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  • 1.
    Loukil, Mohamed
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Microcracking in fiber composites and degradation of thermo-elastic properties of laminates2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The macroscopic failure of composite laminates subjected to tensile increasing load is preceded by initiation and evolution of several microdamage modes. The most common damage mode and the one examined in this thesis is intralaminar cracking in layers. Due to this kind of microdamage the laminate undergoes stiffness reduction when loaded in tension. For example, the elastic modulus in the loading direction and the corresponding Poisson’s ratio will decrease. The degradation of the elastic properties of these materials is caused by reduced stress in the damaged layer which is mainly due to two parameters: crack opening displacement (COD) and crack sliding displacement (CSD). At fixed applied load these parameters depend on the properties of the damaged and surrounding layers, on layer orientation and on thickness. When the number of cracks per unit length is high (high crack density in the layer) the COD and CSD are reduced because of to crack interaction. The main objective of the first paper is to investigate the effect of crack interaction on COD using FEM and to describe the identified dependence on crack density in a simple and accurate form by introducing an interaction function dependent on crack density. This interaction function together with COD of non-interactive crack gives accurate predictions of the damaged laminate thermo-elastic properties. The application of this function to more complex laminate lay-ups is demonstrated. All these calculations are performed assuming that cracks are equidistant. However, the crack distribution in the damaged layer is very non-uniform, especially in the initial stage of multiple cracking. In the second paper, the earlier developed model for general symmetric laminates is generalized to account for non-uniform crack distribution. This model is used to calculate the axial modulus of cross-ply laminates with cracks in internal and surface layers. In parametric analysis the COD and CSD are calculated using FEM, considering the smallest versus the average crack spacing ratio as non-uniformity parameter. It is shown that assuming uniform distribution we obtain lower bond to elastic modulus. A “double-periodic” approach presented to calculate the COD of a crack in a non-uniform case as the average of two solutions for periodic crack systems is very accurate for cracks in internal layers, whereas for high crack density in surface layers it underestimates the modulus reduction. In the third paper, the thermo-elastic constants of damaged laminates were calculated using shear lag models and variational models in a general calculation approach (GLOB-LOC) for symmetric laminates with transverse cracks in 90° layer. The comparison of these two models with FEM was presented for cross-ply and quasi-isotropic laminates.

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  • 2. Loukil, Mohamed Sahbi
    Activity: Caractérisation de l’endommagement des matériaux composites pour l’aéronautique à partir des mesures plein champ des déplacements et modélisation2012Conference paper (Other (popular science, discussion, etc.))
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  • 3.
    Loukil, Mohamed Sahbi
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Activity: Damage Accumulation and Stiffness Degradation in Composite Laminate2011Conference paper (Other (popular science, discussion, etc.))
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    fulltext
  • 4.
    Loukil, Mohamed Sahbi
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Experimental and numerical studies of intralaminar cracking in high performance composites2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The macroscopic failure of composite laminates subjected to tensile increasing load is preceded by initiation and evolution of several microdamage modes. The most common damage mode and the one examined in this thesis is intralaminar cracking in layers. Due to this kind of microdamage the laminate undergoes stiffness reduction when loaded in tension. For example, the elastic modulus in the loading direction and the corresponding Poisson’s ratio will decrease.The degradation of the elastic properties of these materials is caused by reduced stress in the damaged layer which is mainly due to two parameters: crack opening displacement (COD) and crack sliding displacement (CSD). At fixed applied load these parameters depend on the properties of the damaged and surrounding layers, on layer orientation and on thickness. When the number of cracks per unit length is high (high crack density in the layer) the COD and CSD are reduced because of to crack interaction.The main objective of the first paper is to investigate the effect of crack interaction on COD using FEM and to describe the identified dependence on crack density in a simple and accurate form by introducing an interaction function dependent on crack density. This interaction function together with COD of non-interactive crack gives accurate predictions of the damaged laminate properties. The application of this function to more complex laminate lay-ups is demonstrated. All these calculations are performed assuming that cracks are equidistant. However, the crack distribution in the damaged layer is very non-uniform, especially in the initial stage of multiple cracking. In the second paper, the earlier developed model for general symmetric laminates is generalized to account for non-uniform crack distribution. This model is used to calculate the axial modulus of cross-ply laminates with cracks in internal and surface layers. In parametric analysis the COD and CSD are calculated using FEM, considering the smallest versus the average crack spacing ratio as non-uniformity parameter. It is shown that assuming uniform distribution we obtain lower bond to elastic modulus. A “double-periodic” approach presented to calculate the COD of a crack in a non-uniform case as the average of two solutions for periodic crack systems is very accurate for cracks in internal layers, whereas for high crack density in surface layers it underestimates the modulus reduction.In the third paper, the thermo-elastic constants were calculated using shear lag models and variational models in a general calculation approach (GLOB-LOC) for symmetric laminates with transverse cracks in 90° layer. The comparison of these two models with FEM was presented for cross-ply and quasi-isotropic laminates.Using FEM, we assume linear elastic material with ideal crack geometry. Fiber bridging over the crack surface is possible which can affect COD and CSD. The only correct way to validate these assumptions is through experiments.The main objective of the fourth and the fifth paper is to measure these parameters for different laminate lay-ups in this way providing models with valuable information for validation of used assumptions and for defining limits of their application. In particular, the displacement field on the edge of a [90/0]s and [903/0]s carbon fiber/epoxy laminates specimens with multiple intralaminar cracks in the surface layer is studied. The specimen full-field displacement measurement is carried out using ESPI (Electronic Speckle Pattern Interferometry).

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  • 5.
    Loukil, Mohamed Sahbi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Zoubir
    Institut Jean Lamour, University of Lorraine.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    ESPI analysis of crack face displacements in damaged laminates2014In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 94, p. 80-88Article in journal (Refereed)
    Abstract [en]

    Crack opening displacement (COD) and crack sliding displacement (CSD) are the two parameters that define slope of stiffness reduction with increasing crack density. The values of these parameters strongly depend on the crack geometry which is difficult to observe and quantify. In models we usually assume straight crack, no local delaminations (questionable for surface cracks) and use uniform spacing. In this paper COD of cracks in surface layers are analyzed using the displacement field on the edge and on the surface of a [90/0]s and [903/0]s carbon fiber/epoxy laminates subjected to tension. The specimen full-field displacement measurement is carried out using ESPI (Electronic Speckle Pattern Interferometry). It is shown that including in the FEM model crack locations exactly as in the test, the COD of an individual crack is predicted accurately. The model with periodic and symmetric crack distribution significantly underestimates the COD whereas staggered crack distribution model in many cases renders very good results. Crack face sliding displacements, CSD were measured on the edge of [0/704/-704]s GF/EP laminate, showing that the sliding can not be neglected and that the COD versus CSD ratio for this laminate is similar to model predictions.

  • 6.
    Loukil, Mohamed Sahbi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Farge, Laurent
    Institut Jean Lamour, Nancy Universite.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Zoubir
    Institut Jean Lamour, Nancy Universite.
    Characterization of damage evolution in thermo-echanical loading of composites materials2009In: Book of abstracts: 5th EEIGM International Conference on Advanced Materials Research, 2009, p. 32-Conference paper (Refereed)
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  • 7.
    Loukil, Mohamed Sahbi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hussain, W.
    Luleå University of Technology.
    Kirti, A.
    Luleå University of Technology.
    Pupurs, Andrejs
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Thermoelastic constants of symmetric laminates with cracks in 90-layer: application of simple models2013In: Plastics, rubber and composites, ISSN 1465-8011, E-ISSN 1743-2898, Vol. 42, no 4, p. 157-166Article in journal (Refereed)
    Abstract [en]

    The change of thermoelastic properties of cross-ply and quasi-isotropic laminates with intralaminar cracks in layers is analysed. Predictions are performed using previously derived general expressions for stiffness of symmetric damaged laminates as dependent on crack density and crack face opening and sliding. It is shown that the average crack opening displacement can be linked with the average value of axial stress perturbation between two cracks. Using this relationship, analytical shear lag and Hashin’s models, developed for axial modulus, can be applied for calculating thermal expansion coefficients, in-plane moduli and Poisson’s ratios of damaged laminates. The approach is evaluated using finite element method and it is shown that the accuracy is rather similar to that in axial modulus calculation.

  • 8. Loukil, Mohamed Sahbi
    et al.
    Sahbi, Mohamed
    Activity: Degradation of thermo-elastic properties of non-uniformly composite laminates2012Conference paper (Other (popular science, discussion, etc.))
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    FULLTEXT01
  • 9. Loukil, Mohamed Sahbi
    et al.
    Sahbi, Mohamed
    Activity: Thermo-elastic properties of non-uniformly damaged laminates at high crack density2012Conference paper (Other (popular science, discussion, etc.))
    Download full text (pdf)
    FULLTEXT01
  • 10.
    Loukil, Mohamed Sahbi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Z.
    Science et Ingénierie des Matériaux et Métallurgie (SI2M), Institut Jean Lamour, Nancy.
    Damage characterization in glass fiber/epoxy laminates using electronic speckle pattern interferometry2015In: Experimental techniques (Westport, Conn.), ISSN 0732-8818, E-ISSN 1747-1567, Vol. 39, no 2, p. 38-45Article in journal (Refereed)
    Abstract [en]

    The degradation of the elastic properties of composite laminates with intralaminar cracks is caused by reduced stress in the damaged layer which is mainly due to two parameters: the crack opening displacement (COD) and the crack sliding displacement (CSD). In this paper these parameters are measured experimentally, providing laminate stiffness reduction models with valuable information for validation of used assumptions and for defining limits of their application. In particular, the displacement field on the edges of a [0/ +704/ −704]s glass fiber/epoxy laminate specimens with multiple intralaminar cracks is studied, and the COD and CSD dependence on the applied mechanical load is measured. The specimen full-field displacement measurement is carried out using ESPI (electronic speckle pattern interferometry). By studying the displacement discontinuities, the crack face displacements were measured. A comparison between the COD and the CSD (for the same crack) is performed

  • 11.
    Loukil, Mohamed Sahbi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Z.
    Finite element analysis and experimental comparison of the crack opening displacement profile in the damaged cross-ply laminates2013Conference paper (Refereed)
    Abstract [en]

    During the service life composite laminates undergo complex combinations of thermal and mechanical loading leading to microdamage accumulation in the plies. The most common damage mode and the one examined in this work is intralaminar cracking in layers. The crack opening displacement (COD) and the crack sliding displacement (CSD) during loading reduce the average stress in the damaged layer, thus reducing the laminate stiffness. These parameters depend on material properties of the damaged layer and surrounding layers, on layer orientation and thickness. Previously these parameters have been calculated using finite element method (FEM) assuming linear elastic material with idealized geometry of cracks. To validate these assumptions experimentally the displacement field on the surface of a [90/0/90], [90/0]s and [903/0]s carbon fiber/epoxy laminates specimens with multiple intralaminar cracks in the surface layer is studied. The profile of the COD along the width is investigated for each single crack. The specimen full-field displacement measurement is carried out using ESPI (Electronic Speckle Pattern Interferometry). The effect of crack interaction as well as the effect of the thickness of 90° layers on the COD is given in this paper.

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    FULLTEXT01
  • 12.
    Loukil, Mohamed Sahbi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Z.
    Institut Jean Lamour, University of Lorraine, EEIGM 6 Rue Bastien Lepage, F-54010 Nancy.
    Thermo-elastic properties degradation in damaged laminates with high density of transverse cracks2013Conference paper (Refereed)
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    FULLTEXT01
  • 13.
    Loukil, Mohamed Sahbi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Z.
    Institut Jean Lamour, University of Lorraine, EEIGM 6 Rue Bastien Lepage, F-54010 Nancy.
    Validation of FEM based damaged laminate model measuring crack opening displacement in cross-ply laminate using Electronic Speckle Pattern Interferometry (ESPI)2013Conference paper (Refereed)
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    FULLTEXT01
  • 14.
    Loukil, Mohamed Sahbi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Zoubir
    Institut Jean Lamour.
    Applicability of solutions for periodic intralaminar crack distributions to non-uniformly damaged laminates2013In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 47, no 3, p. 287-301Article in journal (Refereed)
    Abstract [en]

    Stiffness reduction simulation in laminates with intralaminar cracks is usually performed assuming that cracks are equidistant and crack density is the only parameter needed. However, the crack distribution in the damaged layer is very non-uniform, especially in the initial stage of multiple cracking. In this article, the earlier developed model for general symmetric laminates is generalized to account for non-uniform crack distribution. This model, in which the normalized average crack-opening and crack-sliding displacements are the main characteristics of the crack, is used to calculate the axial modulus of cross-ply laminates with cracks in internal and surface layers. In parametric analysis, the crack-opening displacement and crack-sliding displacement are calculated using finite element method, considering the smallest versus the average crack spacing ratio as non-uniformity parameter. It is shown that assuming uniform distribution, we obtain lower bond to elastic modulus. A ‘double-periodic’ approach presented to calculate the crack-opening displacement of a crack in a non-uniform case as the average of two solutions for periodic crack systems is very accurate for cracks in internal layers of cross-ply laminates, whereas for high crack density in surface layers, it underestimates the modulus reduction.

  • 15.
    Loukil, Mohamed Sahbi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Zoubir
    Institut Jean Lamour, EEIGM 6 Rue Bastien Lepage, F-54010 Nancy.
    Application of the electronic speckle pattern interferometry (espi) technique for the characterization of damage in composite laminates2012Conference paper (Refereed)
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    FULLTEXT01
  • 16.
    Loukil, Mohamed Sahbi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Zoubir
    Institut Jean Lamour, SI2M, EEIGM 6 Rue Bastien Lepage, F-54010 Nancy.
    Characterization of damaged composite laminates by an optical measurement of the displacement field2011In: Book of abstracts: 6th EEIGM International Conference, Advanced Materials Research7th and 8th November, 2011 EEIGM, Nancy, France, 2011, p. 37-Conference paper (Refereed)
  • 17.
    Loukil, Mohamed Sahbi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Zoubir
    Institut Jean Lamour, (SI2M).
    Characterization of damaged composite laminates by an optical measurement of the displacement field2012In: 6th EEIGM International Conference Advanced Materials Research: 7th and 8th November, 2011 EEIGM, Nancy, France, Bristol: IOP Publishing Ltd , 2012Conference paper (Refereed)
    Abstract [en]

    The degradation of the elastic properties of composite laminates with intralaminar cracks is caused by reduced stress in the damaged layer which is mainly due to two parameters: the crack opening displacement (COD) and the crack sliding displacement (CSD). In this paper these parameters are measured experimentally providing laminate stiffness reduction models with valuable information for validation of used assumptions and for defining limits of their application. In particular, the displacement field on the edges of a [0/ +704/ −704]s glass fiber/epoxy laminate specimens with multiple intralaminar cracks is studied and the COD and CSD dependence on the applied mechanical load is measured. The specimen full-field displacement measurement is carried out using ESPI (Electronic Speckle Pattern Interferometry). By studying the displacement discontinuities, the crack face displacements were measured. A comparison between the COD and the CSD (for the same crack) is performed

    Download full text (pdf)
    FULLTEXT01
  • 18.
    Loukil, Mohamed Sahbi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Zoubir
    Institut Jean Lamour, EEIGM 6 Rue Bastien Lepage, F-54010 Nancy.
    Engineering expressions for thermo-elastic constants of laminates with high density of transverse cracks2013In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 48, no 1, p. 37-46Article in journal (Refereed)
    Abstract [en]

    Thermo-elastic constants of symmetric and balanced laminates with intralaminar cracks in 90-layers depend on the opening displacement (COD) of the crack. The COD dependence on the interaction between cracks in the same layer is studied using FEM. The COD dependence on crack density is described by interaction function in form of tanh(). This interaction function multiplied with COD of non-interactive crack is the input parameter in analytical model for thermo-elastic properties of damaged symmetric and balanced laminates. Predictions performed for cross-ply laminates with cracks in inside and in surface layers and for quasi-isotropic laminates with different position of the 90-layer are in a very good agreement with direct FEM calculations.

  • 19.
    Loukil, Mohamed Sahbi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Zoubir
    Institut Jean Lamour, SI2M, Nancy-Université.
    Parameter determination in damaged laminate model by optical full-field measurement of the displacement using ESPI2011Conference paper (Other academic)
  • 20.
    Loukil, Mohamed Sahbi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Zoubir
    Institut Jean Lamour, SI2M, Nancy-Université.
    Thermo-elastic properties of damaged laminates at high density of cracks in layers2011In: Aerospace - the global innovation driver: 6th International Conference "Supply on the Wings" ; November 02 - 04, 2011, Frankfurt, Germany ; conference proceedings ; in conjunction with AIRTEC, International Aerospace Supply Fair, Frankfurt: airtec GmbH , 2011Conference paper (Refereed)
  • 21.
    Loukil, Mohamed Sahbi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Zoubrir
    Caractérisation de l’endommagement des matériaux composites pour l’aéronautique à partir des mesures plein champ des déplacements et modélisation2012Conference paper (Refereed)
    Download full text (pdf)
    fulltext
    Download full text (pdf)
    fulltext
  • 22.
    Pakkam Gabriel, Vivek Richards
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Loukil, Mohamed Sahbi
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Equivalent stress concept to account for the effect of local cyclic stress ratio on transverse cracking in tension-tension fatigueManuscript (preprint) (Other academic)
  • 23.
    Pupurs, Andrejs
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Loukil, Mohamed
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Swerea SICOMP, Piteå, SE-94129, Sweden.
    Mattsson, David
    Swerea SICOMP, Piteå, SE-94129, Sweden.
    Damage development and stiffness reduction in laminates in out-of-plane loading2014In: 16th European Conference on Composite Materials, ECCM 2014: Seville, Spain, 22 - 26 June 2014, European Conference on Composite Materials, ECCM , 2014Conference paper (Refereed)
    Abstract [en]

    Simple approach based on Classical Laminate Theory (CLT) and effective stiffness of damaged layer is suggested for bending stiffness determination of laminate with intralaminar cracks in surface 90-layers. The effective stiffness of layer with cracks as a function of crack density is back-calculated comparing in-plane stiffness of laminates with and without damage. The accuracy of the CLT and effective stiffness approach is demonstrated comparing with bending stiffness results from FEM simulated 4-point bending test on laminate with damage. Analytical model for damaged laminate stiffness is presented which gives similar values for effective stiffness as FEM calculations for unit cell. Effect of local delaminations initiated from transverse cracks is analyzed.

  • 24.
    Varna, Janis
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Loukil, Mohamed Sahbi
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Microdamage initiation and growth in laminated composites2009Conference paper (Refereed)
    Download full text (pdf)
    FULLTEXT01
  • 25.
    Varna, Janis
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Loukil, Mohamed Sahbi
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Z.
    Degradation of elastic properties of non-uniformly damaged composite laminates2013In: 7th EEIGM International Conference on Advanced Materials Research: 21–22 March 2013, LTU, Luleå, Sweden, IOP Publishing Ltd , 2013, article id 12009Conference paper (Refereed)
    Abstract [en]

    Stiffness reduction model for laminates with non-uniformly distributed intralaminar cracks is presented and used to analyze the effect of non-uniformity and the accuracy of predictions based on uniform spacing. The values of the normalized crack opening displacement (COD) as affected by the presence of other cracks are used to calculate the axial modulus of cross-ply laminates with cracks. The COD is calculated using finite element method (FEM), considering two closest neighbors of the crack and using the smallest versus the average crack spacing ratio as non-uniformity parameter. Assuming uniform spacing the axial modulus reduction is overestimated. A "double-periodic" approach is presented to calculate the COD of a crack in a non-uniform case as the average of two solutions for periodic crack systems.

  • 26.
    Zrida, Hana
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Loukil, Mohamed Sahbi
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Z.
    Institut Jean Lamour, SI2M, EEIGM 6 Rue Bastien Lepage, F-54010 Nancy.
    Crack opening displacement determination in damaged cross-ply laminate using electronic speckle pattern interferometry (ESPI)2012In: 6th EEIGM International Conference Advanced Materials Research: 7th and 8th November, 2011 EEIGM, Nancy, France, Bristol: IOP Publishing Ltd , 2012Conference paper (Refereed)
    Abstract [en]

    Composite laminates during service undergo complex combinations of thermal and mechanical loading leading to microdamage accumulation in the plies. The most common damage mode and the one examined in this work is intralaminar cracking in layers. The crack opening displacement (COD) and the crack sliding displacement (CSD) during loading reduce the average stress in the damaged layer, thus reducing the laminate stiffness. These parameters depend on material properties of the damaged layer and surrounding layers, on layer orientation and thickness. Previously these parameters have been calculated using finite element method (FEM) assuming linear elastic material with idealized geometry of cracks. To validate these assumptions experimentally the displacement field on the surface of a [90/0/90] carbon fiber/epoxy laminate specimens with multiple intralaminar cracks in the surface layer is studied and the COD dependence on the applied mechanical load is measured. The specimen full-field displacement measurement is carried out using ESPI (Electronic Speckle Pattern Interferometry). The displacement jumps corresponding to cracks are clearly visible and can be used to determine the opening displacement along the cracks. The effect of crack interaction on the COD at high crack density is also investigated.

1 - 26 of 26
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