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Bending Stiffness of Damaged Cross-ply Laminates
Lab. of Experimental Mechanics of Materials, Riga Technical University, Latvia; Polymeric Composites Group, Luleå University of Technology, Sweden.
RISE Research Institutes of Sweden, Piteå, Sweden.
Lab of Experimental Mechanics of Materials, Riga Technical University, Latvia; Polymeric Composites Group, Luleå University of Technology, Sweden.
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. Vol. 57, no 1, p. 31-46
Keywords [en]
Intralaminar cracks, delaminations, bending stiffness, FEM, effective ply stiffness
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-175883DOI: 10.1007/s11029-021-09931-8ISI: 000629473900003OAI: oai:DiVA.org:liu-175883DiVA, id: diva2:1557241
Available from: 2021-05-25 Created: 2021-05-25 Last updated: 2022-09-22Bibliographically approved

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Loukil, M.

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