Elena Pierro - Profile on Academia.edu (original) (raw)
Papers by Elena Pierro
Journal of Vibration and Control
Polymers are ultra-versatile materials that adapt to a myriad of applications, as they can be des... more Polymers are ultra-versatile materials that adapt to a myriad of applications, as they can be designed appropriately for specific needs. The realization of new compounds, however, requires the appropriate experimental characterizations, also from the mechanical point of view, which is typically carried out by analyzing the vibrations of beams, but which still have some unclear aspects, with respect to the well-known dynamics of elastic beams. To address this shortcoming, the paper deals with the theoretical modeling of a viscoelastic beam dynamics and pursues the elucidation of underlying how the flexural vibrations may be affected when an axial pre-load, compressive or tensile, is applied. The analytical model presented is able to shed light on a peculiar behavior, which is strongly related to the frequency-dependent damping induced by viscoelasticity. By considering as an example a real polymer, that is, a synthetic rubber, it is disclosed that an axial pre-load, in certain condit...
Cornell University - arXiv, Nov 29, 2018
We discuss the Brownian thermal noise which affects the cantilever dynamics of a dAFM (dynamic at... more We discuss the Brownian thermal noise which affects the cantilever dynamics of a dAFM (dynamic atomic force microscope), both when it works in air and in presence of water. Our scope is to accurately describe the cantilever dynamics, and to get this result we deeply investigate the relationship between the cantilever thermal fluctuations and its interactions with the surrounding liquid. We present a relatively simple and very easy-to-use analytical model to describe the interaction forces between the liquid and the cantilever. The novelty of this approach is that, under the assumption of small cantilever oscillations, by using the superposition principle we found a very simple integral expression to describe fluid-cantilever interactions. More specifically we note that, beside including fluid inertia and viscosity (which is common to many existing models in the literature) an additional diffisivity term needs to be considered, whose crucial influence for the correct evaluation of the cantilever response to the thermal excitation is shown in the present paper. The coefficients of our model are obtained by using numerical results for a 2D fluid flow around a vibrating rectangular cross-section, and depend on the distance from the wall. This allowed us to completely characterize the dynamics of a dAFM cantilever also when it operates in tilted conditions. We validate the analytical model by comparing our results with numerical and experimental dAFM data previously presented in literature, and with experiments carried out by ourselves. We show that we can provide extremely accurate prediction of the beam response up and beyond the second resonant peak.
Advanced Theory and Simulations
We discuss the Brownian thermal noise which affects the cantilever dynamics of a dAFM (dynamic at... more We discuss the Brownian thermal noise which affects the cantilever dynamics of a dAFM (dynamic atomic force microscope), both when it works in air and in presence of water. Our scope is to accurately describe the cantilever dynamics, and to get this result we deeply investigate the relationship between the cantilever thermal fluctuations and its interactions with the surrounding liquid. We present a relatively simple and very easy-to-use analytical model to describe the interaction forces between the liquid and the cantilever. The novelty of this approach is that, under the assumption of small cantilever oscillations, by using the superposition principle we found a very simple integral expression to describe fluid-cantilever interactions. More specifically we note that, beside including fluid inertia and viscosity (which is common to many existing models in the literature) an additional diffisivity term needs to be considered, whose crucial influence for the correct evaluation of the cantilever response to the thermal excitation is shown in the present paper. The coefficients of our model are obtained by using numerical results for a 2D fluid flow around a vibrating rectangular cross-section, and depend on the distance from the wall. This allowed us to completely characterize the dynamics of a dAFM cantilever also when it operates in tilted conditions. We validate the analytical model by comparing our results with numerical and experimental dAFM data previously presented in literature, and with experiments carried out by ourselves. We show that we can provide extremely accurate prediction of the beam response up and beyond the second resonant peak.
Contact Mechanics of Mushroom-Shaped Adhesive Structures
Bio-inspired Structured Adhesives, 2017
Very recently, both experimental and theoretical investigations have shown that micro-structured ... more Very recently, both experimental and theoretical investigations have shown that micro-structured surfaces covered with mushroom shaped micropillars present strongly enhanced adhesive properties if compared to surfaces covered with cylindrical micropillars made of the same material. However, different geometries lead to different adhesive performance, and finding the optimal solution has become of utmost importance. In this chapter we summarize the main detachment mechanisms of flat-topped and mushroom-topped soft micro pillars and show how the geometry of the pillars should be designed in order to obtain the best adhesive performances. We also discuss the effect of air entrapment at the interface between the pillar and the substrate and investigate the influence of the non-uniform pillar height and thermal fluctuations on pull-off force. Comparisons with experiments are shown, to assess the theoretical findings, and the influence of the effect of tilted pull-off on the adhesion of individual mushroom shaped pillar is evaluated.
Tuning the Mechanical Properties of the Viscoelastic Materials, for the Improvement of Their Adhesive Performance
Lecture Notes in Mechanical Engineering, 2022
MEMS-based Tuning Fork microgyroscopes: Dynamical response and functional design
EMA and OMA techniques for vibro-acoustically coupled systems: the example of a helicopter cabin
Noise and vibration levels in vibro-acoustical systems are strictly related, meaning that a good ... more Noise and vibration levels in vibro-acoustical systems are strictly related, meaning that a good knowledge of the structural dynamics is a useful tool for their reduction. Through an intensive testing campaign on a EC-135 helicopter cabin, a few guidelines are given in order to properly capture the coupled vibro-acoustical behaviour of systems. In particular, four experimental modal analyses have been performed on the cabin, a pure acoustical modal analysis of the enclosure, an experimental modal analysis of the internal and external surface and an operational modal analysis of the external surface. The results presented highlight that a direct acoustical excitation is preferred also for the external part in controlled laboratory conditions and an acoustical reference would be more efficient for operational modal analyses
A new technique for the characterization of viscoelastic materials: Theory, experiments and comparison with DMA
Journal of Sound and Vibration
Proceedings of the 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015)
Viscoelastic materials are widely utilized in different engineering areas, however it is still no... more Viscoelastic materials are widely utilized in different engineering areas, however it is still not so easy to properly assess their mechanical properties, in terms of viscoelastic-frequency dependent modulus. Standard experimental procedures are utilized in this direction (e.g. DMA-Dynamic mechanical analysis), but such techniques still present some complexities, and this is why possible alternative approaches would be desirable. For example, the experimental investigation of a viscoelastic beam dynamics would be challenging, especially for the intrinsic simplicity of this kind of test. In this direction, a deep understanding of damping mechanisms in viscoelastic beams results to be a quite important task to better predict their dynamics. With the aim to elucidate damping properties in such structures, in this paper an analytical study of the transversal vibrations of a viscoelastic beam is presented. By means of a dimensional analysis, some key parameters are presented, which depend on the material properties and the beam geometry. In this way, by properly tuning such disclosed parameters, e.g. the dimensionless beam length once the material is chosen, it is possible to enhance or suppress some resonant peaks, one at a time or more simultaneously. This is a remarkable possibility to efficiently control damping in these structures, and the results presented in this paper may help in elucidating experimental procedures for the characterization of viscoelastic materials. 4396 COMPDYN 2019 7 th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering M. Papadrakakis, M. Fragiadakis (eds.
Road vehicles travelling with time-dependent speed: theoretical study on the directional stability
Vehicle System Dynamics
Journal of Vibration and Control
Viscoelasticity plays a key role in many practical applications and in different research fields,... more Viscoelasticity plays a key role in many practical applications and in different research fields, such as in seals, sliding-rolling contacts, and crack propagation. In all these contexts, a proper knowledge of the viscoelastic modulus is very important. However, experimental characterization of the frequency-dependent modulus, carried out through different standard procedures, still presents some complexities; then possible alternative approaches are desirable. For example, experimental investigation of viscoelastic beam dynamics would be challenging, especially for the intrinsic simplicity of this kind of test. This is why a deep understanding of damping mechanisms in viscoelastic beams is found to be a quite important task to better predict their dynamics. With the aim to enlighten damping properties in such structures, an analytical study of the transversal vibrations of a viscoelastic beam is presented in this article. Some dimensionless parameters are defined, depending on the ...
On the peeling of elastic tapes from viscoelastic substrates: Designing materials for ultratough peeling
Tribology International
The Influence of the Fractal Dimension of Rough Surfaces on the Adhesion of Elastic Materials
Journal of Adhesion Science and Technology, 2012
ABSTRACT In this paper we analyse the adhesion between a rubber block and a rigid randomly rough ... more ABSTRACT In this paper we analyse the adhesion between a rubber block and a rigid randomly rough profile. The focus of the investigation is on the influence of the work of adhesion and of the fractal dimension Df of the rough profile on the contact behaviour. In particular, we analyse how the contact area and the power spectral density of the deformed profile are affected by the two aforementioned quantities. We find that at sufficiently small loads the influence of Df is negligible. However, the scenario strongly changes at higher loads as Df strongly affects the number of contact spots. Calculations show that the contact area depends linearly on the work of adhesion, whereas only a negligible influence of the work of adhesion is found on the power spectral density (PSD) of the deformed profile. © 2012 Copyright Taylor and Francis Group, LLC.
![Research paper thumbnail of Publisher's Note: Loading-unloading hysteresis loop of randomly rough adhesive contacts [Phys. Rev. E92, 062404 (2015)]](https://attachments.academia-assets.com/73763102/thumbnails/1.jpg)
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Loading-unloading hysteresis loop of randomly rough adhesive contacts
Physical review. E, Statistical, nonlinear, and soft matter physics, 2015
We investigate the loading and unloading behavior of soft solids in adhesive contact with randoml... more We investigate the loading and unloading behavior of soft solids in adhesive contact with randomly rough profiles. The roughness is assumed to be described by a self-affine fractal on a limited range of wave vectors. A spectral method is exploited to generate such randomly rough surfaces. The results are statistically averaged, and the calculated contact area and applied load are shown as a function of the penetration, for loading and unloading conditions. We found that the combination of adhesion forces and roughness leads to a hysteresis loading-unloading loop. This shows that energy can be lost simply as a consequence of roughness and van der Waals forces, as in this case a large number of local energy minima exist and the system may be trapped in metastable states. We numerically quantify the hysteretic loss and assess the influence of the surface statistical properties and the energy of adhesion on the hysteresis process.
Experimental Guidelines for NVH Improvements in Helicopter Vibro-Acoustic Comfort
Volume 1: 22nd Biennial Conference on Mechanical Vibration and Noise, Parts A and B, 2009
The noise of helicopters has started to become an important issue and the next level technical ch... more The noise of helicopters has started to become an important issue and the next level technical challenge is to include new design parameters such as vibro-acoustic comfort in the design process of a modern rotorcraft. In this scenario a wide experimental campaign has been ...
Eighth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, 2008
ABSTRACT This paper presents a comprehensive study between accelerometer, laser vibrometer and mi... more ABSTRACT This paper presents a comprehensive study between accelerometer, laser vibrometer and microflown probe measurements aimed at comparison of modal model quality assessment. Object of an investigation was a large composite fuselage panel. An extensive test campaign was performed with application of SIMO, MIMO, random and harmonic excitation, velocity and acceleration sensors, contact and non-contact measurement techniques. Advantages and disadvantages of applied instrumentation are discussed taking into account test data variability and the trade-off between workload and test data quality. Presented are real-life measurement problems related to the specific set up conditions. Finally a statistical analysis of estimated models is evaluated to bring to light general assessment of test campaign. Such assessment has a vital importance of successful fault detection based on modal parameters observation as well as in uncertain non-deterministic numerical model updating.
Noise Control, Reduction and Cancellation Solutions in Engineering, 2012
Soft Matter, 2011
The superlative adhesive properties of some biological attachment systems, such as those of gecko... more The superlative adhesive properties of some biological attachment systems, such as those of geckos, spiders, and insects, have inspired researchers from different fields (e.g. biology, physics and engineering) to conceive and design man-made microstructured surfaces that might mimic their performance. Among the several proposed designs, very recently mushroom-shaped adhesive microstructures have drawn the interest of scientists and engineers, because experiments have proved their superiority compared to other micro-and nano-structures. In this article, we explain theoretically the physical mechanism behind the enhanced adhesion of such microstructures, and provide for the first time a useful tool to predict adhesive performance depending on the geometry, mechanical properties of the material, and energy of adhesion. Our theoretical predictions are strongly supported by the available experimental data. The present study can streamline the optimisation of adhesive microstructures for industrial applications.
Soft Matter, 2012
Recent theoretical and experimental studies have shown that mushroom shaped micro-pillars exhibit... more Recent theoretical and experimental studies have shown that mushroom shaped micro-pillars exhibit strongly enhanced adhesive performance in comparison to other pillar shapes. However, in the presence of interfacial impurities (e.g. solid particles or air bubbles) the adhesive strength could drastically drop. In this paper we theoretically investigate the effect of the entrapment of micro-bubbles of air at the interface between the mushroom shaped micro-pillar and a rigid substrate on the adhesive performance. We calculate the critical pull-off stress as a function of the initial volume of the entrapped air, and compare these results with those obtained when, instead of air, small external solid particles are entrapped at the interface. Our results show that the presence of entrapped air is more critical since it strongly reduces the suction effect. The critical stress, indeed, is about 35-40% smaller than the value observed in the case of solid particles, thus resulting in a considerable reduction of the adhesive performance of the mushroom shaped pillar.
Journal of Vibration and Control
Polymers are ultra-versatile materials that adapt to a myriad of applications, as they can be des... more Polymers are ultra-versatile materials that adapt to a myriad of applications, as they can be designed appropriately for specific needs. The realization of new compounds, however, requires the appropriate experimental characterizations, also from the mechanical point of view, which is typically carried out by analyzing the vibrations of beams, but which still have some unclear aspects, with respect to the well-known dynamics of elastic beams. To address this shortcoming, the paper deals with the theoretical modeling of a viscoelastic beam dynamics and pursues the elucidation of underlying how the flexural vibrations may be affected when an axial pre-load, compressive or tensile, is applied. The analytical model presented is able to shed light on a peculiar behavior, which is strongly related to the frequency-dependent damping induced by viscoelasticity. By considering as an example a real polymer, that is, a synthetic rubber, it is disclosed that an axial pre-load, in certain condit...
Cornell University - arXiv, Nov 29, 2018
We discuss the Brownian thermal noise which affects the cantilever dynamics of a dAFM (dynamic at... more We discuss the Brownian thermal noise which affects the cantilever dynamics of a dAFM (dynamic atomic force microscope), both when it works in air and in presence of water. Our scope is to accurately describe the cantilever dynamics, and to get this result we deeply investigate the relationship between the cantilever thermal fluctuations and its interactions with the surrounding liquid. We present a relatively simple and very easy-to-use analytical model to describe the interaction forces between the liquid and the cantilever. The novelty of this approach is that, under the assumption of small cantilever oscillations, by using the superposition principle we found a very simple integral expression to describe fluid-cantilever interactions. More specifically we note that, beside including fluid inertia and viscosity (which is common to many existing models in the literature) an additional diffisivity term needs to be considered, whose crucial influence for the correct evaluation of the cantilever response to the thermal excitation is shown in the present paper. The coefficients of our model are obtained by using numerical results for a 2D fluid flow around a vibrating rectangular cross-section, and depend on the distance from the wall. This allowed us to completely characterize the dynamics of a dAFM cantilever also when it operates in tilted conditions. We validate the analytical model by comparing our results with numerical and experimental dAFM data previously presented in literature, and with experiments carried out by ourselves. We show that we can provide extremely accurate prediction of the beam response up and beyond the second resonant peak.
Advanced Theory and Simulations
We discuss the Brownian thermal noise which affects the cantilever dynamics of a dAFM (dynamic at... more We discuss the Brownian thermal noise which affects the cantilever dynamics of a dAFM (dynamic atomic force microscope), both when it works in air and in presence of water. Our scope is to accurately describe the cantilever dynamics, and to get this result we deeply investigate the relationship between the cantilever thermal fluctuations and its interactions with the surrounding liquid. We present a relatively simple and very easy-to-use analytical model to describe the interaction forces between the liquid and the cantilever. The novelty of this approach is that, under the assumption of small cantilever oscillations, by using the superposition principle we found a very simple integral expression to describe fluid-cantilever interactions. More specifically we note that, beside including fluid inertia and viscosity (which is common to many existing models in the literature) an additional diffisivity term needs to be considered, whose crucial influence for the correct evaluation of the cantilever response to the thermal excitation is shown in the present paper. The coefficients of our model are obtained by using numerical results for a 2D fluid flow around a vibrating rectangular cross-section, and depend on the distance from the wall. This allowed us to completely characterize the dynamics of a dAFM cantilever also when it operates in tilted conditions. We validate the analytical model by comparing our results with numerical and experimental dAFM data previously presented in literature, and with experiments carried out by ourselves. We show that we can provide extremely accurate prediction of the beam response up and beyond the second resonant peak.
Contact Mechanics of Mushroom-Shaped Adhesive Structures
Bio-inspired Structured Adhesives, 2017
Very recently, both experimental and theoretical investigations have shown that micro-structured ... more Very recently, both experimental and theoretical investigations have shown that micro-structured surfaces covered with mushroom shaped micropillars present strongly enhanced adhesive properties if compared to surfaces covered with cylindrical micropillars made of the same material. However, different geometries lead to different adhesive performance, and finding the optimal solution has become of utmost importance. In this chapter we summarize the main detachment mechanisms of flat-topped and mushroom-topped soft micro pillars and show how the geometry of the pillars should be designed in order to obtain the best adhesive performances. We also discuss the effect of air entrapment at the interface between the pillar and the substrate and investigate the influence of the non-uniform pillar height and thermal fluctuations on pull-off force. Comparisons with experiments are shown, to assess the theoretical findings, and the influence of the effect of tilted pull-off on the adhesion of individual mushroom shaped pillar is evaluated.
Tuning the Mechanical Properties of the Viscoelastic Materials, for the Improvement of Their Adhesive Performance
Lecture Notes in Mechanical Engineering, 2022
MEMS-based Tuning Fork microgyroscopes: Dynamical response and functional design
EMA and OMA techniques for vibro-acoustically coupled systems: the example of a helicopter cabin
Noise and vibration levels in vibro-acoustical systems are strictly related, meaning that a good ... more Noise and vibration levels in vibro-acoustical systems are strictly related, meaning that a good knowledge of the structural dynamics is a useful tool for their reduction. Through an intensive testing campaign on a EC-135 helicopter cabin, a few guidelines are given in order to properly capture the coupled vibro-acoustical behaviour of systems. In particular, four experimental modal analyses have been performed on the cabin, a pure acoustical modal analysis of the enclosure, an experimental modal analysis of the internal and external surface and an operational modal analysis of the external surface. The results presented highlight that a direct acoustical excitation is preferred also for the external part in controlled laboratory conditions and an acoustical reference would be more efficient for operational modal analyses
A new technique for the characterization of viscoelastic materials: Theory, experiments and comparison with DMA
Journal of Sound and Vibration
Proceedings of the 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015)
Viscoelastic materials are widely utilized in different engineering areas, however it is still no... more Viscoelastic materials are widely utilized in different engineering areas, however it is still not so easy to properly assess their mechanical properties, in terms of viscoelastic-frequency dependent modulus. Standard experimental procedures are utilized in this direction (e.g. DMA-Dynamic mechanical analysis), but such techniques still present some complexities, and this is why possible alternative approaches would be desirable. For example, the experimental investigation of a viscoelastic beam dynamics would be challenging, especially for the intrinsic simplicity of this kind of test. In this direction, a deep understanding of damping mechanisms in viscoelastic beams results to be a quite important task to better predict their dynamics. With the aim to elucidate damping properties in such structures, in this paper an analytical study of the transversal vibrations of a viscoelastic beam is presented. By means of a dimensional analysis, some key parameters are presented, which depend on the material properties and the beam geometry. In this way, by properly tuning such disclosed parameters, e.g. the dimensionless beam length once the material is chosen, it is possible to enhance or suppress some resonant peaks, one at a time or more simultaneously. This is a remarkable possibility to efficiently control damping in these structures, and the results presented in this paper may help in elucidating experimental procedures for the characterization of viscoelastic materials. 4396 COMPDYN 2019 7 th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering M. Papadrakakis, M. Fragiadakis (eds.
Road vehicles travelling with time-dependent speed: theoretical study on the directional stability
Vehicle System Dynamics
Journal of Vibration and Control
Viscoelasticity plays a key role in many practical applications and in different research fields,... more Viscoelasticity plays a key role in many practical applications and in different research fields, such as in seals, sliding-rolling contacts, and crack propagation. In all these contexts, a proper knowledge of the viscoelastic modulus is very important. However, experimental characterization of the frequency-dependent modulus, carried out through different standard procedures, still presents some complexities; then possible alternative approaches are desirable. For example, experimental investigation of viscoelastic beam dynamics would be challenging, especially for the intrinsic simplicity of this kind of test. This is why a deep understanding of damping mechanisms in viscoelastic beams is found to be a quite important task to better predict their dynamics. With the aim to enlighten damping properties in such structures, an analytical study of the transversal vibrations of a viscoelastic beam is presented in this article. Some dimensionless parameters are defined, depending on the ...
On the peeling of elastic tapes from viscoelastic substrates: Designing materials for ultratough peeling
Tribology International
The Influence of the Fractal Dimension of Rough Surfaces on the Adhesion of Elastic Materials
Journal of Adhesion Science and Technology, 2012
ABSTRACT In this paper we analyse the adhesion between a rubber block and a rigid randomly rough ... more ABSTRACT In this paper we analyse the adhesion between a rubber block and a rigid randomly rough profile. The focus of the investigation is on the influence of the work of adhesion and of the fractal dimension Df of the rough profile on the contact behaviour. In particular, we analyse how the contact area and the power spectral density of the deformed profile are affected by the two aforementioned quantities. We find that at sufficiently small loads the influence of Df is negligible. However, the scenario strongly changes at higher loads as Df strongly affects the number of contact spots. Calculations show that the contact area depends linearly on the work of adhesion, whereas only a negligible influence of the work of adhesion is found on the power spectral density (PSD) of the deformed profile. © 2012 Copyright Taylor and Francis Group, LLC.
Loading-unloading hysteresis loop of randomly rough adhesive contacts
Physical review. E, Statistical, nonlinear, and soft matter physics, 2015
We investigate the loading and unloading behavior of soft solids in adhesive contact with randoml... more We investigate the loading and unloading behavior of soft solids in adhesive contact with randomly rough profiles. The roughness is assumed to be described by a self-affine fractal on a limited range of wave vectors. A spectral method is exploited to generate such randomly rough surfaces. The results are statistically averaged, and the calculated contact area and applied load are shown as a function of the penetration, for loading and unloading conditions. We found that the combination of adhesion forces and roughness leads to a hysteresis loading-unloading loop. This shows that energy can be lost simply as a consequence of roughness and van der Waals forces, as in this case a large number of local energy minima exist and the system may be trapped in metastable states. We numerically quantify the hysteretic loss and assess the influence of the surface statistical properties and the energy of adhesion on the hysteresis process.
Experimental Guidelines for NVH Improvements in Helicopter Vibro-Acoustic Comfort
Volume 1: 22nd Biennial Conference on Mechanical Vibration and Noise, Parts A and B, 2009
The noise of helicopters has started to become an important issue and the next level technical ch... more The noise of helicopters has started to become an important issue and the next level technical challenge is to include new design parameters such as vibro-acoustic comfort in the design process of a modern rotorcraft. In this scenario a wide experimental campaign has been ...
Eighth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, 2008
ABSTRACT This paper presents a comprehensive study between accelerometer, laser vibrometer and mi... more ABSTRACT This paper presents a comprehensive study between accelerometer, laser vibrometer and microflown probe measurements aimed at comparison of modal model quality assessment. Object of an investigation was a large composite fuselage panel. An extensive test campaign was performed with application of SIMO, MIMO, random and harmonic excitation, velocity and acceleration sensors, contact and non-contact measurement techniques. Advantages and disadvantages of applied instrumentation are discussed taking into account test data variability and the trade-off between workload and test data quality. Presented are real-life measurement problems related to the specific set up conditions. Finally a statistical analysis of estimated models is evaluated to bring to light general assessment of test campaign. Such assessment has a vital importance of successful fault detection based on modal parameters observation as well as in uncertain non-deterministic numerical model updating.
Noise Control, Reduction and Cancellation Solutions in Engineering, 2012
Soft Matter, 2011
The superlative adhesive properties of some biological attachment systems, such as those of gecko... more The superlative adhesive properties of some biological attachment systems, such as those of geckos, spiders, and insects, have inspired researchers from different fields (e.g. biology, physics and engineering) to conceive and design man-made microstructured surfaces that might mimic their performance. Among the several proposed designs, very recently mushroom-shaped adhesive microstructures have drawn the interest of scientists and engineers, because experiments have proved their superiority compared to other micro-and nano-structures. In this article, we explain theoretically the physical mechanism behind the enhanced adhesion of such microstructures, and provide for the first time a useful tool to predict adhesive performance depending on the geometry, mechanical properties of the material, and energy of adhesion. Our theoretical predictions are strongly supported by the available experimental data. The present study can streamline the optimisation of adhesive microstructures for industrial applications.
Soft Matter, 2012
Recent theoretical and experimental studies have shown that mushroom shaped micro-pillars exhibit... more Recent theoretical and experimental studies have shown that mushroom shaped micro-pillars exhibit strongly enhanced adhesive performance in comparison to other pillar shapes. However, in the presence of interfacial impurities (e.g. solid particles or air bubbles) the adhesive strength could drastically drop. In this paper we theoretically investigate the effect of the entrapment of micro-bubbles of air at the interface between the mushroom shaped micro-pillar and a rigid substrate on the adhesive performance. We calculate the critical pull-off stress as a function of the initial volume of the entrapped air, and compare these results with those obtained when, instead of air, small external solid particles are entrapped at the interface. Our results show that the presence of entrapped air is more critical since it strongly reduces the suction effect. The critical stress, indeed, is about 35-40% smaller than the value observed in the case of solid particles, thus resulting in a considerable reduction of the adhesive performance of the mushroom shaped pillar.