Evaluation Of Contact Forces Research Articles

Combining engineering and wood science for the conservation of artworks: Hygro-mechanical study of Mona Lisa’s wooden support

Since 2004, the wooden support of Mona Lisa has been studied by an international research team formed by specialists of wood science and optical measurements, interacting closely with curators and restorers, to evaluate the climatic specifications adopted for the then new climate-controlled display case, assess the risk of propagation of a historical crack affecting the Panel, suggest possible improvements to the Panel’s framing, and improve the technological aspects of the current monitoring procedure. The study has been carried out mainly by direct observation and measurements during the yearly opening of the display case, by continuous monitoring of the Panel’s mechanical behaviour and by developing a predictive numerical model based on the finite element method. This paper deals with the following topics: (i) a technological description of the Panel and of its framing, (ii) the non-invasive measurement equipment and monitoring methods developed, (iii) the simulations of the hygro-mechanical behaviour, (iv) the most significant results obtained so far, including the derivation of the elastic parameters of the wooden Panel, the description of the contact zones between Panel and framing, the evaluation of contact forces and possible actions for improving the framing. The model implementation evidences the correspondence between principal strains in the Panel and craquelure patterns in the paint layers, and allows assessing the crack propagation risk.

Resultant Normal Contact Force-Based Contact Friction Model for the Combined Finite-Discrete Element Method and Its Validation

In the conventional FDEM (Combined Finite and Discrete Element Method), each contact pair might have multiple contact points where friction forces are applied, leading to non-unique friction force assignments and potentially introducing computational errors. This study introduces a new contact friction algorithm for FDEM based on the resultant normal contact force. This method necessitates determining the friction force at a unique equivalent contact point, thereby significantly simplifying the computational flow and reducing memory usage. A series of numerical tests are performed to validate the effectiveness of the proposed contact model. Using collision and block sliding tests, the proposed contact friction model is verified to be able to accurately capture the frictional effect between discrete bodies and circumvent the problematic kinetic energy dissipation issue associated with the original contact friction algorithm. For the Brazilian splitting and uniaxial compression tests, the simulated results closely align with those generated using the original contact friction algorithm and match the experimental measurements well, demonstrating the applicability of the proposed algorithm in fracturing analysis. Furthermore, by using the proposed contact friction algorithm, a computational efficiency enhancement of 8% in contact force evaluation can be achieved.

Brush seal contact force theory and correlation with tests

Brush seals are leakage performance systems that are operating against turbine shafts and bucket tips. Flexible bristle structure can compensate the rotor interference during transients, which enables closer clearance control in turbine and turbo-engine applications. During turbomachinery transients, contacting bristles exert force on turbine shaft, which in turn result in wear, frictional heat generation, counter torque and power loss. Brush seal design with proper stiffness has crucial importance since high bristle tip force levels during rotor contact may result in rotor instability, bristle tip melting or thermo-mechanical fatigue due to large amount of local frictional heat input. Counter torque applied by the contacting brush seal with improperly excessive tip force may result in turbine stall and overall efficiency losses. High levels of bristle contact forces may induce elevated wear rates, which degrades the leakage performance of the brush seal during its life cycle. Brush seal contact force evaluation under operating conditions has critical importance and has to be conducted before turbine integration to avoid performance losses and possible turbine failure in some extreme cases. In this paper, ‘Bristle Contact Force Theory’ is developed and closed form bristle tip force (BTF) function is derived where rotor-bristle, inter-bristle and bristle-back plate interactions are included. BTF measurements under pressurized and unpressurized air environment are conducted for the selected test seals by using the custom ‘Rotary Test Rig’. BTF function of bristle contact force theory show high level of correlation with the test data. The effect of cant angle manufacturing tolerance on bristle tip force levels is also examined through bristle tip contact force theory, and compared with the test seal measurements. Methodology for number of bristle row calculation and comparison with the geometric inspection of test seals are also detailed within the content of this paper.

Contact dynamics analysis of the single-pin meshing pair of a tracked vehicle

Single-pin meshing pairs are widely used in light-tracked vehicles. The purpose of this paper is to establish a nonlinear contact algorithm between the sprocket and track for multibody dynamics simulation. Based on the actual configuration, the tooth groove profile is discretized into three cambered surfaces, and the track pin is modeled as a cylinder with a protrusion. A body-fixed frame is introduced for each contact surface to facilitate the geometric contact criteria and contact force evaluation. Then the features of equal-pitch, sub-pitch and extra-pitch meshing are described with multibody dynamics analysis. It indicates that track pitch and sprocket pitch are the critical process parameters. A field test was performed to excavate the cause of chassis vibration. Compared with simulation results, the proposed contact model can effectively simulate the high-frequency excitation applied on a tracked vehicle. To improve its service life, a suggestion for the sprocket and track design is developed to fully use the sub-pitch meshing.

Evaluation of Contact Force between Aneurysm Model and Coil for Embolization of Intracranial Aneurysms.

To ensure safe coil embolization for intracranial aneurysms, it is important to investigate the contact force between the coil and the aneurysm wall. However, it is unclear how the catheter tip position and the diameter of the secondary loop of the coil influence the contact force. In this study, we measured the contact force between a coil and an aneurysm biomodel under different conditions. A commercially available coil was inserted through a microcatheter into a silicone rubber aneurysm model at a constant speed (1 mm/s) using an automatic stage, and the contact force between the coil and the aneurysm wall was measured by a force sensor attached on the aneurysm model. The inner diameter of the spherical aneurysm was 5 mm. The effects of varying the position of the catheter tip (near dome, center, near neck) and the diameter of the secondary coil (4.5 mm) were evaluated. When the catheter tip was inserted more deeply into the aneurysm (especially near the dome), the contact force increased. The contact force also increased as the secondary coil diameter was increased with the catheter tip near and in the center of the dome. These results suggest that the catheter tip position and the secondary coil diameter affect the contact force. In particular, the contact force should be considered large with the catheter tip near the dome to ensure safe coil deployment.

A Novel Dual-Probe-Based Micrograsping System Allowing Dexterous 3-D Orientation Adjustment

This article proposes a two-finger-based micrograsping system with high compliant borosilicate 3.3 glass probes and the corresponding sensing and control algorithms, which enables the orientation manipulation of microparts in three-dimensional (3-D) space. Compared with the existing research, the novelty of this article relies on three aspects: 1) the end-effector of the microgripper is designed to be with high compliance so that the squeeze force exerted on microparts can be more accurately regulated and the proposed microgripper is capable of manipulating fragile microparts; 2) the micrograsping system is endowed the capability to fully manipulate microparts’ orientation without recurring to auxiliary probes or rotary stages; and 3) the vibration characteristic of the grasping arm is investigated as cantilever beam for gasping stability analysis and squeeze force maintaining. In specific, taking spherical microparts with dimensions in the range from tens to hundreds of micrometers as target, the grasping system configuration, and the contact model between the probe and the microparts are first presented. Afterward, kinematics-based motion control strategy for position adjustment and orientation manipulation of microparts is clarified. Then, squeeze force regulation strategy is proposed, including adhesive force evaluation, vision-based squeeze force estimation, and the micropart releasing method. Finally, the vibration characteristic of the grasping arm is investigated as cantilever beam for gasping stability analysis and the squeeze force maintaining. The reliability and availability of the proposed micrograsping system is validated by well-designed experiments. Note to Practitioners —This article is motivated to develop a micrograsping system which enables dexterous rotating manipulation of microparts. The core of the proposed system is the utility of two fistulous tampered borosilicate 3.3 glass probes, which show high compliance in the microdomain. The manifested compliance enables the stably grasping of spherical objects during dexterous rotating manipulation and the vision-based contact force evaluation and regulation. The proposed system can rotate objects about two independent axes so that the orientation of a micropart can be adjusted to the desired one. This is critically important for many practical applications, such as the assembly of microballon and microneedle and the beamed cell penetration.

Numerical investigation of debris impact on spacecraft structure at hyper-high velocity

In this paper, our analysis concentrated on the mechanical behavior of sandwich panel subjected to impact loading. Thus, to improve the resistance of satellite structures from debris collision consequences; we proceed a performance investigation numerically of different materials based on the evaluation of contact force, total energy and kinetic energy generated from the impact of spherical steel debris on sandwich panel. Furthermore, a comparison of deformations and stresses levels in sandwich panel collide by a projectile at hyper-high velocity using finite element with ANSYS code was made. The difference between our models is the type of skins materials which are aluminum and functionally graded material FGM (alumina/nickel). The impact results a total perforation of sandwich panel with aluminum facesheets creating a fragments; contrary to FGM which the projectile penetrates only the front facesheet and honeycomb core. However, for an effective protection of sandwich panel against debris perforation, the introduction of FGM skins technique is considered as a candidate solution.

DEM–FEM simulation of tire–sand interaction based on improved contact model

In the interaction between rubber tire and granular terrain, the dynamic behavior of granular terrain is significantly affected not only by the shape of soil grains, but also by the deformation contact of tread rubber. Therefore, the effect of these two factors should be considered in tire–sand interactions. In this study, an improved contact model including the effect of sand grain shape and tread rubber deformation is developed for dealing with the interaction between rubber tire and sand terrain. In sand–sand contact model, the interaction between sand grains takes the form of surface contact instead of conventional point contact, where the contact calculation contains four interactions, i.e., normal force, tangential force, rolling resistance and twisting resistance. And in tread–sand contact model, the contact between tread rubber and sand grains is surface contact, which includes the rolling resistance and twisting resistance on the grains caused by rubber deformation during contact. As a result, the complete and realistic evaluation of contact forces is accomplished. Next, a comparison of sandpile simulation of coarse particles and experiment is carried out to verify the effectiveness of the sand–sand contact model. Finally, the novel contact model is applied to tire–sand interaction simulations and compared with the single-wheel experiments. The results indicate that the proposed contact model can be a powerful tool to simulate the interactions between rubber tire and sand terrain.

An efficient 3D DEM-FEM contact detection algorithm for tire-sand interaction

The combined discrete-finite element method is often used for dynamic interaction simulations, in which contact detection is the most time-consuming but critical constituent. Therefore, it is significant to develop an accurate and efficient contact detection algorithm. In this study, an efficient contact detection algorithm termed TSC (tire-sand contact) is developed for dealing with the interactions between spherical discrete elements and hexahedral finite elements. The global search of TSC is suitable for the contact detection of tire-sand interaction. In the global search phase, according to the contact characteristics of tire movement on granular terrain, the potential contact pairs are quickly determined by using the method of dynamically changing the slave nodes and master segments within a moving contact region. The local search is based on the principle of inside-outside algorithm, and the contact region is divided into three types, i.e. surface contact region, edge contact region and node contact region. In the local search phase, the invalid contact pairs and repeated contact pairs can be quickly excluded from the multiple potential contact pairs of one particle according to the relevant judgment conditions. And the Hertz-Mindlin contact model is used in corresponding contact force calculation. As a result, the quick contact search and accurate evaluation of contact force are accomplished. Finally, several numerical examples are presented to validate the accuracy and efficiency of the TSC algorithm in 3D contact analysis, which also demonstrates the advantages of the proposed algorithm in tire-sand interaction simulations.

16-16: First evaluation of contact force during atrial fibrillation ablation using a novel robotic system (AMIGO®) combined to a force-sensing catheter. A single centre experience

16-16: First evaluation of contact force during atrial fibrillation ablation using a novel robotic system (AMIGO®) combined to a force-sensing catheter. A single centre experience

An entropy-based evaluation of contact forces in continuum mechanics of elastic structures

The maximum entropy principle has proved to be a versatile tool for solving problems in many fields. In this paper, we extend entropy and its use in statistical physics to evaluate contact forces in the continuum mechanics of elastic structures. Each potential contact node of an elastic structure discretized by finite elements along with the normalized contact force on the node is considered as a system and all potential contact nodes together with their normalized contact forces are considered as a canonical ensemble, with the normalized contact force of each node representing the microstate of the node. The product of non-penetration conditions for potential contact nodes and the normalized nodal contact forces then act as an expectation that its value will be zero, and maximizing the entropy under the constraints of the expectation and the minimum potential energy principle results in an explicit probability distribution for the normalized contact forces that shows the relation between contact forces and displacements in a formulation similar to the formulation for particles occupying microstates in statistical physics. Moreover, an iterative procedure that solves a series of isolated systems to find the contact forces is presented, with a novel termination condition. Finally, some examples are examined to verify the correctness and efficiency of the procedure.

250 km/h급 고속용 강체전차선 및 이행장치 I : 구조설계

With the increasing running speed of trains, new railway lines in metropolitan areas, and the rising demand for green transportations, the number of underground and tunnel sections are constantly becoming larger, and installations of overhead rigid conductor systems are becoming wider. However, domestic commercial products for overhead rigid conductors are limited to 120 km/h train speeds. In this study, to develop a high-speed (250 km/h) overhead rigid conductor, R-Bar (Rigid Bar), the electrical and mechanical stability was enhanced through the improvement of the cross sectional shape of the R-Bar; the transition structure was also designed for flexibility and natural frequency isolation. In addition, the evaluation of contact forces between a pantograph and the overhead rigid conductor system for 250 km/h train speeds was performed using dynamic analysis.

Load assessment and analysis of impacts in multibody systems

The evaluation of contact forces during an impact requires the use of continuous force-based methods. An accurate prediction of the impact force demands the identification of the contact parameters on a case-by-case basis. In this paper, the preimpact effective kinetic energy (Formula presented.) is put forward as an indicator of the intensity of the impact force along the contact normal direction. This represents a part of the total kinetic energy of the system that is associated with the subspace of constrained motion defined by the impact constraints at the moment of contact onset. Its value depends only on the mechanical parameters and the configuration of the system. We illustrate in this paper that this indicator can be used to characterize the impact force intensity. The suitability of this indicator is confirmed by numerical simulations and experiments

Planar roller chain drive dynamics using a cylindrical contact force model

ABSTRACTA multibody dynamics methodology for the study of roller chain drives, which includes the use of a continuous cylindrical contact model, is used here to investigate the influence of energy dissipative factors on the drive dynamics. The chain drive mechanisms are described as a planar multibody system in which the connection between each pair of links is modelled as a multiple revolute clearance joint, instead of the traditional kinematic constraint, and the meshing between the roller and sprocket teeth is also treated as a generalized revolute clearance joint. The contact force model includes the geometric contact detection and the contact force evaluation, which in turn includes energy dissipative features resulting from the friction and restitution coefficients terms used in the model. Recognizing the numerical and physical limitations of the existing cylindrical contact models, an enhanced cylindrical contact model is applied here and demonstrated with the study of the dynamics of a roller chain drive with varied initial pre-tensions and energy dissipative coefficients.

Influence of wheel–rail contact modelling on vehicle dynamic simulation

This paper presents a comparison of four models of rolling contact used for online contact force evaluation in rail vehicle dynamics. Until now only a few wheel–rail contact models have been used for online simulation in multibody software (MBS). Many more models exist and their behaviour has been studied offline, but a comparative study of the mutual influence between the calculation of the creep forces and the simulated vehicle dynamics seems to be missing. Such a comparison would help researchers with the assessment of accuracy and calculation time. The contact methods investigated in this paper are FASTSIM, Linder, Kik–Piotrowski and Stripes. They are compared through a coupling between an MBS for the vehicle simulation and Matlab for the contact models. This way the influence of the creep force calculation on the vehicle simulation is investigated. More specifically this study focuses on the influence of the contact model on the simulation of the hunting motion and on the curving behaviour.

A new rolling contact method applied to conformal contact and the train–turnout interaction

This paper introduces a new computer program called WEAR. It contains a new and more accurate method for calculating wheel–rail contact stresses to predict degradation due to wear, deformation and fatigue. WEAR accounts for conformal contact by using influence numbers that are based on quasi-quarter spaces instead of the traditional half-spaces and considers the varying geometrical spin due to the varying contact angle through a contact patch.This new contact method is applied to two cases: wheel–rail contact in a turnout and conformal contact in a curve with a heavily worn wheel profile. In both cases, many of the assumptions commonly made in excising solution methods for wheel–rail contact problems, such as a small contact patch and a constant spin creepage, may be violated. The case of conformal contact demonstrates the effect of the influence numbers and the varying spin creepage on the resulting stresses and creep forces and provides a comparison of this new method with the well-established contact method CONTACT. For the turnout case, the first task is to obtain realistic input for all timesteps of a vehicle coasting through a turnout (i.e., diverging route) in a simulation. This step is necessary because the contact forces, which cause wear, deformation and fatigue of the wheels and rails, and the dynamics of the vehicle-turnout interaction strongly influence each other. WEAR converged for all timesteps, including many cases with multiple-point contacts at the switch blade and with extremely high creepages. This robustness demonstrates suitability of the new method for online contact force evaluation in vehicle dynamics simulations.

Three-Dimensional Manual Contact Force Evaluation of Graded Perpendicular Push Force Delivery by Second-Year Physiotherapy Students During Simple Feedback Training

Objective The purpose of this study was to investigate a quantitative biomechanical evaluation method for contact forces exerted during a manual examination and treatment technique used in a learning environment. The evaluation was based on three-dimensional (3D) force component data. Methods A hand-/palm-held computerized 3D force component measuring system was used during a simple feedback experiment involving 20 second-year university students of physiotherapy who delivered 5 sets of graded perpendicular manual push forces on the sensor part of the system, which was placed on the padded surface of an examination/treatment table. In an effect study with a multiple time-series design, a randomly chosen subgroup of subjects received concurrent visual 3D kinetic/dynamic force–time feedback. Results The students delivered graded perpendicular forces with good intrasubject consistency (intraclass correlation coefficient [3, 1]: mean, 0.80; range, 0.76-0.88) but with poor intersubject consistency (intraclass correlation coefficient [2, 1]: mean, 0.38; range, 0.15-0.74). A temporary performance improvement in forward-backward force direction deviations from the perpendicular in the subgroup given feedback indicates that students are sensitive to feedback training. Conclusion An evaluation tool using 3D contact force component measurement enables the assessment of the overall magnitude of the manual contact force as well as its directional aspect. Compared with existing evaluations based on 1-dimensional force components, this 3D system allows for a more complete and, at the same time, more specific quantitative evaluation of the manual contact forces. Three-dimensional dynamic/kinetic augmented feedback has the additional potential of helping students and practitioners to improve their palpation and force delivery skills.

Dynamic Response of Sandwich Plates to Medium-velocity Impact

Overall and local deflections of a single span of a continuous sandwich plate are evaluated under local contacts with a rigid indenter, at relative velocities of 10 and 20 m/s (20-40 knots), to simulate the effect of impacts that can be applied to ship sandwich structures by floating objects or moorings. Laminated carbon-vinyl ester face sheets and a H100 PVC foam core, possibly separated from the impacted face sheet by a stiff and ductile polyurethane (PUR) interlayer, comprise the sandwich plate. As in our previous study of the effect of quasi-static contacts (Suvorov, A.P. and Dvorak, G.J. (2005). Protection of Sandwich Plates from Low Velocity Impact, Journal of Composite Materials (to appear)), the focus is on the evaluation of contact forces and deflections of the face sheet and foam core interface, and on the membrane or in-plane strains in the face sheet at the contact point. These quantities are well-known potential sources of damage, causing core crushing, and face sheet delamination and/or penetration. As expected, the results show that the magnitudes of these quantities depend on both the distance of the contact point from the nearest support, and on the initial velocity of the indenter of a given mass. Both local face sheet deflections and core interface indentations are high if the impact point is within a distance from a support that is equal to 2-3 times the total sandwich plate thickness; significantly lower values are found at more distant contact points. These deflections are much reduced by replacing the foam core with an aluminum honeycomb in the supported region of the plate. However, this reinforcement elevates both the contact force and the in-plane strain in the face sheet. Therefore, thickening of the exposed face sheets should be considered around supports. Most of the kinetic energy is absorbed by the core, hence addition of the stiff and ductile PUR interlayer does not have as much effect on the results as it had in quasi-static contact.

Development of a new procedure for the wheel-rail contact force evaluation in simulations of railway dynamics

The numerical solution of the dynamics of a railway vehicle interacting with supporting structures is facilitated by mathematical models and evaluation techniques. In fact, the vehicle multibody modelling, the supporting structure models, and the Hertz and Kalker theories concerning the wheel-rail contact forces are indispensable guides to the dynamic analysis of railway systems. The present work is concerned with an evaluation method for the normal direction contact force component at the point of contact between the rail and wheel profiles. It proposes an alternative approach, which eliminates the typical problems of the Hertz formulation. The evaluation method developed ignores the contact stiffness and is based on the elastic deformation of the supporting structure, which, as the simulations demonstrate, leads to physically more acceptable results and shorter calculation times.

Accurate prediction of delamination in FRP composite laminates resulting from transverse impact

A simple and computationally efficient adaptive finite element analysis strategy has been adopted for accurate and reliable evaluation of contact force and stresses in FRP composite laminates subjected to transverse impact. Stress based delamination criterion has been utilized to study the initiation of delamination. Hence importance of reliable estimation of stresses is very important for proper prediction of delamination. Contact of a spherical and cylindrical impactor on FRP composite laminates are considered. Studies have clearly shown the importance of appropriate finite element mesh for reliable prediction of delamination initiation and growth. A good number of cases have been considered with varying stacking sequences and using appropriate finite element mesh for studying the vulnerability of composite laminates towards delamination when subjected to transverse impact.