IEEE Transactions on Pattern Analysis and Machine Intelligence

Annual review of condensed matter physics

Journal of Statistical Mechanics: theory and experiment

Tables of integrals

Capillarity and Wetting Phenomena: Drops, Bubbles, Pearls, Waves

The real area of contact of a frictional interface changes rapidly when the normal load is altered, and evolves slowly when normal load is held constant, aging over time. Traditionally, the total area of contact is considered a proxy for the frictional strength of the interface. Here we show that the state of a frictional interface is not entirely defined by the total real area of contact but depends on the geometrical nature of that contact as well. We directly visualize an interface between rough elastomers and smooth glass and identify that normal loading and frictional aging evolve the interface differently, even at a single contact level. We introduce a protocol wherein the real area of contact is held constant in time. Under these conditions, the interface is continually evolving; small contacts shrink and large contacts coarsen.

Influences of microcontact shape on the state of a frictional interface.

Fractures are a critical process in how materials wear, weaken, and fail, whose unpredictable behavior can have dire consequences. While the behavior of smooth cracks in ideal materials is well understood, it is assumed that for real, heterogeneous systems, fracture propagation is complex, generating rough fracture surfaces that are highly sensitive to specific details of the medium. Here we show how fracture roughness and material heterogeneity are inextricably connected via a simple framework. Studying hydraulic fractures in brittle hydrogels that have been supplemented with microbeads or glycerol to create controlled material heterogeneity, we show that the morphology of the crack surface depends solely on one parameter: the probability to perturb the front above a critical size to produce a steplike instability. This probability scales linearly with the number density, and with heterogeneity size to the 5/2 power. The ensuing behavior is universal and is captured by the 1D ballistic propagation and annihilation of steps along the singular fracture front.

How Material Heterogeneity Creates Rough Fractures.

Recent research into the buckling load of thin shells has focused on local poking of the shell. In this approach, the shell is poked under load to extract its stability landscape, and a ridge tracking method is performed to estimate the buckling load of the shell. It is the current understanding that the stability landscape measures the local stability of the shell and, as a result, that the accuracy of ridge tracking greatly relies on the location of poking. Currently, there is no method that can predict where poking should be performed on an experimental system. Here, we examine the global response of thin shells to poking through the energy landscape. We present an experimental method for measuring the energy landscape of thin shells and demonstrate its application on a thin plate strip. We show that by analysing the dynamics of the shell in the energy landscape we can experimentally measure the buckling mode of the system, which gives the correct point of poking for accurate ridge tracking, and identify two kinds of buckling points. Finally, we propose how this approach can be applied to more complex systems such as thin cylinders. This article is part of the theme issue ‘Probing and dynamics of shock sensitive shells’.

Measuring the energy landscape: an experimental approach to the study of buckling in thin shells

The impact of a liquid drop on a solid surface involves many intertwined physical effects, and is influenced by drop velocity, surface tension, ambient pressure and liquid viscosity, among others. Experiments by Kolinski et al. (2014b) show that the liquid-air interface begins to deviate away from the solid surface even before contact. They found that the lift-off of the interface starts at a critical time that scales with the square root of the kinematic viscosity of the liquid. To understand this, we study the approach of a liquid drop towards a solid surface in the presence of an intervening gas layer. We take a numerical approach to solve the Navier-Stokes equations for the liquid, coupled to the compressible lubrication equations for the gas, in two dimensions. With this approach, we recover the experimentally captured early time effect of liquid viscosity on the drop impact, but our results show that lift-off time and liquid kinematic viscosity have a more complex dependence than the square root scaling relationship. We also predict the effect of interfacial tension at the liquid-gas interface on the drop impact, showing that it mediates the lift-off behavior.

Computing the viscous effect in early-time drop impact dynamics

Natural faults are intrinsically heterogeneous where jogs, edges and steps are common. We experimentally explore how fault edges may affect earthquake and slip dynamics by applying shear to the edge of one of two flat blocks in frictional contact. We show that slip occurs via a sequence of rapid rupture events that arrest after a finite distance. Successive events extend the slip size, transfer the applied shear across the block, and cause progressively larger changes of the contact area along the contact surface. Each sequence of events dynamically forms an asperity near the edge and largely reduces the contact area beyond. These sequences of rapid events all culminate in slow slip events that lead to major, unarrested slip along the entire contact surface. These results show that a simple deviation from uniform shear loading configuration can significantly and qualitatively affect both earthquake nucleation processes and the evolution of fault complexity.

Shmuel M. Rubinstein

Papers

Influences of microcontact shape on the state of a frictional interface.

How Material Heterogeneity Creates Rough Fractures.

Measuring the energy landscape: an experimental approach to the study of buckling in thin shells

Computing the viscous effect in early-time drop impact dynamics

Slip Sequences in Laboratory Experiments as Analogues to Earthquakes Associated with a Fault Edge