Micromechanical Modeling Approach Research Articles

Plasticity based interface model for failure modelling of unreinforced masonry under cyclic loading

In this work our objective is to understand the failure behaviour of unreinforced masonry under in-plane cyclic loading. For this purpose we proposed a plasticity based interface model consists of a single yield surface criteria which is a direct extension of Mohr-Coulomb criteria with a tension cut and compression cap and a back stress vector is introduced as a mixed hardening law variable in the adopted yield surface to capture the unloading/reloading behaviour of masonry under cyclic loading. A simplified micromechanical interface modelling approach is adopted to capture all the failure modes of masonry. The integration of the differential constitutive equation is done by using implicit Euler backward integration approach and the obtained non-linear set of equations are solved by a combined local/global Newton solver. The proposed constitutive model is implemented in ABAQUS by writing UMAT (user-defined subroutine) and the obtained numerical results are compared with experimental results available in the literature.

Aspects of ductile failure prediction of interstitial‐free steel based on a Gurson‐type damage model

AbstractNumerical simulation of manufacturing processes has been gaining widespread attention owing to importance in the development of new products and components. In a parallel path, there has been a substantial development of steels with improved mechanical characteristics, such as the interstitial‐free (IF) steel. The present work is inserted within this context and introduces application of a micromechanical modelling approach to an interstitial‐free steel based on a Gurson‐type constitutive model with the objective of assessing the evolution of mechanical degradation and failure prediction in fracture‐free materials. The inelastic material parameters were obtained from tensile tests of cylindrical specimens. Evolution of the mechanical degradation, represented by a micromechanical damage measure, is discussed based on three‐point bend tests.

A Peridynamics-Based Micromechanical Modeling Approach for Random Heterogeneous Structural Materials.

This paper presents a peridynamics-based micromechanical analysis framework that can efficiently handle material failure for random heterogeneous structural materials. In contrast to conventional continuum-based approaches, this method can handle discontinuities such as fracture without requiring supplemental mathematical relations. The framework presented here generates representative unit cells based on microstructural information on the material and assigns distinct material behavior to the constituent phases in the random heterogenous microstructures. The framework incorporates spontaneous failure initiation/propagation based on the critical stretch criterion in peridynamics and predicts effective constitutive response of the material. The current framework is applied to a metallic particulate-reinforced cementitious composite. The simulated mechanical responses show excellent match with experimental observations signifying efficacy of the peridynamics-based micromechanical framework for heterogenous composites. Thus, the multiscale peridynamics-based framework can efficiently facilitate microstructure guided material design for a large class of inclusion-modified random heterogenous materials.

Characterization of unidirectional fiber reinforced polymer composites manufactured through resin film infusion process using micromechanical modeling

Resin Film Infusion (RFI) process is used for manufacturing large and thick unidirectional fiber reinforced polymer (UD FRP) composite structures for load bearing applications. Designing these load bearing structures requires the knowledge of effective elastic and strength characteristics of these composites. In this study, strength and stiffness properties of UD FRP manufactured through RFI process are predicted using a micromechanical modeling approach. A 3D representative volume element (3DRVE) with hexagonal array of fibers is used and all nine elastic constants of UD FRP composite are predicted. Failure models for fiber and resin are used to predict longitudinal tension/compression, transverse tension/compression and longitudinal shear strengths. Experiments were conducted on UD FRP composite manufactured through RFI process to obtain strength and stiffness properties. Results of experiment and simulations are compared and results validated.

Application of different plasticity models to PC/ABS blends within micromechanical approaches

AbstractRubber‐toughened thermoplastic polymers such as PC/ABS blends exhibit a non‐monotonic dependence of fracture toughness on composition, e.g. [6]. The key parameters determining the mechanical response of PC/ABS are the PC vs. ABS ratio and the rubber content in ABS. In this contribution, two micromechanical modeling approaches (single particle unit cell models, random representative volume elements) are considered to investigate this behavior. Thereby, different visco‐plasticity models are utilized to capture the specific deformation behavior of each phase. Computational studies of both micromechanical modeling approaches are compared to each other as well as to experimental data.

Piezoelectric Metamaterial with Negative and Zero Poisson’s Ratios

AbstractThis study presents the finite element–based micromechanical modeling approach to obtain the electromechanical properties of the piezoelectric metamaterial based on honeycomb (HC) cellular ...

Micromechanical modeling of cleavage fracture for a ferritic-pearlitic steel

Despite efficient computational capability of phenomenological macromechanical models to predict cleavage fracture, they still lack microstructure sensitive information for material design. Therefore, a microstructure-based micromechanical modeling approach is proposed to predict cleavage fracture for a steel of grade AISI 1045 at different stress states. For the micromechanical modeling, virtual experiments are performed on an artificial microstructure model to derive the plasticity and cleavage damage initiation strain for the investigated material at −196 °C. The predicted microcrack initiation strains of cleavage fracture at two different states (plane strain tension and equibiaxial tension) agree well with the calibrated results of macromechanical modeling, illustrating the validity and predictive capability of the proposed approach. Furthermore, the approach is applied to a microstructure sensitivity study on artificial microstructure models with different microstructure constitutes to investigate the influence of microstructure on the behavior of cleavage fracture. Therefore, the new approach is contributing to the material design directly.

SRVE modeling of particulate polymer matrix composites with irregularly shaped inclusions: Application to a green stone composite

Particulate polymer matrix composites (PPMCs) play a significant role in a wide range of applications from tissue engineering to aero-structures. Modeling thermoelastic properties of PPMCs can save sizable experimental time and costs, as it provides the capability of predicting the composite’s response to different loading conditions with acceptable accuracies. Micromechanical modeling approach is employed in this investigation to predict the thermoelastic properties of a new particulate polymer matrix composite, made of granite powder as inclusion and the acrylonitrile butadiene styrene (ABS) as matrix—called green stone composite. The reinforcing particles are modeled according to their shape irregularities. Namely, a statistical representative volume element (SRVE) is developed using the concept of integral range, with randomly distributed particles with irregular shapes. Experiments have been conducted to examine the validity of the proposed modeling approach. Numerical and experimental results both show that adding granite powder to pure ABS up to 38% (volume fraction) can notably increase the composite’s thermoelastic properties (bulk and shear moduli as well as thermal conductivity), as high as 200%.

Influence of Microstructural Features on the Strain Hardening Behavior of Additively Manufactured Metallic Components

Additive manufacturing (AM) has recently become one of the key manufacturing processes in the era of Industry 4.0 because of its highly flexible production scheme. Due to complex thermal cycles during the manufacturing process itself and special solidification conditions, the microstructure of AM components often exhibits elongated grains together with a pronounced texture. These microstructural features significantly contribute to an anisotropic mechanical behavior. In this work, the microstructure and mechanical properties of additively manufactured samples of 316L stainless steel are characterized experimentally and a micromechanical modeling approach is employed to predict the macroscopic properties. The objective of this work is to study the effects of texture and microstructural morphology on yield strength and strain hardening behavior of face‐centered cubic additively manufactured metallic components. To incorporate the texture in synthetic representative volume elements (RVE), the proposed approach considers both the crystallographic and grain boundary textures. The mechanical behavior of these RVEs is modeled using crystal plasticity finite element method, which incorporates size effects through the implementation of strain gradients.

Investigation on Microstructural Damage Properties of Asphalt Mixture Using Linear and Damage-Coupled Viscoelastic Model

This paper presents an image-based micromechanical modeling approach for simulating the damage-couple viscoelastic response of asphalt mixture. Details of the numerical damage-couple viscoelastic constitutive formulation implemented in a finite element code are presented and illustrated by using the ABAQUS user material subroutine (UMAT). Then, an experimental procedure based on the Linear Amplitude Sweep test for obtaining the viscoelastic and damage parameters at a given temperature was conducted. An improved morphological multi-scale algorithm was employed to segment the adhesive coarse aggregate images. We developed a pixel-based digital reconstruction model of asphalt mixture with the X-ray CT image after being processed. Finally, the image-based FE model incorporated with damage-coupled viscoelastic asphalt mastic phase and elastic aggregates was used for the compressive test simulations successfully in this study. Simulation results showed that the damaged simulation results have a larger stress distribution compared with the undamaged simulation due to the irregularity of the coarse aggregates. The von Mises stress distribution is smaller as the loading time increases due to the viscoelastic behavior of asphalt mastic. It can also provide insight on the damaged mechanisms and the possible location in asphalt mixture where microscopic cracking would most likely occur.

On the micro- and macroscopic elastoplastic deformation behaviour of cast iron when subjected to cyclic loading

The complicated constitutive behaviour of cast iron, involving a non-linear elastic regime, tension-compression stress asymmetry, varying elastic modulus and an inflection in the tension-to-compression hardening curve, is investigated using a micromechanical modelling approach. In this way, it is demonstrated that the abnormalities observed in the constitutive behaviour are qualitatively and quantitatively explained by the interaction behaviour between the matrix and graphite constituents. In initial tension, the absence of linearity is rationalised by the successive loss in load-carrying capacity of the graphite phase due to debonding, which in subsequent cycling, results in the opening and re-contact of the matrix-graphite interface. This effect is demonstrated to result in tension-compression asymmetry in stress and elastic modulus, as well as the inflection in tension-to-compression loading. The given model of explanation is validated by comparison to the experimentally acquired microscopic strain field in EN-GJV-400 at locations where stress concentrations are generated due to the matrix-graphite debonding, using high-resolution digital image correlation of scanning electron images.

The effect of fiber distribution on the compressive strength of hybrid polymer composites

The effect of fiber distribution, in glass/carbon hybrid fiber composites, on the compressive kinking strength is studied using a 3D finite element-based micromechanical model. Existing experimental data from literature have indicated negative effects of hybridizing glass to carbon on the compressive strength. In this study a micromechanical modeling approach has been adopted to study the role of relative locations of glass and carbon fibers and their distributions on the predicted peak compressive strength. In the micromechanical model, the hybridization ratio was varied by changing the number of glass fibers relative to the number of carbon fibers. The effect of fiber distribution was studied by changing the interfiber spacing and location. Results obtained from the analysis indicate the importance of symmetric fiber distribution. It was found that the distribution with glass fiber in the center with a distribution of carbon fibers on the exterior is able to enhance the compressive strength as compared to an unsymmetrical arrangement of fibers in the model.

Thermomechanical investigation of unidirectional carbon fiber-polymer hybrid composites containing CNTs

In this research, the thermoelastic response of unidirectional carbon fiber (CF)-reinforced polymer hybrid composites containing carbon nanotubes (CNTs) are analyzed using a physics-based hierarchical micromechanical modeling approach. The developed model consists of a unit cell-based scheme along with the Eshelby method which can consider random orientation, random distribution, directional behavior, non-straight shape of CNTs and interphase region generated due to the non-bonded van der Waals interaction between a CNT and the polymer matrix. The predictions are compared with the experimental data available in the literature and a quite good agreement is pointed out for the fibrous polymer composite, CNT-polymer nanocomposite and fiber/CNT-polymer hybrid composite systems. The influences of several factors, including volume fraction, aspect ratio, off-axis angle and arrangement type of CFs as well as CNT volume fraction on the thermoelastic behavior of CF/CNT-polymer hybrid composites are examined in detail. The results indicate that the transverse CTE of a unidirectional CF-reinforced composite is significantly improved due to the addition of CNTs, while the hybrid composite CTE in the longitudinal direction is negligibly affected by the CNTs. Also, it is found that the role of CNT in the hybrid composite thermoelastic behavior becomes more prominent as the CF aspect ratio decreases.

Micromechanical analysis of carbon nanotube-coated fiber-reinforced hybrid composites

A multiscale micromechanical modeling approach is developed to predict elastic properties of carbon fiber (CF)-reinforced polymer hybrid composites. In this type of hybrid composite, the unidirectional fibers are coated with randomly oriented carbon nanotubes (CNTs). Two fundamental aspects affecting the mechanical behavior of the hybrid composites are investigated herein; namely, CNT non-straight shape and the existence of an interphase region between a CNT and the polymer matrix. An excellent agreement is observed between the predictions of the new micromechanical method and available experimental data. The results reveal that for an accurate prediction of the elastic properties of the CNT-coated CF-reinforced hybrid composite, the consideration of waviness and transversely isotropic behavior of CNT, CNT/polymer interphase region and random arrangement of CFs is essential. It is found that the contribution of CNTs to the elastic response of the hybrid composite in longitudinal direction can be neglected. However, transverse elastic modulus of the CNT-coated CF-reinforced hybrid composite is significantly improved over that of the conventional CF-reinforced composite without CNT coating. Also, the maximum value of transverse elastic modulus can be obtained when the uniformly aligned straight CNTs are radially grown on the surface of the horizontal CFs.

A micro-mechanical modeling approach for dynamic fragmentation in brittle multi-phase materials

Understanding the response of structures exposed to high rate mechanical loading is important for improved protection and security. Modeling the behavior of these structural materials and components can be performed at different scales. However, a detailed picture of the behavior of the material under high strain rates can only be gained by treating each of its components independently. In this work, we present a one-dimensional finite element model to study dynamic fragmentation in multi-phase materials, and we applied it to study masonry as an example of multi-phase material for structural applications. The model follows a micro-mechanical approach where the matrix (brick), inclusions (mortar), and interfaces between matrix and inclusions are represented separately. Within each constituent, the heterogeneity in the material is introduced through a critical strength distribution. A cohesive zone model has also been incorporated to model progressive damage. Results show the influence of the volume fraction and the inclusion size on the average fragment-size and fragment-size distributions for strain rates between 102 and 105 s−1. Based on these results, a mathematical expression that captures the dependence of the average fragment-size on the strain rate, volume fraction and inclusion size has also been formulated. The observed increase on the average fragment-size with decreasing the inclusion size suggests the existence of a critical length that depends on the strain rate and material properties below which, no additional fragments of the inclusion-material are created.

A Simplified Micromechanical Modeling Approach to Predict the Tensile Flow Curve Behavior of Dual-Phase Steels

Micromechanical modeling is used to predict material’s tensile flow curve behavior based on microstructural characteristics. This research develops a simplified micromechanical modeling approach for predicting flow curve behavior of dual-phase steels. The existing literature reports on two broad approaches for determining tensile flow curve of these steels. The modeling approach developed in this work attempts to overcome specific limitations of the existing two approaches. This approach combines dislocation-based strain-hardening method with rule of mixtures. In the first step of modeling, ‘dislocation-based strain-hardening method’ was employed to predict tensile behavior of individual phases of ferrite and martensite. In the second step, the individual flow curves were combined using ‘rule of mixtures,’ to obtain the composite dual-phase flow behavior. To check accuracy of proposed model, four distinct dual-phase microstructures comprising of different ferrite grain size, martensite fraction, and carbon content in martensite were processed by annealing experiments. The true stress–strain curves for various microstructures were predicted with the newly developed micromechanical model. The results of micromechanical model matched closely with those of actual tensile tests. Thus, this micromechanical modeling approach can be used to predict and optimize the tensile flow behavior of dual-phase steels.

Micromechanical modeling approach to derive the yield surface for BCC and FCC steels using statistically informed microstructure models and nonlocal crystal plasticity

In order to describe irreversible deformation during metal forming processes, the yield surface is one of the most important criteria. Because of their simplicity and efficiency, analytical yield functions along with experimental guidelines for parameterization become increasingly important for engineering applications. However, the relationship between most of these models and microstructural features are still limited. Hence, we propose to use micromechanical modeling, which considers important microstructural features, as a part of the solution to this missing link. This study aims at the development of a micromechanical modeling strategy to calibrate material parameters for the advanced analytical initial yield function Barlat YLD 2004-18p. To accomplish this, the representative volume element is firstly created based on a method making use of the statistical description of microstructure morphology as input parameter. Such method couples particle simulations to radical Voronoi tessellations to generate realistic virtual microstructures as representative volume elements. Afterwards, a nonlocal crystal plasticity model is applied to describe the plastic deformation of the representative volume element by crystal plasticity finite element simulation. Subsequently, an algorithm to construct the yield surface based on the crystal plasticity finite element simulation is developed. The primary objectives of this proposed algorithm are to automatically capture and extract the yield loci under various loading conditions. Finally, a nonlinear least square optimization is applied to determine the material parameters of Barlat YLD 2004-18p initial yield function of representative volume element, mimicking generic properties of bcc and fcc steels from the numerical simulations.

Failure mechanism and mode of Ti-6Al-4V alloy under uniaxial tensile loading: Experiments and micromechanical modeling

The failure of dual-phase alloys under tensile loading conditions is often due to the nucleation, growth and coalescence of voids at the interface between different phases from micromechanical point of view. The aim of this paper is to identify the failure mechanism and mode of dual-phase Ti-6Al-4V alloy in the form of plastic strain localization due to the incompatible deformation between the softer α phase and the harder β phase under the uniaxial tensile loading condition. The failure modes of as-received and heat-treated alloy are determined by tensile tests using sheet specimens. Then, a micromechanical modeling approach is developed on the basis of actual microstructure to predict the failure modes and ultimate ductility. Two different failure modes, i.e., shear band and vertical split band, can be found for as-received material. However, only vertical split failure is observed for heat-treated alloy. The predicted results agree well with the experimental observations. The microstructure-level inhomogeneity and incompatible deformation between the hard and soft phases are the main reason for failure.

Explicit multiscale modelling of impact damage on laminated composites – Part II: Multiscale analyses

This work describes a multiscale impact damage prediction methodology for laminated composite structures which is based on the HFGMC micromechanical model and the MMCDM damage formulation. The numerical approach is intended for application within explicit finite element analyses and has been employed for modelling of high-velocity impact damage in laminated composite structures. Structural-scale applications and the multiscale framework of the method are presented in this paper whereas introduction and validation of the methodology have been presented in Part I of the paper.By applying the described method, the micromechanical model calculates the local stress/strain fields within the unidirectional composite material, whereas the structural-scale computations have been performed employing Abaqus/Explicit. The Mixed Mode Continuum Damage Mechanics (MMCDM) theory has been utilised as to model the damage and failure modes of the composite material at the micromechanical level. As demonstrated in the Part I paper, the HFGMC and MMCDM model enable modelling of the microdamage nonlinearities at in-plane shear and transverse compressive loading of the composite plies. The micromechanical damage modelling approach has been employed at high-velocity soft-body impact on CFRP and GFRP composite plates in this work. Results of the multiscale damage model have been validated using available experimental data and by comparison with the numerical results obtained using the commonly used ply-level failure criteria and damage models.

An Image-Based Finite Element Approach for Simulating Viscoelastic Response of Asphalt Mixture

This paper presents an image-based micromechanical modeling approach to predict the viscoelastic behavior of asphalt mixture. An improved image analysis technique based on the OTSU thresholding operation was employed to reduce the beam hardening effect in X-ray CT images. We developed a voxel-based 3D digital reconstruction model of asphalt mixture with the CT images after being processed. In this 3D model, the aggregate phase and air void were considered as elastic materials while the asphalt mastic phase was considered as linear viscoelastic material. The viscoelastic constitutive model of asphalt mastic was implemented in a finite element code using the ABAQUS user material subroutine (UMAT). An experimental procedure for determining the parameters of the viscoelastic constitutive model at a given temperature was proposed. To examine the capability of the model and the accuracy of the parameter, comparisons between the numerical predictions and the observed laboratory results of bending and compression tests were conducted. Finally, the verified digital sample of asphalt mixture was used to predict the asphalt mixture viscoelastic behavior under dynamic loading and creep-recovery loading. Simulation results showed that the presented image-based digital sample may be appropriate for predicting the mechanical behavior of asphalt mixture when all the mechanical properties for different phases became available.