Micromechanically Based Constitutive Relations for Polycrystalline Solids

A basic method to estimate the overall mechanical response of solids which contain periodically distributed defects is presented. The method estimates the shape and growth pattern of voids periodically distributed over the grain boundaries in a viscous matrix. The relaxed moduli are obtained for a polycrytalline solid that undergoes relaxation by grain boundary sliding which accounts for the interaction effects. The overall inelastic nonlinear response at elevated temperatures in terms of a model which considers nonlinear power law creep within the grains, and linear viscous flow in the grain boundaries is discussed

Torsional Instability of Cantilevered Bars Subjected to Nonconservative Loading

Cantilever bar torsional instability under nonconservative compression loadin

On the stability of equilibrium of continuous systems Technical report no. 65-1

Stability of equilibrium of linear elastic continuum - Galerkin metho

On the Stability Equilibrium of Continuous Systems

Sufficiency theorem for stability of linearly viscoelastic solid subjected to partial follower surface traction

Destabilizing effect of velocity-dependent forces in nonconservative continuous systems Technical report no. 65-4

Velocity dependent force destabilizing effect in cantilevered continuous pipe conveying fluid at constant velocit

Deformation and Failure of Amorphous Solidlike Materials

Since the 1970's, theories of deformation and failure of amorphous, solidlike materials have started with models in which stress-driven, molecular rearrangements occur at localized flow defects via "shear transformations". This picture is the basis for the modern theory of "shear transformation zones" (STZ's), which is the focus of this review. We begin by describing the structure of the theory in general terms and by showing several applications, specifically: interpretation of stress-strain measurements for a bulk metallic glass, analysis of numerical simulations of shear banding, and the use of the STZ equations of motion in free-boundary calculations. In the second half of this article, we focus for simplicity on what we call an "athermal" model of amorphous plasticity, and use that model to illustrate how the STZ theory emerges within a systematic formulation of nonequilibrium thermodynamics.Comment: 28 pages, 4 figures, submitted to Annual Reviews of Condensed Matter Physic

Interaction Between an Incident Wave and a Dynamically Transforming Inhomogeneity

Transformation-toughening of ceramics has attracted considerable attention [1,2,3] in recent years. The key mechanism in this toughening is the stress-induced phase transformation of the partially stabilized zirconia (PSZ) inhomogeneities, which accompanies volumetric expansion. Due to this expansion, the composite material consisting of PSZ inhomogeneities in a brittle matrix becomes more resistant to fracturing. While this problem has been studied for guasi-static loadings [4,5], the corresponding dynamic case has remained relatively unexplored

Memory of the Unjamming Transition during Cyclic Tiltings of a Granular Pile

Discrete numerical simulations are performed to study the evolution of the micro-structure and the response of a granular packing during successive loading-unloading cycles, consisting of quasi-static rotations in the gravity field between opposite inclination angles. We show that internal variables, e.g., stress and fabric of the pile, exhibit hysteresis during these cycles due to the exploration of different metastable configurations. Interestingly, the hysteretic behaviour of the pile strongly depends on the maximal inclination of the cycles, giving evidence of the irreversible modifications of the pile state occurring close to the unjamming transition. More specifically, we show that for cycles with maximal inclination larger than the repose angle, the weak contact network carries the memory of the unjamming transition. These results demonstrate the relevance of a two-phases description -strong and weak contact networks- for a granular system, as soon as it has approached the unjamming transition.Comment: 13 pages, 15 figures, soumis \`{a} Phys. Rev.

Models demonstrating instability of nonconservative mechanical systems Technical report no. 66-4

Models demonstrating instability on nonconservative mechanical system

Toughening and asymmetry in peeling of heterogeneous adhesives

The effective adhesive properties of heterogeneous thin films are characterized through a combined experimental and theoretical investigation. By bridging scales, we show how variations of elastic or adhesive properties at the microscale can significantly affect the effective peeling behavior of the adhesive at the macroscale. Our study reveals three elementary mechanisms in heterogeneous systems involving front propagation: (i) patterning the elastic bending stiffness of the film produces fluctuations of the driving force resulting in dramatically enhanced resistance to peeling; (ii) optimized arrangements of pinning sites with large adhesion energy are shown to control the effective system resistance, allowing the design of highly anisotropic and asymmetric adhesives; (iii) heterogeneities of both types result in front motion instabilities producing sudden energy releases that increase the overall adhesion energy. These findings open potentially new avenues for the design of thin films with improved adhesion properties, and motivate new investigation of other phenomena involving front propagation.Comment: Physical Review Letters (2012)