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Thermo-elastic properties degradation in damaged laminates with high density of transverse cracks
Division of Materials Science, Luleå University of Technology, Luleå, Sweden.
Division of Materials Science, Luleå University of Technology, Luleå, Sweden.ORCID iD: 0000-0001-9649-8621
Institut Jean Lamour, University of Lorraine, EEIGM 6 Rue Bastien Lepage, F-54010 Nancy, France.
2013 (English)Conference paper, Oral presentation only (Other academic)
Abstract [en]

During the service life multidirectional laminate with an arbitrary lay-up is subjected to varying thermo-mechanical loading and in result different number on intralaminar cracks can develop in different layers of the laminate. These cracks called also transverse cracks are reducing the thermo-elastic properties of laminates. A model called GLOB-LOC model was developed in [1,2] to calculate these properties for any given damage state. This analytical calculation scheme is exact if the input information is exact. However, the expressions contain two important approximate parameters (functions) which are obtained summarizing/fitting parametric analyzes results using FEM. These parameters are proportional to the average stress state change between two cracks with respect to the undamaged stress. The parameters govern the stiffness reduction of the laminate and have the physical meaning of average opening displacement (COD) and average sliding displacement (CSD) of a crack. The parameters COD and CSD depend mostly on neighboring layer thickness and stiffness which makes them robust parameters in the model. Unfortunately, the situation changes when the crack density (number of cracks per mm) is high and the distance between cracks is comparable with the crack size (cracked layer thickness). In this crack density range the cracks are interacting and the COD and CSD depend on the distance between them. In this paper the crack interaction effects on laminate stiffness are analyzed using FEM. Based on FEM results a simple interaction function which depends on the cracked and neighboring layer thickness, elastic properties and the distance between cracks is suggested. This interaction function multiplied with COD of a non-interactive crack is the input parameter in analytical model for thermo-elastic properties of damaged symmetric and balanced laminates. It is shown that these functions when used in the GLOB-LOC model give high accuracy for all thermo-elastic constants of damaged laminates. As an example, the predicted axial modulus and Poisson’s ratio of cross-ply laminates with cracks in inside 90-layer are shown for GF/EP composite in Fig.1. FEM data are shown with symbols, predictions according to the interaction function by solid curves and dotted lines represent the ply-discount model. It has to be reminded that the normalized crack density is introduced as inverse to the crack spacing normalized with ply thickness. Therefore, the values of the normalized density larger than 1 are extremely high and are with no practical interest. Data in this region are shown to demonstrate the asymptotic approaching to the ply-discount value.

Place, publisher, year, edition, pages
2013.
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
URN: urn:nbn:se:liu:diva-150442OAI: oai:DiVA.org:liu-150442DiVA, id: diva2:1241273
Conference
International Conference on Deformation and Fracture of Composites & Structural Integrity and Multi-Scale Modelling (SI-6), 8-11 April 2013, Cambridge, UK
Note

Godkänd; 2013; 20130611 (andbra)

Available from: 2018-08-23 Created: 2018-08-23 Last updated: 2018-08-23Bibliographically approved

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Loukil, Mohamed Sahbi

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