Viscoelastic Cohesive Zone Model Research Articles

Atomic force microscopy, deformation-recovery and numerical study of wheat dough

Experimental and numerical modelling work related to microstructure and deformation of starch, gluten and wheat dough was presented. Atomic force microscopy analyses through force spectroscopy on starch samples showed elastic behaviour of both dried and reconstituted wet starch granules, where wet starch was shown to be more cohesive than dried starch. Deformation-recovery test over time under compression mode showed almost complete recovery to original sample height of gluten, whereas only a slight recovery was observed for dough. Finite element modelling was then commenced to simulate gluten deformation-recovery and starch-gluten dough deformation. The gluten geometry used for the starch-gluten dough model was obtained from cryo-SEM image from the previous work before the starch geometry was then included. The interface between the starch and gluten model was defined using viscoelastic cohesive zone elements. The modelling results suggested significant influence of gluten cellular structure towards starch-gluten dough integrity. In addition, the results from the current work further supported the previous report of the starch-gluten interfacial behaviour using viscoelastic cohesive zone model.

Multiscale modeling of unfolding and bond dissociation of rubredoxin metalloprotein

Mechanical properties of proteins that have a crucial effect on their operation. This study used a molecular dynamics simulation package to investigate rubredoxin unfolding on the atomic scale. Different simulation techniques were applied, and due to the dissociation of covalent/hydrogen bonds, this protein demonstrates several intermediate states in force-extension behavior. A conceptual model based on the cohesive finite element method was developed to consider the intermediate damages that occur during unfolding. This model is based on force-displacement curves derived from molecular dynamics results. The proposed conceptual model is designed to accurately identify bond rupture points and determine the associated forces. This is achieved by conducting a thorough comparison between molecular dynamics and cohesive finite element results. The utilization of a viscoelastic cohesive zone model allows for the consideration of loading rate effects. This rate-dependent model can be further developed and integrated into the multiscale modeling of large assemblies of metalloproteins, providing a comprehensive understanding of mechanical behavior while maintaining a reduced computational cost.

A viscoelastic cohesive zone model for starch-gluten interface to simulate dough deformation

A viscoelastic cohesive zone model was proposed to simulate rate-dependent starch-gluten interface debonding. The debonding was believed to influence stress-strain curves of tensile and shear tests at different strain rates. The model was written as a user-defined finite element subroutine codes, which was then included into an interface element geometry between starch filler and gluten matrix. The finite element modelling results showed agreement with experimental data under uniaxial tension and simple shear at different strain rates (5/min and 0.5/min). This was due to the viscoelastic effect of the interface model, which caused difference between traction initiation at different rates for the cohesive zone model (i.e. ∼1.1kPa and ∼0.5kPa at 5/min and 0.5/min, respectively). In addition, it was shown that critical shear stress is a very important debonding parameter, where slight changes of the shear traction values caused the model stress-strain curve to deviate from the experimental results. Simulations of starch-gluten dough deformation were then conducted at different strain rates to imitate dough processes like baking, extrusion and proving (0.003/s, 1/s and 10/s, respectively). The interface model was shown to influence stress-strain curve at lower strain rate processes like baking and extrusion.

Cohesive zone model for mode-I fracture with viscoelastic-sensitivity

A viscoelastic cohesive zone model (CZM) is formulated herein to model the time- and temperature-dependent fracture process of the interface between the solid propellant and insulation. The model is suitable for the simulation of a wide range of problems especially for the relaxation response of the fracture process. Independent control parameters of the Park-Paulino-Roesler (PPR) models are deduced first. By introducing the relaxed critical displacement, cohesive strength and initial slope parameter into the static PPR model, a viscoelastic CZM is established. Numerical time integration about obtaining the reduced time is described considering the change of the temperature. The properties of the proposed model are discussed in detail through the stretch and relaxation test of the double cantilever beam (DCB). Stretch test of the double cantilever sandwich beam (DCSB) under different loading rates and loading temperatures are designed to inverse the time-dependent and temperature-dependent model parameters respectively. To check the effectiveness of the proposed model and the accuracy of the inversed model parameters, three different tests including stretch test, multiple stretch-relaxation test, and creep test are conducted. The agreement is achieved between the numerical and experimental results.

Two-Way Coupled Multiscale Model for Predicting Mechanical Behavior of Bone Subjected to Viscoelastic Deformation and Fracture Damage

This paper presents a two-way linked computational multiscale model and its application to predict the mechanical behavior of bone subjected to viscoelastic deformation and fracture damage. The model is based on continuum thermos-mechanics and is implemented through the finite element method (FEM). Two physical length scales (the global scale of bone and local scale of compact bone) were two-way coupled in the framework by linking a homogenized global object to heterogeneous local-scale representative volume elements (RVEs). Multiscaling accounts for microstructure heterogeneity, viscoelastic deformation, and rate-dependent fracture damage at the local scale in order to predict the overall behavior of bone by using a viscoelastic cohesive zone model incorporated with a rate-dependent damage evolution law. In particular, age-related changes in material properties and geometries in bone were considered to investigate the effect of aging, loading rate, and damage evolution characteristics on the mechanical behavior of bone. The model successfully demonstrated its capability to predict the viscoelastic response and fracture damage due to different levels of aging, loading conditions (such as rates), and microscale damage evolution characteristics with only material properties of each constituent in the RVEs.

Numerical modeling of inelastic structures at loading of steady state rolling

In order to gain a deeper knowledge of the interactions in the coupled tire-pavement-system, e.g. for the future design of durable pavement structures, the paper presents recent results of research in the field of theoretical-numerical asphalt pavement modeling at material and structural level, whereby the focus is on a realistic and numerically efficient computation of pavements under rolling tire load by using the finite element method based on an Arbitrary Lagrangian Eulerian (ALE) formulation. Inelastic material descriptions are included into the ALE frame efficiently by a recently developed unsplit history update procedure. New is also the implementation of a viscoelastic cohesive zone model into the ALE pavement formulation to describe the interaction of the single pavement layers. The viscoelastic cohesive zone model is further extended to account for the normal pressure dependent shear behavior of the bonding layer. Another novelty is that thermo-mechanical effects are taken into account by a coupling of the mechanical ALE pavement computation to a transient thermal computation of the pavement cross-section to obtain the varying temperature distributions of the pavement due to climatic impact. Then, each ALE pavement simulation considers the temperature dependent asphalt material model that includes elastic, viscous and plastic behavior at finite strains and the temperature dependent viscoelastic cohesive zone formulation. The temperature dependent material parameters of the asphalt layers and the interfacial layers are fitted to experimental data. Results of coupled tire-pavement computations are presented to demonstrate potential fields of application.

Characterization of bitumen fracture using tensile tests incorporated with viscoelastic cohesive zone model

This paper presents an experimental test method incorporated with a cohesive zone model to characterize viscoelastic fracture damage of asphalt binders and mastics. The testing presented herein is specifically aimed at identifying rate-dependent, non-constant fracture characteristics of ductile asphalt binders and mastics. Test results that are dependent on materials and specimen geometry such as the film thickness of asphalt binder/mastic are presented. The testing results were then incorporated with a viscoelastic cohesive zone model to identify the material-specific damage evolution characteristics and its mechanical impacts on the overall performance of asphalt mixtures by conducting computational microstructure model simulations. Test results and subsequent microstructure model simulations clearly indicate the significance of component-level material properties and their linkage to mixture performance. The experimental protocol incorporated with the cohesive zone model presented in this paper are expected to provide an efficient tool to evaluate damage-induced mechanical performance of mixtures with small-scale material properties.

A thermomechanically coupled viscoelastic cohesive zone model at large deformation

A new viscoelastic cohesive zone model is formulated for large deformation conditions and within a fully coupled thermomechanical framework. The model is suitable for the simulation of a wide range of problems especially for polymeric materials. It can capture viscoelastic crack propagation as well as energy dissipation due to this process. Starting from the principles of thermodynamics, a 3D finite element formulation is derived for a fully coupled simultaneous solution of the thermal field and the deformation field. The viscoelastic model is constructed by extending an elastic exponential traction separation law using a simple rheology. The viscous part of the tractions is postulated to have the same characteristic length as the elastic part and that they are related by a single material parameter. A Newtonian dashpot is used to describe the evolution of the viscous separation. Furthermore, thermal effects are accounted for using temperature expressions in both the traction laws and the viscosity of the dashpot, and using a heat conduction law across the interface. The model is implemented within an implicit finite element code and the internal variable is calculated using an internal iteration. Different numerical examples are used to verify the model and a comparison with experimental data shows a satisfactory agreement.

Computational model for predicting nonlinear viscoelastic damage evolution in materials subjected to dynamic loading

Many inelastic solids accumulate numerous cracks before failure due to impact loading, thus rendering any exact solution of the IBVP untenable. It is therefore useful to construct computational models that can accurately predict the evolution of damage during actual impact/dynamic events in order to develop design tools for assessing performance characteristics. This paper presents a computational model for predicting the evolution of cracking in structures subjected to dynamic loading. Fracture is modeled via a nonlinear viscoelastic cohesive zone model. Two example problems are shown: one for model validation through comparison with a one-dimensional analytical solution for dynamic viscoelastic debonding, and the other demonstrates the applicability of the approach to model dynamic fracture propagation in the double cantilever beam test with a viscoelastic cohesive zone.

A model for predicting the multiscale crack growth due to an impact in heterogeneous viscoelastic solids

A two-scale model for predicting the multiple crack growth in viscoelastic solids due to an impact is presented. The cracks are considered only at the local scale through the use of a micromechanical viscoelastic cohesive zone model. The multiscale model has been implemented in a finite-element code. In order to minimize the computation time, the local finite-element meshes are solved in parallel by multiple processors. An example problem is given in order to demonstrate the capabilities of the model.

Computational Constitutive Model for Predicting Nonlinear Viscoelastic Damage and Fracture Failure of Asphalt Concrete Mixtures

A computational constitutive model was developed to predict damage and fracture failure of asphalt concrete mixtures. Complex heterogeneity and inelastic mechanical behavior are addressed by the model by using finite-element methods and elastic–viscoelastic constitutive relations. Damage evolution due to progressive cracking is represented by randomly oriented interface fracture, which is governed by a newly developed nonlinear viscoelastic cohesive zone model. Computational simulations demonstrate that damage evolution and failure of asphalt concrete mixtures is dependent on the mechanical properties of the mixture. This approach is suitable for the relative evaluation of asphalt concrete mixtures by simply employing material properties and fracture properties of mixture components rather than by performing expensive laboratory tests recursively, which are typically required for continuum damage mechanics modeling.

Damage-Induced Modeling of Elastic-Viscoelastic Randomly Oriented Particulate Composites

This paper presents a model for predicting the damage-induced mechanical response of particle-reinforced composites. The modeling includes the effects of matrix viscoelasticity and fracture, both within the matrix and along the boundaries between matrix and rigid particles. Because of these inhomogeneities, the analysis is performed using the finite element method. Interface fracture is predicted by using a nonlinear viscoelastic cohesive zone model. Rate-dependent viscoelastic behavior of the matrix material and cohesive zone is incorporated by utilizing a numerical time-incrementalized algorithm. The proposed modeling approach can be successfully employed for numerous types of solid media that exhibit matrix viscoelasticity and complex damage evolution characteristics within the matrix as well as along the matrix-particle boundaries. Computational results are given for various asphalt concrete mixtures. Simulation results demonstrate that each model parameter and design variable significantly influences the mechanical behavior of the mixture.

A model for predicting the evolution of damage in viscoelastic particle-reinforced composites

A viscoelastic cohesive zone model is employed within the framework of a finite element code to analyze a two-phase viscoelastic particle-reinforced composite material consisting of a relatively stiff aggregate embedded in a copolymer binder. The composite of interest, LX17, is noted to have a very large aggregate volume fraction and as such, aggregate grain boundaries were generated within finite element meshes along which viscoelastic cohesive zones have been embedded to model the binder. It has been observed experimentally that the majority of damage in LX17 occurs within the binder, and thus, a damage evolution law has been applied to the viscoelastic cohesive zones that is phenomenological in nature. The responses obtained for the composite from the FEM analysis are then compared to the experimental data compiled by Lawrence Livermore National Labs for various constant strain rate tests conducted by Groves and Cunningham [Tensile and compressive mechanical properties of billet pressed LX17-1 as a function of temperature and strain rate. UCRL-ID-137477. Internal report prepared for Lawrence Livermore National Laboratory, Livermore, CA].

Model for Predicting Damage Evolution in Heterogeneous Viscoelastic Asphaltic Mixtures

Cracking in the asphaltic layer of pavements has been shown to be a major source of distress in roadways. Previous studies in asphaltic mixture cracking typically have not considered the material heterogeneity. The sequel of a study in which the binder and the aggregates were treated as distinct materials is presented. Besides consideration of the viscoelastic behavior of the bulk asphalt binder, a micromechanical viscoelastic cohesive zone model introducing ductility at the crack tip has been considered. The simulations performed are verified and calibrated from simple and conventional laboratory tests. The study investigates crack evolution under monotonic loading, even though the method outlined can be further developed for the investigation of asphalt mixture fatigue.

A micromechanically-based model for predicting dynamic damage evolution in ductile polymers

A new micromechanically-based viscoelastic cohesive zone model is proposed that extends the features of a quasi-static model previously developed by the authors. A statistical distribution of fibril radii is assumed, and a critical fibril radius is introduced as a fracture criterion. Results are presented for various loading rates, and it is found that this dynamic damage model is both physically motivated and capable of modeling complex phenomena in cohesive zones.