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Loukil, Mohamed Sahbi, Senior Associate Professor
Alternative names
Publications (10 of 38) Show all publications
Souissi, M., Trigui, A., Jedidi, I., Loukil, M. S. & Abdelmouleh, M. (2023). Bio-based composite as phase change material including spent coffee grounds and beeswax paraffin. Korean Journal of Chemical Engineering, 40(9), 2342-2355
Open this publication in new window or tab >>Bio-based composite as phase change material including spent coffee grounds and beeswax paraffin
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2023 (English)In: Korean Journal of Chemical Engineering, ISSN 0256-1115, E-ISSN 1975-7220, Vol. 40, no 9, p. 2342-2355Article in journal (Refereed) Published
Abstract [en]

New types of bio-composite phase change materials (BCPCM) with improved thermal properties were made from spent ground coffee powder (C), beeswax (W) and low density polyethylene (LDPE). Beeswax is a relatively accessible phase change material of organic origin, with a significantly lower unit price compared to conventional phase change materials (PCM). The observations by SEM and FTIR spectroscopy showed that the BCPCMs were physically combined. Through these techniques, it was discovered that ground coffee was effectively impregnated with natural wax and LDPE. According to the thermal gravimetric analysis (TGA), the thermal stability of BCPCM was improved, due to the use of waste coffee grounds, in the working temperature range. The biocomposite possesses excellent performance as characterized by 136.9 J/g (W70C10PE20)>, 127.31 J/g (W70C20PE10)>, 126.95 J/g (W70C30)>, 121.08 J/g (W70PE30) of latent heat storage and tends to decrease the supercooling degree as compared with pure beeswax during melting/solidification process. By adding LDPE to the PCM, the melting time is reduced, demonstrating an improvement in thermal energy storage (TES) reaction time to the demand. The experimental results showed that the fraction of oils (12%) in spent ground coffee powder can participate in the improvement of the thermal properties of BCPMC. The use of biocompatible PCM by-products is suitable for applications in the field of heat storage because it is affordable and environmentally beneficial.

Place, publisher, year, edition, pages
KOREAN INSTITUTE CHEMICAL ENGINEERS, 2023
Keywords
Bio-composite; Phase Change Material (PCM); Spent Coffee Ground; Beeswax; Low Density Polyethylene (LDPE)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-196085 (URN)10.1007/s11814-023-1448-5 (DOI)001000591300012 ()
Available from: 2023-07-04 Created: 2023-07-04 Last updated: 2024-03-28Bibliographically approved
Hozić, D., Thore, C.-J., Cameron, C. & Loukil, M. S. (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, 2023
Keywords
Failure criterion; Hyperbolic function parametrization; Laminated composites; Material uncertainty; Robust optimization; Structural optimization
National Category
Aerospace Engineering
Identifiers
urn:nbn:se:liu:diva-197377 (URN)10.1016/j.compstruct.2023.117336 (DOI)2-s2.0-85165542694 (Scopus ID)
Note

Funding Agencies|Vetenskapsrådet, VR: 2019-04615; Energimyndigheten: P48175-1

Available from: 2023-09-03 Created: 2023-09-03 Last updated: 2023-12-11
Varna, J., Loukil, M. S., Pupurs, A. & Joffe, R. (2022). Damage and Failure Analysis for Composites (2ed.). In: M H Ferri Aliabadi and Winston O. Soboyejo (Ed.), Comprehensive Structural Integrity: (pp. 225-246). Elsevier
Open this publication in new window or tab >>Damage and Failure Analysis for Composites
2022 (English)In: Comprehensive Structural Integrity / [ed] M H Ferri Aliabadi and Winston O. Soboyejo, Elsevier , 2022, 2, p. 225-246Chapter in book (Other academic)
Abstract [en]

Intralaminar cracking in plies of composite laminates is the first microdamage mode that affects thermo-elastic properties and may trigger local delaminations and final failure of the composite. Intralaminar cracks are like tunnels running along the fiber direction in the ply. The number of cracks increases with the increase of the applied load or with the number of cycles in fatigue loading. In this article, the cracking evolution is analyzed distinguishing two phases in development: initiation and propagation. For laminates with thick plies, the initiation ends with triggering sudden propagation and, therefore, concept of statistical initiation stress distribution in the ply together with Monte Carlo method is used for analysis. For thin-ply laminates, crack initiation does not lead to immediate propagation and the energy release concept is used to analyze crack propagation.

Place, publisher, year, edition, pages
Elsevier, 2022 Edition: 2
Keywords
Delaminations, Energy release rate, Fatigue, Intralaminar cracks, Monte Carlo method, Quasi-static loading, Weibull distribution, Applied Mechanics, Teknisk mekanik
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:liu:diva-197380 (URN)10.1016/B978-0-12-822944-6.00020-7 (DOI)9780323919456 (ISBN)
Note

This is an update of A. Corigliano, 3.09 - Damage and Fracture Mechanics Techniques for Composite Structures edited by I. Milne, R.O. Ritchie, B. Karihaloo, Comprehensive Structural Integrity, Pergamon, 2003, Pages 459–539.

Available from: 2023-09-03 Created: 2023-09-03 Last updated: 2023-11-09Bibliographically approved
Pupurs, A., Loukil, M. S. & 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.

Place, publisher, year, edition, pages
SPRINGER, 2022
Keywords
Composite laminates; Intralaminar cracks; Bending stiffness; Digital image correlation; Beam theory
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:liu:diva-187371 (URN)10.1007/s10443-022-10045-0 (DOI)000826833200002 ()
Available from: 2022-08-19 Created: 2022-08-19 Last updated: 2023-03-16Bibliographically approved
Loukil, M. S., Bergwall, M., Prasad, D., Moreau, F., Segersäll, M. & Kapidzic, Z. (2022). EXPERIMENTAL INVESTIGATION ON BEARING BEHAVIOR AND FAILURE MECHANISM OF HYBRID THIN/THICK-PLY COMPOSITE LAMINATES. In: Vassilopoulos A.P., Michaud V. (Ed.), ECCM 2022 - Proceedings of the 20th European Conference on Composite Materials: Composites Meet Sustainability: . Paper presented at 20th European Conference on Composite Materials: Composites Meet Sustainability, ECCM 2022, Lausanne 26 June - 30 June 2022 (pp. 999-1006). Composite Construction Laboratory (CCLab), Ecole Polytechnique Federale de Lausanne (EPFL), 3
Open this publication in new window or tab >>EXPERIMENTAL INVESTIGATION ON BEARING BEHAVIOR AND FAILURE MECHANISM OF HYBRID THIN/THICK-PLY COMPOSITE LAMINATES
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2022 (English)In: ECCM 2022 - Proceedings of the 20th European Conference on Composite Materials: Composites Meet Sustainability / [ed] Vassilopoulos A.P., Michaud V., Composite Construction Laboratory (CCLab), Ecole Polytechnique Federale de Lausanne (EPFL) , 2022, Vol. 3, p. 999-1006Conference paper, Published paper (Refereed)
Abstract [en]

The effect of using thin plies to increase the bearing strength of composite laminates was investigated. Five different composite laminates were manufactured using a single material system with varying proportions of thin plies (100% thick-ply, 50% thin-ply and 100% thin-ply). Bearing tests were performed and the results from the tests are investigated. The results show that performance in terms of bearing strength at onset of damage, and ultimate bearing stress increase proportionally with the increasing amount of thin plies within the stack. Microscopic examination of the failure modes for all laminates was performed at the center of the hole to determine the dominant failure mode. Transition zone was investigated where both thin and thick plies were designed so that the thin plies are used only when more strength is required. © 2022 Loukil et al.

Place, publisher, year, edition, pages
Composite Construction Laboratory (CCLab), Ecole Polytechnique Federale de Lausanne (EPFL), 2022
Keywords
Bearing strength; Hybrid laminate; Matrix crack; Thin Ply
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:liu:diva-197379 (URN)2-s2.0-85149170816 (Scopus ID)9782970161400 (ISBN)
Conference
20th European Conference on Composite Materials: Composites Meet Sustainability, ECCM 2022, Lausanne 26 June - 30 June 2022
Available from: 2023-09-03 Created: 2023-09-03 Last updated: 2023-09-03
Pakkam, G., Loukil, M. S., Fernberg, P. & Varna, J. (2022). METHODOLOGY FOR TRANSVERSE CRACKING SIMULATION IN 90 PLIES OF COMPOSITE LAMINATE UNDER FATIGUE LOADING. In: Vassilopoulos A.P., Michaud V. (Ed.), ECCM 2022 - Proceedings of the 20th European Conference on Composite Materials: Composites Meet Sustainability: . Paper presented at 20th European Conference on Composite Materials: Composites Meet Sustainability, ECCM 2022 Lausanne 26 June - 30 June 2022 (pp. 16-22). Composite Construction Laboratory (CCLab), Ecole Polytechnique Federale de Lausanne (EPFL), 6
Open this publication in new window or tab >>METHODOLOGY FOR TRANSVERSE CRACKING SIMULATION IN 90 PLIES OF COMPOSITE LAMINATE UNDER FATIGUE LOADING
2022 (English)In: ECCM 2022 - Proceedings of the 20th European Conference on Composite Materials: Composites Meet Sustainability / [ed] Vassilopoulos A.P., Michaud V., Composite Construction Laboratory (CCLab), Ecole Polytechnique Federale de Lausanne (EPFL) , 2022, Vol. 6, p. 16-22Conference paper, Published paper (Refereed)
Abstract [en]

Methodology for crack density evolution simulation in tension-tension fatigue and parameter determination in a model that relies on failure stress distribution (Weibull) in the 90 ply is presented. Cyclic loading is performed at one stress level to obtain detailed crack density dependence on the number of cycles. In addition, one data point (crack density at specified number of cycles) is necessary at a different stress level. Non-interactive crack density region is used to determine Weibull parameters. Then, crack density in a whole crack density range and for arbitrary stress level is predicted using the obtained Weibull parameters, the Monte Carlo method for failure stress distribution and a novel model for stress distribution between cracks. The predictions are in good agreement with test results. © 2022 Pakkam Gabriel et al.

Place, publisher, year, edition, pages
Composite Construction Laboratory (CCLab), Ecole Polytechnique Federale de Lausanne (EPFL), 2022
Keywords
Fatigue loading; Monte-Carlo simulations; Transverse cracking; Weibull failure stress distribution
National Category
Applied Mechanics
Identifiers
urn:nbn:se:liu:diva-197378 (URN)2-s2.0-85149406235 (Scopus ID)9782970161400 (ISBN)
Conference
20th European Conference on Composite Materials: Composites Meet Sustainability, ECCM 2022 Lausanne 26 June - 30 June 2022
Note

Funding Agencies|2019-02777

Available from: 2023-09-03 Created: 2023-09-03 Last updated: 2023-09-03
Cameron J, C., Larsson, J., Loukil, M. S., Murtagh, T. & Wennhage, P. (2021). Bearing strength performance of mixed thin/thick-ply, quasi-isotropiccomposite laminates. Composite structures, 261, Article ID 113312.
Open this publication in new window or tab >>Bearing strength performance of mixed thin/thick-ply, quasi-isotropiccomposite 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.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Thin ply, bearing strength, composite failure
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-175882 (URN)10.1016/j.compstruct.2020.113312 (DOI)000641800400018 ()
Available from: 2021-05-25 Created: 2021-05-25 Last updated: 2022-12-21Bibliographically 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
Intralaminar cracks, delaminations, bending stiffness, FEM, effective ply stiffness
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-175883 (URN)10.1007/s11029-021-09931-8 (DOI)000629473900003 ()
Available from: 2021-05-25 Created: 2021-05-25 Last updated: 2022-09-22Bibliographically approved
Loukil, M. S. & Varna, J. (2020). Effective shear modulus of a damaged ply in laminate stiffness analysis: Determination and validation. Journal of composite materials, 54(9), 1161-1176
Open this publication in new window or tab >>Effective shear modulus of a damaged ply in laminate stiffness analysis: Determination and validation
2020 (English)In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 54, no 9, p. 1161-1176Article in journal (Refereed) Published
Abstract [en]

The concept of the "effective stiffness" for plies in laminates containing intralaminar cracks is revisited presenting rather accurate fitting expressions for the effective stiffness dependence on crack density in the ply. In this article, the effective stiffness at certain crack density is back-calculated from the stiffness difference between the undamaged and damaged laminate. Earlier finite element method analysis of laminates with cracked 90-plies showed that the effective longitudinal modulus and Poissons ratio of the ply do not change during cracking, whereas the transverse modulus reduction can be described by a simple crack density dependent function. In this article, focus is on the remaining effective constant: in-plane shear modulus. Finite element method parametric analysis shows that the dependence on crack density is exponential and the fitting function is almost independent of geometrical and elastic parameters of the surrounding plies. The above independence justifies using the effective ply stiffness in expressions of the classical laminate theory to predict the intralaminar cracking caused stiffness reduction in laminates with off-axis plies. Results are in a very good agreement with (a) finite element method calculations; (b) experimental data, and (c) with the GLOB-LOC model, which gives a very accurate solution in cases where the crack face opening and sliding displacements are accurately described.

Place, publisher, year, edition, pages
SAGE PUBLICATIONS LTD, 2020
Keywords
Effective shear modulus; effective stiffness; stiffness prediction; transverse cracking
National Category
Applied Mechanics
Identifiers
urn:nbn:se:liu:diva-161862 (URN)10.1177/0021998319874369 (DOI)000491802900001 ()
Available from: 2019-11-11 Created: 2019-11-11 Last updated: 2021-07-06
Bergwall, M., Hederberg, H., Calmunger, M., Murtagh, T., Rinn, F. & Loukil, M. S. (2019). Innovative Out-of-Autoclave Composite Manufacturing Method for Saving Cost. In: : . Paper presented at EUROMAT19, Stockholm, 2-5 September 2019.
Open this publication in new window or tab >>Innovative Out-of-Autoclave Composite Manufacturing Method for Saving Cost
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2019 (English)Conference paper, Oral presentation only (Refereed)
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-162818 (URN)
Conference
EUROMAT19, Stockholm, 2-5 September 2019
Available from: 2019-12-19 Created: 2019-12-19 Last updated: 2020-02-06
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