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Talks and Poster Presentations (with Proceedings-Entry):

M. Rodríguez-Hortalá, J. Hatzmann, H.P. Degischer:
"Structural characterisation of defects in CFRP laminates produced with different epoxy resin systems and their influence on the mechanical properties";
Talk: 15th European Conference on Composite Materials (ECCM 15), Venedig; 06-24-2012 - 06-28-2012; in: "Proceedings of the 15th European Conference on Composite Materials", M. Quaresimin et al. (ed.); ECCM15, Venezia (2012), ISBN: 978-88-88785-33-2; Paper ID 2000, 8 pages.



English abstract:
Because of their high stiffness and strength in combination with low weight, fibre reinforced polymers (FRP) are used
commonly. Though design, dimensioning and manufacturing of such structures varies a lot compared to monolithic light
weight materials like aluminium alloys for example. Whilst dimensioning using finite element methods is no longer a big
issue, the correlation between voids and other defects, which are always inherent in composite structures and their effect
on the types of failure of fibre composite components was not yet fully investigated. Carbon fibre reinforced polymer
(CFRP) composites are manufactured mainly by hand layup. Epoxy resin is very often used as matrix material. The
mechanical properties are directly influenced by the constitution, the fibre volume fraction and the porosity of the material.
The interface properties between fibre and matrix material are also very important.
The studied materials are CFRP laminates produced by hand layup using the same carbon fibre fabric and two different
epoxy resin systems. The composites architecture was analyzed (light microscopy, scanning electron microscopy and
computed tomography) to identify and characterize existing defects within the microstructure of the samples. Furthermore
the mechanical parameters like Young´s, and shear modulus, stress and strain at failure and inter-laminar shear strength
were determined by bending and short beam shear tests. Thermal parameters like glass transition temperature and
coefficient of thermal expansion were also studied using DMA (Dynamic Mechanical Analysis), DSC (Differential Scanning
Calorimetry) and TMA (Thermo Mechanical Analysis). Thermogravimetrical analysis (TGA) was conducted to estimate
fibre volume fraction and porosity content.
Bending tests with acoustic emission (AE) measurements reveal local damage much earlier than global failure. Two sorts
of voids, big pores between fibre bundles and small voids within the bundles were observed. The different porosity
contents of each laminate type were correlated to their mechanical performance, underlining the importance of the
adequate curing conditions and the influence of the matrix on the global composite performance. Different failure modes
occurring during material testing were confirmed by fractography. Moreover typical fractographic features of the tension
and compression sides, like cusps, DAFF (Directly Attributed Fibre Failure), scallops, kink-band terraces and ply splitting
were observed on the tested bending samples. Computed tomography allows us to study the composites architecture in a
three-dimensional way, fibre bundles and porosity could be segmented and quantitatively analyzed.

Keywords:
CFRP laminates, epoxy resin, porosity, computed tomography, bending test, thermal analysis

Created from the Publication Database of the Vienna University of Technology.