On the Effect of Shear Loading Rate on Contact Area Shrinking in Adhesive Soft Contacts

AbstractAdhesion and, its interplay with friction, is central in several engineering applications involving soft contacts. Recently, there has been an incredible push towards a better understanding on how the apparent contact area evolves when a shear load is applied to an adhesive soft contact, both experimentally and theoretically. Although soft materials are well-known to exhibit rate-dependent properties, there is still a lack of understanding in how the loading rate could affect the contact area shrinking. Indeed, most of the experiments involving a sphere-flat contact have been conducted at a fixed loading rate, and, so far, analytical models have assumed a constant work of adhesion, independent on the peeling velocity. Here, by using linear elastic fracture mechanics, an analytical model is derived for the contact of a rigid sphere on a soft adhesive substrate, which is aimed at elucidating the effect that a rate-dependent work of adhesion has on the contact area shrinking. The model results show that contact area reduction is very sensitive to the loading rate, with slower loading rates promoting a stronger shrinking, which seems in agreement with Literature results. Furthermore it is shown that rate effects enhance the apparent interfacial toughness, i.e. more energy is needed to drive the system from full stick up to gross sliding.

Download Full-text

On mixed-mode fracture mechanics models for contact area reduction under shear load in soft materials

Journal of the Mechanics and Physics of Solids ◽

10.1016/j.jmps.2018.10.011 ◽

2019 ◽

Vol 124 ◽

pp. 159-171 ◽

Cited By ~ 16

Author(s):

A. Papangelo ◽

M. Ciavarella

Keyword(s):

Fracture Mechanics ◽

Contact Area ◽

Mixed Mode ◽

Soft Materials ◽

Mixed Mode Fracture ◽

Shear Load ◽

Mode Fracture ◽

Area Reduction

Download Full-text

Evolution of real contact area under shear and the value of static friction of soft materials

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1706434115 ◽

2018 ◽

Vol 115 (3) ◽

pp. 471-476 ◽

Cited By ~ 50

Author(s):

R. Sahli ◽

G. Pallares ◽

C. Ducottet ◽

I. E. Ben Ali ◽

S. Al Akhrass ◽

...

Keyword(s):

Contact Area ◽

Normal Load ◽

Scaling Law ◽

Reduction Rate ◽

Static Friction ◽

Soft Materials ◽

Real Contact Area ◽

The Real ◽

Real Contact ◽

Area Reduction

The frictional properties of a rough contact interface are controlled by its area of real contact, the dynamical variations of which underlie our modern understanding of the ubiquitous rate-and-state friction law. In particular, the real contact area is proportional to the normal load, slowly increases at rest through aging, and drops at slip inception. Here, through direct measurements on various contacts involving elastomers or human fingertips, we show that the real contact area also decreases under shear, with reductions as large as 30%, starting well before macroscopic sliding. All data are captured by a single reduction law enabling excellent predictions of the static friction force. In elastomers, the area-reduction rate of individual contacts obeys a scaling law valid from micrometer-sized junctions in rough contacts to millimeter-sized smooth sphere/plane contacts. For the class of soft materials used here, our results should motivate first-order improvements of current contact mechanics models and prompt reinterpretation of the rate-and-state parameters.

Download Full-text

A mechanism for enhanced static sliding resistance owing to surface waviness

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2010.0617 ◽

2011 ◽

Vol 467 (2132) ◽

pp. 2209-2223 ◽

Cited By ~ 6

Author(s):

J. F. Waters ◽

P. R. Guduru

Keyword(s):

Contact Area ◽

Flat Surface ◽

Mechanical Energy ◽

Wavy Surface ◽

Work Of Adhesion ◽

Rigid Sphere ◽

Surface Waviness ◽

Additional Energy ◽

Normal Separation ◽

Sliding Resistance

This paper presents an analysis of static sliding resistance of a rigid sphere on a soft elastic material with axisymmetric waviness. When the sphere is loaded laterally under a fixed normal force, the contact area is subjected to mixed-mode loading. It is shown that, as the lateral loading increases, the decrease in contact area involves unstable jumps; and each unstable jump dissipates mechanical energy. The additional energy dissipation increases the peak force required for gross sliding of the interface compared with that of a flat surface. Thus, a mechanism is proposed for enhanced static sliding resistance on the surface of a soft material owing to surface waviness-induced instabilities. Such an increase in sliding resistance is analogous to a similar increase in the detachment force between a sphere and a wavy surface during normal separation, which was reported elsewhere. The influence of mode-mixity-dependent work of adhesion on the static sliding resistance of a wavy surface is also considered.

Download Full-text

On the Effect of a Rate-Dependent Work of Adhesion in the Detachment of a Dimpled Surface

Applied Sciences ◽

10.3390/app11073107 ◽

2021 ◽

Vol 11 (7) ◽

pp. 3107

Author(s):

Antonio Papangelo

Keyword(s):

Power Law ◽

Soft Materials ◽

Work Of Adhesion ◽

Patterned Surfaces ◽

Weak State ◽

Partial Contact ◽

Rate Dependent ◽

Pressure Sensitive ◽

Full Contact ◽

Unloading Rate

Patterned surfaces have proven to be a valuable design to enhance adhesion, increasing hysteresis and the detachment stress at pull-off. To obtain high adhesive performance, soft materials are commonly, used, which easily conform to the countersurface, such as soft polymers and elastomers. Such materials are viscoelastic; i.e., they show rate-dependent properties. Here, the detachment of two half spaces is studied, one being flat and the other having a dimple in the limit of short range adhesion and a power law rate-dependent work of adhesion, as observed by several authors. Literature results have suggested that the dimpled surface would show pressure-sensitive adhesion, showing two possible adhered states, one weak, in partial contact, and one strong when full contact is achieved. By accounting for a power law rate-dependent work of adhesion, the “weak state” may be much stronger than it was in the purely elastic case, and hence the interface may be much more tough to separate. We study the pull-off detachment stress of the dimpled surface, showing that it weakly depends on the preload, but it is strongly affected by the dimensionless unloading rate. Finally, possible implications of the presented results in the detachment of soft materials from rough substrates are discussed.

Download Full-text

Mode-mixity-dependent adhesive contact of a sphere on a plane surface

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2009.0461 ◽

2009 ◽

Vol 466 (2117) ◽

pp. 1303-1325 ◽

Cited By ~ 48

Author(s):

Julie F. Waters ◽

Pradeep R. Guduru

Keyword(s):

Contact Area ◽

Phenomenological Model ◽

Plane Surface ◽

Strong Dependence ◽

Contact Problems ◽

Work Of Adhesion ◽

Rigid Sphere ◽

Mode Mixity ◽

Normal Loading ◽

Effective Work

Tangential loading in the presence of adhesion is highly relevant to biological locomotion, but mixed-mode contact of biological materials or similar soft elastomers remains to be well understood. To better capture the effects of dissipation in such contact problems owing to viscoelasticity or irreversible interfacial adhesive processes, a model is developed for the combined adhesive and tangential loading of a rigid sphere on a flat half-space which incorporates a phenomenological model of energy dissipation in the form of increased effective work of adhesion with increasing degree of mode mixity. To verify the model, contact experiments are performed on polydimethylsiloxane (PDMS) samples using a custom-built microtribometer. Measurements of contact area during mixed normal/tangential loading indicate that the strong dependence of the effective work of adhesion upon mode mixity can be captured effectively by the phenomenological model in the regime where the contact area stayed circular and the slip was negligible. Rate effects were seen to be described by a power-law dependence upon the crack front velocity, similar to observations of rate-dependent contact seen for pure normal loading.

Download Full-text

Discrete Element Analysis of High-Pressure Zones of Sea Ice on Vertical Structures

Journal of Marine Science and Engineering ◽

10.3390/jmse9030348 ◽

2021 ◽

Vol 9 (3) ◽

pp. 348

Author(s):

Xue Long ◽

Lu Liu ◽

Shewen Liu ◽

Shunying Ji

Keyword(s):

High Pressure ◽

Sea Ice ◽

Failure Mode ◽

Contact Area ◽

Loading Rate ◽

Discrete Element ◽

Offshore Platforms ◽

Marine Structures ◽

Element Analysis ◽

Ice Pressure

In cold regions, ice pressure poses a serious threat to the safe operation of ship hulls and fixed offshore platforms. In this study, a discrete element method (DEM) with bonded particles was adapted to simulate the generation and distribution of local ice pressures during the interaction between level ice and vertical structures. The strength and failure mode of simulated sea ice under uniaxial compression were consistent with the experimental results, which verifies the accuracy of the discrete element parameters. The crushing process of sea ice acting on the vertical structure simulated by the DEM was compared with the field test. The distribution of ice pressure on the contact surface was calculated, and it was found that the local ice pressure was much greater than the global ice pressure. The high-pressure zones in sea ice are mainly caused by its simultaneous destruction, and these zones are primarily distributed near the midline of the contact area of sea ice and the structure. The contact area and loading rate are the two main factors affecting the high-pressure zones. The maximum local and global ice pressures decrease with an increase in the contact area. The influence of the loading rate on the local ice pressure is caused by the change in the sea ice failure mode. When the loading rate is low, ductile failure of sea ice occurs, and the ice pressure increases with the increase in the loading rate. When the loading rate is high, brittle failure of sea ice occurs, and the ice pressure decreases with an increase in the loading rate. This DEM study of sea ice can reasonably predict the distribution of high-pressure zones on marine structures and provide a reference for the anti-ice performance design of marine structures.

Download Full-text

A simplified formulation of adhesion problems with elastic plates

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2009.0060 ◽

2009 ◽

Vol 465 (2107) ◽

pp. 2217-2230 ◽

Cited By ~ 24

Author(s):

Carmel Majidi ◽

George G. Adams

Keyword(s):

Potential Energy ◽

Contact Area ◽

Contact Region ◽

Bending Moment ◽

Total Potential Energy ◽

Work Of Adhesion ◽

Contact Radius ◽

Algebraic Complexity ◽

Elastic Plates ◽

Total Potential

The solution of adhesion problems with elastic plates generally involves solving a boundary-value problem with an assumed contact area. The contact region is then found by minimizing the total potential energy with respect to the contact area (i.e. the contact radius for the axisymmetric case). Such a procedure can be extremely long and tedious. Here, we show that the inclusion of adhesion is equivalent to specifying a discontinuous internal bending moment at the contact region boundary. The magnitude of this moment discontinuity is related to the work of adhesion and flexural rigidity of the plate. Such a formulation can greatly reduce the algebraic complexity of solving these problems. It is noted that the related plate contact problems without adhesion can also be solved by minimizing the total potential energy. However, it has long been recognized that it is mathematically more efficient to find the contact area by specifying a continuous internal bending moment at the boundary of the contact region. Thus, our moment discontinuity method can be considered to be a generalization of that procedure which is applicable for problems with adhesion.

Download Full-text

A Microstructure-Level Material Model for Simulating the Machining of Carbon Nanotube Reinforced Polymer Composites

Journal of Manufacturing Science and Engineering ◽

10.1115/1.2917564 ◽

2008 ◽

Vol 130 (3) ◽

Cited By ~ 15

Author(s):

Ashutosh Dikshit ◽

Johnson Samuel ◽

Richard E. DeVor ◽

Shiv G. Kapoor

Keyword(s):

Carbon Nanotube ◽

Weight Fraction ◽

Material Model ◽

Material Behavior ◽

Compression Tests ◽

Linear Elastic ◽

Rate Dependent ◽

Wide Range ◽

Parametrization Scheme ◽

Fraction Length

A continuum-based microstructure-level material model for simulation of polycarbonate carbon nanotube (CNT) composite machining has been developed wherein polycarbonate and CNT phases are modeled separately. A parametrization scheme is developed to characterize the microstructure of composites having different loadings of carbon nanotubes. The Mulliken and Boyce constitutive model [2006, “Mechanics of the Rate Dependent Elastic Plastic Deformation of Glassy Polymers from Low to High Strair Rates,” Int. J. Solids Struct., 43(5), pp. 1331–1356] for polycarbonate has been modified and implemented to capture thermal effects. The CNT phase is modeled as a linear elastic material. Dynamic mechanical analyzer tests are conducted on the polycarbonate phase to capture the changes in material behavior with temperature and strain rate. Compression tests are performed over a wide range of strain rates for model validation. The model predictions for yield stress are seen to be within 10% of the experimental results for all the materials tested. The model is used to study the effect of weight fraction, length, and orientation of CNTs on the mechanical behavior of the composites.

Download Full-text

Wetting transitions in droplet drying on soft materials

Nature Communications ◽

10.1038/s41467-019-12093-w ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 10

Author(s):

Julia Gerber ◽

Tobias Lendenmann ◽

Hadi Eghlidi ◽

Thomas M. Schutzius ◽

Dimos Poulikakos

Keyword(s):

Contact Line ◽

Traction Force ◽

Soft Materials ◽

Wetting Transition ◽

Surface Design ◽

Complex Processes ◽

Compliant Substrates ◽

Rate Dependent ◽

Liquid Removal ◽

Droplet Drying

Abstract Droplet interactions with compliant materials are familiar, but surprisingly complex processes of importance to the manufacturing, chemical, and garment industries. Despite progress—previous research indicates that mesoscopic substrate deformations can enhance droplet drying or slow down spreading dynamics—our understanding of how the intertwined effects of transient wetting phenomena and substrate deformation affect drying remains incomplete. Here we show that above a critical receding contact line speed during drying, a previously not observed wetting transition occurs. We employ 4D confocal reference-free traction force microscopy (cTFM) to quantify the transient displacement and stress fields with the needed resolution, revealing high and asymmetric local substrate deformations leading to contact line pinning, illustrating a rate-dependent wettability on viscoelastic solids. Our study has significance for understanding the liquid removal mechanism on compliant substrates and for the associated surface design considerations. The developed methodology paves the way to study complex dynamic compliant substrate phenomena.

Download Full-text