|Tetsuo Yamaguchi||Last modified date：2018.03.12|
Associate Professor / Machine elements and design engineering laboratory / Department of Mechanical Engineering / Faculty of Engineering
|Tetsuo Yamaguchi||Last modified date：2018.03.12|
|1.||Tetsuo Yamaguchi, Coexistence of fast/slow slips in sliding friction of elastic bodies, YITP Workshop on non Gaussian fluctuations in solids, 2017.03, We conducted friction experiments between polymer gels. We found that the slow slip phenomena and the fast slip coexist during friction. We explained the behavior with a theoretical model. .|
|2.||Tetsuo Yamaguchi, Laboratory experiment of seismic cycles using compliant viscoelastic materials, AGU Fall Meeting, 2016.12, It is well known that surface asperities at fault interfaces play an essential role in stick-slip friction.There have been many laboratory experiments conducted using rocks and some analogue materials to understand the effects of asperities and the underlying mechanisms. Among such materials, soft polymer gels have great advantages of slowing down propagating rupture front speed as well as shear wave speed: it facilitates observation of the dynamic rupture behavior. However, most experiments were done with bimaterial interfaces (combination of soft and hard materials) and there are few experiments with an identical (gel on gel) setup. Furthermore, there have been also few studies mentioning the link between local asperity contact and macroscopic dynamic rupture behavior. In this talk, we report our experimental studies on stick-slip friction between gels having controlled artificial asperities. We show that, depending on number density and configuration randomness of the asperities, the rupture behavior greatly changes: when the asperities are located periodically with optimum number densities, fast rupture propagation occurs, while slow and heterogeneous slip behavior is observed for samples having randomly located asperities. We discuss the importance of low frequency (large wavelength) excitation of the normal displacement contributing to weakening the fault interface. We also discuss the observed regular to slow slip transition with a simple model..|
|3.||Adhesion and Debonding learned from nature.|
|4.||Tetsuo Yamaguchi, Stick-slip Friction of Polymer Gels Having Controlled Surface Asperities, Materials Science and Technology 2016, 2016.10, We report our experimental studies on stick-slip friction between polymer gels having controlled artificial surface asperities. We show that, depending on number density and configuration randomness of the asperities, the stick-slip behavior greatly changes: when the asperities are located periodically with optimum number densities, fast and regular stick-slip motions occur, while slow and heterogeneous slip behavior is observed for samples having randomly located asperities. We discuss the importance of low frequency (large wavelength) excitation of the normal displacement contributing to weakening the frictional interface. We also discuss the observed regular to slow slip transition with a simple model..|
|5.||Dynamics of fatigue crack propagation and wear in brittle gels.|
|6.||Geometry, topology and fracture in cross-linked polymers.|
|7.||High precision prediction of dynamic instabilities.|
|8.||Tetsuo Yamaguchi, Yudai Onoue, Yoshinori Sawae, Geometry, topology, and fracture of model crosslinked polymers, EMN Meeting on Hydrogels, 2016.05, Toughening of crosslinked polymers like rubbers or gels is one of the most important problems in polymer science. While novel types of tough gels have been developed in the last decade, the toughening mechanism is not well understood: for example, it is not still so clear whether heterogeneous structures (molecular weight distributions) enhance the fracture toughness or weaken the system. In this study, we focus on geometrical aspects of crosslinked polymers (how the molecular weight distribution of partial chains affects toughness) as well as topological ones (how the network structure of polymers controls toughness). We created macroscopic crosslinked polymers made of rubber strings and connecters, and performed fracture experiments of such model polymers with various degrees of molecular weight variations and different topological structures, as shown in Fig1. We found that small degrees of heterogeneity of molecular weight contribute to weakening while large variations to slowing down of crack propagation and significant toughening. We also found that star-like polymers exhibited great improvement in toughness compared with regular structures. In our talk, we will explain the details of our experiments and discuss the results based on theoretical models..|
|9.||Tetsuo Yamaguchi, Yutaka Himeno, Yoshinori Sawae, Collective behavior of multiple asperities in sliding friction between polymer gels, International Tribology Conference Tokyo 2015, 2015.09, We report on our experimental studies on stick-slip motions between polymer gels having artificial surface asperities. We show that, depending on density and randomness in spacing of the asperities, the stick-slip behavior greatly changes. .|
|10.||Tetsuo Yamaguchi, Heterogeneous stick-slip friction in polymer gels, International Conference on Rheology and Modeling of Materials, 2015.10, We report our studies on stick-slip friction experiments inspired by seismic cycles in subduction zones. We conducted experiments between a Plexiglass block and a Silicone Gel plate driven at a constant plate velocity..|
|11.||Tetsuo Yamaguchi, Yutaka Himeno, Yoshinori Sawae, Stick-slip motions of polymer gels having multiple artificial asperities, Malaysian Tribology Conference, 2015.11, We report our experimental studies on stick-slip motions between polymer gels having artificial surface asperities. .|
|12.||Tetsuo Yamaguchi, Laboratory experiments for fault instability due to CO2 injection, I2CNER annual syposium of CO2 storage, 2016.02, We introduce our laboratory experiments on seismic faults and discuss possibilities to evaluate risk of seismicity due CO2 injection. .|
|13.||Physics of soft materials .|
|14.||Adhesion Debonding Dynamics of Gecko Inspired Adhesives.|
|15.||High precision prediction of dynamic instabilities.|
|16.||Tetsuo Yamaguchi, Dynamic friction of O-rings, 2015 HYDROGENIUS & I2CNER Tribology Symposium, 2015.02, We studied dynamic friction of rubber O-rings under compression conditions. We observed that O-rings inflate drastically in a heterogeneous manner. .|
|17.||Tetsuo Yamaguchi, Mechanics of a single gecko-like adhesive pad, World Congress on Adhesion and Related Problems, 2014.09, Gecko has attracted much attention from a wide range of scientists and engineers due to its superior adhesion properties of its feet, i.e., they can attach with sufficient strength as gecko needs and can easily detach from an object so that it can walk not only on the ground, on the wall, but also on the ceiling. Many efforts has been devoted to understand the underlying mechanisms on gecko pads and to mimic its performance. Some researchers studied gecko itself, while others created gecko-inspired adhesives having a large number of thin fibrils or other structures. On the other hand, Zhao and co-workers focused on the relationship between structure and function of a single spatula. They pointed out the importance of mechanics of a tilted adhesive pad with a curved stem to obtain easy adhesion/detachment properties. This approach of studying a single adhesive pad is considered to be important in terms of structural optimization of the gecko mimetic adhesives. .|
|18.||Tetsuo Yamaguchi, Effects of bulk transport in surface friction of hydrogels, IUMRS-ICA2014, 2014.08, When hydrogels are slid against a rigid and smooth substrate, they often exhibit low friction. As the low friction mechanisms, the following has been proposed: (1) formation of the static lubrication layer due to swelling of poly-electrolyte network and (2) reduction in effective normal stress of solid phase due to the biphasic lubrication. Among the above mechanisms, the biphasic lubrication mechanism becomes important for neutral gels (having no electrolyte inside polymer) in pure water environment. In this paper, we discuss the frictional properties of PVA (poly(vinyl alcohol) hydrogels within the framework of the biphasic lubrication. .|
|19.||Tetsuo Yamaguchi, Effects of electric fields on sliding friction of hydrogels, IUMRS-ICA2014, 2014.08, Frictional properties of hydrogels have attracted much attention due to its low friction. In particular, friction coefficient of polyelectrolyte hydrogels can be as small as 0.001. In this talk, we report our studies on friction of polyelectrolyte hydrogels and electric field effects, i.e., 1) friction control of polyelectrolyte hydrogels using electric fields and 2) preparation of polyelectrolyte hydrogels under electric fields. Through the discussions, we will point out the importance of electric charges for reduction or control in friction of hydrogels..|
|20.||Tetsuo Yamaguchi, Sliding friction of sticky gels, Gordon Research Conference on Tribology, 2014.07, When a soft and sticky gel is slid against a smooth surface, stick-slip motion does not occur grobally but in a localized manner.
As slip regions propagate, they move randomly: they start to move and arrest suddenly, coalesce with each other, break into several parts, or even wander around the frictional interface in backward direction. Furthermore, the slip size statistics follows the power law, like Gutenberg-Richter law for earthquakes. In this talk, we discuss why and how such complexity emerges during friction through the in-situ visualization of frictional stresses. .
|21.||Tetsuo Yamaguchi, Laboratory experiments of seismic cycles: effects of normal stress and its gradient, Seismological Society of America, Annual Meeting, 2014.04, We report our studies on laboratory experiments inspired by seismic cycles in subduction zones. We conducted friction experiments between a Plexiglass block and a Silicone Gel plate driven at a constant plate velocity . By changing the normal force and the inclination angle of the upper block, we controlled the normal stress level and its gradient. As a result, we successfully observed a wide variety of slip events and size statistics . In small normal force and small inclination angle conditions, slip events were dominated by slow events which occur uniformly at the block-plate interface, and the size statistics obeyed the power law with cutoff. In intermediate force and angle conditions, coexistence of small slow events in “deep” (large normal stress) regions and giant events rupturing “shallower” regions were clearly seen and the size distributions obeyed power-law with a peak at large sizes. In larger force and angle conditions, however, the giant slip events disappeared and only small and intermediate slip events were observed. Interestingly, when we did experiments at the boundary between the latter two regimes, very complex stick-slip cycles wandering about the latter 2 dynamics modes were seen.
Based on our visualization of 2D displacement fields at the frictional interface, we determined epicenter, rupture area, and the moment magnitude for each event, and we also estimated 2D stress distributions during stress accumulation processes. We found that rupture behavior for a giant event was significantly influenced by the stress distribution or stress history before the event. .
|22.||Tetsuo Yamaguchi, Spatio-tempoal heterogeneity in sliding friction of soft and hard matter
, Workshop on Non-equilibrium complex fluids, 2013.03, Sliding friction is a well-known phenomenon in our daily life, but many questions remain unsloved. Quite recently, importance of spatio-temporal heterogeneity has been realized in some examples. In this presentation, I will present 2 different topics: (i) laboratory earthquake experiments using polymer gels, and (ii) theory on oxidative wear of metals. Through these geophysical and mechanical
engineering problems, I would like to point out that spatio-temporal heterogeneity is essential in understanding the steady state in sliding friction..
|23.||Tetsuo Yamaguchi, Spatio-temporal behavior in sliding friction of polymer gels, International Symposium on Research Frontiers of Physics, Earth and Space Science, 2013.12, We report on our experimental studies of the sliding friction between a hard poly-methyl methacrylate (PMMA, plexiglass) block and a soft poly-dimethyl siloxane (PDMS, silicone) gel plate to mimic seismic cycles in subduction zones. Spatio-temporally heterogeneous stick-slip motions were observed and the statistics of the slip size obeyed power-law distributions. By changing the inclination angle (corresponding to the subduction angle) of the upper block, the system underwent subcritical-supercritical-subcritical re-entrant transitions. In particular, at larger inclination angles, slip events were made of slow slip at the large normal stress region (corresponding to deep region) and fast rupture at the intermediate or small normal stress region, and sometimes slow slip triggered fast and giant events. We applied the PIV (Particle Image Velocimetry) technique to visualize 2D distributions of the particle velocity and the shear stress at the frictional interface. We succeeded in visualizing the rupture processes of slip events and also heterogeneous accumulation of the stress fields towards a large slip event. In this presentation, we will report further details of our results. .|
|24.||Tetsuo Yamaguchi, Teruo Murakami, Effects of bulk transport on surface friction of hydrogels, World triboloy Congress, 2013.09, When hydrogels are slid against a rigid and smooth substrate, they often exhibit low friction. As the low friction mechanisms, the following are proposed: (1) formation of the static lubrication layer due to swelling of poly-electrolyte network, (2) formation of the protective layer due to protein/lipid adsorption, and (3) reduction in effective normal stress of solid phase due to the biphasic lubrication. Among the above 3 mechanisms, the biphasic lubrication mechanism becomes important for neutral gels (having no electrolyte inside polymer) in pure water environment. In this paper, we discuss the frictional properties of PVA (poly(vinyl alcohol) hydrogels within the framework of the biphasic lubrication. .|
|25.||Mechanical approaches for developpment of gecko-inspired structures.|
|26.||Tetsuo Yamaguchi, Fast and Slow Earthquakes in Laboratory Experiments, AOGS2013, 2013.06, We report on experimental studies of spatio-temporally heterogeneous stick-slip motions in the sliding friction between a hard poly-methyl methacrylate (PMMA, plexiglass) block and a soft poly-dimethyl siloxane (PDMS, silicone) gel plate. In our experiment, the statistics of the slip size shows the Gutenberg-Richter law as well as the peak at a size corresponding to giant slip events. We also prepared gels having more viscous characters, and studied the size-duration relation. It obeys $T \to M_0^(1/2)$, which is similar to that reported by Ide. By applying the PIV technique to visualize 2D distributions of the particle velocity during slip events and of the shear stress during stick-slip cycles, we succeeded in visualizing the rupture process of slip events and also heterogeneous accumulation of the stress fields towards a large slip event. In the presentation, we will report more details of our results. .|
|27.||Tetsuo Yamaguchi, Ryuji Suzuki, Masao Doi, Frictional property of hydrogels prepared under electric fields, Biotribology Xian, 2012.05, In this presentation, we propose a simple method to facilitate the surface modification on gels: gelation of a neutral gel with a small amount of electrolyte monomers under electric fields. .|
|28.||Tetsuo Yamaguchi, Gutenberg-Richter law, giant earthquakes and slow events in laboratory experiment, ECGS Workshop: Earthquake Source Physics on Various Scales, 2012.10, We report on experimental studies of spatio-temporally heterogeneous stick-slip motions in the sliding friction between a hard poly-methyl methacrylate (PMMA, plexiglass) block and a soft poly-dimethyl siloxane (PDMS, silicone) gel plate. .|
|29.||Tetsuo Yamaguchi, Sliding friction of polymer gels: from slippery to sticky surfaces, Joint Symposium of ISPMS'12 & OUMS'12, 2012.11, In this presentation, we introduce our two different topics discussing low friction and high friction in polymer gels. The first topic is the effects of stress-diffusion coupling (“biphasic lubrication” in biomechanics society) in sliding friction of PVA (poly-vinyl alcohol) hydrogels, where frictional behavior is dominated by transient diffusive process of water. In the second part, we discuss spatio-temporally heterogeneous stick-slip motions in sliding friction of adhesive gel-sheets. The system shows formation of the inchworm-like detachment waves (Schallamach waves) in the frictional interface and exhibits regular-chaos transition of the detachment wave patterns, dependent on the driving velocity. Through these two examples, we will stress the importance of coarse-grained or mesoscopic description on frictional properties for polymer gels..|
|30.||When soft and sticky materials are detached from or slid against a rigid substrate, specific types of meso-scale dynamics accompanying large deformation and pattern formation are observed. In this paper, we introduce our studies on the in-situ visualization of cavitation during debonding of soft adhesives and also of the Schallamach waves in sliding friction of adhesive gel- sheets. .|
|31.||Tetsuo Yamaguchi, Gutenberg-Richter law, giant earthquakes and slow events in laboratory experiment, Americal Geophysical Union Fall Meeting, 2012.12, We report on experimental studies of spatio-temporally heterogeneous stick-slip motions in the sliding friction between a hard poly-methyl methacrylate (PMMA, plexiglass) block and a soft poly-dimethyl siloxane (PDMS, silicone) gel plate..|
|32.||Tetsuo Yamaguchi, Non-linear Mechanics in Debonding of Pressure-Sensitive Adhesives, The Adhesion Society Annual Meeting, 2013.03, We report on the debonding process of a double-sided adhesive tape sandwiched between two glass plates as an example showing the importance of non-linear mechanics in pressure-sensitive adhesives. .|
|33.||Tetsuo Yamaguchi, Sliding friction of sticky gel-sheets, The Adhesion Society Annual Meeting, 2013.03, We report our recent results on the image analyses of the spatio-temporal patterns of the stick-slip motions. .|