Showing papers by "Zhigang Suo published in 2001"
TL;DR: In this article, the inelastic deformation of Nacre from mollusc shells has been experimentally examined, with a focus on understanding the underlying mechanisms and their significance for the design of robust ceramics.
Abstract: Nacre (mother-of-pearl) from mollusc shells is a biologically formed lamellar ceramic. The inelastic deformation of this material has been experimentally examined, with a focus on understanding the underlying mechanisms. Slip along the lamellae tablet interface has been ascertained by testing in compression with the boundaries oriented at 45° to the loading axis. The steady-state shear resistance τss has been determined and inelastic strain shown to be as high as 8%. The inelastic deformation was realized by massive interlamellae shearing. Testing in tension parallel to the tablets indicates inelastic strain of about 1%, occurring at a steady-state stress, σsss ≈ 110 MPa. The strain was associated with the formation of multiple dilatation bands at the intertablet boundaries accompanied by interlamellae sliding. Nano-asperities on the aragonite tablets and their interposing topology provide the resistance to interfacial sliding and establish the level of the stress needed to attain the inelastic strain. Detailed mechanisms and their significance for the design of robust ceramics are discussed.
731 citations
TL;DR: In this article, a model for the inelastic behavior, measured in tension, along the axis of the aragonite plates was developed, based on observations for abalone nacre that the deformation is associated with periodic dilatation bands.
Abstract: The inelastic deformation of nacre that leads to its structural robustness has been characterized in a recent experimental study. This article develops a model for the inelastic behavior, measured in tension, along the axis of the aragonite plates. The model is based on observations for abalone nacre that the inelasticity is associated with periodic dilatation bands. These bands contain coordinated separations at the periphery of the plates. The separations open as the material strains. The response is attributed to nanoscale asperities on the surfaces of the plates. The model calculates the stresses needed to displace the plates, resisted by elastic contacts at the asperities. The results are compared with the measured stress/strain curves.
333 citations
TL;DR: In this paper, a two-phase monolayer grown on an elastic substrate may form stripes or dots on the scale of nanometers, and sometimes these stripes and dots order into superlattices.
Abstract: A two-phase monolayer grown on an elastic substrate may form stripes or dots on the scale of nanometers. Sometimes these stripes and dots order into superlattices. This paper reports on a simulation on the basis of a model proposed by the authors recently. The size selection and spatial ordering result from two competing actions: the phase boundary energy tends to coarsen the phases, and the concentration-dependent surface stress tends to refine the phases. A nonlinear diffusion equation couples the concentration field in the epilayer and the stress field in the substrate. The simulation reveals remarkably rich dynamics. An epilayer may evolve into various patterns, suggesting a significant degree of experimental control in growing nanoscale superlattices, just as in growing atomic crystals.
105 citations
TL;DR: In this paper, a linear-stability analysis is performed to determine the onset and maximally unstable mode of this buckling instability as a function of misfit strain, viscous layer thickness, and viscosity.
Abstract: Compressively-stressed elastic films on finite-thickness viscous substrates can undergo a buckling instability that relieves stresses but destroys the planarity of the film. A linear-stability analysis is performed to determine the onset and maximally unstable mode of this buckling instability as a function of misfit strain, viscous layer thickness, and viscosity. We find that the onset of the buckling instability of the film on a glass layer is the same as that for a compressively stressed free-standing film. However, the maximally unstable wavelength increases as the glass layer thickness increases. Comparisons with experimental data are provided.
88 citations
TL;DR: In this article, the authors investigated an intriguing failure mode observed in thermal cycling, where metal interconnects can crawl toward the center of the die during thermal cycling and they developed an idealized model to demonstrate this mechanism, and to study the effects of temperaturedependent yield strength and strain hardening.
54 citations
TL;DR: In this article, a theory of the stability of the island lattice is presented. But the theory assumes that the total interface energy reduces when the island diameter increases, while the electrostatic free energy reduces if the island size decreases.
Abstract: Recent experiments show that, when a two-phase fluid confined between parallel substrates is subject to an electric field, one phase can self-assemble into a triangular lattice of islands in another phase. We describe a theory of the stability of the island lattice. It is well known that the total interface energy reduces when the island diameter increases. We show that, under certain conditions, the electrostatic free energy reduces when the island diameter decreases. The islands select the equilibrium diameter to minimize the combined interface energy and electrostatic energy. We describe the conditions for electrostatic field to stabilize the island lattice, and analyze an idealized model. The theory suggests considerable experimental control over stable island size.
31 citations
TL;DR: In this paper, the authors present a review of the current understanding of the subject and present a linear perturbation analysis to identify the stability condition, which differs substantially from the well known stability condition based on the driving force alone.
Abstract: On the interface between a solid and a fluid, a reaction can occur in which atoms either leave the solid to join the fluid, or leave the fluid to join the solid. If the solid is in addition subject to a mechanical load, two outcomes may be expected. The reaction may proceed uniformly, so that the interface remains flat as the solid recedes or extends. Alternatively, the reaction may cause the interface to roughen and develop sharp cracks, leading to fracture. This paper reviews the current understanding of the subject. The solid-fluid is a thermodynamic system: the solid is in elastic equilibrium with the mechanical load, but not in chemical equilibrium with the fluid. Thermodynamic forces that drive the interfacial reaction include chemical energy difference between the solid and the fluid, elastic energy stored in the solid, and interfacial energy. The reaction is taken to be thermally activated. A kinetic law is adopted in which the stress affects both the activation energy and the driving force of the interface reaction. A linear perturbation analysis identifies the stability condition, which differs substantially from the well known stability condition based on the driving force alone. Large perturbations are examined by assuming that the interface varies as a family of cycloids, from slight waviness to sharp cracks. An analytic elasticity solution is used to compute the stress field in the solid, and a variational method to evolve the shape of the interface.
28 citations
TL;DR: In this article, a finite element method is presented to simulate the stress-assisted surface reaction, where the reduction of the total free energy associated with gaining unit volume of solid defines the driving force.
21 citations
TL;DR: In this article, a two-dimensional (2D) model for inplane expansion and wrinkling was proposed. But the effect of winkling was not considered. And the results from the model are compared with the experiments with small SiGe islands.
Abstract: Experiments were conducted with SiGe film islands on a layer of borophosphorosilicate glass (BPSG). Initially the SiGe is under compression. Upon annealing, the glass flows and the SiGe islands relax by both inplane expansion and wrinkling. This paper provides a two-dimensional (2D) model for inplane expansion. The results from the model are compared with the experiments with small SiGe islands. The effect of winkling, which is ignored in the present model, is discussed qualitatively.
19 citations
TL;DR: In this article, the authors show that the role of elasticity is reversed: with the ceiling, the total elastic energy stored in the system increases as the islands coarsen laterally.
Abstract: In the Stranski–Krastanov system, the lattice mismatch between the film and the substrate causes the film to break into islands. During annealing, both surface energy, and elastic energy drive the islands to coarsen: some islands enlarge and others shrink, keeping the total island volume constant. The islands produced this way are usually uneven in size and spacing. Motivated by several related studies, we suggest that stable, uniform islands should form when a stiff ceiling is placed at a small gap above the film. After contacting the ceiling, the islands are constrained to grow laterally and remain coherent with the substrate, preventing further stress relaxation. In fact, we show that the role of elasticity is reversed: with the ceiling, the total elastic energy stored in the system increases as the islands coarsen laterally. On the other hand, the total surface energy decreases as the islands coarsen. Consequently, the islands select an equilibrium size to minimize the combined elastic energy and surface energy. We estimate the equilibrium island size by analyzing an idealized model.
Book Chapter•
01 Jan 2001
TL;DR: In this article, the mechanics of rolling and deforming thin foil substrates in two and three dimensions are discussed, and the authors propose a two-dimensional (2D) and three-dimensional model for the same problem.
Abstract: In this paper, the mechanics of rolling and deforming thin foil substrates in two and three dimensions are discussed.
25 Jun 2001
TL;DR: In this article, the first transistors fabricated on a substrate that is then plastically deformed are reported, and they can withstand an average substrate strain of 6%, as the substrate is deformed into a spherical cap shape subtending angles as large as 66/spl deg/ (1 steradian solid angle).
Abstract: In this paper we report the first transistors fabricated on a substrate that is then plastically deformed. Using amorphous silicon (a-Si) device islands on a polyimide substrate, TFTs can withstand an average substrate strain of 6%, as the substrate is deformed into a spherical cap shape subtending angles as large as 66/spl deg/ (1 steradian solid angle).
TL;DR: In this article, Nacre (mother-of-pearl), the pearly internal layer of many mollusc shells, was examined using a stereo microscope and a metallurgical microscope, followed by analysis of the structural details using scanning electron microscopy.
Abstract: Princeton Materials Institute, Princeton University, Princeton, New Jersey 08544 Some biological materials exhibit structural robustness, despite the brittle nature of their constituents.Nacre (mother-of-pearl), the pearly internal layer of many mollusc shells, is addressed in this study. This material comprises about 95% aragonite tablets (a mineral form of CaC03), The polygonal tablets were glued with only a few percent of biological macromolecules into layered structure. The goal of the present study is to elucidate the basic inelastic deformation mechanisms. Typical stress /strain curves in tension and compression are plotted in Fig. 1. All tensile curves exhibited extensive inelastic deformation. After testing, the samples were initially examined using a stereo microscope (Leica MZ8) and a metallurgical microscope (Leica MEF4M) followed by analysis of the structural details using scanning electron microscopy (Philip XL-30). Optical imaging provided a visualization of the inelastic zone, manifest as white tension lines.