Evolution of real area of contact due to combined normal load and sub-surface straining in sheet metal

Understanding asperity flattening is vital for a reliable macro-scale modeling of friction and wear.In sheet metal forming processes,sheet surface asperities are deformed due to contact forces between the tools and the workpiece.In addition,as the sheet metal is strained while retaining the normal load,the asperity deformation increases significantly.Deformation of the asperities determines the real area of contact which influences the friction and wear at the tool-sheet metal contact.The real area of contact between two contacting rough surfaces depends on type of loading,material behavior,and topography of the contacting surfaces.In this study,an experimental setup is developed to investigate the effect of a combined normal load and sub-surface strain on real area of contact.Uncoated and zinc coated steel sheets(GI)with different coating thicknesses,surface topographies,and substrate materials are used in the experimental study.Finite element(FE)analyses are performed on measured surface profiles to further analyze the behavior observed in the experiments and to understand the effect of surface topography,and coating thickness on the evolution of the real area of contact.Finally,an analytical model is presented to determine the real area contact under combined normal load and sub-surface strain.The results show that accounting for combined normal load and sub-surface straining effects is necessary for accurate predictions of the real area of contact.

Finger pad friction and tactile perception of laser treated,stamped and cold rolled micro-structured stainless steel sheet surfaces

Tactile perception is a complex system,which depends on frictional interactions between skin and counter-body.The contact mechanics of tactile friction is governed by many factors such as the state and properties of skin and counter-body.In order to discover the connection between perception and tactile friction on textured stainless steel sheets,both perception experiments (subjective) and tactile friction measurements (objective) were performed in this research.The perception experiments were carried out by using a panel test method to identify the perceived roughness,perceived stickiness and comfort level from the participants.For the friction experiments,tactile friction was measured by a multi-axis force/torque transducer in vivo.The perceived stickiness was illustrated as an effective subjective stimulus,which has a negative correlation to the comfort perception.No significant evidence was revealed to the connection between the perceived roughness and comfort perception,and this relationship may be influenced by the participants' individual experience,gender and moisture level of skin.Furthermore,the kinetic tactile friction was concluded as an objective stimulus to the comfort perception with a negative correlation.

Skin tribology:Science friction?

The application of tribological knowledge is not just restricted to optimizing mechanical and chemical engineering problems.In fact,effective solutions to friction and wear related questions can be found in our everyday life.An important part is related to skin tribology,as the human skin is frequently one of the interacting surfaces in relative motion.People seem to solve these problems related to skin friction based upon a trial-and-error strategy and based upon on our sense for touch.The question of course rises whether or not a trained tribologist would make different choices based upon a science based strategy?In other words:Is skin friction part of the larger knowledge base that has been generated during the last decades by tribology research groups and which could be referred to as Science Friction?This paper discusses the specific nature of tribological systems that include the human skin and argues that the living nature of skin limits the use of conventional methods.Skin tribology requires in vivo,subject and anatomical location specific test methods.Current predictive friction models can only partially be applied to predict in vivo skin friction.The reason for this is found in limited understanding of the contact mechanics at the asperity level of product-skin interactions.A recently developed model gives the building blocks for enhanced understanding of friction at the micro scale.Only largely simplified power law based equations are currently available as general engineering tools.Finally,the need for friction control is illustrated by elaborating on the role of skin friction on discomfort and comfort.Surface texturing and polymer brush coatings are promising directions as they provide way and means to tailor friction in sliding contacts without the need of major changes to the product.

Dopamine hydrochloride and carboxymethyl chitosan coatings for multifilament surgical suture and their influence on friction during sliding contact with skin substitute

In order to reduce the damage to tissue and fill the interstices between fibers,multifilament sutures are frequently treated with certain coating materials.The objective of this study was to create and characterize dopamine hydrochloride(DA)and carboxymethyl chitosan(CMCS)coatings on surgical sutures and investigate their effects on the frictional performance of the surgical sutures during sliding through a skin substitute.The effects of the treatment on the physical and chemical characteristics of the surgical sutures were evaluated.The friction force of the surgical sutures during sliding through the skin substitute was experimentally determined using a penetration friction apparatus.The coefficient of friction(COF)was calculated using a linear elastic model and was used to estimate the frictional behavior of the surgical suture‐skin interactions.The results showed that the DA coating could evenly deposit on the surface of the etched multifilament surgical suture surfaces in a weakly alkaline buffer solution.The CMCS coating material could form a uniform film on the surface of the sutures.Minor changes in the surface roughness of the multifilament surgical sutures with different treatments occurred in this study.The friction force and the COF of the multifilament surgical sutures with DA and CMCS coating showed little change when compared with untreated multifilament surgical sutures.

A tribo-chemical view on astringency of plant-based food substances

Consumption of plant-based food products having high composition of polyphenols leads to the sensation of astringency.For sliding oral surfaces,friction is an essential property during the oral perception of roughness and dryness which are attributes associated with astringency.Different factors including the chemical composition of interacting layers,structure and operation of interfaces have an effect on the astringency development process.The manner of interactions occurring at oral interfaces suggest there is a system dependence of astringency and highlights the importance of adopting a tribosystems approach.Available measurement techniques have shown an existing relationship between salivary protein-polyphenol interaction and an astringent mouthfeel.Nevertheless,the tribo-chemistry involved in this multifaceted sensation remains largely unexplored in a comprehensive manner.In this review the underlying tribo-chemical processes useful in understanding the mechanism of astringency are highlighted and discussed considering current techniques employed to investigate astringency perception.Loss of lubrication on oral surfaces owing to the tribo-chemical interactions involving saliva and astringent plant proteins requires subsequent deformations of oral tissues which are significant enough to induce strains at mechanoreceptor locations,leading to the sensation of astringency.It is proposed that micro-scale contact modelling on the interaction of food particles/aggregates,boundary layers and oral surfaces shows potential in addressing the knowledge gap between tribo-chemical measurement techniques and panel tests,making it possible to attain a predictor for astringency.

Influence of surgical suture properties on the tribological interactions with artificial skin by a capstan experiment approach

Tribological interactions between surgical suture and human tissue play an important role in the stitching process.The purpose of the paper is to understanding the tribological behavior of surgical suture interacting with artificial skin,with respect to surgical suture material and structure,by means of a capstan experiment approach and a contact area model.The results indicated that structure and surface topography of the surgical suture had a pronounced effect on the tribological interactions.The apparent coefficient of friction of vicryl surgical suture was the smallest among the three surgical suture materials.As the sliding velocity increased,or the applied load decreased,the coefficient of friction increased.Furthermore,stick-slip phenomena were observed during the sliding procedure.

Multiscale friction model for hot sheet metal forming

The accurate description of friction is critical in the finite element(FE)simulation of the sheet metal forming process.Usually,friction is oversimplified through the use of a constant Coulomb friction coefficient.In this study,the application of an existing multiscale friction model is extended to the hot stamping process.The model accounts for the effects of tool and sheet metal surface topography as well as the evolution of contact pressure,temperature,and bulk strain during hot stamping.Normal load flattening and strip drawing experiments are performed to calibrate the model.The results show that the model can relatively well predict friction in strip draw experiments when the tool surface evolution due to wear is incorporated.Finally,the application of the formulated multiscale friction model was demonstrated in the FE simulation of a hot-stamped part.

Selection of micro-fabrication techniques on stainless steel sheet for skin friction

This review gives a concise introduction to the state-of-art techniques used for surface texturing, e.g., wet etching, plasma etching, laser surface texturing (LST), 3D printing, etc. In order to fabricate deterministic textures with the desired geometric structures and scales, the innovative texturing technologies are developed and extended. Such texturing technology is an emerging frontier with revolutionary impact in industrial and scientific fields. With the help of the latest fabrication technologies, surface textures are scaling down and more complex deterministic patterns may be fabricated with desired functions, e.g., lotus effect (hydrophobic), gecko feet (adhesive), haptic tactile, etc. The objective of this review is to explore the surface texturing technology and its contributions to the applications.

Design of bidirectional frictional behaviour for tactile contact using ellipsoidal asperity micro-textures

Tactile perception and friction can be modified by producing a deterministic surface topography.Change of surface feature arrangement and texture symmetry can produce an anisotropic frictional behaviour.It is generally achieved through skin hysteresis by promoting its deformation.This work investigates whether a bidirectional friction can be created with microscale ellipsoidal asperity textures,thus relying on the adhesive component of friction.For this purpose,four textured samples with various asperity dimensions were moulded with a silicone rubber having an elastic modulus comparable to that of the skin.Coefficient of friction measurements were conducted in-vivo in two sliding directions with a range of normal loads up to 4 N.Finite element method(FEM)was used to study elastic deformation effects,explain the observed friction difference,and predict surface material influence.Measurements performed perpendicular to the asperity major radii showed consistently higher friction coefficients than that during parallel sliding.For the larger asperity dimensions,a change of the sliding direction increased friction up to a factor of 2.The numerical analysis showed that this effect is mostly related to elastic asperity deflection.Bidirectional friction differences can be further controlled by asperity dimensions,spacing,and material properties.