A polyacrylamide hydrogel exhibits near-perfect elasticity: its stress-stretch curve is rate-independent and has negligible hysteresis. The near-perfect elasticity results from the large amount of water between the polymer chains. Water has low viscosity and lubricates polymer chains. Here we report that the polyacrylamide hydrogel exhibits rate-dependent toughness when the polymer chains are long

Cauchy-elastic solids include hyper-elasticity and a subset of elastic materials for which the stress does not follow from a scalar strain potential. More in general, hypo-elastic materials are only defined incrementally and comprise Cauchy-elasticity. Infringement of the hyper-elastic ‘dogma’ is so far unattempted and normally believed to be impossible, as it apparently violates thermodynamics, because

A crack terminating at an arbitrary angle to the interface between two neo-Hookean sheets is investigated under plane stress conditions using finite deformation theory. The asymptotic crack-tip deformation and stress fields are analyzed as a function of the ratio of the moduli and the angle of the crack relative to the interface. Full-field numerical calculations and experimental studies validate the

Power law distributed fluctuations are known to accompany terminal failure in disordered brittle solids. The associated intermittent scale-free behavior is of interest from the fundamental point of view as it emerges universally from an intricate interplay of threshold-type nonlinearity, quenched disorder, and long-range interactions. We use the simplest mean-field description of such systems to show

“Viscosity is the most ubiquitous dissipative mechanical behavior” (Maugin, 1999). Despite its ubiquity, even for those systems where the mechanisms causing viscous and other forms of dissipation are known there are only a few quantitative models that extract the macroscopic rheological response from these microscopic mechanisms. One such mechanism is the stochastic breaking and forming of bonds which

Constitutive modeling of dielectric elastomers has been of long standing interest in mechanics. Over the last two decades rigorous constitutive models have been developed that couple the electrical response of these polymers with large deformations characteristic of soft solids. A drawback of these models is that unlike classic models of rubber elasticity they do not consider the coupled electromechanical

We investigate volume-element sampling strategies for the stochastic homogenization of particle-reinforced composites and show, via computational experiments, that an improper treatment of particles intersecting the boundary of the computational cell may affect the accuracy of the computed effective properties. Motivated by recent results on a superior convergence rate of the systematic error for periodized

When they are damaged or injured, soft biological tissues are able to self-repair and heal. Mechanics is critical during the healing process, as the damaged extracellular matrix (ECM) tends to be replaced with a new undamaged ECM supporting homeostatic stresses. Computational modeling has been commonly used to simulate the healing process. However, there is a pressing need to have a unified thermodynamics

The thermal barrier coatings (TBCs) are serviced in elevated thermal conditions characterized by chemo-thermo-mechanical (C-T-M) failure mechanism and multiscale failure modes. In the present work, isothermal, cyclic thermal and mechanical induced spalling tests were carried out. Since the contribution of aluminum migration in TBCs damage evolution and failure was confirmed, the C-T-M life prediction

In many applications, glass fabrics are subject to cyclic forces. Here we show that a glass fabric can tear under a much lower cyclic force than monotonic force. For samples of a given width, a threshold force exists below which the fabric does not tear under cyclic load, and a critical force exists at which the fabric tears under monotonic load. For example, for 80 mm wide sample, the threshold force

The Eshelby formalism for an inclusion in a solid is of significant theoretical and practical implications in mechanics and other fields of heterogeneous media. Eshelby’s finding that a uniform eigenstrain prescribed in a solitary ellipsoidal inclusion in an infinite isotropic medium results in a uniform elastic strain field in the inclusion leads to the conjecture that the ellipsoid is the only inclusion

This study presents a new methodology for estimating the effective properties of solids containing cracks along the inter-granular boundaries, using analytical developments and numerical simulations. The latter are based on the generation of virtual microstructures of such type obtained by superimposing a Voronoï tessellation modeling the granular network with a random dispersion of overlapping spheres

Owing to the recoverable nature of noncovalent interactions, laminated nanocomposites dominated by noncovalent interfaces can deform inelastically and generate large relative sliding between building bricks under external loading, which not only contributes to outstanding mechanical properties at the macroscale but also induces coordinated deformation behavior over several hierarchical length scales

The mechanical properties of hydrogels involve solvent diffusion as well as viscous dissipation in the network, with the coupling called poroviscoelasticity. To explore the poroviscoelastic behavior, we performed tests on a gelatin-based hydrogel in which poroelastic swelling/drying occurred at controlled humidity levels while simultaneously developing creep deformation under a uniaxial load. These

Through the suitable geometry of a repeating unit, a metamaterial can exhibit a property not present in the base material. Here, we propose a class of low area-fraction, bending-dominated metamaterials that exhibit apparent piezoelectricity, even though the base material is not piezoelectric. The proposed metamaterials exploit a universal electromechanical coupling operative at sub-micron scales, flexoelectricity

A comprehensive experimental study performed under a combination of thermo-electro-mechanical loads applied to a widely used electro-active polymer, is presented in the Part I of this work (Mehnert et al., 2021). Soft polymeric materials, used as base materials in electro-active polymers, are highly susceptible to temperature changes. Hence, thermal influences on their behavior have to be investigated

Curved features are ubiquitous on solid surfaces, but the effect of surface curvatures on growth of two-dimensional (2D) materials has not yet been established. Using a newly developed method based on the Metropolis algorithm and taking graphene as a prototype, we find that a curved feature on substrates can result in a variety of topological defects in 2D materials. As the feature's size increases

Fracture prediction is indispensable for polymers, like rubbers, which have a broad range of applications mainly due to their high extensibility. The phenomenon known as strain-induced crystallization further contributes to the fracture toughness of certain rubbers. In this study, a criterion based on internal bond energy, incorporating the effects of crystallization, is proposed to predict fracture

Two-dimensional (2D) materials as exemplified by graphene have received a bunch of attention for their outstanding properties and enormous application potential. Recently, a macroscopic graphene-based material was fabricated simply by stacking the few-layer graphene flakes. The resulting film, called SGA, exhibits unusual mechanical behavior, which implies the existence of tension-compression asymmetry

A geometrically nonlinear phase field theory accounting for dissipation, rate effects, nonlinear thermoelasticity, fracture, and other structural changes is constructed in the context of continuum thermodynamics. First, a general framework accommodating arbitrary strain energy potentials, inelastic deformation kinematics, and unlimited order parameters is formulated. Next, the framework is specialized

Wave propagation in granular materials is one of the most fundamental problems in mechanics and physics, with both scientific fascination and practical importance. Whether elastic waves in granular media are affected by particle morphology and, if yes, how they are affected remain open questions. Here we present a novel grain-scale model to address these fundamental questions. Efficient techniques

Multi-stable structures offer a unique set of mechanical properties, such as the ability to undergo large reversible deformations, the ability to provide mechanical protection and efficient shock absorption, and the ability to retain variety of geometrical configurations after loads have been removed. In addition, the study of lattice-based multi-stable structures is of relevance to a wide range of

Damage and fracture can be induced not only by mechanical loading but also due to chemical interactions within a solid. On one hand, species concentration may embrittle or toughen the material and on the other hand, the mechanical state adds additional driving force for diffusion. We propose a chemo-mechanically coupled cohesive fracture model with several novel features. It distinguishes the mode-dependent

Dielectric elastomers are a class of solid polymeric materials that are sufficiently soft to deform under the application of an electric field due to the interaction of quasi-static electric charges. Their potential to undergo large deformations renders them promising candidates for the design of energy harvesters, sensors and soft actuators. For their application however, the influence of additional

Interlocking composites have become increasingly popular in recent years. A key motivation is the impressive performance of natural interlocking protective structures. A large number of these structures – from human craniums to alligator armour – contain sutures; those are soft interfaces that join adjacent stiff plates with interdigitating protrusions. These interfaces have the potential to significantly

In recent years, the investigation of adhesion properties of thin films on brittle substrates is receiving more attention due to the spread of thin film applications (coatings, protective layers, conductive layers in microelectronics, etc.). However, a basic approach for adhesion measurements proposed by Hutchinson and Suo almost three decades ago is still widely used due to its easy applicability

Reaction-diffusion models have been widely used to elucidate pattern formation in developmental biology. More recently, they have also been applied in modeling cell fate patterning that mimics early-stage human development events utilizing geometrically confined pluripotent stem cells. However, the traditional reaction-diffusion equations could not satisfactorily explain the concentric ring distributions

Terrestrial snakes, aquatic snakes, and sandfish lizards are observed to adopt different configurations for locomotion, although they all employ the snake-like un-dulatory wriggling motion. Here we show that these differences may be dominated by the movement and energy efficiencies imposed by mechanical deformation and interaction with environments. Based on a slender soft beam model, a systematical

Hard-magnetic soft materials, which consist of soft matrix embedded with hard-magnetic particles, have attracted tremendous interests owing to their untethered control capability, rapid response, and flexible programmability. This work introduces a topology optimization framework to guide the rational design of hard-magnetic soft materials and structures with precisely programmable functionalities

Here we consider the possible bulk and shear moduli of planar polycrystals built from a single crystal in various orientations. Previous work gave a complete characterization for crystals with orthotropic symmetry. Specifically, bounds were derived separately on the effective bulk and shear moduli, thus confining the effective moduli to lie within a rectangle in the (bulk, shear) plane. It was established

High-mobility semiconductive ultrathin films of bismuth oxyselenide (Bi2O2Se) have attracted great interest due to their potential applications in advanced electronic and photoelectronic devices. Enthusiasm aside, future success of such applications hinges upon the fundamental understanding of two dimensional (2D) Bi2O2Se, which is far from mature. In particular, unlike many other 2D materials with

Theories describing the important role of small particles for strengthening of metals have evolved since the pioneering work of Orowan. Here, this problem is analysed by a strain gradient plasticity (SGP) theory. The structure of the governing equations on non-dimensional form reveals that the plastic strain in the matrix material is to zeroth order approximation constant for a sufficiently small particle

This paper presents a novel in-silico tool for the design of complex multilayer Dielectric Elastomers (DEs) characterised by recently introduced layer-by-layer reconfigurable electrode meso-architectures. Inspired by cutting-edge experimental work at Clarke Lab (Harvard) Hajiesmaili and Clarke (2019), this contribution introduces a novel approach underpinned by a diffuse interface treatment of the

A strain gradient void-driven ductile fracture model of single crystals is proposed and applied to simulate crack propagation in single and oligo-crystal specimens. The model is based on a thermodynamical framework for homogenized porous solids unifying and generalizing existing thermodynamical formulations. This porous single crystal ductile fracture model relies on a multi-surface representation

A multi-physics model is proposed to predict the changes in the constitutive behavior of cross-linked polymeric systems due to damages induced by deformation, oxidation, moisture, and temperature. Coupling the concept of network evolution, hydrolysis, and thermo-oxidation aging, we hypothesize that the synergized effects of deformation-induced damage, as well as different environmental factors such

Injectable bioelectronic devices provide programmable drug volume delivery control via flexible electrochemical pumps featuring scalable designs for localized drug delivery experiments involving small animals and future drug delivery in humans, especially for life saving medication. A model for the drug delivery time is established from the ideal gas law, finite-deformation theory of flexible membrane

Propagating cracks may deflect due to dynamic instability, running into pre-existing weak regions of heterogeneous media, or encountering variation in driving forces. The mechanical analysis of a kinked crack is of engineering significance for safety control and crack-network formation. Existing theories for kinked cracks relied on the perturbation method, as befit small kinks. The stress intensity

Sucrose is a commonly used energetic material simulant for β-HMX. However, its behavior under extreme loading conditions remains poorly understood. Pressure-Shear Plate Impact (PSPI) experiments have been conducted to provide an experimental foundation for developing a suitable constitutive model for sucrose. Experiments have been performed at two different nominal normal stress values, 3 and 9.5 GPa

Dry adhesives that rely on surface force mediated adhesion, such as van der Waals forces, are important in applications ranging from robotics to manufacturing. The maximum theoretical adhesion strength of a contact is achieved when the stress is uniformly distributed over the entire contact area as the full potential of all the bonds at the interface is realized in this scenario. Most dry adhesive

Stress concentration occurs at the crack tip of a notched sample when loaded. The crack tip region has been recognized of consisting of two regions: the inner (or end) region, which is also called the fracture process zone, and the surrounding outer region where inelastic deformation occurs. The size of these regions is strongly related to the fatigue threshold and the toughness of the material, and

Liquid crystal elastomers combine the hyperelasticity of elastomers with the multi-functionality of liquid crystals and have emerged as an important class of soft active materials. Monodomain liquid crystal elastomers under loading exhibit the soft elastic behavior due to the stress induced director rotation and the resulting spontaneous strain. Here, we numerically study their stress and strain concentration

During plastic deformation of crystalline materials, point defects such as vacancies and interstitials are generated by jogs on moving dislocations. A detailed model for jog formation and transport during plastic deformation was developed within the vector density-based continuum dislocation dynamics framework (Lin and El-Azab, 2020; Xia and El-Azab, 2015). As a part of this model, point defect generation

Universal deformations of an elastic solid are deformations that can be achieved for all possible strain–energy density functions and suitable boundary conditions. They play a central role in nonlinear elasticity and their classification has been mostly accomplished for isotropic solids following Ericksen’s seminal work. Here, we address the same problem for transversely isotropic, orthotropic, and

When subjected to some anti-plane shear mode III loading, segmentation of the crack front frequently occurs during propagation: even if the crack is initially planar, propagation produces facets/segments rotated toward the shear free direction. Here, we examine, both experimentally and theoretically, the effect of this microstructure on the effective macroscale brittle fracture toughness. Experiments

Frictional sliding is an intrinsically complex phenomenon, emerging from the interplay between driving forces, elasto-frictional instabilities, interfacial nonlinearity and dissipation, material inertia and bulk geometry. We show that homogeneous rate-and-state dependent frictional systems, driven at a prescribed boundary velocity — as opposed to a prescribed stress — in a range where the frictional

Fiber-reinforced soft composites with anisotropic mechanical properties exist widely in nature, forming complex shape-morphing structures during the growth or hydration processes. In this paper, we employ the 3D printing method, termed direct ink writing (DIW), to fabricate the hydrogel-fiber composites. It is found that the fiber distribution is controlled by printing parameters, such as printing

Elastomers are used in a wide range of applications because of their large strain to failure, low density, and tailorable stiffness and toughness. The mechanical behavior of elastomers derives mainly from the entropic elasticity of the underlying network of polymer chains. Elastomers under large deformation experience bonds breaking within the backbone chains that constitute the polymer network. This

BN fiber coatings in SiC-SiC composites are vulnerable to oxidation and volatilization at elevated temperature in the presence of water vapor. These processes lead to coating recession in the composite interior with recession fronts starting from matrix cracks and proceeding axially along the fibers. In some operational domains, the main effect of recession is to de-couple the fibers from the matrix

Combining experimental and computational studies of nanocomposite interfaces is highly needed to gain insight into their performance. However, there are very few literature reports, combining well-controlled atomic force microscopy experiments with molecular dynamic simulations, which explore the role of polymer chemistry and assembly on interface adhesion and shear strength. In this work, we investigate

Fracture is a highly nonlinear problem, especially under a large deformation in cross-linked elastomers. Existing constitutive theories and fracture models fail to predict the fracture behavior of cross-linked elastomers because of the absence of the random polymer network structure. Meanwhile, few numerical methods can present the realistic fracture process of a polymer network. In this study, we

Epitaxial growth on a surface vicinal to a high-symmetry crystallographic plane occurs through the propagation of atomic steps, a process called step-flow growth. In some instances, the steps tend to form close groups (or bunches), a phenomenon termed step bunching, which corresponds to an instability of the equal-spacing step propagation. Over the last fifty years, various mechanisms have been proposed

The adhesive interactions between polymer nanofibers strongly influence the mechanical behavior of their networks in synthetic materials and biological systems. A treatment of the adhesive interactions at polymer contacts must take into account the viscoelastic behavior of the material in the contact region and the associated energy dissipation. This study focuses on the rate-dependent adhesion of

There has been increasing experimental evidence of non-affine elastic deformation mechanisms in biological soft tissues. These observations call for novel constitutive models which are able to describe the dominant underlying micro-structural kinematic aspects, in particular relative motion characteristics of different phases. This paper proposes a flexible and modular framework based on a micromorphic

The quasistatic approximation is a useful but questionable simplification for analyzing step instabilities during the growth/evaporation of vicinal surfaces. Using this approximation, we characterized in Part I of this work the effect on stability of different mechanisms and their interplay: elastic step-step interactions, the Schwoebel barrier, and the chemical coupling of the diffusion fields on

Geometrically frustrated elastic ribbons exhibit, in many cases, significant changes in configuration depending on the relation between their width and thickness. We show that the existence of such a transition, and the scaling at which it occurs, strongly depend on the system considered. Using an asymptotic approach, treating the width as a small parameter, we find the leading energy terms resulting