scholarly journals Surface strain measurements of fingertip skin under shearing

2016 ◽  
Vol 13 (115) ◽  
pp. 20150874 ◽  
Author(s):  
Benoit Delhaye ◽  
Allan Barrea ◽  
Benoni B. Edin ◽  
Philippe Lefèvre ◽  
Jean-Louis Thonnard
Keyword(s):  
Contact Area ◽  
Normal Force ◽  
Complex Geometry ◽  
Tangential Direction ◽  
Surface Strain ◽  
Haptic Interfaces ◽  
Dexterous Manipulation ◽  
Strain Waves ◽  
Theoretical Predictions ◽  
High Resolution Images

The temporal evolution of surface strain, resulting from a combination of normal and tangential loading forces on the fingerpad, was calculated from high-resolution images. A customized robotic device loaded the fingertip with varying normal force, tangential direction and tangential speed. We observed strain waves that propagated from the periphery to the centre of the contact area. Consequently, different regions of the contact area were subject to varying degrees of compression, stretch and shear. The spatial distribution of both the strains and the strain energy densities depended on the stimulus direction. Additionally, the strains varied with the normal force level and were substantial, e.g. peak strains of 50% with a normal force of 5 N, i.e. at force levels well within the range of common dexterous manipulation tasks. While these observations were consistent with some theoretical predictions from contact mechanics, we also observed substantial deviations as expected given the complex geometry and mechanics of fingertips. Specifically, from in-depth analyses, we conclude that some of these deviations depend on local fingerprint patterns. Our data provide useful information for models of tactile afferent responses and background for the design of novel haptic interfaces.

Experimental Study of the Plastic Interaction of Model Surface Asperities during Sliding

1968 ◽  
Vol 10 (2) ◽  
pp. 121-132 ◽  
Author(s):  
C. M. Edwards ◽  
J. Halling
Keyword(s):  
Experimental Study ◽  
Friction And Wear ◽  
Normal Force ◽  
Tangential Force ◽  
Experimental Results ◽  
Interfacial Conditions ◽  
High Adhesion ◽  
Theoretical Predictions ◽  
Very High ◽  
Low Shear

The paper describes an experimental study of the plastic interaction of triangular shaped lead model asperities deformed under conditions of plane strain. The investigation yields values of the normal and tangential force variations throughout the junction interaction and details of the plastic deformation particularly in relation to junction growth. A number of asperity interfacial conditions are considered ranging from complete adhesion to very low shear strengths achieved using p.t.f.e. strip. The experimental results are compared with an earlier theoretical solution to this problem and show reasonable agreement with the theoretical predictions. In particular it is shown that the normal force, which is usually compressive, may become tensile for conditions of high adhesion between the asperities. This leads to very high values of the macroscopic friction coefficient such as occur in hard vacuum situations. The experimental results for the various surface conditions show sufficient agreement with theoretical predictions to justify the use of this type of theoretical approach for the wider study of the friction and wear of mating surfaces.

scholarly journals The effect of processing parameters on the mechanical characteristics of PLA produced by a 3D FFF printer

2020 ◽  
Vol 111 (3-4) ◽  
pp. 695-709
Author(s):  
H. Gonabadi ◽  
A. Yadav ◽  
S. J. Bull
Keyword(s):  
Tensile Strength ◽  
Young’S Modulus ◽  
Process Parameters ◽  
Mechanical Response ◽  
Complex Geometry ◽  
Young's Modulus ◽  
Laminate Plate ◽  
Surface Strain ◽  
Image Correlation ◽  
Build Orientation

Abstract 3D printing by fused filament fabrication (FFF) provides an innovative manufacturing method for complex geometry components. Since FFF is a layered manufacturing process, effects of process parameters are of concern when plastic materials such as polylactic acid (PLA), polystyrene and nylon are used. This study explores how the process parameters, e.g. build orientation and infill pattern/density, affect the mechanical response of PLA samples produced using FFF. Digital image correlation (DIC) was employed to get full-field surface-strain measurements. The results show the influence of build orientation and infill density is significant. For on-edge orientation, the tensile strength and Young’s modulus were 55 MPa and 3.5 GPa respectively, which were about 91% and 40% less for the upright orientation, demonstrating a significant anisotropy. The tensile strength and Young’s modulus increased with increasing infill density. In contrast, different infill patterns have no significant effect. Considering the influence of build orientation, based on the experimental results, a constitutive model derived from the laminate plate theory was employed. The material parameters were determined by tensile tests. Results demonstrated a reasonable agreement between the experimental data and the predictive model. Similar anisotropy to tension was observed in shear tests; shear modulus and shear strength for 45° flat orientation were about 1.55 GPa and 36 MPa, whereas for upright specimens they were about 0.95 GPa and 18 MPa, respectively. The findings provide a framework for systematic mechanical characterisation of 3D-printed polymers and potential ways of choosing process parameters to maximise performance for a given design.

Humanoid Robot Hand and its Applied Research

2019 ◽  
Vol 31 (1) ◽  
pp. 16-26 ◽  
Author(s):  
Haruhisa Kawasaki ◽  
◽  
Tetsuya Mouri
Keyword(s):  
Research And Development ◽  
Humanoid Robot ◽  
Applied Research ◽  
Haptic Interfaces ◽  
Robot Hand ◽  
Hand Rehabilitation ◽  
Dexterous Manipulation ◽  
Prosthetic Hands ◽  
Application Systems ◽  
Robot Hands

Humanoid robot hands are expected to replace human hands in the dexterous manipulation of objects. This paper presents a review of humanoid robot hand research and development. Humanoid hands are also applied to multifingered haptic interfaces, hand rehabilitation support systems, sEMG prosthetic hands, telepalpation systems, etc. The developed application systems in our group are briefly introduced.

Effect of Interosseous Membrane on Load Transfer in Rat Forelimb Using Finite Element Analysis

2004 ◽  
Author(s):  
A. E. Tami ◽  
G. Suresh ◽  
R. B. Patel ◽  
M. L. Knothe Tate
Keyword(s):  
Finite Element ◽  
Strain Distribution ◽  
Load Transfer ◽  
Complex Geometry ◽  
Lateral Displacement ◽  
Surface Strain ◽  
Interosseous Membrane ◽  
Distribution Data ◽  
Element Analysis ◽  
Element Mesh

Due to the curvature of the ulna and the complex geometry of the ulna and radius as well and their interaction with and possible transfer of load through the interosseous membrane that joins them, an understanding of the loading situation is not trivial. The IOM might counteract the bending effect resulting from the curvature of the ulna, therefore stabilizing the lateral displacement of the ulna and decreasing the ratio between bending and compression. Thus, in order to understand the mechanisms underlying effects of the mechanical stimulation applied using the end-loading model of the ulna, it is necessary to have a fundamental understanding of the loading mechanics and strain distribution. Hence, the goals of this study were: i) to develop a three dimensional finite element mesh of a mature rat ulna, ii) to measure experimental surface strain values of rat forelimbs with intact and non-intact interosseous membranes, iii) to compare experimental and computational strain distribution data, and iv) to analyze for the first time the effect of the radius and interosseous membrane on axial load distribution through the ulna.

Modeling the Thermal Responses of the Skin Surface During Hand-Object Interactions

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Hsin-Ni Ho ◽  
Lynette A. Jones
Keyword(s):  
Skin Temperature ◽  
Measurement System ◽  
Contact Area ◽  
Thermal Model ◽  
Time Course ◽  
Thermal Contact ◽  
Contact Forces ◽  
Thermal Measurement ◽  
Theoretical Predictions ◽  
Object Interactions

The objective of this research is to analyze and model the decreases in skin temperature when the hand makes contact with an object at room temperature so that thermal feedback can be incorporated into haptic displays. A thermal model is proposed that predicts the thermal responses of the skin and object surface as well as the heat flux exchanged during hand-object interactions. The model was evaluated by comparing the theoretical predictions of temperature changes to those experimentally measured using an infrared thermal measurement system. The thermal measurement system was designed to overcome the limitations imposed by contact thermal sensors, and was able to measure skin temperature during contact, together with the contact area and contact force. The experimental results indicated that over the pressure range of 0.73–10.98kPa, changes in skin temperature were well localized to the contact area and were affected by contact pressure. The pressure in turn influenced both thermal contact resistance and blood flow. Over the range of contact forces typically used in manual exploration, blood perfusion and metabolic heat generation do not appear to have a significant effect on the skin’s thermal responses. The theoretical predictions and the measured data were consistent in characterizing the time course and amplitude of the skin temperature change during contact with differences typically being less than 1°C between the two for pressures greater than 4kPa. These findings indicate that the proposed thermal model is able to characterize and predict the skin temperature responses during hand-object interactions and could be used in a thermal display that simulates the properties of different materials.

Friction Due to Elastic-Plastic Contact of Rough Surfaces

2007 ◽  
Author(s):  
A. Sepehri ◽  
K. Farhang
Keyword(s):  
Half Plane ◽  
Normal Force ◽  
Tangential Force ◽  
Three Dimensional ◽  
Tangential Direction ◽  
Tangential Component ◽  
Force Term ◽  
Three Dimensional Model ◽  
Tangential Plane ◽  
Elastic Plastic

A three dimensional model based on CEB elastic-plastic contact leads to the derivation of two force components due to the shoulder-shoulder interaction of the asperities. A normal force component is resulted that upon summation of all possible interactions, in a statistical sense, obtains the normal force between the two surfaces. A second component of asperity force would be along the tangential plane (mean plane). When there is not net applied tangential force the tangential component of force on an asperity due to all its interactions would vanish. Upon impending motion, however, the tangential force can no longer cancel since the existence of a net tangential applied load would disrupt the symmetry of loading in the tangential direction. A three dimensional elastic-plastic model then furnishes a half-plane tangential elastic-plastic force term that would exist when relative movement of one surface on another occurs along an arbitrary axis in the tangential plane. This paper addresses an account of friction due to the elastic-plastic interaction of two surfaces by recognizing that the tangential half-plane elasto-plastic force term is the resisting force when two surfaces in elastic-plastic contact are made to slide.

The influence of screw torque in the application of bone plates

2001 ◽  
Vol 14 (02) ◽  
pp. 78-83 ◽  
Author(s):  
T.C. Hearn ◽  
T.D. Woodside ◽  
J.R. Field
Keyword(s):  
Contact Area ◽  
Plate Fixation ◽  
Clinical Situation ◽  
Surface Strain ◽  
Bone Plates ◽  
Bone Plate ◽  
Clinical Criteria ◽  
Axial Tension ◽  
Interface Contact ◽  
Plate Reconstruction

SummaryThe applied level of screw torque has a significant impact on both the mechanical and vascular environment in bone following the application of a bone plate. The amount of torque applied dictates the resultant level of axial tension generated in the screw and the compressive forces between the plate and underlying bone. The interface contact area between the plate and underlying bone is also affected. As a consequence, screw torque can be implicated in the pathogenesis of implant induced osteopenia and other pathological occurrences that follow bone plate fixation.The work performed was designed to evaluate the effect of the applied level of screw torque. The construction stiffness (rigidity) and bone surface strain was quantitated in response to variable levels of screw torque. This was performed utilizing intact and osteotomized cadaveric bone.The current level of screw torque applied in the clinical situation, for 4.5 mm cortical screws, is approximately 5 Newton metres (Nm). It appears from the work presented herein, that lowering the level of applied screw torque does not adversely affect the rigidity of the final construction. This fact may serve to ameliorate the pathological consequences of applying screws and plates using current clinical criteria.The amount of torque applied to screws in the application of bone plates has a profound effect on a number of elements, namely the interface contact area and force. The work presented examines the effect of screw torque on the rigidity and bone strain distribution of fractured bone following bone plate reconstruction. It appears that the use of lower levels of screw torque, than currently used in clinical practice, does not adversely effect the rigidity of the final construction. These findings support the notion that the level of screw torque applied may have a role in ameliorating the pathogenic response that occur following bone plate application, namely osteopaenia.

Thermal Damage and Rail Load Stresses in a 33-Inch Railroad Car Wheel

1978 ◽  
Vol 100 (3) ◽  
pp. 363-369 ◽  
Author(s):  
H. R. Wetenkamp ◽  
R. M. Kipp
Keyword(s):  
Fatigue Damage ◽  
Experimental Work ◽  
Contact Area ◽  
Thermal Damage ◽  
Combined Loading ◽  
Thermal Loads ◽  
Theoretical Predictions

Stresses in a 33-inch (.840 m) railroad car wheel in response to static rail loadings are presented on the basis of experimental work and theoretical predictions. In regions away from the contact area, the theoretical predictions are verified by experiment. The rail load stresses are compared to theoretically damaging thermal loads, and a possible method of analysis of fatigue damage from the combined loading is discussed.

An Enhanced Dynamic Model in Turning Including the Effect of Ploughing Forces

1997 ◽  
Vol 119 (1) ◽  
pp. 10-20 ◽  
Author(s):  
A. M. Shawky ◽  
M. A. Elbestawi
Keyword(s):  
Complex Geometry ◽  
Cutting Process ◽  
Force Model ◽  
Machined Surface ◽  
Process Dynamics ◽  
Surface Errors ◽  
Theoretical Predictions ◽  
Dynamic Components ◽  
Clearance Face ◽  
Good Agreement

In this paper computer simulation of cutting process dynamics in turning, using a mechanistic cutting force model, is significantly enhanced by incorporating a dynamic ploughing force model. The ploughing forces are decomposed into static and dynamic components. The effect of tool feed on increasing the clearance face contact is described mechanistically. The ploughing model is developed for the complex geometry of a multi-edge cutting tool and the effect of integrated tool/workpiece vibrations is considered. The cutting process damping is predicted by tracking the dynamic ploughed volume resulting from the interaction with machined surface undulations. The model has been used through computer simulations to predict the cutting forces and machined surface errors. The results clearly demonstrate the effect of including the ploughing model on the process dynamics. The theoretical predictions show a good agreement with the experimental results.

Experimental Verification of Friction Behaviors Under Periodically-Varied Normal Force by Developing a Two-Directional Friction Test System

2015 ◽  
Author(s):  
Kunio Asai ◽  
Muzio M. Gola
Keyword(s):  
Contact Pressure ◽  
Contact Area ◽  
Normal Force ◽  
Contact Stiffness ◽  
Tangential Force ◽  
Test System ◽  
Dissipated Energy ◽  
Friction Test ◽  
Force Coefficient ◽  
Tangential Contact

In order to achieve more accurate friction damping of turbine blades equipped with shroud covers and under-platform dampers, it is necessary to clarify such friction behaviors as tangential contact stiffness, micro-slips, and dissipated energy, under periodically varied normal force instead of constant normal force. Although some analytical studies were reported on the contact mechanics under alternating normal force, only minimal research has been conducted on the experimental verification of such behaviors, as friction tests were commonly done under constant normal force. In this study, we developed an original two-directional friction test system that can apply any combination of alternating normal and tangential forces by changing the displacement-controlled loading direction. In this system, relative displacement and contact force were measured simultaneously by using a laser Doppler displacement sensor and force transducers of the strain gage type. By using our original test system, we examined the dissipated energy under constant normal force and periodically-varied normal force whose amplitude is the same as that of tangential force with no phase difference. We then obtained a new finding that dissipated energy depends on alternating normal force under the same mean normal force and alternating tangential force. More specifically, when the tangential force coefficient, defined as the ratio of the amplitude of alternating tangential force to mean normal force, is large enough to cause a macro-slip, dissipated energy under variable normal force is smaller than that under constant normal force. Conversely, when tangential force coefficient is small in the micro-slip region, dissipated energy under variable normal force is larger than that under constant normal force. This behavior was successfully reproduced by FE analysis based on a macro-slip model, where an array of macro-slip elements was used to describe micro-slip behavior. It was found that alternating normal force makes it easier to cause a micro-slip in a certain area of the contact surface under variable normal force, resulting in higher dissipated energy than at constant normal force when tangential force coefficient is small. In this study, basic friction data were also obtained regarding the tangential contact stiffness with variations in contact pressure, as well as the relation between a micro-slip and the tangential force coefficient. Tangential contact stiffness increases as contact pressure increases. In addition, tangential contact stiffness increases with the nominal contact area, but is not proportional to the area. The non-dimensional slip range (corresponding to the ratio of slip range to stick displacement) was confirmed as being described in a unified form against different contact area (6 and 18 mm2) and contact pressure ranging from 3 to 40 MPa.

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