Chung‐Yuen Hui 교수

Stamp deformation can affect the dimensional stability of the microcontact printing process. We consider limitations imposed due to reversible deformation of a single stamp. Detailed analyses of several modes of stamp deformation have been carried out. Stability criteria have been obtained for both vertical and lateral collapse of surface relief features, including buckling. The shape change of surface features imposed by surface tension has been analyzed, and the corresponding internal stresses

This study addresses the strength and toughness of generic fibrillar structures. We show that the stress sigmac required to pull a fibril out of adhesive contact with a substrate has the form sigma(c) = sigma(0)Phi(chi). In this equation, sigma(0) is the interfacial strength, Phi(chi) is a dimensionless function satisfying 0 <or= Phi(chi) <or= 1 and chi is a dimensionless parameter that depends on the interfacial properties, as well as the fibril stiffness and radius. Pull-off is flaw sensitive

The fracture mechanics of hydrogels, especially those with significantly enhanced toughness, has attracted extensive research interests. In this article we discuss the experimental measurement and theoretical interpretation of the fracture toughness for soft hydrogels. We first review the definition of fracture toughness for elastic materials, and the commonly used experimental configurations to measure it. In reality most gels are inelastic. For gels that are rate insensitive, we discuss how to

When a material is so soft that the cohesive strength (or adhesive strength, in the case of interfacial fracture) exceeds the elastic modulus of the material, we show that a crack will blunt instead of propagating. Large–deformation finite–element model (FEM) simulations of crack initiation, in which the debonding processes are quantified using a cohesive zone model, are used to support this hypothesis. An approximate analytic solution, which agrees well with the FEM simulation, gives additional

The swelling of a polymer glass by sorption of a small molecule penetrant is considered in a regime characterized by so-called case-II diffusion. Attention is focused on the polymer so that the swelling process can be investigated apart from diffusion. The model of Thomas and Windle (TW) is used to predict the surface swelling as a function of exposure time. This model assumes that the swelling is driven by the osmotic pressure which relaxes to zero as the surface penetrant volume fraction φs ap

The extension of the Johnson−Kendall−Roberts (JKR) theory of contact to viscoelastic materials is addressed. Because the energy flow to the material at the moving edge of contact is coupled to the local bonding or debonding process for viscoelastic materials, any such extension must account for the micromechanical process of bonding or failure if it is to avoid a paradoxical prediction. A crack bonding theory due to Schapery that uses a very simple model of the crack closing process is applied t

We consider front formation and steady-state front motion in a one-dimensional polymer system undergoing case-II diffusion. The polymer system approximates a polymer sheet whose thickness is very small compared with its lateral dimensions. The osmotic pressure of Thomas and Windle (TW) is used in the theoretical analysis. The transient problem of front formation is formulated. It is found that the original coupled system of partial differential equations proposed by TW can be reduced to one equa

The rate dependence of fracture has been studied in a series of physically associating triblock copolymer gels that have a well-defined molecular structure. Compressive experiments were performed to develop a strain energy function that accurately captures the strain hardening behavior of these materials. This same strain energy function was utilized in a finite element model of the crack tip stresses, which become highly anisotropic at stress values below the failure strength of the gels. The r

Abstract Simple closed form expressions for the effective tensile moduli of an unidirectionally aligned two phase composite reinforced by fiber‐like or flake‐like inclusions of aspect ratio α are obtained. The case of α ≫ 1 corresponds to fiber‐like inclusions whereas the case of α ≪ 1 corresponds to flake‐like inclusions. These expressions are based on the exact results obtained by Tandon and Weng, who used the Mori‐Tanaka method to obtain the effective moduli of such composites. These expressi

Exact equations are derived governing the evolution of fiber fragments in a Weibull fiber loaded according to the “single filament composite test”. These equations differ from those formulated by others who have made a priori assumptions on the shape of the fragment distribution that are shown to be incorrect. An explicit closed form solution of the governing equations is derived for arbitrary Weibull modulus ϱ and for random initial breaks with exponentially distributed spacings of a given norm

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMicromechanics of crack growth into a craze in a polymer glassC. Y. Hui, A. Ruina, C. Creton, and E. J. KramerCite this: Macromolecules 1992, 25, 15, 3948–3955Publication Date (Print):July 1, 1992Publication History Published online1 May 2002Published inissue 1 July 1992https://doi.org/10.1021/ma00041a018RIGHTS & PERMISSIONSArticle Views750Altmetric-Citations81LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article dow

Exact closed-form solutions are obtained for the stress and induction field of a spheroidal piezo-electric inclusion in an infinite piezo-electric matrix subjected to spatially homogeneous mechanical and electrical loadings far away from the inclusion. Three types of loading are considered: axisymmetric, in-plane and out-of-plane shear. A limiting case of this solution allows us to determine the stress and induction field of a penny-shaped crack in a piezo-electric material. Closed-form expressi