Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session G49: Fracture, Friction, and Deformation |
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Sponsoring Units: GSOFT Chair: Mike Salerno, Sandia National Laboratories Room: 217D |
Tuesday, March 3, 2015 11:15AM - 11:27AM |
G49.00001: Popping balloons: formation of a crack network in rubber membranes Sebastien Moulinet, Mokhtar Adda-bedia Everyone can make the observation: a rubber balloon inflated until it spontaneously pop breaks into a large number of shreds. In contrast, a balloon pierced with a needle at an early stage of its inflation breaks into two large pieces. Using model latex balloons, we have experimentally investigated the transition between these two breaking regimes. We have showed that, above a threshold stress in the latex membrane, a single crack become unstable and separates into two new cracks. Then, a cascade of tip-splitting generates a network of cracks that eventually form a large number of fragments. We have observed that the instability of the crack occurs when it reaches a limit velocity that could the speed of sound. By studying the energy balance during the explosion, we can determine the intrinsic fracture energy of rubber, a measurement difficult to achieve with usual tensile testing. [Preview Abstract] |
Tuesday, March 3, 2015 11:27AM - 11:39AM |
G49.00002: Do thermal fluctuations stabilize an extensible buckling rod? Deshpreet Bedi, Xiaoming Mao The classical problem of a rod buckling under a compressive force, ``Euler buckling,'' has long been studied and solved in physics; however, the classical theory of Euler buckling does not take into account thermal fluctuations. At small enough scales, entropic effects become significant, and a more intricate analysis incorporating thermal fluctuations is needed, for instance, in the study of biopolymers and nanotubes. In this talk, we discuss buckling of an extensible, semi-flexible rod embedded in two and three dimensions. We systematically examine the problem both analytically, using a momentum-space renormalization group procedure, and numerically, using Monte Carlo simulations, to determine the topology of the phase diagram containing the unbuckled and buckled states. In two dimensions, for instance, we determine that thermal fluctuations tend to stabilize the straight-rod state over the buckled state and that this stabilization increases with temperature. We also analyze the mechanical response of the rod in order to study the differing scaling regimes of the system. [Preview Abstract] |
Tuesday, March 3, 2015 11:39AM - 11:51AM |
G49.00003: Localized Disturbance in a 2D Cohesive Granular Packing Jennifer Rieser, Mathilde Laplagne, Douglas Durian How the local structural configuration influences large-scale deformation in disordered materials is not known. Inspired by nano-indentation experiments, we characterize the response of disordered granular packing to a localized disturbance by driving a triangular wedge into the packing. The extent of the disturbance is explored by performing experiments with several wedge angles. The two-dimensionality of the system allows for direct observation of all particle dynamics during the indentation. The grains can be cohesive, with an attraction governed by tunable capillary forces that are induced through an interstitial fluid. Topological quantities derived from a radical Voronoi diagram as well as the resulting triangulation are used to characterize local structure within the packing. Dynamics are characterized by local deformations to the triangulation as well as the local non-affine motion. For all wedge angles, a boundary develops between moving and static grains. This size and shape of this boundary depend on the indenter angle, and in all cases, the size of the boundary increases with time. During the deformation, non-affine grain motion occurs both throughout the moving region as well as along the boundary, while holes tend to develop primarily along this boundary. [Preview Abstract] |
Tuesday, March 3, 2015 11:51AM - 12:03PM |
G49.00004: Shells on lattice-mismatched colloidal spheres, cubes, and peanuts Melinda Sindoro, Steve Granick Cavities form spontaneously due to geometrical frustration when crystalline shells is gradually grown on non-linear surfaces. This we conclude experimentally from growing lattice mismatched shells on colloidal spheres, cubes, and peanuts, all of them providing different local curvature. According to the core shape, the underlying interfacial curvature promotes different cavity formation which we can follow over time. The resulting spatio-temporal heterogeneity adds up to a propagation of an increasingly strong mechanical stress at the core-shell interface, inducing core-shells transformation to yolk-shells. [Preview Abstract] |
Tuesday, March 3, 2015 12:03PM - 12:15PM |
G49.00005: Adhesion and Wetting of Soft Nanoparticles on Textured Surfaces: Transition between Wenzel and Cassie-Baxter States Zhen Cao, Mark Stevens, Jan-Michael Carrillo, Andrey Dobrynin We use a combination of the molecular dynamics simulations and scaling analysis to study interactions between gel-like nanoparticles and substrates covered with rectangular shape posts. Nanoparticle in contact with a substrate undergo a first order transition between Wenzel and Cassie-Baxter states depending on nanoparticle shear modulus, the strength of nanoparticle-substrate interactions, height of the substrate posts and nanoparticle size, $R_{\mathrm{p}}$. There is a range of system parameters where these two states coexist such that the average indentation $\delta $ produced by substrate posts changes monotonically with nanoparticle shear modulus. We have developed a model that describes deformation of nanoparticle in contact with patterned substrate. The effect of the patterned substrate can be taken into account by introducing an effective work of adhesion, $W_{\mathrm{eff}}$, which describes the first order transition between Wenzel and Cassie-Baxter states. There are two different shape deformation regimes for nanoparticles with shear modulus $G_{\mathrm{p}}$ and surface tension $\gamma_{\mathrm{p}}$. Shape of small nanoparticles with size $R_{p} <\gamma_{p}^{3/2} G_{p}^{-1} W_{eff}^{-1/2} $ is controlled by capillary forces while deformation of large nanoparticles, $R_{p} >\gamma_{p}^{3/2} G_{p}^{-1} W_{eff}^{-1/2} $, is determined by nanoparticle elastic and contact free energies. [Preview Abstract] |
Tuesday, March 3, 2015 12:15PM - 12:27PM |
G49.00006: Self-affine parameters of fracture surfaces of high strength steels Mois\'es Hinojosa, Elisa Schaeffer, Yoshua Guzm\'an, Jorge Aldaco We report the experimental study of crack nucleation and propagation on AISI 4340 and Premomet steels, submitted to different thermal treatments that resulted in different properties and microstructures. Crack initiation and propagation under fatigue, tension and impact conditions were analyzed at different lengthscales. The SEM fractographic study allowed the correlation of the observed mechanisms with the patterns observed on the fracture surfaces. The scaling properties were explored and correlated to the observed mechanisms. Using the topographic data of 3D reconstructed surfaces obtained by laser scanning, we calculated both global and local roughness exponents using different variable-bandwidth methods, obtaining the statistical distributions as a function of the orientation. Although the results tend to the same average global value (close to 0.8) for both steels regardless of the heat-treating condition, their statistical distributions are sensitive to the anisotropy of the microstructure, we also found a correlation of the local roughness exponents with the local orientation of the microstructure and the dimples observed on the fracture surfaces. [Preview Abstract] |
Tuesday, March 3, 2015 12:27PM - 12:39PM |
G49.00007: Probing Interfacial Friction and Dissipation in Granular Gold Nickel Alloys with a Quartz Crystal Oscillator in an External Magnetic Field K.M. Stevens, J. Krim We present here a quartz crystal microbalance study of two-phase gold nickel alloys whose internal granular properties are probed by exposure to a fluctuating external magnetic field. The work is motivated by prior studies demonstrating that granular two-phase materials exhibited lower friction and wear than solid solution alloys with identical compositions [1]. In particular, we report a ``flexing'' effect which appears when an external magnetic field is applied, and is manifested as a decrease in the magnitude of oscillation amplitude that is synchronized with the applied field; the effect is not seen on the complimentary solid solution samples. The effect is consistent with internal interfacial friction between nickel and gold grains, indicating a degree of freedom which may decrease friction even in the absence of an external magnetic field. This is supported through analysis of energy dissipation in the system, using the Butterworth-Van Dyke equivalent circuit model [2]. Data and interpretation are also presented that rule out alternate explanations such as giant magnetoresistance [3] and/or other resistive phenomenon within the film.\\[4pt] [1] L. Pan, Ph.D. Thesis, NCSU (2011).\\[0pt] [2] R. Cernosek et al, IEEE Transactions Ultrasonics, 45 (5) 1998\\[0pt] [3] J. Xiao et al., PRL 68 (25) 1992 [Preview Abstract] |
Tuesday, March 3, 2015 12:39PM - 12:51PM |
G49.00008: Stick-slip patterns in a model frictional interface Georgios Tsekenis, Demet Tatar, Shmuel Rubinstein, David Weitz, Michael Aziz, Frans Spaepen We present measurements of the local displacements during slip-stick motion of two rough surfaces sliding over one another. The surfaces are cast in polymer and have roughness on the order of 30 $\mu m$. The displacements are observed by confocal microscopy of embedded fluorescent particles, and measured by PIV. The displacement patterns during large and small slip events are directly observed and analyzed by statistical methods. [Preview Abstract] |
Tuesday, March 3, 2015 12:51PM - 1:03PM |
G49.00009: Stiff particles on highly compliant solid substrates: adhesion or wetting? Katharine Jensen, Eric Dufresne The classic theories of contact mechanics with deformable materials account only for the competition between adhesion energy and elasticity. However, for compliant materials, solid surface tension also plays an important role in resisting shape change, and may significantly modify the physics of contact with soft matter. We report experiments bringing small, stiff spheres into adhesive contact with compliant silicone substrates. We observe the quasi-static deformation of the substrate in two sticky situations: with zero applied force, where the spheres are allowed to settle to an equilibrium position, and during forced withdrawal from contact starting from from an initial condition of zero displacement. In both cases, we map the profiles of the deformed silicone surface, and compare to capillary and elastic theories. The similarities -- and differences -- between our experimental measurements and the classic theories point to a crossover form a capillary-dominated near field response close to the contact line to an elastic-dominated response in the far field. [Preview Abstract] |
Tuesday, March 3, 2015 1:03PM - 1:15PM |
G49.00010: Single-asperity friction during quasi-static sliding Tristan Sharp, Lars Pastewka, Mark Robbins The static friction of an asperity is investigated using atomic-scale simulations. We explore scale effects by varying the sphere radius R and the contact radius a from nanometers to micrometers. We first consider commensurate contact between bare lattices with repulsive interactions across the interface. In small contacts, all contacting atoms move coherently and the friction coefficient $\mu$ is independent of contact radius and load. In larger contacts, interfacial slip is mediated by localized dislocations, and the static friction coefficient $\mu$ $\sim$ (Ra$_{0}$/a$^{2})^{2/3}$, where a$_{0}$ is the nearest-neighbor spacing. In very large contacts $\mu$ stops decreasing and begins to increase with a, at fixed R. The results are in sharp contrast to Cattaneo-Mindlin continuum theory where $\mu$ is independent of contact size. Separate simulations are performed to connect the results to the dislocation-based models of contact-size effects due to Hurtado and Kim, and Gao, which assume adhesive interactions between surfaces and find $\mu$ $\sim$ (a$_{0}$/a)$^{1/2}$. Simulations for incommensurate contacts show a transition from superlubricity for rigid contacts to a finite friction associated with the Peierls stress in very large contacts. Support from: DMR-1006805; NSF IGERT-0801471; OCI-0963185; CMMI-0923018 [Preview Abstract] |
Tuesday, March 3, 2015 1:15PM - 1:27PM |
G49.00011: Penetration drag in loosely packed granular materials Stephan Bless, Mehdi Omidvar, Magued Iskander The drag coefficient for penetration of granular materials by conical-nosed penetrators was computed by assuming the particles are non-interacting and rebound elastically off of the advancing penetrator. The solution was C $=$4 [sin(theta)]**2, where theta is the half angle of the cone. Experiments were conducted in which the drag coefficient was measured over the range 30 to 80 m/s for four types of sand: Ottawa silica sand, crushed quartz glass, coral sand, and aragonite sand. The sands were tested at relative densities of 40 and 80{\%}. The drag coefficients for the low density materials were in excellent agreement with this simple model. The high density material had a drag considerably larger than predicted, presumably because of particle-to-particle interactions. [Preview Abstract] |
Tuesday, March 3, 2015 1:27PM - 1:39PM |
G49.00012: Geometrically Frustrated Fracture Mechanics Noah Mitchell, Vinzenz Koning, Vincenzo Vitelli, William T. M. Irvine When a flat elastic sheet is forced to conform to a surface with Gaussian curvature, stresses arise in the sheet. The mismatch between initial and final metrics gives rise to new fracture behavior which cannot be achieved by boundary loading alone. Using experiments of PDMS sheets frustrated on 3D-printed surfaces and a linearized analytical model, we demonstrate the ability of curvature to govern the sheets' fracture phenomenology. In this talk, we first show that curvature can both stimulate and suppress fracture initiation, depending on the position and orientation of the initial slit. Secondly, we show that curvature can steer the path of a crack as it propagates through the material. Lastly, the curvature can arrest cracks which would otherwise continue to propagate. [Preview Abstract] |
Tuesday, March 3, 2015 1:39PM - 1:51PM |
G49.00013: Kibble-Zurek Mechanism in Microscopic Acoustic Cracking Noises Hamed O. Ghaffari, Philip Benson, K. Xia, R. Paul Young The fast evolution of microstructure is key to understanding ``crackling'' phenomena. It has been proposed that formation of a nonlinear zone around a moving crack tip controls the crack tip velocity. Progress in understanding the physics of this critical region has been limited by our lack of hard data describing the detailed physical processes that occur within. For the first time, we show that the signature of the non-linear elastic zone around a microscopic dynamic crack maps directly to generic phases of acoustic noises, supporting the formation of a strongly weak zone near the moving crack tips. We additionally show that the rate of traversing to non-linear zone controls the rate of weakening, i.e. speed of global rupture propagation. We measure the power-law dependence of nonlinear zone size on the traversing rate, and show that our observations are in agreement with the Kibble-Zurek mechanism (KZM). In addition, we illustrate that cracks exhibiting global rupture fronts with velocity faster than Rayleigh waves (i.e., super-shear rupture fronts) display a complex configuration of non-linear zone prior to the fast weakening phase. [Preview Abstract] |
Tuesday, March 3, 2015 1:51PM - 2:03PM |
G49.00014: Optical Characterization of Temperature-Dependent Microstructure of Polymeric Asphalt Binders Adam Ramm, Farbod Shafiei, Maryam Zamani, Sharmin Sultana, Amit Bhasin, M. C. Downer Asphalt binders used in construction of pavements must be chemically engineered to withstand wide climatic variations. Ideal binders possess high stiffness at high temperatures, low stiffness with high relaxation rates at low temperatures, and high resistance to fatigue cracking at intermediate temperatures. Such bulk properties are conventionally measured with rheometers, but appear to be closely connected with temperature-dependent microstructural changes. AFM has been used to observe such microstructures, but is only possible near room temperature [1]. Here we characterize asphalt binder microstructure over a wide range of temperatures and chemical compositions using noninvasive optical microscopy correlated with linear and second-harmonic optical scatter to measure statistical fluctuations. For example, micron-size ``bee''-structures previously observed by AFM [1] are resolved optically, and are observed to vary as temperature and composition change, while inducing corresponding changes in optical scatter. We will present these and other optical measurements, and discuss their connection to bulk material properties. [1] Pauli et al., Internat. J. Pavement Engin. 12, 291 (2011). [Preview Abstract] |
Tuesday, March 3, 2015 2:03PM - 2:15PM |
G49.00015: Rings and rackets from single-wall carbon nanotubes: manifestations of mesoscopic mechanics Yuezhou Wang, Matthew Semler, Igor Ostanin, Erik Hobbie, Traian Dumitrica We combine distinct element method simulations and experiments to understand the stability of rings and rackets formed by single-walled carbon nanotubes assembled into ropes. Bending remains a soft deformation mode in ropes because intra-rope sliding of the constituent nanotubes occurs with ease. Our simulations indicate that the formation of these aggregates can be attributed to the mesoscopic mechanics of entangled nanotubes and to the sliding at the contacts. Starting from the single-walled carbon nanotubes, the sizes of the rings and rackets' heads increase with the rope diameter, indicating that the stability of the experimental aggregates can be largely explained by the competition between bending and van der Waals adhesion energies. Our results and simulation method should be useful for understanding nanoscale fibers and self-assembling process in general. \\[4pt] References:\\[0pt] Y. Wang, M. R. Semler, I. Ostanin, E. K. Hobbie, and T. Dumitric\u{a}, Soft Matter, 2014, 10, 8635, 2014. \newline Y. Wang, C. Gaidau, I. Ostanin and T. Dumitric\u{a}, Appl. Phys. Lett., 2013, 103, 183902. \newline I. Ostanin, R. Ballarini, D. Potyondy, and T. Dumitric\u{a}, Journal of the Mechanics and Physics of Solids, 2013, 61, 762-782. [Preview Abstract] |
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