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Sahbi Loukil, M., Costa, S., Bergwall, M., Deepthi Prasad, H. S., Moreau, F., Segersäll, M., . . . Olsson, R. (2024). Experimental and numerical investigation on bearing behavior of hybrid thin/thick-ply composite laminates. Composite structures, 331, Article ID 117888.
Open this publication in new window or tab >>Experimental and numerical investigation on bearing behavior of hybrid thin/thick-ply composite laminates
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2024 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 331, article id 117888Article in journal (Refereed) Published
Abstract [en]

Experimental and numerical studies were carried out to characterize hybrid thin- and thick-ply composite laminates and assess modelling capabilities. Five different composite laminates were manufactured using a single material system with varying proportions of thin plies (0%, 50%, and 100% thin-ply). Bearing tests were performed and the results from the tests were investigated. The results showed that performance, in terms of bearing strength at onset of damage and ultimate bearing stress, increased proportionally with the increasing amount of thin plies within the laminate. Microscopic examination of the failure modes for all laminates was performed at the center of the hole to determine the dominant failure mode. The numerical investigation uses a highly detailed mesoscale model previously validated for crash simulations but never used successfully to bearing damage areas. The results showed a good correlation regarding both the load response and the morphology of damage. 

Place, publisher, year, edition, pages
Elsevier Ltd, 2024
Keywords
Bearing strength, Composites, Hybrid laminate, Matrix crack, Thin Ply, Failure modes, Hybrid composites, Bearing behaviors, Bearing strengths, Composite laminate, Experimental and numerical studies, Experimental investigations, Hybrid laminates, Numerical investigations, Ply composites, Laminated composites
National Category
Materials Engineering
Identifiers
urn:nbn:se:ri:diva-71952 (URN)10.1016/j.compstruct.2024.117888 (DOI)2-s2.0-85182392642 (Scopus ID)
Available from: 2024-02-27 Created: 2024-02-27 Last updated: 2024-02-27Bibliographically approved
Pupurs, A., Loukil, M., Marklund, E., Varna, J. & Mattsson, D. (2024). Transverse Crack Initiation in Thin-Ply Laminates Subjected to Tensile Loading at Low and Cryogenic Temperatures. Mechanics of composite materials, 59(6), 1049-1064
Open this publication in new window or tab >>Transverse Crack Initiation in Thin-Ply Laminates Subjected to Tensile Loading at Low and Cryogenic Temperatures
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2024 (English)In: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 59, no 6, p. 1049-1064Article in journal (Refereed) Published
Abstract [en]

Laminates with ultra-thin plies is a promising new development for polymeric composite materials expected to provide superior resistance to intralaminar crack propagation. The ply thickness effect on the crack initiation stress that according to some theoretical studies on fiber/matrix debonding does not depend on the ply thickness was investigated. Ultra-thin ply carbon fiber/epoxy cross-ply laminates subjected to tensile loading at room, –50, and –150°C temperatures relevant for cryogenic fuel storage, aeronautical, and aerospace applications were studied. The stochastic nature of the crack initiation stress in the 90°-plies was analyzed using Weibull strength distribution. The results obtained show delayed transverse crack initiation only in the thinnest plies with a clear trend that the scale parameter is much larger. This thickness effect on initiation is different than that for crack propagation which is observable in much larger ply thickness range. Regarding crack propagation, it was found that in most cases even at very high applied strain levels (1.5%) only a few transverse cracks have propagated from the specimen edges to its middle. 

Place, publisher, year, edition, pages
Springer, 2024
Keywords
cryogenic temperatures, experimental testing, thin-ply laminates, transverse cracking, Aerospace applications, Carbon fibers, Crack propagation, Fuel storage, Laminated composites, Tensile stress, Weibull distribution, Cracks initiations, Cracks propagation, Ply laminates, Ply thickness, Tensile loading, Thin-ply laminate, Transverse crack, Stochastic systems
National Category
Materials Engineering
Identifiers
urn:nbn:se:ri:diva-71964 (URN)10.1007/s11029-023-10156-0 (DOI)2-s2.0-85181248582 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, No.1.1.1.2/VIAA/3/19/408
Note

This work was supported by the European Regional Development Fund within the Activity 1.1.1.2 “Post-doctoral Research Aid” of the Specifc Aid Objective 1.1.1 “To increase the research and innovative capacity of scientifc institutions of Latvia and the ability to attract external fnancing, investing in human resources and infrastructure” of the Operational Programme “Growth and Employment” (No.1.1.1.2/VIAA/3/19/408). The authors would also like to acknowledge research project “Cryogenic Hypersonic Advanced Tank Technologies (CHATT)” coordinated by DLRSART and funded by the EU within the 7th Framework Programme Theme 7 Transport. Experimental work of Mr. Hugo Scaglia is greatly acknowledged.

Available from: 2024-02-26 Created: 2024-02-26 Last updated: 2024-02-26Bibliographically approved
Hozić, D., Thore, C.-J., Cameron, C. & Loukil, M. (2023). Deterministic-based robust design optimization of composite structures under material uncertainty. Composite structures, 322, Article ID 117336.
Open this publication in new window or tab >>Deterministic-based robust design optimization of composite structures under material uncertainty
2023 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 322, article id 117336Article in journal (Refereed) Published
Abstract [en]

We propose a new deterministic robust design optimization method for composite laminate structures under worst-case material uncertainty. The method is based on a simultaneous parametrization of topology and material and combines a design problem and a material uncertainty problem into a single min–max optimization problem which provides an efficient approach to handle variation of material properties in stiffness driven design optimization problems. An analysis is performed using a design problem based on a failure criterion formulation to evaluate the ability of the proposed method to generate robust composite designs. The design problem is solved using various loads, boundary conditions and manufacturing constraints. The designs generated with the proposed method have improved objective responses compared to the worst-case response of designs generated with nominal material properties and are less sensitive to the variation of material properties. The analysis indicates that the proposed method can be efficiently applied in a robust structural optimization framework. © 2023 The Author(s)

Place, publisher, year, edition, pages
Elsevier Ltd, 2023
Keywords
Failure criterion, Hyperbolic function parametrization, Laminated composites, Material uncertainty, Robust optimization, Structural optimization, Failure (mechanical), Hyperbolic functions, Composites structures, Design problems, Deterministics, Failure criteria, Parametrizations, Robust design optimization, Structural optimisations
National Category
Computational Mathematics
Identifiers
urn:nbn:se:ri:diva-65692 (URN)10.1016/j.compstruct.2023.117336 (DOI)2-s2.0-85165542694 (Scopus ID)
Note

 Correspondence Address: D. Hozić; RISE Research Institutes of Sweden, Division of Materials and Production, Polymers, Fibers and Composites Department, Borås, Box 857, 501 15, Sweden; 

This work was financed by the Swedish Energy Agency (Energimyndigheten) through grant number P48175-1 and the Swedish Research Council under grant agreement No. 2019-04615 , and is associated with the Swedish Electromobility Center 1 1 (SEC). Their support is gratefully acknowledged. The authors would also like to thank Krister Svanberg for providing his implementation of GCMMA.

Available from: 2023-08-09 Created: 2023-08-09 Last updated: 2023-08-09Bibliographically approved
Hozić, D., Thore, C.-J., Cameron, C. & Loukil, M. (2023). Material uncertainty quantification for optimized composite structures with failure criteria. Composite structures, 305, Article ID 116409.
Open this publication in new window or tab >>Material uncertainty quantification for optimized composite structures with failure criteria
2023 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 305, article id 116409Article in journal (Refereed) Published
Abstract [en]

We propose a method to analyze effects of material uncertainty in composite laminate structures optimized using a simultaneous topology and material optimization approach. The method is based on computing worst-case values for the material properties and provides an efficient way of handling variation in material properties of composites for stiffness driven optimization problems. An analysis is performed to evaluate the impact of material uncertainty on designs from two design problems: Maximization of stiffness and minimization of a failure criteria index, respectively. The design problems are solved using different loads, boundary conditions and manufacturing constraints. The analysis indicates that the influence of material uncertainty is dependent on the type of optimization problem. For compliance problems the impact on the objective value is proportional to the changes of the constitutive properties and the effect of material uncertainty is consistent and predictable for the generated designs. The strength-based problem shows that material uncertainty has a significant impact on the response, and the effects of material uncertainty is not consistent and changes for different design requirements. In addition, the results show an increase of up to 25% of the maximum failure index when considering the worst-case deviation of the constitutive properties from their nominal values. © 2022 The Author(s)

Place, publisher, year, edition, pages
Elsevier Ltd, 2023
Keywords
Hyperbolic function parametrization (HFP), Laminated composites, Material uncertainty, Robust optimization, Structural optimization, Uncertainty quantification, Failure (mechanical), Hyperbolic functions, Materials handling, Stiffness, Uncertainty analysis, Design problems, Effects of materials, Failure criteria, Hyperbolic function parametrization, Optimization problems, Parametrizations, Structural optimisations, Uncertainty quantifications
National Category
Computational Mathematics
Identifiers
urn:nbn:se:ri:diva-62563 (URN)10.1016/j.compstruct.2022.116409 (DOI)2-s2.0-85145607861 (Scopus ID)
Note

 Funding details: Vetenskapsrådet, VR, 2019–04615; Funding details: Energimyndigheten, P48175-1; Funding text 1: This work is financed by the Swedish Energy Agency (Energimyndigheten) through grant number P48175-1 and the Swedish Research Council under grant agreement No 2019–04615, and is associated with the Swedish Electromobility Center 1 (SEC). Their support is gratefully acknowledged. The authors would also like to thank Krister Svanberg for providing his implementation of GCMMA.; Funding text 2: This work is financed by the Swedish Energy Agency (Energimyndigheten) through grant number P48175-1 and the Swedish Research Council under grant agreement No 2019–04615 , and is associated with the Swedish Electromobility Center 1 1 (SEC). Their support is gratefully acknowledged. The authors would also like to thank Krister Svanberg for providing his implementation of GCMMA.

Available from: 2023-01-23 Created: 2023-01-23 Last updated: 2023-01-23Bibliographically approved
Pupurs, A., Loukil, M. & Varna, J. (2022). Digital Image Correlation (DIC) Validation of Engineering Approaches for Bending Stiffness Determination of Damaged Laminates. Applied Composite Materials, 29, 1937-1958
Open this publication in new window or tab >>Digital Image Correlation (DIC) Validation of Engineering Approaches for Bending Stiffness Determination of Damaged Laminates
2022 (English)In: Applied Composite Materials, ISSN 0929-189X, E-ISSN 1573-4897, Vol. 29, p. 1937-1958Article in journal (Refereed) Published
Abstract [en]

During the last decade new models for bending stiffness prediction of damaged composite laminates have been proposed in the literature advancing the earlier developed engineering approaches in accuracy and in complexity. However, experimental data for validation of complex analytical or engineering models are almost non-existent in the literature. In the present work a detailed experimental study was performed to investigate the bending stiffness reduction of composite cross-ply laminates with evolving micro-damage. Intralaminar cracks and local delaminations in the bottom surface 90-degree layer of carbon/epoxy and glass/epoxy cross-ply laminates were introduced in 4-point bending tests. Digital Image correlation (DIC) technique was used to experimentally determine the midplane curvature. The accuracy of beam theory for bending stiffness determination was assessed. The measured bending stiffness reduction with respect to transverse crack density was also compared with FEM predictions. The results show that the beam theory gives slightly underestimated curvature at low deflections, whereas at large deflections the beam theory overestimates the curvature and the moment–curvature relation becomes nonlinear. Nevertheless, the overall agreement between beam theory and DIC-based results is still very good, which leads to conclude that beam theory based data reduction schemes have sufficient accuracy for predicting bending stiffness even for highly damaged laminates. © 2022, The Author(s)

Place, publisher, year, edition, pages
Springer Science and Business Media B.V., 2022
Keywords
Beam theory, Bending stiffness, Composite laminates, Digital image correlation, Intralaminar cracks, Bending tests, Cracks, Forecasting, Laminated composites, Stiffness, Strain measurement, Beam theories, Composite laminate, Cross-ply laminate, Digital image correlations, Engineering modelling, Micro damage, Stiffness prediction, Stiffness reduction, Image correlation
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:ri:diva-59854 (URN)10.1007/s10443-022-10045-0 (DOI)2-s2.0-85134507480 (Scopus ID)
Note

No funding was received for conducting this study.

Available from: 2022-08-02 Created: 2022-08-02 Last updated: 2023-07-06Bibliographically approved
Hozić, D., Thore, C.-J., Cameron, C. & Loukil, M. (2021). A new method for simultaneous material and topology optimization of composite laminate structures using Hyperbolic Function Parametrization. Composite structures, 276, Article ID 114374.
Open this publication in new window or tab >>A new method for simultaneous material and topology optimization of composite laminate structures using Hyperbolic Function Parametrization
2021 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 276, article id 114374Article in journal (Refereed) Published
Abstract [en]

This paper presents a new discrete parametrization method for simultaneous topology and material optimization of composite laminate structures, referred to as Hyperbolic Function Parametrization (HFP). The novelty of HFP is the way the candidate materials are parametrized in the optimization problem. In HFP, a filtering technique based on hyperbolic functions is used, such that only one design variable is used for any given number of material candidates. Compared to state-of-the-art methods such Discrete Material and Topology Optimization (DMTO) and Shape Function with Penalization (SFP), HFP has much fewer optimization variables and constraints but introduces additional non-linearity in the optimization problems. A comparative analysis of HFP, DMTO and SFP are performed based on the problem of maximizing the stiffness of composite plates under a total volume constraint and multiple manufacturing constraints using various loads, boundary conditions and input parameters. The comparison shows that all three methods are highly sensitive to the choice of input parameters for the optimization problem, although the performance of HFP is overall more consistent. HFP method performs similarly to DMTO and SFP in terms of the designs obtained and computational cost. However, HFP obtains similar or better objective function values compared to the DMTO and SFP methods. © 2021 The Author(s)

Place, publisher, year, edition, pages
Elsevier Ltd, 2021
Keywords
Composite sizing optimization, Hyperbolic function parametrization, Laminated composites, Multi-material optimization, Structural Optimization, Topology Optimization, Hyperbolic functions, Shape optimization, Topology, Discrete material optimizations, Discrete topology, Multi-material optimizations, Optimization function, Parametrizations, Shape functions, Structural optimisations, Topology optimisation
National Category
Computational Mathematics
Identifiers
urn:nbn:se:ri:diva-56006 (URN)10.1016/j.compstruct.2021.114374 (DOI)2-s2.0-85112835915 (Scopus ID)
Note

 Funding details: Energimyndigheten, P48175-1; Funding text 1: This work is financed by the Swedish Energy Agency (Energimyndigheten) through Grant No. P48175-1, and is associated with the Swedish Electromobility Center 3 3 (SEC). Their support is gratefully acknowledged. The authors would also like to thank Krister Svanberg for providing his implementation of GCMMA on which our optimization solver is based.

Available from: 2021-08-26 Created: 2021-08-26 Last updated: 2021-08-26Bibliographically approved
Pakkam Gabriel, V., Loukil, M. & Varna, J. (2021). Analysis of intralaminar cracking in 90-plies of GF/EP laminates with distributed ply strength. Journal of composite materials, 55(26), 3925-3942
Open this publication in new window or tab >>Analysis of intralaminar cracking in 90-plies of GF/EP laminates with distributed ply strength
2021 (English)In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 55, no 26, p. 3925-3942Article in journal (Refereed) Published
Abstract [en]

Intralaminar cracking in relatively thick 90-plies of [(Formula presented.)]s laminates is analyzed using experimental data for two Glass fiber/Epoxy (GF/EP) material systems. Weibull parameters for transverse failure stress of the 90-ply are obtained from experimental intralaminar crack density versus applied strain data, showing that a reliable analysis requires sufficient amount of data in so called noninteractive crack density region. Monte Carlo simulations of cracking were performed using stress distribution between two cracks calculated using two models: Hashin’s model and a novel model that ensures that the average stress is exactly the same as in FEM solution. Due to its features, the Hashin’s model predicts too low intralaminar crack density (it predicts too strong interaction between cracks). The results emphasize the importance of having a proper stress distribution model when performing Monte Carlo simulations. Simulations were used not only to simulate intralaminar cracking in high and very low crack density regions but also for improving the procedure of Weibull parameter determination.

Place, publisher, year, edition, pages
SAGE Publications Ltd, 2021
Keywords
initiation strength, intralaminar cracking, Monte Carlo simulations, Transverse cracks, Weibull distribution, Stress concentration, Average stress, Intralaminar crackings, Intralaminar cracks, Material systems, Stress distribution models, Strong interaction, Transverse failure, Weibull parameters, Monte Carlo methods
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:ri:diva-55490 (URN)10.1177/00219983211027346 (DOI)2-s2.0-85109421846 (Scopus ID)
Note

 Funding details: 2019-02777; Funding details: VINNOVA; Funding text 1: This work has been performed within the Swedish Aeronautical Research Program (NFFP7), Project 2019-02777.; Funding text 2: The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work is jointly funded VINNOVA (Sweden's innovation agency) and GKN Aerospace Engines Sweden.

Available from: 2021-08-04 Created: 2021-08-04 Last updated: 2022-07-13Bibliographically approved
Cameron, C., Larsson, J., Loukil, M., Murtagh, T. & Wennhage, P. (2021). Bearing strength performance of mixed thin/thick-ply, quasi-isotropic composite laminates. Composite structures, 261, Article ID 113312.
Open this publication in new window or tab >>Bearing strength performance of mixed thin/thick-ply, quasi-isotropic composite laminates
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2021 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 261, article id 113312Article in journal (Refereed) Published
Abstract [en]

The effect of using thin plies to increase the bearing strength of composite laminates has been investigated. A series of 5 laminates of theoretically identical stiffness with varying proportions of thin plies were manufactured using a single material system. Four specimens from each plate were tested for bearing strength and damage was subsequently characterized using an optical microscope. The results show that performance in terms of bearing stiffness, strength at onset of damage, and ultimate bearing stress increase proportionally with the increasing amount of thin plies within the stack. Shifting from a 100% conventional ply laminate to a 100% thin-ply laminate gave an increase of 47% in the strength at onset of damage. Placement of the thin plies within the stack was also shown to be important for strength at initial onset of damage. Microscopic examination of the failure modes for all samples showed fiber kinking, localized to the center of the hole, to be the dominant failure mode regardless of the stacking sequence. © 2020 The Authors

Place, publisher, year, edition, pages
Elsevier Ltd, 2021
Keywords
Bearing strength, Composite failure, Thin ply, Stiffness, Bearing stiffness, Bearing strengths, Bearing stress, Composite laminate, Fiber-kinking, Material systems, Quasi-isotropic, Stacking sequence, Laminated composites
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-51468 (URN)10.1016/j.compstruct.2020.113312 (DOI)2-s2.0-85097745471 (Scopus ID)
Available from: 2021-01-11 Created: 2021-01-11 Last updated: 2021-06-21Bibliographically approved
Pupurs, A., Loukil, M. & Varna, J. (2021). Bending Stiffness of Damaged Cross-Ply Laminates. Mechanics of composite materials, 57(1), 31-46
Open this publication in new window or tab >>Bending Stiffness of Damaged Cross-Ply Laminates
2021 (English)In: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 57, no 1, p. 31-46Article in journal (Refereed) Published
Abstract [en]

The bending stiffness of carbon/epoxy and glass/epoxy cross-ply laminates with intralaminar cracks in the surface 90° plies and local delaminations were studied experimentally using 4-point bending tests. The bending stiffness is defined as the slope of the relation between the applied bending moment and the corresponding midplane curvature. To measure the midplane curvature of laminates with different damage states, the digital image correlation system was used. The reduction in the bending stiffness with increasing density of transverse cracks and delamination length was also analyzed using a 3-D FEM model. The analysis and optical microscopy observations showed that, in the initial stage of damage evolution, local delaminations were small, but with increasing load, the delaminations grew rapidly from the tips of existing and newly created cracks, enhancing the bending stiffness degradation. As an alternative to the 3-D FEM modelling of the test, analytical approaches in conjunction with the classical laminate theory were suggested. The analytical approach was based on the concept of the “effective stiffness of damaged ply,” where the initial stiffness of the damaged ply was replaced by the effective stiffness depending on the damage state. In the present work, two routines were used to determinate the effective stiffness of the damaged ply: a) back-calculation from the difference in the stiffnesses of damaged and undamaged laminates employing the FEM model of the representative volume element; b) simple analytical fitting functions. It is shown that the analytical approach suggested is accurate and convenient for predicting the degradation of bending stiffness of a laminate with an evolving microdamage. 

Place, publisher, year, edition, pages
Springer, 2021
Keywords
bending stiffness, delaminations, effective ply stiffness, FEM, intralaminar cracks, Bending (forming), Bending tests, Laminated composites, 4-point bending tests, Analytical approach, Applied bending moments, Classical laminate theory, Digital image correlations, Effective stiffness, Representative volume element (RVE), Stiffness
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:ri:diva-52640 (URN)10.1007/s11029-021-09931-8 (DOI)2-s2.0-85102945817 (Scopus ID)
Available from: 2021-03-30 Created: 2021-03-30 Last updated: 2021-06-16Bibliographically approved
Loukil, M. & Varna, J. (2019). Crack face sliding displacement (CSD) as an input in exact GLOB-LOC expressions for in-plane elastic constants of symmetric damaged laminates. International journal of damage mechanics, 29(4), 547-569
Open this publication in new window or tab >>Crack face sliding displacement (CSD) as an input in exact GLOB-LOC expressions for in-plane elastic constants of symmetric damaged laminates
2019 (English)In: International journal of damage mechanics, ISSN 1056-7895, E-ISSN 1530-7921, Vol. 29, no 4, p. 547-569Article in journal (Refereed) Published
Abstract [en]

The crack opening and crack sliding displacements of both faces of an intralaminar crack are the main parameters defining the significance of each crack in laminate stiffness degradation, according to the previously published GLOB-LOC approach for symmetric laminates with an arbitrary number of cracks in all plies. In the exact stiffness expressions of this approach, the crack density is always multiplied by crack opening displacement and crack sliding displacement. The dependence of crack opening displacement on geometrical and elastic parameters of adjacent plies was studied previously and described by simple fitting functions. The crack sliding displacement has been analyzed for low-crack densities only and the proposed finite element method-based fitting expressions are oversimplified not including the out-of-plane ply stiffness effects. Based on finite element method analysis, more accurate expressions for so-called non-interactive cracks are suggested in the presented article. For the first time the shear stress perturbations are analyzed and interaction functions are presented with the feature that they always lead to slightly conservative predictions. The presented simple fitting functions, when used in the GLOB-LOC model, give predictions that are in a good agreement with finite element method results and with experimental data for laminates with damaged off-axis plies in cases when crack face sliding is of importance. The significance of including crack sliding displacement in stiffness predictions is demonstrated. 

Place, publisher, year, edition, pages
SAGE Publications Ltd, 2019
Keywords
Composite laminates, crack sliding displacement, damage, finite element analysis, transverse cracking, Forecasting, Laminated composites, Shear stress, Stiffness, Stress intensity factors, Composite laminate, Crack opening displacements, Crack sliding, Finite element method analysis, Interaction functions, Sliding displacements, Finite element method
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-39794 (URN)10.1177/1056789519866000 (DOI)2-s2.0-85070320457 (Scopus ID)
Available from: 2019-08-19 Created: 2019-08-19 Last updated: 2021-06-16Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-4472-1742

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