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Experimental methods to determine model parameters for failure modes of CFRP
University of Skövde, School of Technology and Society. University of Skövde, The Virtual Systems Research Centre.
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The focus of this thesis is to develop methods to predict the damage response of Carbon Fibre Reinforced Polymers (CFRP). In the pursuit of reducing the manufacturing cost and weight of CFRP components, it is crucial to enable modelling of the non-linear response associated with various failure modes. Two failure modes are considered in this thesis: fibre compressive failure and interlaminar delamination. Multidirectional laminated composites are commonly used when a low weight is desired due to their high specific strength and stiffness. In a carbon/epoxy composite, almost exclusively the fibres carry the load. However, along the fibre direction, the compressive strength is considerably lower than the tensile strength. With the same reasoning, the transverse strength is considerably lower than the in-plane strength. This makes delamination and fibre compressive failure two of the major concerns in structural design. Moreover, the presence of delaminations severely reduces the compressive strength of a laminate. This can cause catastrophic failure of the structure. In Paper A, we suggest a test method for determining fracture properties associated with fibre compressive failure. A modified compact compression specimen is designed for this purpose and compressive failure takes place in a region consisting exclusively of fibres oriented parallel to the loading direction. The evaluation method is based on a generalized J-integral and full field measurements of the strain field on the surface of the specimen. Thus, the method is not restricted to small damage zones. Paper B focuses on measuring cohesive laws for delamination in pure mode loading. The cohesive laws in mode I and mode II are measured with the DCB- and ENF-specimen, respectively. With a method based on the J-integral, the energy release rate associated with the crack tip separation is measured directly. From this, the cohesive laws are derived. It is concluded that the nonlinear response at the crack tip is crucial in the evaluation of the mode II fracture energy.

Place, publisher, year, edition, pages
Göteborg: Chalmers University of Technology , 2013. , viii, 14 s. (tot 68) p.
Series
Technical report - Department of Applied Mechanics, Chalmers University of Technology, Göteborg, Sweden, ISSN 1652-8565 ; 2013:07
Keyword [en]
composite, delamination, compressive failure, energy release rate, cohesive modelling
National Category
Materials Engineering
Research subject
Technology
Identifiers
URN: urn:nbn:se:his:diva-8389Libris ID: 13988899OAI: oai:DiVA.org:his-8389DiVA: diva2:639932
Presentation
2013-03-27, MA, Hörsalsvägen 7, 10:00
Opponent
Supervisors
Note

Delarbeten:

Paper AD. Svensson, K. S. Alfredsson, U. Stigh and N. E. Jansson. An experimental method to determine the fracture properties of compressivefibre failure in unidirectional CFRP. To be submitted for international publication (2013)

Paper BK. S. Alfredsson, D. Svensson, U. Stigh and A. Biel. Measurement of cohesive laws for initiation of delamination of CFRP. Submitted for international publication (2013)

Available from: 2013-08-12 Created: 2013-08-12 Last updated: 2013-08-12Bibliographically approved

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