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Περίσφιγξη υποστηλωμάτων ορθογωνικής διατομής μεγάλου λόγου πλευρών με ινοπλισμένα πολυμερήΣταθοπούλου, Μαρία 18 June 2014 (has links)
Πειραματική διεκπεραίωση 24 υποστυλωμάτων ορθογωνικής διατομής με μεγάλο λόγο πλευρών 3:1 και 4:1, κατασκευασμένα υπό κλίμακα, ενισχυμένα με ινοπλισμένα πολυμερή άνθρακα και εφαρμογή σχετικών προσομοιωμάτων υπάρχουσας βιβλιογραφίας. / Experimental procedure of 24 large-scale column specimens 3:1 and 4:1 reinforced with carbon fiber polymers CFRP and comparison of the test results with those calculated from the existing models of large-scale columns.
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Thermal residual stresses in bonded composite repairs on cracked metal structuresAlbat, Andreas Michael 05 1900 (has links)
The objective of this research is to determine the thermal residual stresses and strains in
bonded composite repairs on cracked metal structures. This work is an essential contribution
to a fatigue damage initiation model for bonded composite repair, where knowledge of
the initial stress/strain state after an elevated temperature cure is important. Furthermore,
this work is an elementary part for the development of a generic certification approach to
bonded composite repairs. Accounting properly for thermal residual stresses in test specimens
and in real applications will assist in determining the true feasibility of a bonded
composite repair.
The objective of this work was realized in four stages of research. In the first stage, seven
AMRL sandwich type composite bonded repair specimens were manufactured, of which
one was instrumented by placing 44 strain gauges at eight planar locations and within
five different interfaces. Residual strains at ambient temperature (including both thermal
residual strains and other process induced strains) were measured during the manufacturing
process. In the second stage, the stress free temperature for the repaired specimen was
experimentally determined and the thermal residual strains measured as a function of
operating temperature. In the third stage, a theoretical analysis was carried out to estimate
the thermal residual stress and strain distributions in various bonded repairs. This analysis
also addressed the effect of symmetrical disbonds around the crack. Finally, a finite element
analysis was carried out to assess the limitations of the theoretical analysis as well as to
provide a more detailed insight into the complex thermal residual stress and strain state of
the AMRL sandwich type specimen.
During this work it was found that high thermal residual strains (reaching 15% of the
yield strain) are present in the bonded repair specimen at ambient temperature. Previous analysis schemes predicted results nearly 60% higher. The thermal residual strain versus
temperature measurement showed that only very small changes in thermal residual strains
occurred above 90°C leading to a defined effective stress free temperature of 85.8°C for the
employed adhesive FM 73M. By utilizing an effective stress free temperature, a linear-elastic
approach was used to model thermal residual stresses and strains in composite bonded
repairs. Major achievements in the theoretical analysis include a linear-elastic closed form
solution for tapered joints and reinforcements without the need for a numerical solution
scheme, a stress field prediction ahead of the crack tip for the metal substrate of a bonded
repair based on a concise complete solution of the classical fracture mechanics problem of
a center crack in an infinite plate and, an extended Rose model for the prediction of the
stress intensity factor of a bonded repair with symmetrical disbonds showing the severity
of thermal residual stresses especially for partially disbonded composite repairs to cracked
metal specimens.
The key to precise predictions of thermal residual stresses in bonded composite repairs is
the knowledge of the adhesive behaviour at elevated temperatures under thermal residual
stress loading. A generic type specimen is presented which allows to investigate the relevant
adhesive behaviour.
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Accelerated environmental degradation of GRP composite materials.Dlamini, Power Madoda. January 2004 (has links)
The use of fibre reinforced polymer composites and development of structural composites has expanded rapidly in the Southern African region over the past ten years. The long-term effect of placing these materials outdoors in the Southern African climate is unknown with exposure data for these materials being primarily European and North American based. This study intends to take a broad-based study to the problem of environmental degradation of
advanced composite structures. This work is intended to study different degradation mechanisms. Work performed includes: a study of literature on degradation and protective measures; identification of dominant degradation mechanisms; manufacture of specimens; accelerated environmental testing; and an assessment of the effect of the exposure on the chemical properties
The goal of this work is to produce information, which can be subsequently used to determine the rate of damage, methods of suitable protection and necessary maintenance intervals for polymer composite components. The approach was: to simulate outdoor exposure within a reduced period of time; to establish correlation of results with actual outdoor exposure; and to determine how the gel coats compare with other protective methods. As part of the objectives of the study (i.e. to assess the durability of polymer matrix
composites materials subjected to environmental exposure), an experimental study was carried out to establish the durability of specific gel coats against ultraviolet (DV) and moisture degradation. An investigation of the effectiveness of the various protective measures has begun with a review of selected gel coats available as a protective coating. Laminates with these gel coats have been set up for both accelerated and natural exposure tests.
3000, 2500, 2000, 1600, and 800 hours of accelerated DV exposure tests were performed on polyester GRP laminates with gel coats. No measurable strength loss occurred on protected laminates; there was significant increase in yellowness on un-protected laminates; all protected specimens showed a fair retention of gloss; fibre prominence occurred on unprotected laminates; and the glass transition of samples had dropped from the normal polyester glass transition temperature range. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2004.
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Using surface plasmon resonance spectroscopy to characterize thin composite filmsShinall, Brian Darnell 12 1900 (has links)
No description available.
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Analysis of damage in composite laminates under bendingKuriakose, Sunil 05 1900 (has links)
No description available.
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Strength of composite lattice structuresHou, An 05 1900 (has links)
No description available.
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Non-classical non-linear effects in thin-walled composite beamsHarursampath, Dineshkumar 12 1900 (has links)
No description available.
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Single and multiple delamination behavior in composite platesHuang, Haiying 12 1900 (has links)
No description available.
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Life prediction evaluation and damage mechanism identification for SCS-6/Timetal 21S composites subjected to thermomechanical fatigueCalcaterra, Jeffrey Ronald 12 1900 (has links)
No description available.
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Development of stress gradient enhanced piezoelectric composite unimorph actuatorsHopkinson, David P. 08 1900 (has links)
No description available.
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