References of "Wu, Ling"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailBayesian Identification of Mean-Field Homogenization model parameters and uncertain matrix behavior in non-aligned short fiber composites
Mahamedou, Mohamed; Zulueta Uriondo, Kepa; Chung, Chi Nghia et al

in Composite Structures (2019), 220

We present a stochastic approach combining Bayesian Inference (BI) with homogenization theories in order to identify, on the one hand, the parameters inherent to the model assumptions and, on the other ... [more ▼]

We present a stochastic approach combining Bayesian Inference (BI) with homogenization theories in order to identify, on the one hand, the parameters inherent to the model assumptions and, on the other hand, the composite material constituents behaviors, including their variability. In particular, we characterize the model parameters of a Mean-Field Homogenization (MFH) model and the elastic matrix behavior, including the inherent dispersion in its Young's modulus, of non-aligned Short Fibers Reinforced Polymer (SFRP) composites. The inference is achieved by considering as observations experimental tests conducted at the SFRP composite coupons level. The inferred model and material law parameters can in turn be used in Mean-Field Homogenization (MFH)-based multi-scale simulations and can predict the confidence range of the composite material responses. [less ▲]

Detailed reference viewed: 57 (10 ULiège)
Full Text
Peer Reviewed
See detailA micro-mechanical model of reinforced polymer failure with length scale effects and predictive capabilities. Validation on carbon fiber reinforced high-crosslinked RTM6 epoxy resin
Nguyen, Van Dung ULiege; Wu, Ling ULiege; Noels, Ludovic ULiege

in Mechanics of Materials (2019), 133

We propose a micro-mechanical numerical model able to predict the nonlinear behavior and failure of unidirectional fiber reinforced high-crosslinked epoxy subjected to transverse loading conditions ... [more ▼]

We propose a micro-mechanical numerical model able to predict the nonlinear behavior and failure of unidirectional fiber reinforced high-crosslinked epoxy subjected to transverse loading conditions. Statistical microstructural volume elements (SMVE) of a realistic composite material are generated from the statistical characterization of the fibers distribution and fiber radius estimated from SEM images of a similar material system. The fibers are assumed to be transversely hyperelastic isotropic and the matrix obeys a hyperelastic viscoelastic-viscoplastic constitutive model enhanced by a multi-mechanism nonlocal damage model. This polymer model captures the pressure dependency and strain rate effects. Besides, it also accounts for size effects through its internal length scales, allowing capturing, with the same unique set of parameters, the behaviors of the epoxy as pure material as well as matrix phase in composites, which are experimentally observed to be different. Additionally, since fiber/matrix interfaces of the considered composite material are categorized as strong ones, the true underlying failure mechanism is located in the matrix close to the fibers, and the interface does not need to be explicitly introduced in the model. The model prediction is found to be in good agreement with experimental results in terms of the global nonlinear stress-strain curves over various strain rates and pressure conditions, on the one hand for pure matrix samples, and on the other hand for the composite coupons, making the proposed framework a predictive virtual testing facility for material design. Finally, using this model, we study the localization behavior in order to characterize the post-failure behavior of the composite material: the cohesive strength is given by the stress-strain curve peak stress while the critical energy release rate is estimated by evaluating the dissipated energy accumulated during the post-peak localization stage. Finally, different SMVE realizations are considered allowing assessing the discrepancy in the failure characteristics of composites. [less ▲]

Detailed reference viewed: 71 (23 ULiège)
Full Text
Peer Reviewed
See detailAn inverse micro-mechanical analysis toward the stochastic homogenization of nonlinear random composites
Wu, Ling ULiege; Nguyen, Van Dung ULiege; Adam, Laurent et al

in Computer Methods in Applied Mechanics and Engineering (2019), 348

An inverse Mean-Field Homogenization (MFH) process is developed to improve the computational efficiency of non-linear stochastic multiscale analyzes by relying on a micro-mechanics model. First full-field ... [more ▼]

An inverse Mean-Field Homogenization (MFH) process is developed to improve the computational efficiency of non-linear stochastic multiscale analyzes by relying on a micro-mechanics model. First full-field simulations of composite Stochastic Volume Element (SVE) realizations are performed to characterize the homogenized stochastic behavior. The uncertainties observed in the non-linear homogenized response, which result from the uncertainties of their micro-structures, are then translated to an incrementalsecant MFH formulation by defining the MFH input parameters as random effective properties. These effective input parameters, which correspond to the micro-structure geometrical information and to the material phases model parameters, are identified by conducting an inverse analysis from the full-field homogenized responses. Compared to the direct finite element analyzes on SVEs, the resulting stochastic MFH process reduces not only the computational cost, but also the order of uncertain parameters in the composite micro-structures, leading to a stochastic Mean-Field Reduced Order Model (MF-ROM). A data-driven stochastic model is then built in order to generate the random effective properties under the form of a random field used as entry for the stochastic MF-ROM embedded in a Stochastic Finite Element Method (SFEM). The two cases of elastic Unidirectional (UD) fibers embedded in an elasto-plastic matrix and of elastic UD fibers embedded in a damage-enhanced elasto-plastic matrix are successively considered. In order to illustrate the capabilities of the method, the stochastic response of a ply is studied under transverse loading condition. [less ▲]

Detailed reference viewed: 85 (25 ULiège)
Full Text
Peer Reviewed
See detailA finite strain incremental-secant homogenization model for elasto-plastic composites
El Ghezal, Marieme Imene; Wu, Ling ULiege; Noels, Ludovic ULiege et al

in Computer Methods in Applied Mechanics and Engineering (2019), 347

This paper presents a finite strain extension of the incremental-secant mean-field homogenization (MFH) formulation for two-phase elasto-plastic composites. The formulation of the local finite strain ... [more ▼]

This paper presents a finite strain extension of the incremental-secant mean-field homogenization (MFH) formulation for two-phase elasto-plastic composites. The formulation of the local finite strain elasto-plastic constitutive equations of each phase is based on a multiplicative decomposition of the deformation gradient as suggested by Simo in (Computer Methods in Applied Mechanics and Engineering, 99(1):61–112, 1992.). The latter has proposed algorithms which preserve the classical return mapping schemes of the infinitesimal theory by using principal Kirchhoff stresses and logarithmic eigenvalues of the left elastic Cauchy-Green strain. Relying on this property, we show that, by considering a quadratic logarithmic free energy and J2-flow theory at the local level, infinitesimal strain incremental-secant MFH is readily extended to finite strains. The proposed formulation and corresponding numerical algorithms are then presented. Finally, the predictions are illustrated with several numerical simulations which are verified against full-field finite element simulations of composite cells, demonstrating that the micro-mechanically based approach is able to predict the influence of the micro-structure and of its evolution on the macroscopic properties in a very cost-effective manner. [less ▲]

Detailed reference viewed: 66 (12 ULiège)
Full Text
See detailDamage to crack transition for ductile materials using a cohesive-band /discontinuous Galerkin framework
Leclerc, Julien ULiege; Nguyen, Van Dung ULiege; Wu, Ling ULiege et al

Conference (2019, March 13)

Numerical predictions of the ductile failure process are still challenging. Indeed, such failure combines a diffuse damage stage followed by damage localisation and crack initiation/propagation. On the ... [more ▼]

Numerical predictions of the ductile failure process are still challenging. Indeed, such failure combines a diffuse damage stage followed by damage localisation and crack initiation/propagation. On the one hand, continuous damage models are suited for the diffuse damage stage but not for the description of physical discontinuities. On the other hand, discontinuous approaches, such as cohesive zone models, can reproduce crack initiation and propagation, but not the diffuse damage stage. In this work, we present a numerical scheme combining both approaches in a discontinuous Galerkin finite element framework. First, a non-local implicit damage model computes the initial diffuse damage stage beyond the softening point without mesh-dependency. Second, a crack is introduced using a cohesive band [1,2]. Contrarily to classical cohesive models, a 3D state is recreated at the crack interface by considering a small, but finite, fictitious cohesive thickness allowing a strain tensor to be evaluated from the cohesive jump and the neighbouring bulk deformation gradient. A stress tensor at the interface, from which the cohesive forces are deduced, is computed using an appropriate local damage law. The ductile failure is thus modelled by a combination of the Gurson and the Thomason evolution laws [3]. First, the initial diffuse void growth phase is modelled by the (non-local) Gurson model [4] accounting for shear effects [5]. Second, a crack is introduced when the coalescence is reached and the behaviour of the cohesive law is computed from the Thomason model [3]. The framework capabilities are demonstrated by reproducing the slanted and the cup-cone failure respectively of a plane strain specimen and a round bar. Ack.: The research has been funded by the Walloon Region under the agreement no.7581-MRIPF in the context of the 16th MECATECH call. REFERENCES [1] J.J.C. Remmers, R. de Borst., C.V. Verhoosel and A. Needleman. “The cohesive band model: a cohesive surface formulation with stress triaxiality”, Int. J. Fract. 181 (2013). [2] J. Leclerc, L. Wu, V.D. Nguyen and L. Noels, “Cohesive band model: a cohesive model with triaxiality for crack transition in a coupled non-local implicit discontinuous Galerkin/extrinsic cohesive law framework”, Int. J. for Num. Methods in Eng. (2018) [3] A.A. Benzerga, J.-B. Leblond, A. Needleman, V. Tvergaard. Ductile failure modelling. Int J Fract 201 (2016). [4] F. Reusch, B. Svendsen and D. Klingbeil. A non-local extension of Gurson-based ductile damage modelling. Comp. Mat. Sci. 26 (2003). [5] K. Nahshon and J.W. Hutchinson, “Modification of the Gurson Model for shear failure”, European Journal of Mechanics A/Solids 27 (2008). [less ▲]

Detailed reference viewed: 55 (6 ULiège)
Full Text
Peer Reviewed
See detailEvaluation of microdamage initiation in Z-pinned laminates by means of automated RVE computations
Pierreux, Gerrit; Wu, Ling ULiege; Van Hemelrijck, Danny et al

in Composite Structures (2018), 206

Z-pinning was originally designed to improve the delamination toughness and the impact resistance of composite laminates. However, there is extensive experimental evidence that this improvement is ... [more ▼]

Z-pinning was originally designed to improve the delamination toughness and the impact resistance of composite laminates. However, there is extensive experimental evidence that this improvement is accompanied by a reduction of the in-plane properties. The main mechanisms responsible for this deterioration are the local change in fiber content, fiber distortion, and the inclusion of resin-rich regions near the Z-pin. The shape of these geometrical features strongly depends on the laminate stacking sequence and on pin parameters such as pin diameter, pin content, and initial pin inclination angle. Their shape complexity challenges analytical modelling approaches which are currently used to generate RVE geometries for simulations. A computational approach is presented to generate such geometrical models. Resin-rich regions are modelled by initially straight discretized lines which are gradually shaped by a set of geometrical operations mimicking pin insertion, pin rotation and fiber deflection. Fiber distortion is modelled in a post-processing stage in cross-sections accounting for the preservation of the amount of fibers. These models are then transformed into finite element mechanical models in order to investigate how local fiber volume fraction changes, fiber misalignment, or distortions in reinforcement due to pin rotation, affect the global stiffness and local stress concentrations. [less ▲]

Detailed reference viewed: 53 (3 ULiège)
Full Text
Peer Reviewed
See detailA micro-mechanics-based inverse study for stochastic order reduction of elastic UD-fiber reinforced composites analyzes
Wu, Ling ULiege; Adam, Laurent; Noels, Ludovic ULiege

in International Journal for Numerical Methods in Engineering (2018), 115(12), 1430-1456

This research develops a stochastic mean-field-homogenization (MFH) process that is used as Reduced Order Model (ROM) to carry out a statistical multiscale analysis on unidirectional (UD) fiber reinforced ... [more ▼]

This research develops a stochastic mean-field-homogenization (MFH) process that is used as Reduced Order Model (ROM) to carry out a statistical multiscale analysis on unidirectional (UD) fiber reinforced composites. First full-field simulations of UD Stochastic Volume Elements (SVEs), whose statistical description is obtained from SEM images, are conducted to define statistical meso-scale apparent properties. A stochastic Mori-Tanaka MFH model is then developed through an inverse stochastic identification process performed on the apparent elastic properties obtained by full-field simulations. As a result, a random vector of the effective elastic properties of phases and micro-structure information of the Mori-Tanaka model is inferred. In order to conduct Stochastic Finite Element Method (SFEM) analyzes, a generator of this random vector is then constructed using the copula method, allowing predicting the statistical response of a composite ply under bending. The statistical dependence of the random vector entries is shown to be respected by the generator. Although this work is limited to the elastic response, we believe that the stochastic Mori-Tanaka model can be extended to nonlinear behaviors in order to conduct efficient stochastic multiscale simulations. [less ▲]

Detailed reference viewed: 85 (16 ULiège)
Full Text
See detailA stochastic Mean-Field Reduced Order Model of Unidirectional Composites
Wu, Ling ULiege; Noels, Ludovic ULiege

Scientific conference (2018, September 07)

Detailed reference viewed: 21 (3 ULiège)
Full Text
See detailA Damage to Crack Transition Framework for Ductile Materials Accounting for Stress Triaxiality
Leclerc, Julien ULiege; Wu, Ling ULiege; Nguyen, Van Dung ULiege et al

Conference (2018, July 25)

Predicting the entire ductile failure process is still a challenge task since it involves different processes: damage first diffuses before localizing, eventually leading to a micro-crack initiation and ... [more ▼]

Predicting the entire ductile failure process is still a challenge task since it involves different processes: damage first diffuses before localizing, eventually leading to a micro-crack initiation and propagation. On the one hand, discontinuous approaches can describe localised processes such as crack propagation but fail in capturing diffuse damage evolution. On the other hand, continuous approaches such as continuum damage models are suited for diffuse damage modelling, but cannot represent properly physical discontinuities. In this work both approaches are combined in a hybrid implicit non-local damage model combined with an extrinsic cohesive law in a discontinuous Galerkin finite element framework [1]. The implicit non-local damage model reproduces the initial diffuse damage stage without mesh-dependency. Upon transition at void coalescence or intensive plastic localisation, a crack is introduced using a cohesive band model. Contrarily to cohesive elements, cohesive band models capture in-plane stretch effects, and thus account for stress triaxiality [2]. Indeed, by considering a band of small but finite thickness ahead of the crack surface, the strain field inside this band is evaluated from the neighbouring strains and from the cohesive jump [2]. Then, an appropriate damage model is used to compute the stress-state inside the band and the cohesive traction forces on the crack lips. The approach is first applied in the case of elastic damage for which the band thickness is evaluated to ensure the energetic consistency of the damage to crack transition with respect to purely non-local continuum damage mechanics [1]. Then, the scheme is formulated to the case of a non-local porous-plastic damage Gurson model. In particular, the law governing void growth accounts for shear effects, while the void coalescence mechanism, hence the damage to crack transition criterion, is predicted using the Thomason model [3]. References: [1] Leclerc J., Wu L., Nguyen V.D., Noels L. Cohesive band model: a cohesive model with triaxiality for crack transition in a coupled non-local implicit discontinuous Galerkin/extrinsic cohesive law framework. Int. J. for Num. Methods in Eng. (2017): In press. [2] Remmers J. J. C., de Borst R., Verhoosel C. V., Needleman A. The cohesive band model: a cohesive surface formulation with stress triaxiality. Int. J. Fract. 181 (2013). [3] Benzerga A.A., Leblond J.-B., Needleman A., Tvergaard V. Ductile failure modelling. Int J Fract 201 (2016). [less ▲]

Detailed reference viewed: 52 (8 ULiège)
Full Text
See detailA probabilistic Mean-Field-Homogenization approach applied to study unidirectional composite structures
Wu, Ling ULiege; Adam, Laurent; Noels, Ludovic ULiege

Conference (2018, July 25)

In order to account for micro-structural geometrical and material properties in an accurate way, homogenization-based multiscale approaches have been widely developed. However, most of the approaches ... [more ▼]

In order to account for micro-structural geometrical and material properties in an accurate way, homogenization-based multiscale approaches have been widely developed. However, most of the approaches assume the existence of a statistically Representative Volume Element (RVE), which does not always exist for composite materials due to the existing micro-structural uncertainties, in particular when studying the onset of failure. In this work we develop a stochastic multi-scale approach for unidirectional composite materials in order to predict scatter at the structural behavior. First Stochastic Volume Elements (SVE) [1] are built from experimental measurements. Toward this end, statistical functions of the fibers features are extracted from SEM images to generate statistical functions of the micro-structure. The dependent variables are then represented using the copula framework, allowing generating micro-structures, which respect the statistical information, using a fiber additive process [2]. Probabilistic meso-scale stochastic behaviors are then extracted from direct numerical simulations of the generated SVEs, defining random fields of homogenized properties [3]. Finally, in order to provide an efficient way of generating meso-scale random fields, while keeping information, such as stress/strain fields, at the micro-scale during the resolution of macro-scale stochastic finite element, a probabilistic Mean-Field-Homogenization (MFH) method is developed. To this end, the phase parameters of the MFH are seen as random fields defined by inverse stochastic identification of the stochastic homogenized properties obtained through the stochastic direct simulations of the SVEs. As a result, non-deterministic macro-scale behaviors can be studied while having access to the micro-scale different phases stress-strain evolution, allowing to predict composite failure in a probabilistic way. [1] M. Ostoja-Starzewski, X. Wang, Stochastic finite elements as a bridge between random material microstructure and global response, Computer Methods in Applied Mechanics and Engineering 168 (14) (1999) 35 - 49, [2] L. Wu, C.N. Chung, Z. Major, L. Adam, L. Noels. From SEM images to elastic responses: a stochastic multiscale analysis of UD fiber reinforced composites. Submitted to Composite Structures. [3] V. Lucas, J.-C. Golinval, S. Paquay, V.-D. Nguyen, L. Noels, L. Wu, A stochastic computational multiscale approach; Application to MEMS resonators, Computer Methods in Applied Mechanics and Engineering 294 (2015) 141 - 167 [less ▲]

Detailed reference viewed: 39 (1 ULiège)
Full Text
See detailNon-local damage to crack transition framework for ductile failure based on a cohesive band model
Nguyen, Van Dung ULiege; Leclerc, Julien ULiege; Wu, Ling ULiege et al

Conference (2018, July 02)

A damage process starts with a diffuse stage followed by a localized stage in which the initiation and propagation of cracks can occur. To model this whole failure process, on the one hand, continuous ... [more ▼]

A damage process starts with a diffuse stage followed by a localized stage in which the initiation and propagation of cracks can occur. To model this whole failure process, on the one hand, continuous approaches formulated under the framework of continuum damage models succeed in capturing the material degradation but are unable to represent properly physical discontinuities. On the other hand, discontinuous approaches describe the failure process such as cracks by propagating field discontinuities. However, they usually do not capture the diffuse damage evolution and in-plane stretch effects which are the consequences of stress triaxiality and must be taken into account for accurate ductile failure simulations. Clearly both described approaches cannot separately represent the whole ductile failure process with accuracy. In this work, the advantages of these two approaches are combined in a single one, so-called non-local damage to crack transition. The non-local porous-plastic damage Gurson model [1] is used to reproduce the initial diffuse damage stage without mesh-dependency. In particular, the law governing void growth accounts for large shear effects [2], while the void coalescence mechanism, hence the damage to crack transition criterion is predicted using the Thomason model [3]. At the transition point, a crack is initiated using a cohesive band model represented by a cohesive law including in-plane stretch effects [4]. By assuming that all the damaging process is concentrated within a band of small but finite thickness, the deformation state inside this band is obtained from the one of neighboring material points and from the displacement jump. Then, the underlying constitutive law is still used to compute the stress state from which the cohesive traction across the cohesive band is estimated. This combined framework is implemented in a discontinuous Galerkin/ extrinsic cohesive zone method finite element framework, which has successfully been applied for elastic-damage problems in which the band thickness was evaluated to ensure the energetic consistency of the damage to crack transition with respect to purely non-local continuum damage mechanics [5]. The proposed framework is shown to capture the damage diffuse stage as well as crack initiation and propagation of the whole ductile failure process. [1] Reusch F., Svendsen B., and Klingbeil D., A non-local extension of Gurson-based ductile damage modelling, Comp. Mat. Sci., 26, (2013). [2] Nahshon K., Hutchinson J. W., Modification of the Gurson Model for shear failure, Eur. J. Mech. A Solids, 27, (2008). [3] Benzerga A.A., Leblond J.-B., Needleman A., Tvergaard V., Ductile failure modelling, Int. J. Fract., 201, (2016). [4] Remmers J. J. C., de Borst R., Verhoosel C. V., Needleman A., The cohesive band model: a cohesive surface formulation with stress triaxiality, Int. J. Fract., 181, (2013). [5] Leclerc J., Wu L., Nguyen V.D., Noels L., A damage to crack transition model accounting for stress triaxiality formulated in a hybrid non-local implicit discontinuous Galerkin - cohesive band model framework, Int. J. for Num. Methods in Eng., 113 (3), (2018) [less ▲]

Detailed reference viewed: 51 (5 ULiège)
Full Text
See detailA stochastic Mean Field Homogenization model of Unidirectional composite materials
Wu, Ling ULiege; Noels, Ludovic ULiege

Scientific conference (2018, June 22)

Homogenization-based multiscale approaches have been widely developed in order to account for micro-structural geometrical and material properties in an accurate way. However, most of the approaches ... [more ▼]

Homogenization-based multiscale approaches have been widely developed in order to account for micro-structural geometrical and material properties in an accurate way. However, most of the approaches assume the existence of a statistically Representative Volume Element (RVE), which does not always exist for composite materials due to the existing micro-structural uncertainties, in particular when studying the onset of failure. To address this lack of representativity, a stochastic multi-scale approach for unidirectional composite materials is developed with the aim of predicting scatter in the structural behavior. The first step consists in building Stochastic Volume Elements (SVE) [1] from experimental measurements. Toward this end, statistical functions of the fibers features are extracted from SEM images to generate statistical functions of the micro-structure. The dependent variables are then represented using the copula framework, allowing generating micro-structures respecting the statistical information using a fiber additive process [2]. Probabilistic meso-scale stochastic behaviors are then extracted from direct numerical simulations of the generated SVEs, defining random fields of homogenized properties [2]. Finally, in order to provide an efficient way of generating meso-scale random fields, while keeping information such as stress/strain fields at the micro-scale during the resolution of macro-scale stochastic finite element, a probabilistic Mean-Field-Homogenization (MFH) method is developed, first in the linear range [3] and then in the non-linear one. To this end, the phase parameters of the MFH are seen as random fields defined by inverse stochastic identification of the stochastic homogenized properties obtained through the stochastic direct simulations of the SVEs. The resulting micro-mechanics-based reduced order model allows studying composite failure in a probabilistic way. [1] M. Ostoja-Starzewski, X. Wang, Stochastic finite elements as a bridge between random material microstructure and global response, Computer Methods in Applied Mechanics and Engineering 168 (14) (1999) 35 - 49, [2] L. Wu, C.N. Chung, Z. Major, L. Adam, L. Noels. From SEM images to elastic responses: a stochastic multiscale analysis of UD fiber reinforced composites. Submitted to Composite Structures. [3] L. Wu, L. Adam, L. Noels, A micro-mechanics-based inverse study for stochastic order reduction of elastic UD-fiber reinforced composites analyzes, International Journal for Numerical Methods in Engineering (2018) [less ▲]

Detailed reference viewed: 36 (1 ULiège)
See detailAn implicit non-local damage to crack transition framework for ductile materials involving a cohesive band model
Leclerc, Julien ULiege; Wu, Ling ULiege; Nguyen, Van Dung ULiege et al

Conference (2018, May 31)

Accurate numerical predictions of the entire ductile failure process is still challenging. There are two main philosophies to model the process consisting in an initial diffuse stage followed by localised ... [more ▼]

Accurate numerical predictions of the entire ductile failure process is still challenging. There are two main philosophies to model the process consisting in an initial diffuse stage followed by localised crack initiations and propagations. On the one hand, discontinuous approaches are adapted to localised processes as crack propagation but fail in capturing diffuse damage evolution. Moreover, they do not usually capture stress triaxiality effects, required for accurate ductile failure simulations. On the other hand, continuum damage models are suited for diffuse damage modelling but are unable to represent properly physical discontinuities. In order to describe the entire ductile failure process, the numerical scheme proposed here combines both approaches through a mesh-independent implicit non-local damage model combined with a cohesive band model, an extrinsic cohesive law, in a discontinuous Galerkin finite element framework. By assuming that all the damaging process is concentrated inside a band of small but finite thickness ahead of the crack surface, the cohesive forces are computed from neighbouring strains and the cohesive jump using an appropriate damage model. By this way, this approach naturally incorporates stress triaxiality effects. It has successfully been applied in the case of elastic damage for which the band thickness was evaluated to ensure the energetic consistency of the damage to crack transition with respect to purely non-local continuum damage mechanics [1]. In the present work, the scheme is extended to the case of non-local porous-plastic damage Gurson model accounting for large shear effects. A crack is introduced at the transition corresponding to intensive plastic localisation or void coalescence predicted by the Thomason model. [1] Leclerc J., Cohesive band model: a cohesive model with triaxiality for crack transition in a coupled non-local implicit discontinuous Galerkin/extrinsic cohesive law framework. Int. J. Num. Meth. Eng. (2017). [less ▲]

Detailed reference viewed: 63 (14 ULiège)
Full Text
See detailStochastic study of unidirectional composites: from micro-structural statistical information to multi-scale analyzes
Wu, Ling ULiege

Scientific conference (2018, April 04)

Homogenization-based multiscale approaches have been widely developed in order to account for micro-structural geometrical and material properties in an accurate way. However, most of the approaches ... [more ▼]

Homogenization-based multiscale approaches have been widely developed in order to account for micro-structural geometrical and material properties in an accurate way. However, most of the approaches assume the existence of a statistically Representative Volume Element (RVE). Such a RVE does not always exist for composite materials due to the existing micro-structural uncertainties, motivating the development of a stochastic multi-scale approach for unidirectional composite materials. First Stochastic Volume Elements (SVE) [1] are built from experimental measurements using statistical functions of the fibers features extracted from SEM images and used to generate statistical functions of the micro-structure. The dependent variables are then represented using the copula framework in order to generate micro-structures, which respect the statistical information, using a fiber additive process [1]. Probabilistic meso-scale stochastic behaviors are then extracted from direct numerical simulations of the generated SVEs, defining random fields of homogenized properties [2]. Finally, in order to generate in an efficient way meso-scale random fields, a probabilistic Mean-Field-Homogenization (MFH) method is developed. To this end, the phase parameters of the MFH are seen as random fields defined by inverse stochastic identification of the stochastic homogenized properties obtained through the stochastic direct simulations of the SVEs. As a result, non-deterministic macro-scale behaviors can be studied while having access to the micro-scale different phases stress-strain evolution, allowing to predict composite failure in a probabilistic way. [1] M. Ostoja-Starzewski, X. Wang, Stochastic finite elements as a bridge between random material microstructure and global response, Computer Methods in Applied Mechanics and Engineering 168 (14) (1999) 35 - 49, [2] L. Wu, C.N. Chung, Z. Major, L. Adam, L. Noels. From SEM images to elastic responses: a stochastic multiscale analysis of UD fiber reinforced composites. Composite Structures 189C (2018), 206-227 [3] V. Lucas, J.-C. Golinval, S. Paquay, V.-D. Nguyen, L. Noels, L. Wu, A stochastic computational multiscale approach; Application to MEMS resonators, Computer Methods in Applied Mechanics and Engineering 294 (2015) 141 - 167 [less ▲]

Detailed reference viewed: 34 (3 ULiège)
Full Text
Peer Reviewed
See detailFrom SEM images to elastic responses: a stochastic multiscale analysis of UD fiber reinforced composites
Wu, Ling ULiege; Chung, Chi Nghia; Major, Zoltan et al

in Composite Structures (2018), 189C

In this work, the elastic response of unidirectional fiber (UD) reinforced composites is studied in a stochastic multiscale way. First, the micro-structure of UD carbon fiber reinforced composites is ... [more ▼]

In this work, the elastic response of unidirectional fiber (UD) reinforced composites is studied in a stochastic multiscale way. First, the micro-structure of UD carbon fiber reinforced composites is statistically studied based on SEM images of its cross-section and an algorithm to generate numerical micro-structures with an equivalent random distribution of fibers is developed. In particular, based on the images spatial analysis, the empirical statistical descriptors are considered as dependent variables and represented using the copula framework, allowing generating micro-structure realizations used as Stochastic Volume Elements (SVEs). Second, a stochastic scale transition is conducted through the homogenization of SVEs. With a view to the use of the resulting meso-scale random field in structural stochastic analyzes, the homogenization is performed in two steps in order to respect the statistical content from the micro-meter-long SVEs to the millimeter-long structural finite elements. To this end, the computational homogenization is applied in a hierarchy model: i) Micro-structure generator produces Small SVEs (SSVEs) which are homogenized; ii) Big SVEs (BSVEs) are constructed from the SSVEs. Finally, it is shown on simple illustrative examples that the scatter of the (homogenized) stress distribution in a composite ply can be simulated by means of the developed methodology. [less ▲]

Detailed reference viewed: 169 (37 ULiège)
Full Text
Peer Reviewed
See detailStochastic multiscale model of MEMS stiction accounting for high order statistical moments of non-Gaussian contacting surfaces
Hoang Truong, Vinh ULiege; Wu, Ling ULiege; Golinval, Jean-Claude ULiege et al

in IEEE/ASME Journal of Microelectromechanical Systems (2018), 27(2), 137-155

Stiction is a failure mode of microelectromechanical systems (MEMS) involving permanent adhesion of moving surfaces. Models of stiction typically describe the adhesion as a multiple asperity adhesive ... [more ▼]

Stiction is a failure mode of microelectromechanical systems (MEMS) involving permanent adhesion of moving surfaces. Models of stiction typically describe the adhesion as a multiple asperity adhesive contact between random rough surfaces, and they thus require a sufficiently accurate statistical representation of the surface, which may be non-Gaussian. If the stiction is caused primarily by multiple asperity adhesive contact in only a small portion of the apparent area of the contacting surfaces, the number of adhesive contacts between asperities may not be sufficiently statistically significant for a homogenized model to be representative. In [Hoang et al., A computational stochastic multiscale methodology for MEMS structures involving adhesive contact, Tribology International, 110:401-425, 2017], the authors have proposed a probabilistic multiscale model of multiple asperity adhesive contact that can capture the uncertainty in stiction behavior. Whereas the previous paper considered Gaussian random rough surfaces, the aim of the present paper is to extend this probabilistic multiscale model to non-Gaussian random rough surfaces whose probabilistic representation accounts for the high order statistical moments of the surface height. The probabilistic multiscale model thus obtained is validated by means of a comparison with experimental data of stiction tests of cantilever beams reported in the literature. [less ▲]

Detailed reference viewed: 88 (30 ULiège)
Full Text
Peer Reviewed
See detailA damage to crack transition model accounting for stress triaxiality formulated in a hybrid non-local implicit discontinuous Galerkin - cohesive band model framework
Leclerc, Julien ULiege; Wu, Ling ULiege; Nguyen, Van Dung ULiege et al

in International Journal for Numerical Methods in Engineering (2018), 113(3), 374-410

Modelling the entire ductile fracture process remains a challenge. On the one hand, continuous damage models succeed in capturing the initial diffuse damage stage but are not able to represent ... [more ▼]

Modelling the entire ductile fracture process remains a challenge. On the one hand, continuous damage models succeed in capturing the initial diffuse damage stage but are not able to represent discontinuities or cracks. On the other hand, discontinuous methods, as the cohesive zones, which model the crack propagation behaviour, are suited to represent the localised damaging process. However, they are unable to represent diffuse damage. Moreover, most of the cohesive models do not capture triaxiality effect. In this paper, the advantages of the two approaches are combined in a single damage to crack transition framework. In a small deformation setting, a non-local elastic damage model is associated with a cohesive model in a discontinuous Galerkin finite element framework. A cohesive band model is used to naturally introduce a triaxiality-dependent behaviour inside the cohesive law. Practically, a numerical thickness is introduced to recover a 3D-state, mandatory to incorporate the in-plane stretch effects. This thickness is evaluated to ensure the energy consistency of the method and is not a new numerical parameter. The traction-separation law is then built from the underlying damage model. [less ▲]

Detailed reference viewed: 186 (79 ULiège)
Full Text
See detailA stochastic 3-scale method to predict the thermo-elastic behaviors of polycrystalline structures
Wu, Ling ULiege; Lucas, Vincent; Golinval, Jean-Claude ULiege et al

Conference (2017, November 07)

The purpose of this work is to upscale material uncertainties in the context of thermo-elastic response of polycrystalline structures. The probabilistic behavior of micro-resonators made of ... [more ▼]

The purpose of this work is to upscale material uncertainties in the context of thermo-elastic response of polycrystalline structures. The probabilistic behavior of micro-resonators made of polycrystalline materials is evaluated using a stochastic multi-scale approach defined using the following methodology. 1. Stochastic volume elements (SVEs) [1] are defined from Voronoi tessellations using experimental measurements of the grain size, orientation, and surface roughness [2]; 2. Mesoscopic apparent thermo-elastic properties such as elasticity tensor, thermal conductivity tensor, and thermal dilatation tensor are extracted using a coupled homogenization theory [3, 4] applied on the SVE realizations; 3. A stochastic model of the homogenized properties extracted from Voronoi tessellations using a moving window technique is then constructed in order to be able to generate spatially correlated meso-scale random fields; 4. These meso-scale random fields are then used as input for stochastic finite element simulations. As a result, the probabilistic distribution of micro-resonator properties can be extracted. The applications are two-fold: 1. A stochastic thermo-elastic homogenization, see Fig. 1(a), is coupled to thermoelastic 3D models of the micro-resonator in order to extract the probabilistic distribution of the quality factor of micro-resonators [5]; 2. A stochastic second-order mechanical homogenization, see Fig. 1(b), is coupled to a plate model of the micro-resonator in order to extract the effect of the uncertainties related to the surface roughness of the polycrystalline structures [2]. References [1] Ostoja-Starzewski, M., Wang, X. Stochastic finite elements as a bridge between random material microstructure and global response. Comput. Meth. in Appl. Mech. and Eng. (1999) 168: 35-49. [2] Lucas, V., Golinval, J.-C., Voicu, R., Danila, M., Gravila, R., Muller, R., Dinescu, A., Noels, L., Wu, L. Propagation of material and surface profile uncertainties on MEMS micro-resonators using a stochastic second-order computational multi-scale approach. Int. J. for Num. Meth. in Eng. (2017). [3] Temizer, I., Wriggers, P. Homogenization in finite thermoelasticity.J. of the Mech. and Phys. of Sol. (2011) 59, 344-372. [4] Nguyen, V. D., Wu, L., Noels, L. Unified treatment of boundary conditions and efficient algorithms for estimating tangent operators of the homogenized behavior in the computational homogenization method. Computat. Mech. (2017) 59, 483-505. [5] Wu, L., Lucas, V., Nguyen, V. D., Golinval, J.-C., Paquay, S., Noels, L. A Stochastic Multi-Scale Approach for the Modeling of Thermo-Elastic Damping in Micro-Resonators. Comput. Meth. in Appl. Mech. and Eng. (2016) 310, 802-839. [less ▲]

Detailed reference viewed: 24 (2 ULiège)
Full Text
See detailGeneration of unidirectional composite stochastic volume elements from micro-structural statistical information
Wu, Ling ULiege; Bidaine, Benoit; Major, Zoltan et al

Conference (2017, November 07)

The purpose of this work is to generate Stochastic Volume Element (SVE) of unidirectional composites using statistical information obtained from imaging technique in order to study the effect of the micro ... [more ▼]

The purpose of this work is to generate Stochastic Volume Element (SVE) of unidirectional composites using statistical information obtained from imaging technique in order to study the effect of the micro-structure uncertainty on the meso-scale behavior. When considering a homogenization-based multiscale approach, the material properties are obtained at each integration point of a macro-structure from the resolution of a micro-scale boundary value problem. When the separation of scales holds, the macro-point is viewed at the micro-level as the center of a Representative Volume Element (RVE). However, for composite materials which suffer from a large scatter in their constituent properties and microstructure, the separation of scales does not always hold, in particular at the onset of failure, and structural properties exhibit a scatter. In order to predict this scatter, Stochastic Volume Elements (SVE) [1, 2] of unidirectional fiber composite materials should be built from experimental measurements, see Fig. 1(a). Toward this end, statistical functions of the fibers features such as radius, the closest neighboring distance etc. [3] are extracted from several SEM images to generate statistical functions of the micro-structure. The dependent variables are then represented using the copula framework, allowing generating micro-structures, see Fig. 1(b), using an inclusions additive process. Simulations on the generated SVEs are then used to extract the probabilistic meso-scale stochastic behavior. In the future the extracted behaviors will be used to build a stochastic model of homogenized properties based on Mean-Field-Homogenization in order to predict statistical macro-scale behaviors and in particular the failure onset. References [1] Ostoja-Starzewski, M., Wang, X. Stochastic finite elements as a bridge between random material microstructure and global response. Comput. Meth. in Appl. Mech. and Eng. (1999) 168: 35-49. [2] Lucas, V., Golinval, J.-C., Paquay, S., Nguyen, V.-D., Noels, L., Wu, L. A stochastic computational multiscale approach; Application to MEMS resonators. Comput. Meth. in Appl. Mech. and Eng. (2015) 294, 141-167. [3] Vaughan, T.J., McCarthy C.T. A combined experimentalnumerical approach for generating statistically equivalent fibre distributions for high strength laminated composite materials. Compos. Sci. and Tech. (2010) 70, 291-297. [less ▲]

Detailed reference viewed: 45 (3 ULiège)
Full Text
Peer Reviewed
See detailAn incremental-secant mean-field homogenization method with second statistical moments for elasto-visco-plastic composite materials
Wu, Ling ULiege; Adam, Laurent; Doghri, Issam et al

in Mechanics of Materials (2017), 114

This paper presents an extension of the recently developed incremental-secant mean-field homogenization (MFH) procedure in the context of elasto-plasticity to elasto-visco-plastic composite materials ... [more ▼]

This paper presents an extension of the recently developed incremental-secant mean-field homogenization (MFH) procedure in the context of elasto-plasticity to elasto-visco-plastic composite materials while accounting for second statistical moments. In the incrementalsecant formulation, a virtual elastic unloading is performed at the composite level in order to evaluate the residual stress and strain states in the different phases, from which a secant MFH formulation is applied. When applying the secant MFH process, the Linear-Comparison-Composite is built from the piece-wise heterogeneous residual strain-stress state using naturally isotropic secant tensors defined using either first or second statistical moment values. As a result non-proportional and non-radial loading conditions can be considered because of the incremental-secant formulation, and accurate predictions can be obtained as no isotropization step is required. The limitation of the incremental-secant formulation previously developed was the requirement in case of hard inclusions to cancel the residual stress in the matrix phase, resulting from the composite material unloading, to avoid over-stiff predictions. It is shown in this paper that in the case of hard inclusions by defining a proper second statistical moment estimate of the von Mises stress, the residual stress can be kept in the different composite phases. Moreover it is shown that the method can be extended to visco-plastic behaviors without modifying the homogenization process as the incremental-secant formulation only requires the definition of the secant operator of the different phase material models. Finally, it is shown that although it is also possible to define a proper second statistical moment estimate of the von Mises stress in the case of soft inclusions, this does not improve the accuracy as compared to the increment-secant method with first order statistical moment estimates. [less ▲]

Detailed reference viewed: 80 (9 ULiège)