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ردیف | عنوان | نوع |
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1 |
Coupled elasto-viscoplastic and damage model accounting for plastic anisotropy and damage evolution dependent on loading conditions
الاستو ویسکوپلاستیک همراه و مدل آسیب محاسبه ناهمسانگردی پلاستیک و تکامل آسیب وابسته به شرایط بارگذاری-2021 This work presents an unconventional fully coupled elasto-viscoplastic and damage constitutive model that is suitable for
investigating the failure mechanism of metallic materials. The constitutive equations are developed within a finite elastoplasticity
framework under the assumption of hypoelastic-based plasticity. Anisotropic plastic potential and plastic-induced anisotropy
are modelled by means of the Hill48 yield criterion and a Chaboche-type non-linear kinematic hardening law, respectively. A
modified Voce-type law is assumed for the isotropic hardening behaviour. A novel law is proposed to account for an evolution of
the damage depending on the loading directions. The proposed model was implemented via user subroutine for the commercial
finite elements (FE) software Abaqus/Standard and used for the prediction of the cyclic failure of lead-free solder materials, the
crack formation in anisotropic AISI 316L steel specimens and the description of the failure behaviour of carbon steel notched
round bars and flat grooved plates.
Keywords: Rate-dependent plasticity | Damage anisotropic evolution | Plastic anisotropy | Kinetic logarithmic spin | Hypoelastic-based plasticity |
مقاله انگلیسی |
2 |
New method for a SEM-based quantitative microstructural clay analysis - MiCA
روش جدید برای تجزیه و تحلیل کمی خاک رس ریزساختاری مبتنی بر SEM - MiCA-2021 The soil microstructure is recognised to strongly influence the mechanical behaviour of both coarse and fine geomaterials. Proper identification and tracking of the shape and position of the particles has become more and more critical to form a link between the micro and macro behaviour. Scanning Electron Microscopy (SEM) has been widely used in the last decades to study the clay fabric variation with its mechanical behaviour and physical properties. However, the particles orientation has so far been discussed only from a qualitative point of view due to the lack of updated, automatised quantification tools. Consequently, developing constitutive models that correlate the soil micro structure to its mechanical behaviour is not feasible. In order to make a step forward in this direction, an Image Analysis based code called MiCA (microstructural clay analyser) capable of quantifying the particle orientation and the porosity of clay samples through the analysis of SEM micrographs was developed in this study. The code reliability was first validated through the application to geometrical reference patterns, then to textbook micrographs illustrating typical clay fabrics (dispersed, honeycomb, flocculated and aggre- gated), and finally to high quality images. MiCA showed good accuracy in the results obtained, regardless of the number of lines in the image, the complexity of the geometrical shapes and the pixel size of the analysed graphs. Therefore, MiCA can be considered suitable for quantitative analysis of the particle orientation and/or pores shape in clay materials. Keywords: Image analysis | Computer vision | Quantitative analysis | Clay particles orientation | SEM | Clay porosity |
مقاله انگلیسی |
3 |
Multiscale modelling of granular materials in boundary value problems accounting for mesoscale mechanisms
مدلسازی چند مقیاسی مواد دانهای در مسائل ارزش مرزی برای مکانیزمهای مقیاس متوسط-2021 The proper solution of geotechnical boundary value problems requires robust constitutive models that can
describe the mechanical behavior of geomaterials under various loading conditions, while also accounting as
closely as possible for the different material scales of interest. This is even more relevant to granular media where
the complexity of the mechanical behaviour is not limited to the nature of the contact law between grains, and
instead originates from the multiplicity of contacts oriented along all the directions of the physical space to form
distinctive mesostructures. This paper revisits the so-called H-model, which belongs to the broad family of
micromechanical approaches whereby an intermediate scale (mesoscale) is explicitly introduced into the
formulation. One great advantage of the model is that it can be extended by accounting for further multi-physical
couplings, as for example the presence of capillary bridges between grains. This versatile model was imple-
mented within an explicit finite difference based computational software (FLAC), and the present work dem-
onstrates its ability to analyze engineering problems with a microstructural viewpoint, while also providing new
insights in microstructural mechanisms of failure difficult to capture with standard phenomenological models. keywords: مواد گرانول | یکسان سازی | رویکرد چند منظوره | نظریه چندگانه | ریز ساختار | مقیاس Mesoscopic | مدل سازی سازنده | مدل H | مشکلات ارزش مرزی | Granular material | Homogenization | Multiscale approach | Multislip theory | Microstructure | Mesoscopic scale | Constitutive modeling | H-model | Boundary value problems |
مقاله انگلیسی |
4 |
Prediction of perforation into concrete accounting for saturation ratio influence at high confinement
پیش بینی سوراخ شدن در بتن برای تأثیر نسبت اشباع در محصور شدن بالا-2021 This paper provides both an analytical and a finite element models aiming at better predicting possible perfo-
ration of reinforced concrete slabs submitted to impacts. Both models account for free water saturation ratio and
high triaxial stress induced into concrete by the impact. Finite element simulations are performed with Abaqus
explicit code using a revised constitutive model for concrete; this coupled damage plasticity model (PRM) ac-
counts for strain rate effects and the influence of saturation ratio on the triaxial behavior. Complementary
original analytical predictions of ballistic limit and residual velocities are provided for both hard and soft im-
pacts. These predictions depend on a recent deviatoric stress-based formulation of compressive strength of
concrete. Numerical and analytical results are consistent with bending and punching experimental tests. keywords: اثرات نرم و سخت | سرعت باقی مانده | بتن آرمه | ظرفیت سوراخ کردن | نسبت اشباع | Soft and hard impacts | Residual velocity | Reinforced concrete | Perforation capacity | Saturation ratio |
مقاله انگلیسی |
5 |
An evolution law for fabric anisotropy and its application in micromechanical modelling of granular materials
قانون تکامل برای ناهمسانگردی پارچه و کاربرد آن در مدل سازی میکرومکانیکی مواد دانه ای-2020 Micromechanical studies of granular materials have demonstrated the importance of their microstruc- ture to their behaviour. This microstructure is often characterized by fabric tensors. Experimental and computational studies have shown that the fabric can change significantly during deformation. Therefore, the evolution of fabric is important to constitutive modelling. Current fabric evolution laws for granular materials have generally been developed for continuum-mechanical models, and use a loading index mul- tiplier associated with a yield surface. Such evolution laws can not be employed with micromechanical models that do not involve an explicit macro-scale yield surface. This study develops an evolution law for fabric anisotropy, based on observations from experiments and Discrete Element Method simulations from literature. The proposed evolution law considers the effects of inherent anisotropy, void ratio, stress ratio, loading direction and intermediate principal stress ratio. In the critical state, the value of the fabric anisotropy depends only on the Lode angle. The predicted evolution of fabric anisotropy is in good agreement with results of Discrete Element Method simulations, showing both hardening and softening behaviour and describing the influence of the initial void ratio. The proposed evolution law can be embedded into micromechanics-based constitutive relations as well as conventional continuum-mechanical models. As an example, a well-established micromechanical model (in which the fabric is considered as constant) has been extended by accounting for the variations in fabric, in combination with the proposed fabric evolution law. The performance of this enhanced mi- cromechanical model has been demonstrated by a comparison between the predicted behaviour and ex- perimental results from literature for Toyoura sand under various loading conditions. Keywords: Granular material | Fabric | Micromechanics | Constitutive modelling |
مقاله انگلیسی |
6 |
Structural models based on 3D constitutive laws: Variational structure and numerical solution
مدل های ساختاری مبتنی بر قوانین سازنده سه بعدی: ساختار تغییرات و راه حل عددی-2020 In all structural models, the section or fiber response is a relation between the strain measures and the stress resultants. This
relation can only be expressed in a simple analytical form when the material response is linear elastic. For other, more complex
and interesting situations, kinematic and kinetic hypotheses need to be invoked, and a constrained three-dimensional constitutive
relation has to be employed at every point of the section in order to implement non-linear and dissipative constitutive laws
into dimensionally reduced structural models. In this article we explain in which sense reduced constitutive models can be
expressed as minimization problems, helping to formulate the global equilibrium as a single optimization problem. Casting
the problem this way has implications from the mathematical and numerical points of view, naturally defining error indicators.
General purpose solution algorithms for constrained material response, with and without optimization character, are discussed
and provided in an open-source library. Keywords: Structural models | Constitutive models | Variational method | Error estimation |
مقاله انگلیسی |
7 |
From S-N to the Paris law with a new mixed-mode cohesive fatigue model for delamination in composites
از S-N گرفته تا قانون پاریس با یک مدل جدید خستگی منسجم مختلط برای لایه لایه شدن در کامپوزیت ها-2020 The relationship between fatigue life and fatigue crack propagation rate in composites is explored with a new cohesive damage model. The parameters of the model are obtained from idealizations of S-N diagrams used in engineering design. The model assumes that the quasi-static cohesive law that describes tearing is the envelope of the fatigue damage. Fatigue damage within the cohesive envelope accumulates at a rate that satisfies the S-N diagram and Miner’s cumulative fatigue damage rule. The fatigue model was implemented as a UMAT subroutine for Abaqus cohesive elements by adding fatigue damage accumulation within a cohesive model based on the Turon mixed-mode model. The analyses were conducted using a simplified cyclic loading procedure in which the maximum load is applied quasistatically and load cycling is represented within the constitutive model. The predicted propagation rates of delamination in mode I and mixed mode were compared to experimental results for IM7/8552 graphite/epoxy tape. Several aspects of the results were investigated, including the effects of R-curves, the stress ratio R, and the difference between displacement and force control. |
مقاله انگلیسی |
8 |
A micromorphic crystal plasticity model with the gradient-enhanced incremental hardening law
مدل انعطاف پذیری بلور میکرومورفیک با قانون سخت شدن افزایشی شیب-2020 A model of crystal plasticity is developed in which the effects of plastic flow non-uniformity are
described through the full dislocation density tensor. The micromorphic approach is used in
which the dislocation density tensor is represented by the curl of an independent constitutive
variable called microdeformation. The microdeformation tensor is enforced by an energetic
penalty term to be close to the actual plastic distortion tensor. The curl of microdeformation
tensor enters the constitutive model in two independent but complementary ways. First, it is an
argument of the free energy density function, which describes the kinematic-type hardening in
cyclic non-uniform deformation. Second, its rate influences the rates of critical resolved shear
stresses, which corresponds to additional isotropic hardening caused by incompatibility of the
plastic flow rate. The latter effect, missing in the standard slip-system hardening rule, is described
in a simple manner that does not require any extra parameter in comparison to the non-gradient
theory. In the proposed model there are two independent internal length scales whose interplay is
examined by means of 1D and 2D numerical examples of plastic shearing of a single crystal. Keywords: Gradient theory | Crystal plasticity | Dissipation | Length scale | Cyclic deformation | Numerical regularization |
مقاله انگلیسی |
9 |
Extending uniaxial material laws to multiaxial constitutive relations: H-approach
گسترش قوانین مواد تک محوره به روابط سازنده چند محور: رویکرد H-2020 A simple method is presented, allowing us to extend any one-dimensional material model to a general material
law suitable for arbitrary multiaxial loading conditions. The resulting system of constitutive equations respects
the general principles of constitutive modelling, thus preserving thermodynamic consistency and objectivity. The
method is based on a certain modification of the concept of representative directions. Since it operates with
logarithmic Hencky strains we call it H-approach. In contrast to the conventional concept of representative directions,
which we call now C-approach, the H-approach does not require artificial deviatorization of the stress
tensor. Moreover, the H-approach allows one to model initially isotropic materials with a smaller number of
representative directions, thus reducing the computational costs. The performance of the H-approach regarding
the description of second-order effects under simple shear is tested. The flexibility of the H-approach in
describing mechanical response of a real material is also demonstrated. Toward that end, a complex mechanical
behaviour of certain electrospun polymer is rendered. Keywords: Finite strains | Constitutive modelling | Concept of representative directions | Hencky strain | Electrospun polymer |
مقاله انگلیسی |
10 |
Constitutive modelling of cemented paste backfill: A data-mining approach
مدل سازی سازنده پشتی خمیر سیمانی: یک روش داده کاوی-2019 The environmental risks posed by mine tailings suggest the necessity of recycling tailings as cemented
paste backfill (CPB) and constitutive modelling is an important step to understand its mechanical stability.
In the present work, a novel data-mining approach is proposed for the stress–strain relationship modelling
of CPB considering the coupled effect of cement/tailings ratio, solids content and curing time. The
proposed approach is based on the random forest (RF) and firefly algorithm (FA), which can operate on
large quantities of data for nonlinear and complex relationships modelling. RF was used to model the
CPB constitutive relations while FA was used to tune the RF hyper-parameters. Unconfined compression
tests were performed for the dataset preparation. The reliability and robustness of the proposed
approach, the RF_FA, has been verified against experimental data. Results showed that the hyperparameters
of RF could be efficiently tuned by FA and the optimum hyper-parameters were obtained
at the fifth generation. Moreover, the RF_FA possessed excellent prediction capability for the stress–strain
relationship modelling (the correlation coefficient values between predicted and experimental stress values
were 0.991 on the training set and 0.989 on the testing set). External verifications were further carried
out to illustrate the performance of the RF_FA using several statistical criteria recommended in the
literature. Consequently, it can be suggested that the RF_FA paves a new way in the constitutive modelling
of CPB, which is of great significance for its engineering application Keywords: Cemented paste backfill | Constitutive modelling | Unconfined compression tests | Random forest | Firefly algorithm |
مقاله انگلیسی |