Franck Vernerey - Academia.edu (original) (raw)

Papers by Franck Vernerey

Biophysical Journal, 2016

International Journal for Multiscale Computational Engineering, 2013

Computer Methods in Applied Mechanics and Engineering, 2014

We introduce an adaptive concurrent multiscale methodology (ACM 2 ) to handle situations in which... more We introduce an adaptive concurrent multiscale methodology (ACM 2 ) to handle situations in which both macroscopic and microscopic deformation fields strongly interact near the tip of a crack. The method is based on the balance between numerical and homogenization error; while the first type of error states that elements should be refined in regions of high deformation gradients, the second implies that element size may not be smaller than a threshold determined by the size of the unit cell representing the material's microstructure. In this context, we build a finite element framework in which unit cells can be embedded in continuum region through appropriate macro-micro boundary coupling conditions. By combining the idea of adaptive refinement with the embedded unit cell technique, the methodology ensures that appropriate descriptions of the material are used adequately, regardless of the severity of deformations. We will then show that our computational technique, in conjunction with the extended finite element method, is ideal to study the strong interactions between a crack and the microstructure of heterogeneous media. In particular, it enables an explicit description of microstructural features near the crack tip, while a computationally inexpensive coarse scale continuum description is used in the rest of the domain. The paper presents several examples of crack propagation in materials with random microstructures and discuss the potential of the multiscale technique in relating microstructural details to material strength and toughness.

Computer Methods in Applied Mechanics and Engineering, 2012

Advanced Healthcare Materials, 2016

Enzyme-sensitive hydrogels are promising for cell encapsulation and tissue engineering, but resul... more Enzyme-sensitive hydrogels are promising for cell encapsulation and tissue engineering, but result in complex spatiotemporal degradation behavior that is characteristic of reaction-diffusion mechanisms. An experimental and theoretical approach is presented to identify dimensionless quantities that serve as a design tool for engineering enzyme-sensitive hydrogels with controlled degradation patterns by tuning the initial hydrogel properties and enzyme kinetics.

The multi-scale micromorphic theory developed in our previous paper is used to predict the failur... more The multi-scale micromorphic theory developed in our previous paper is used to predict the failure of heterogeneous materials illustrated by a high strength steel alloy possessing two populations of hard particles distributed at two distinct length scales in an alloy matrix. To account for the effect and size of microstructural features during fracture, additional kinematic variables are added, giving rise to the couple stresses associated with each population of particles. The various stress and strain measures must satisfy a set of 1 Corresponding author: f-vernerey@northwestern.edu 2 Corresponding author : w-liu@northwestern.edu 2 coupled multi-scale governing equations derived from the principle of virtual power. A three-scale constitutive model is then developed to represent the failure of the alloy from nucleation, growth and coalescence of voids from each population of particles. For this, three distinct yield functions, each corresponding to a different scale, are introduced. Cell model simulations using finite elements are performed to determine the constitutive relations based on the key microstructural features. Two-dimensional failure analyses are then presented in tension and in shear, and show good agreement with direct numerical simulation of the microstructure.

Coupled Eulerian-Lagrangian extended fi nite element approach to simulating the mechanics and gro... more Coupled Eulerian-Lagrangian extended fi nite element approach to simulating the mechanics and growth of biofi lm,

Computer Methods in Applied Mechanics and Engineering, 2015

Conference Proceedings of the Society for Experimental Mechanics Series, 2011

High-performance natural materials and system are now serving as models for new engineering desig... more High-performance natural materials and system are now serving as models for new engineering designs. In this work we have investigated the structure and mechanics of a single teleost fish scale from striped bass Morone saxatilis as part of larger project on novel flexible protective systems inspired from fish skin. These scales are about 300 microns thick and consist of a hard outer bony layer supported by a cross ply of collagen fibrils. Basic properties were obtained from tensile tests on single scales. While the bony layer is brittle, the collagen layer can undergo large deformations, eventually failing by extensive fiber pullout. Perforation tests with a sharp needle on a single scale resting on a soft substrate were also used to assess the performance and mechanics of a scale under a predator's bite. We found that multiple small circumferential cracks developed on the top surface of the bony layer near the penetration site, while four major radial cracks formed through the thickness of bony layer.

International Journal of Solids and Structures, 2010

Biological and manmade structures often share the same specifications and design constraints: str... more Biological and manmade structures often share the same specifications and design constraints: structural support, lightweight or protection against specific threats. In this context, the structure of fishscales, consisting of small rigid plates growing out of the skin of a majority of fish species, are characterized by a large variety of shape, size and properties in order to achieve particular functions. The present study introduces a basic two-dimensional micromechanical model that permits to establish a correlation between the flexural response of a scaled skin and the nature of its underlying structure, including both geometric and material aspects. The model is used to predict trends in the structure's response and illustrates the fact that the scale design, arrangement and properties can be tailored to achieve a wide spectrum of response. In particular, fishscale structure possesses an inherent strain-stiffening response that can be suppressed or magnified by certain structural features. This particularity, shared by most biological materials, ensures that the structure provides both a structural and protective support for the animal.

International Journal of Solids and Structures, 2014

Polymer, 2015

Concentrating on the case of poly(ethylene glycol) hydrogels, this paper introduces a methodology... more Concentrating on the case of poly(ethylene glycol) hydrogels, this paper introduces a methodology that enables a natural integration between the development of a so-called mechanistic model and experimental data relating material&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s processing to response. In a nutshell, we develop a data-driven modeling component that is able to learn and indirectly infer its own parameters and structure by observing experimental data. Using this method, we investigate the relationship between processing conditions, microstructure and chemistry (cross-link density and polymer-solvent interactions) and response (swelling and elasticity) of non-degradable and degradable PEG hydrogels. We show that the method not only enables the determination of the polymer-solvent interaction parameter, but also it predicts that this parameter, among others, varies with processing conditions and degradation. The proposed methodology therefore offers a new approach that accounts for subtle changes in the hydrogel processing.

Computational Mechanics, 2007

To understand the mechanics of materials, it is important to faithfully model the physics due to ... more To understand the mechanics of materials, it is important to faithfully model the physics due to interactions at the microstructural scales. While brute-force modeling of all the details of the microstructure is too costly, current homogenized continuum models suffer from their inability to sufficiently capture the correct physics -especially where localization and failure are concerned. To overcome this limitation, a multi-scale continuum theory is proposed so that kinematic variables representing the deformation at various scales are incorporated. The method of virtual power is then used to derive a system of coupled governing equations, each equation representing a particular scale and its interactions with the macro-scale. A constitutive relation is then introduced to preserve the underlying physics associated with each scale. The inelastic behavior is represented by multiple yield functions, each representing a particular scale of microstructure, but collectively coupled through the same set of internal variables. We present some applications of the theory in high strength steels, whose microstructure consists of two populations of inclusions at distinct scales, in an alloy matrix. We then give an overview of undergoing research including the modeling of cortical bone, and thermal-mechanical-chemical-electrical materials

ACS Applied Materials & Interfaces, 2015

The scaled skin of fish is a high-performance natural armor that represents a source of inspirati... more The scaled skin of fish is a high-performance natural armor that represents a source of inspiration for novel engineering designs. In this paper, we present a biomimetic fish skin material, fabricated with a design and components that are simple, that achieves many of the advantageous attributes of natural materials, including the unique combination of flexibility and mechanical robustness. The bioinspired fish skin material is designed to replicate the structural, mechanical, and functional aspects of a natural teleost fish skin comprised of leptoid-like scales, similar to that of the striped red mullet Mullus surmuletus. The man-made fish skin material consists of a low-modulus elastic mesh or "dermis" layer that holds rigid, plastic scales. The mechanics of the synthetic material is characterized under in-plane, bending, and indentation modes of deformation and is successfully described by theoretical deformation models that have been developed. This combined experimental and modeling approach elucidates the critical mechanisms by which the composite material achieves its unique properties and provides design rules that allow for the engineering of scaled skins. Such artificial scaled skins that are flexible, lightweight, transparent, and robust under mechanical deformation may thus have potential as thin protective coatings for soft materials.

Handbook of Micromechanics and Nanomechanics, 2013

MRS Proceedings, 2012

In this work, we have studied the structure and mechanics of fish scales from striped bass (Moron... more In this work, we have studied the structure and mechanics of fish scales from striped bass (Morone saxatilis). This scale is about 200-300 µm thick and consists of a hard outer bony layer supported by a softer cross-ply of collagen fibrils. Puncture tests with a sharp needle indicated that a single fish scale provides a high resistance to penetration which is superior to polystyrene and polycarbonate, two engineering polymers that are typically used for light transparent packaging or protective equipment. Under puncture, the scale undergoes a sequence of two distinct failure events: First, the outer bony layer cracks following a well defined cross-like pattern which generates four "flaps" of bony material. The deflection of the flaps by the needle is resisted by the collagen layer, which in biaxial tension acts as a retaining membrane. Remarkably this second stage of the penetration process is highly stable, so that an additional 50% puncture force is required to eventually penetrate the collagen layer. The combination of a hard layer that can fail in a controlled fashion with a soft and extensible backing layer is the key to the resistance to penetration of individual scales.

Computational Methods in Applied Sciences, 2007

For the design of materials, it is important to faithfully model the physics due to interactions ... more For the design of materials, it is important to faithfully model the physics due to interactions at the microstructural scales . While bruteforce modeling of all the details of the microstructure is too costly, current homogenized continuum models suffer from their inability to sufficiently capture the correct physics -especially where localization and failure are concerned. To overcome this limitation, a multi-scale continuum theory is proposed so that kinematic variables representing the deformation at various scales are incorporated. The method of virtual power is then used to derive a system of coupled governing equations, each equation representing a particular scale and its interactions with the macro-scale. A constitutive relation is then introduced to preserve the underlying physics associated with each scale. The inelastic behavior is represented by multiple yield functions, each representing a particular scale of microstructure, but collectively coupled through the same set of internal variables. The proposed theory is applied to model porous metals and high strength steel. For the high strength steel the microstructure of interest consists of two populations of inclusions at distinct scales, in an alloy matrix.