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Evaluation of energy of fatigue damage into GFRC through digital image correlation and thermography
No full textTwo different full-field techniques are here used to investigate the heat sources and dissipation sources
that compare onto the surface of a composite laminate under fatigue load. The material here studied is a
glass fibre reinforced epoxy laminate employed in the field of wind turbine. During fatigue tests, 8-bit
(256 grey levels) images and thermal images were acquired and elaborated to relate the hysteresis area
and the heat sources, finding the energy of damage in three points of specimens. The data shows a clear
intensification of dissipative phenomena just in that region where final failure is then registered
Studio sul comportamento di un acciaio per assili ferroviari sottoposto a carichi di fatica
No full textCharacterization of fatigue damage in long fiber epoxy composite laminates
Full text linkA study and characterization of a GFRC
material is here presented. Forty fatigue tests
(twenty for each of the two considered stacking
sequence) have been carried out and by means of
them S-N curves have been traced. Two quantities
have been chosen for monitoring damage evolution
during each test: stiffness and dissipated energy per
cycle. The presence of three zones in obtained
graphs can be observed and it is evident that the
most important and dangerous structural
transformations take place only in very final part of
life. This consideration seems to be confirmed by the
analysis of micrographies effected on fractured
specimens and also on only partially damaged
specimen
Characterization of fatigue damage in long fiber epoxy composite laminates
No full textA study of damage characterization of a GFRC laminate is resented here. Forty fatigue tests were executed and S–N curves traced. Two parameters were chosen to monitor damage evolution during each test: stiffness and dissipated energy per cycle. Moreover, the presence of three zones in graphs of rocessed data can be observed and it is evident that the most important structural transformations take place only in the very final part of life. Adopting a continuum mechanics approach, the degradation
through the whole life in composite is evaluated and it is shown that the two parameters are strictly related to damage state of composite material. A method for predicting the remaining life in a GFRC is here proposed
Fatigue damage in notched GFR composites with thermal and digital image measurements
No full textComplex time dependent damage phenomena are characteristic of Composites under fatigue; this is due to material structural heterogeneity and fibre/matrix interactions. Fatigue life is mainly determined by the progressive damage evolution, difficult to be modeled with numerical tools or mathematical frames. Experimental methods are to be applied to achieve
correct information about the evolving fatigue damage and the authors propose a methodology based on Digital and Thermal Image analyses, to measure on notched GFRC specimens the dissipative sources in terms of temperature and deformation based data;
starting from previous works, the measurements procedures were improved for these techniques, in order to obtain useful results with notched composites and capable to detect
different damage states on specimen surface
Localizzazione e valutazione del Danneggiamento mediante Tecnica di Correlazione di Immagini
Full text linkQuesto lavoro presenta una tecnica sperimentale di misura a campo intero delle deformazioni applicata allo studio di due provini differenti (Al 7075-O e AISI 304-L) sottoposti a carico quasi-statico. La tecnica è basata sulla correlazione di immagini digitali (DIC, Digital Image Correlation). Quella della DIC è una tecnica di successo nello studio delle eterogeneità che evolvono in un materiale durante l’applicazione di carico quasi-statico o dinamico, perché sotto determinate condizioni, garantisce affidabilità e precisione difficili da ottenere mediante l’impiego di altre tecniche di misura. La metodologia proposta è illustrata mettendo in evidenza, come di seguito esposto, alcuni importanti fenomeni di localizzazione durante due test statici
ND small defects detection of GFRP laminates using pulsed thermography
No full textThree symmetrical composite panels reinforced with fiberglass (unidirectional E type fiberglass and epoxy resin) were realized through hand lay‐up and artificial inter‐laminar delaminations of various geometry were introduced at different depths.
Several thermal stimulation procedures with different ways to consider the defects in the specimens enable to
optimize the thermographic technique, by solving some initial problems related to the experimental set -up and issues.
Above all, the minimum requirements for defect which can be revealed trough pulsed thermography have been
established, according to present experience
Fatigue life prediction under variable loading based on a new non-linear continuum damage mechanics model
No full textThis work presents a non-linear continuum damage mechanics model based on general thermodynamic framework developed by Lemaitre and Chaboche. The proposed model has been formulated to take into account the material damage evolution at different load levels and it allows the effect of the loading sequence to be included; by means of a recurrence formula derived for multilevel loading, complex load sequences can be considered. The fatigue test data for a hardened and tempered steel have been used to verify the model proposed in this paper and the results show a good agreement to predict fatiguelifeunder complex load sequences
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