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PhD lecture by Georgios Martakos

Dissertation title "ENHANCED PERFORMANCE OF SANDWICH STRUCTURES BY IMPROVED DAMAGE TOLERANCE"

Tidspunkt

20.01.2017 kl. 10.00 - 13.00

Beskrivelse

ENHANCED PERFORMANCE OF SANDWICH STRUCTURES BY IMPROVED DAMAGE TOLERANCE

ABSTRACT

The PhD thesis investigates the enhancement of the damage tolerance of sandwich structures by the embedding of a new type of core inserts that act as face/core interface crack stopping elements. The thesis presents the results of a series of experimental investigations where the new crack stopping elements were embedded in both sandwich beam and panel/plate specimens subjected to quasi-static as well as cyclic fatigue loading. The experimental observations has provided the basis for evaluating the efficiency of the proposed crack stopping inserts. For the experiments, Digital Image Correlation (DIC) was used to measure the local strain fields and overall deformation behaviour around the new crack stopper elements.  In support of the experimental investigations, a Finite Element  (FE) analysis based methodology, including fracture mechanics analysis and the so-called ‘cycle jump’ technique for fatigue simulations, was developed and applied to predict the progression of damage in sandwich beam and panel specimens with embedded crack stoppers.

Different configurations of the peel stopper were tested and the conditions for crack deflection for all configurations were identified by proposing and applying a fracture mechanics based crack kinking criterion. By use of the numerical fracture mechanics based modelling tools, both fatigue crack growth and crack arrest in the specimens were simulated.  It was shown that the crack stoppers in all cases were capable of effectively capturing and containing a propagating interface debond crack, both for quasi-static and fatigue loading conditions. It was further shown that the presence of embedded crack stoppers significantly increased the fatigue life of the tested sandwich specimens. Finally, it was shown that the strains responsible for crack re-initiation on the back side of the new crack stopper can be accurately calculated enabling the prediction of the fatigue life of the specimens.

The lecture will be held in english.

LINK TO INVITATION

 

ASSESSMENT COMMITTEE

Associate Professor Jørgen Kepler, Aalborg University (chairman)

Professor Bent F. Sørensen, Technical University of Denmark

Professor Paul M. Weaver, University of Bristol, UK

 

SUPERVISOR(S)

Professor Ole Thybo Thomsen, Aalborg University

Associate Professor Jens H. Andreasen, Aalborg University (co-supervisor)

 

The Department of Mechanical and Manufacturing Engineering will host an informal reception after the defence (Fibigerstræde 14, Common Room). Everybody is welcome. 

Arrangør

Department of Mechanical and Manufacturing Engineering

Adresse

Fibigerstræde 16, auditorium 1.108

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