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Validation of FEM based damaged laminate model measuring crack opening displacement in cross-ply laminate using Electronic Speckle Pattern Interferometry (ESPI)
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 (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. Finite element method (FEM) studies were performed in [1,2] to understand which material and geometry parameters affect the COD and CSD most and simple empirical relationships (power law) were suggested. All these studies and analysis assume a linear elastic material with idealized geometry of cracks. The only correct way to validate these assumptions is through experiments. The effect of material properties on COD was measured experimentally using optical microscopy of loaded damaged specimens in [3,4]. It was shown that the measured average values of COD are affected by the constraining layer orientation and stiffness. The experimental determination of the average COD and CSD needs the measurement of the displacement for all points of the crack surfaces, which justifies the use of full-field measurement technique, Electronic Speckle Pattern Interferometry (ESPI). ESPI is an optical technique that provides the displacement for every point on a surface and offers the possibility to measure both, the in-plane and out-of-plane displacement without surface preparation. This technique was used in [5,6] to measure the COD for inside cracks on the specimen’s edge. It was shown that the profile of the crack on the edge is elliptical. The main objective of this paper is to study cracks in surface layers by measuring the COD along the crack path. For this reason the cross-ply laminate with surface cracks was selected. In particular, the displacement field on the surface of a [903/0]S carbon fiber/epoxy laminate specimen with multiple intralaminar cracks is studied and the relative displacement dependence on the applied mechanical load is measured. By looking to the displacement field the cracks appear as singularities and the corresponding displacement jumps are directly related to COD and CSD. The transverse cracks are parallel to the fiber orientation in the layer, which in our case corresponds to a 90 direction with respect to the tensile axis. Consequently, there is no relative sliding of the crack faces and the only displacement of these crack faces corresponds to COD. In other words, the crack displacement discontinuity measured on the surface is directly the COD.

Place, publisher, year, edition, pages
2013.
Keywords [en]
Damaged Laminate, Crack opening displacement (COD), ESPI, FEM
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
URN: urn:nbn:se:liu:diva-150443OAI: oai:DiVA.org:liu-150443DiVA, id: diva2:1241266
Conference
6th International Conference on Composites Testing and Model Identification, Aalborg, Denmark 22-24 April 2013
Note

Godkänd; 2013; 20130611 (andbra)

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

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Validation of FEM based damaged laminate model measuring crack opening displacement in cross-ply laminate using Electronic Speckle Pattern Interferometry (ESPI)(218 kB)8 downloads
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Loukil, Mohamed Sahbi

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