or direction using EMG-informed neuromusculoskeletal modelling, though is likely essential for investigations of deep hip muscle function.

The Role of Foam in Improving the Workability of Sand: Insights from DEM

Foam as a soil conditioner can transform the mechanical properties of the excavated natural muck and lubricate the interface between the cutting tools and muck, thus reducing the tools’ wear and promoting the efficiency of earth pressure balance (EPB) shield tunneling. This paper aims to explore the meso-mechanism of foam in improving the workability of sand by combining discrete element modeling (DEM) with experimental investigations of slump tests. A “sand-foam” mixture DEM model was generated by simplifying the sand grains and foam as individual particles with different properties. The particle-scale simulated parameters were calibrated based on a series of experimental observations. The effects of foam on the inter-particle contact distribution and the evolution of contact forces during the slumping process were investigated in detail through numerical modeling. It was found that injecting foam into sand specimens could increase the coordination number and the contact number around sand grains. Although the force transmission pattern changes from “sand-sand” into the coexistence of “sand-foam”, “sand-sand” and “foam-foam” contacts, the magnitude of contact forces transferred by foam particles is significantly lower than that by sand particles. The presence of foam reduces contact-scale frictional strength and thus reduces the stability of the microstructures of sand. In addition, the normal direction of inter-particle contact force deflects from the vertical to the horizontal and the magnitude of contact force decreases significantly with the influence of foam.

Study on the influence of different discrete forms of DDA block on mechanical properties of coarse granular material

In the triaxial compression test of soil engineering, particle breakage may occur under the double action of axial and lateral loads. So, for the DDA simulation, the internal discretization of DDA block should be carried out at first. However, different discretization may affect the final simulation results. To solve this problem, the DDA numerical models based on triangular discretization, Voronoi discretization and no discretization are established to carry out the triaxial test simulation of coarse granular material, and the influence of different discretization of DDA block on mechanical properties of coarse granular materials was compared. An improved DDA was used to simulate the triaxial tests under different confining pressures, The numerical results show that the deviatoric stress-strain curves of the three discrete forms become steeper and the peak strength also increases with the increase of confining pressure. Under the same confining pressure, the deviatoric stress-strain curve with no discretization is the steepest and the peak strength is also the largest. Although deviatoric stress-strain curve of the triangular discretization is gentler, its peak strength is closer to that with no discretization compared with the Voronoi discretization. The triangular discretization model gradually changes from contraction to dilation in the loading process, and the higher the confining pressure is, the more obvious the contraction is. At the same time, the direction of contact force gradually changes from the initial minor principal stress direction to the major principal stress direction, forming an obvious force chain, and the final particle breakage mostly occurs in an ‘X’ shaped region. The developed DDA method can accurately reflect the evolution of mechanical properties of coarse granular materials under various working conditions, and the research results can provide reference for the discrete form of blocks in similar simulation.

Bioinspired High-Degrees of Freedom Soft Robotic Glove for Restoring Versatile and Comfortable Manipulation.

The human hand is one of the most complex and compact grippers that has arisen as a product of natural genetic engineering; it is highly versatile, as it handles power and precision tasks. Since proper contact points and force directions are required to ensure versatility and secure a stable grip on an object, there must be a large workspace and controllable tip force directions for the digits. Although they are important, many individuals with neuromuscular diseases experience loss of these features. Thus, we propose a high-degree-of-freedom (DOF) soft robotic glove inspired by the anatomical features of human hands. The mechanism for adjusting the position and force direction of each tip is based on the structure of the extrinsic and intrinsic muscle-tendon units. The large thumb workspace was achieved by assisting opposition/reposition and flexion/extension to enable various grasping postures. A bidirectional actuation control mechanism with a cable-actuated agonist and an elastomer antagonist increased the assisted DOF and maintained compactness. The kinematic and kinetic performances of our device were evaluated by performing tests with eight stroke survivors. The thumb workspace increased by 43%, 207%, and 248% in the distal-proximal, dorsal-palmar, and radial-ulnar directions, respectively. The pinching shear force decreased by 54% and 45% for the nonthumb digits and thumb, respectively. These device-assisted improvements allowed objects to be stably grasped and manipulated in various postures. The novel device can assist individuals with impaired hand function to improve their grasping performance. Clinical Research Information Service (CRIS) Registration Number: KCT0004855.

Artificially innervated self-healing foams as synthetic piezo-impedance sensor skins

Human skin is a self-healing mechanosensory system that detects various mechanical contact forces efficiently through three-dimensional innervations. Here, we propose a biomimetic artificially innervated foam by embedding three-dimensional electrodes within a new low-modulus self-healing foam material. The foam material is synthesized from a one-step self-foaming process. By tuning the concentration of conductive metal particles in the foam at near-percolation, we demonstrate that it can operate as a piezo-impedance sensor in both piezoresistive and piezocapacitive sensing modes without the need for an encapsulation layer. The sensor is sensitive to an object’s contact force directions as well as to human proximity. Moreover, the foam material self-heals autonomously with immediate function restoration despite mechanical damage. It further recovers from mechanical bifurcations with gentle heating (70 °C). We anticipate that this material will be useful as damage robust human-machine interfaces.

Discrete Element Analysis of the Strength Anisotropy of Fiber-Reinforced Sands Subjected to Direct Shear Load

Soil reinforcement with natural or synthetic fibers enhances its mechanical behavior in various applications. Fiber-reinforced sands (FRS) can be relatively anisotropic because of the fiber self-weight and the compaction technique. However, the microscopic mechanisms underlying the anisotropy are still poorly understood. This study used a discrete element approach to analyze the microscopic mechanisms underlying the strength anisotropy of FRS due to fiber orientation. Analysis of contact networks revealed that the optimum fiber orientation angle is perpendicular to the main direction of strong contact force in direct shear testing. These fibers produced the largest increase in shear zone thickness, normal force around the fiber body, effective contact area, tensile force along fibers, and energy storage/dissipation. This study is valuable for further understanding of the mechanical behaviors of FRS.

Vibration mechanism analysis for cylindrical roller bearings with single/multi defects and compound faults

The generation of defects has a great influence on the vibration characteristic of roller bearings. Thus, it is very important to analyze the vibration mechanism of bearings with different kinds of defects by dynamic models which can make systematic descriptions of truly dynamic behavior. In this paper, dynamic models are developed based on the model proposed by Gupta to investigate the vibration mechanism of cylindrical roller bearings with localized defects. The inner raceway and rollers have five degrees of freedom (DOFs) in the model to better describe the complex dynamic behavior of bearings. Gyroscopic moment, centrifugal force and lubrication traction/slip between roller/raceway, roller/cage, cage/raceway are completely included. Moreover, modeling methods of single defect, multi-defects and compound faults are introduced with the consideration of additional deflection and the change of contact force direction caused by defects. The differential equations used to describe the motions of bearing components are solved by the fourth order Runge-Kutta-Fehlberg scheme with step-changing criterion. Vibration responses of bearings with single defect, multi-defects and compound faults are simulated by the models and analyzed in both time domain and frequency domain. Experiments have been carried out on bearing test rig. The validity of models built in the paper is proved by comparing the simulation results with experiments. In addition, fruitful vibration responses are discovered and proposed, which will provide strong theoretical supports for fault diagnosis of cylindrical roller bearings.

Experimental observations and dynamic modeling of vibration characteristics of a cylindrical roller bearing with roller defects

The better understanding of the vibration characteristics of a bearing with defects is crucial for the fault diagnosis of rolling element bearings (REBs). In the current paper, the vibration responses of a cylindrical roller bearing when a roller defect goes around outer and inner races are investigated. Firstly, an experiment was carried out and the experimental results are observed to discuss the multiple impulses which are generated when a roller defect goes around a race. Then a dynamic model is proposed for cylindrical roller bearings with roller defects. In the proposed dynamic model, the relative slippage, the finite size of a roller, and the change of contact force direction as a roller defect impacts with a race are all considered. Based on the proposed dynamic model, the vibration responses of the bearing when a roller defect goes around the outer and the inner races are investigated. The results show that, besides the impulses generated when the roller edges roll through the line connecting the roller and race centers, other impulses can also be generated due to the impact between the roller defect and the race. Furthermore, the roller defect impacts both with the outer race and the inner race as it rotates in the loaded zone, while the roller defect only impacts with the outer race in the unloaded zone for the radially loaded cylindrical roller bearing. In addition, the interaction time between the roller defect and the inner race is generally longer than that between the roller defect and the outer race.

An Electronic Force Sensor for Medical Jet Injection

In medical jet injection, a narrow fluid drug stream is propelled at high velocity into skin without a needle. Previous studies have shown that the volume delivered is highly dependent on a number of factors. This paper details the development of an electronic force sensor for medical jet injection and shows that the normal contact force exerted on the tissue by the nozzle is an additional factor affecting volume delivered. Using this sensor, we measure the forces at the nozzle tip in the normal direction with a sensitivity of 18 μN, calibrated over a range from 1 N to 8 N with a mean absolute error of 8 mN, and a maximum overload of 300 N. We further measure forces at the nozzle tip in the lateral direction with a sensitivity of 8 μN, calibrated over a range from 0.1 N to 7 N, with a mean absolute error of 101 mN for lateral contact force magnitude and 1.60 deg for lateral contact force direction. Experimental validation confirms that the force sensor does not adversely affect the accuracy and precision of ejected volume from the jet injector. We use this setup to examine the effect of normal contact force on volume delivered into postmortem porcine tissue. Experimental results demonstrate that volume delivered with normal contact force between 4 N and 8 N is significantly more accurate and precise compared to volume delivered with normal contact force between 0 N and 3.9 N.

Wearable Finger Tracking and Cutaneous Haptic Interface with Soft Sensors for Multi-Fingered Virtual Manipulation

Multi-Fingered haptics is imperative for truly immersive virtual reality experience, as many real-world tasks involve finger manipulation. One of the key lacking aspect for this is the absence of technologically and economically viable wearable haptic interfaces that can simultaneously track the finger/hand motions and display multi-degree-of-freedom (DOF) contact forces. In this paper, we propose a novel wearable cutaneous haptic interface (WCHI), which consists of 1) finger tracking modules (FTMs) to estimate complex multi-DOF finger and hand motion; and 2) cutaneous haptic modules (CHMs) to convey three-DOF contact force at the finger-tip. By opportunistically utilizing such different types of sensors as inertial measurement units, force sensitive resistor sensors, and soft sensors, the WCHI can track complex anatomically consistent multi-DOF finger motion while avoiding FTM-CHM electromagnetic interference possibly stemming from their collocation in the small form-factor interface; while also providing the direction and magnitude of three-DOF finger-tip contact force, the feedback of which can significantly enhance the precision of contact force generation against variability among users via their closed-loop control. Human subject study is performed with a virtual peg insertion task to show the importance of both the multi-DOF finger tracking and the three-DOF cutaneous haptic feedback for dexterous manipulation in virtual environment.