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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
901

A Study on the Ball Shear Test of Sn-Ag-Cu and Sn-Pb Solder Balls

Chiu, Wen-Chun 08 September 2004 (has links)
In this thesis, the relation between shear load and displacement for the lead-free solder (Sn3.0Ag0.5Cu) and the tin-lead solder (63Sn37Pb) are investigated. Except that, a new shear strength of the solder balls is suggested with considering the plastic strain energy of the solder balls. Three diameters of the Sn/Ag/Cu and Sn/Pb solder balls are studied. The variation of the plastic strain energies for the balls undergone different number of thermal cycles is compared. The effect of high temperature aging on the shear strength is also discussed. The difference between the failure fractures of the Sn/Ag/Cu and Sn/Pb solder ball are executed by using SEM. The experimental results show that the failure mechanism for the Sn/Ag/Cu is quite different from the Sn/Pb solder ball. Generally, the lead-free Sn/Ag/Cu solder is much ductile than the Sn/Pb solder ball in the shear test. Also the better fatigue performances are observed for the Sn/Ag/Cu solder balls.
902

Effect Of Aging On The Mechanical Properties Of Boron Carbide Particle Reinforced Aluminum Metal Matrix Composites

Karakas, Mustafa Serdar 01 October 2007 (has links) (PDF)
Metal matrix composites (MMCs) of Al - 4 wt.% Cu reinforced with different volumetric fractions of B4C particles were produced by hot pressing. The effect of aging temperature on the age hardening response of the composites was studied and compared with the characteristics exhibited by the matrix alloy. Reinforcement addition was found to considerably affect the age hardening behavior. Detailed transmission electron microscopy and differential scanning calorimetry observations were made to understand the aging response of the composites. The low strain rate and high strain rate deformation behavior of the MMCs were determined utilizing low velocity transverse rupture tests and true armor-piercing steel projectiles, respectively. Increasing the volume fraction of B4C led to a decrease in flexural strength. The flexural strength vs. strain rate plots showed a slight increase in strength followed by a decrease for all samples. The mechanical performance of the composites and the unreinforced alloy were greatly improved by heat treatment. The MMCs were found to be inferior to monolithic ceramics when used as facing plates in armors.
903

Analysis Of Corner Effects On In-situ Walls Supporting Deep Excavations: Comparison Of Plane Strain And Three Dimensional Analyses

Unlu, Guliz 01 December 2008 (has links) (PDF)
In this thesis, hypothetical cases of in-situ walls, that are supported at one, two and four levels, as well as cantilever walls, are analyzed using plane strain and 3D finite element programs. A parametric study is performed by varying the soil stiffness. Deflection, moment, anchor loads and effective lateral earth pressures acting on the walls are examined to understand corner effect. Comparisons are made between plane strain and 3D without corner analysis results to confirm that two programs yield similar results. Moreover, two deep excavation case histories namely: i) Ankara &Ccedil / ankaya trade center and residence and, ii) Ekol construction are analyzed using calibrated models. Calibrations of the models are made using inclinometer data. In hypothetical models, it is found that corner effects on deflections diminish after 20m distance from the corner for excavations that are 8m and 12m deep. Corner effects on deflection decrease as elastic modulus of soil or stiffness of the system increase. Moment diagram pattern changes along the excavation side in cantilever case study. Moment diagram obtained around a corner in 3D analysis and diagrams obtained from the plane strain analyses by modeling the corner as a strut are quite similar. The anchor loads increase until 10-15m distance from the corner. After this distance they become nearly constant. In the analysis of case histories, a trial error solution is adopted to fit the deformed shape of piled wall obtained from 3D analysis to the deformations recorded by inclinometers. These results are compared with the results of plane strain analyses. Ankara-&Ccedil / ankaya project is solved by modeling the corner as strut in plane strain analyses. Results of this analyze agrees with field monitoring data, indicating that corner effects could be simulated by modeling the perpendicular pile wall as a strut in plane strain analysis.
904

Distribution Of Bending Moments In Laterally Loaded Passive Pile Groups A Model Study

Ozturk, Sevki 01 February 2009 (has links) (PDF)
In this study, bending moment distributions developed in laterally loaded passive pile and passive pile groups in cohesionless soil were investigated in laboratory conditions through model pile experiments. Different from the active pile loading, the lateral load was given directly to the piles using a movable large direct shear box. In these experiments strain gauges fastened to the piles and a computer based data reading system were used. The strain values were measured at five levels on the piles. The behavior of a single pile and a pile group having five piles were investigated through strain measurements in order to observe bending moment distribution on the piles. After evaluating the test results, the behavior of passive single pile was found to be similar to the results obtained in early studies. Negative bending moments were observed at the specified depths above the shear plane and positive bending moments were measured at the level of the shear plane and below the shear plane. Maximum bending moments were obtained at 0.7L (L: Length of Pile) for single piles and piles in the group. Above the shear plane, maximum bending moments within the pile group were found to be developed on the piles nearest to the loading. On the shear plane maximum bending moments were developed on the piles farthest from the loading just like active piles. Below the shear plane, maximum bending moments were developed mainly on the piles nearest to the loading.
905

The study on Photoreflectance spectra of Zn1-xMnxSe/GaAs

Lin, Huang-Nan 25 June 2001 (has links)
In this work¡Awe studied the strain effects on heavy hole (hh) and light hole (lh) bands of Zn1-xMnxSe/GaAs by photoreflectance (PR) spectroscopy . The Zn1-xMnxSe epilayers were grown on GaAs substrates by the MBE technique . There is a biaxial compressive strain exist in the epilayer, due to the different lattice constants between epilayers and substrates .The biaxial strain will shift hh and lh bands and lift the hh-lh degeneracy. In our experiment ,we found that the splitting of the hh and lh transition energies is almost lineally proportional to the Mn ion concentrations. It can be ascribed to the strain in the epilayer . We have also measured the PR of Zn0.96Mn0.04Se/GaAs at various temperatures , and analyzed the transition energy of different temperatures in terms of Varshni relation.
906

A Density Functional Study on Mechanical and Electronic Properties of Single-Wall Silicon-Carbon Nanotube under the Deformation by External Force

Lee, Shin-Chin 20 August 2009 (has links)
In this thesis, mechanical and electronic properties of a (4,4) SiC nanotube under different tensile strain were investigated by density functional theory (DFT) calculation. The HOMO-LUMO gap of nanotube will significantly decrease linearly with the increase of axial strain. Two different slopes are found before and after an 11% strain in the profile of HOMO-LUMO gap versus strain. The partial density of states, bond order and electronic deformation density were discussed for demonstrating the strain effect on the electronic properties of SiC nanotube under axial strain. The adsorption mechanism of CO on SiC nanotubes with different axial strains as well as the charge distributions after the adsorption were also discussed.
907

Micro-mechanical sensor for the spectral decomposition of acoustic signals

Kranz, Michael S. 21 January 2011 (has links)
An array of electret-biased frequency-selective resonant microelectromechanical system (MEMS) acoustic sensors was proposed to perform analysis of stress pulses created during an impact between two materials. This analysis allowed classification of the stiffness of the materials involved in the impact without applying post-impact signal processing. Arrays of resonant MEMS sensors provided filtering of the incident stress pulse and subsequent binning of time-domain waveforms into frequency-based spectra. Results indicated that different impact conditions and materials yielded different spectral characteristics. These characteristics, as well as the resulting sensor array responses, are discussed and applied to impact classification. Each individual sensor element in the array was biased by an in situ charged electret film. A microplasma discharge apparatus embedded within the microsensor allowed charging of the electret film after all device fabrication was complete. This enabled electret film integration using high-temperature surface micromachining processes that would typically lead to discharge of traditionally formed electret materials. This also eliminated the traditional wafer-bonding and post-fabrication assembly processes required in conventional electret integration approaches. The microplasma discharge process and resulting electret performance are discussed within the context of the MEMS acoustic sensor array.
908

Microstructure and strain rate effects on the mechanical behavior of particle reinforced epoxy-based reactive materials

White, Bradley William 05 October 2011 (has links)
The effects of reactive metal particles on the microstructure and mechanical properties of epoxy-based composites are investigated in this work. To examine these effects castings of epoxy reinforced with 20-40 vol.% Al and 0-10 vol.% Ni were prepared, while varying the aluminum particle size from 5 to 50 microns and holding the nickel particle size constant at 50 microns. In total eight composite materials were produced, possessing unique microstructures. The microstructure is quantitatively characterized and correlated with the composite constitutive response determined from quasi-static and dynamic compressive loading conditions at strain-rates from 1e-4 to 5e3 /s. Microstructures from each composite and at each strain rate were analyzed to determine the amount of particle strain as a function of bulk strain and strain rate. Using computational simulations of representative microstructures of select composites, the epoxy matrix-metallic particle and particle-particle interactions at the mesoscale under dynamic compressive loading conditions were further examined. From computational simulation data, the stress and strain localization effects were characterized at the mesoscale and the bulk mechanical behavior was decomposed into the individual contributions of the constituent phases. The particle strain and computational analysis provided a greater understanding of the mechanisms associated with particle deformation and stress transfer between phases, and their influence on the overall mechanical response of polymer matrix composites reinforced with metallic particles. The highly heterogeneous composite microstructure and the high contrasting properties of the individual constituents were found to drive localized deformations that are often more pronounced than those in the bulk material. The strain rate behavior of epoxy is shown to cause a strain rate dependent deformation response of reinforcement particle phases that are typically strain rate independent. Additionally, the epoxy matrix strength behavior was found to have a higher dependence on strain rate due to the presence of metal particle fillers. Discrepancies between experimental and simulation mechanical behavior results and these findings indicate a need for epoxy constitutive models to incorporate effects of particle reinforcement on the mechanical behavior.
909

Influence of the probiotic strain Escherichia coli Nissle 1917 on experimental infections with Salmonella Enteritidis PT4 in chickens

Mohamed, Imad 17 December 2004 (has links) (PDF)
Zusammenfassung Untersuchungen zur Beeinflussung von experimentellen Salmonella Enteritidis PT4 Infektionen bei Küken durch den probiotischen Stamm Escherichia coli Nissle 1917 Imad Azmi Awadein Mohamed Institut für Bakteriologie und Mykologie, Veterinärmedizinische Fakultät, Universität Leipzig und Institut für Geflügelkrankheiten, Veterinärmedizinische Fakultät, Freie Universität Berlin Eingereicht im Januar, 2004 Schlüsselworte: (E. coli Stamm Nissle 1917, Küken, S. Enteritidis, Probiotika, Bdellovibrionen) (94 Seiten, 48 Abbildungen, 16 Tabellen und 150 Referenzen) 1- Untersucht wurden die Auswirkungen der oralen Applikation von E. coli Stamm Nissle 1917 und Bdellovibrio bacteriovorus auf die Reduktion der Ansiedlung von S. Enteritidis PT4, auf die Reduktion der Mortalitätsrate, auf die Gesamtzahl aerober und Gram-negativer Bakterien, auf die Anzahl von Bdellovibrionen und auf das Körpergewicht von SPF-Hühnern. Im Vergleich zur positiven Kontrollgruppe konnten bei der Ansiedlung von S. Enteritidis PT4 im Caecum der Testgruppen an den Tagen 14, 21 und 28 signifikante Unterschiede festgestellt werden. Im Vergleich zur positiven Kontrollgruppe, die eine Mortalitätsrate von 10% aufweist, war die Mortalitätsrate der Testgruppen deutlich reduziert. Ebenso waren in den Testgruppen die aerobe und Gram-negative Gesamtkeimzahl am Tag 28 im Vergleich zur positiven Kontrollgruppe deutlich verringert. Signifikanten Anstieg der Bdellovibrionen Anzahl zeigten die Testgruppen sowohl im Vergleich zur positiven als auch negativen Kontrollgruppe. Beim Vergleich zwischen dem Gesamtkörpergewicht der Testgruppen zu dem der negativen und den überlebenden Tieren der positiven Kontrollgruppe gab es keine signifikanten Unterschiede. 2- Untersucht wurden die Auswirkungen der oralen Applikation von E. coli Stamm Nissle 1917 und Bdellovibrio bacteriovorus auf die Reisolation von S. Enteritidis PT4 aus verschiedenen Teilen des Intestinaltrakts und diverser Organe von SPF-Hühnern. In Kropf, Proventrikel, Herzblut, Lunge, Leber und Milz der Testgruppen konnte im Vergleich zur positiven Kontrollgruppe eine Reduktion ermittelt werden, die Reisolation von S. Enteritidis aus dem Caecum der Testgruppen zeigte keinen Unterschied im Vergleich zur positiven Kontrollgruppe. 3- Untersucht wurden die Auswirkungen der oralen Applikation von E. coli Stamm Nissle 1917 und Bdellovibrio bacteriovorus an Konzentrationen von Serum-Avidin, IgY gegen S. Enteritidis und IgY gegen E. coli Nissle 1917 bei experimentell mit S. Enteritidis-infizierten SPF-Hühnern. Die Untersuchungen ergaben eine signifikante Senkung der Serum-Avidin-Konzentration im Vergleich zur positiven Kontrollgruppe, vor allem sieben Tage post infectionem mit S. Enteritidis. Ein signifikanter Anstieg der Konzentration von IgY gegen S. Enteritidis konnte bei den Testgruppen im Vergleich zur positiven Kontrollgruppe vor allem an den Tagen sieben verzeichnet werden. Ein signifikanter Anstieg der Konzentration von IgY gegen E. coli Nissle 1917 konnte in allen Testgruppen im Vergleich zur positiven Kontrollgruppe festgestellt werden. 4- Untersucht wurden die Auswirkungen der oralen Applikation von E. coli Nissle 1917 mit und ohne Plasmid auf die Reduktion der Ansiedelung von S. Enteritidis PT4, auf die Reduktion der Mortalitätsrate, die aerobe und Gram-negative Gesamtkeimzahl, die Bdellovibrionen-Gesamtkeimzahl, Keimzahlen von Lactobacillus, Bifidobacterium und C. perfringens und das Körpergewicht von SPF-Hühnern. Im Vergleich zur positiven Kontrollgruppe konnte im Caecum der Testgruppen ein signifikanter Rückgang der Ansiedelung von S. Enteritidis an den Tagen 7, 21 und 28 verzeichnet werden, außerdem konnte bei den Testgruppen kein Todesfall festgestellt werden, wohingegen die Sterblichkeitsrate der positiven Kontrollgruppe bei 15% lag. Ein signifikantes Absinken in der totalen Gesamtkeimzahl und der Gram-negativen Gesamtkeimzahl konnte für die Testgruppen im Vergleich zur positiven Kontrollgruppe an den Tagen 21 beziehungsweise 28 verzeichnet werden. Die Isolation von Bdellovibrionen aus den Testgruppen ergab keinen Unterschied zu den Kontrollgruppen. Die Lactobacillus-Bifidobacterium-Keimzahl war in den Testgruppen im Vergleich zur positiven Kontrollgruppe signifikant erhöht, vor allem am Tag sieben. Die C. perfringens-Keimzahl war in der positiven Kontrollgruppe gegenüber den Testgruppen am Tag 7 und 14 signifikant erhöht. Die Vergleiche des Körpergewichts der Testgruppen, negativer und überlebender Tiere der positiven Kontrollgruppe zeigten keinen signifikanten Unterschied. 5- Untersucht wurden die Auswirkungen der oralen Applikation von E. coli Stamm Nissle 1917 mit und ohne Plasmid auf die Reisolation von S. Enteritidis aus unterschiedlichen Teilen des Intestinaltraktes und aus Organen von SPF-Hühnern. Im Kropf, Proventrikel, Duodenum, Herzblut, Lunge, Leber und Milz konnte bei den Testgruppen im Vergleich zur positiven Kontrollgruppe eine Senkung der Reisolationsrate festgestellt werden, wohingegen sich keine Unterschied beim Vergleich der Caeca von positiver Kontrollgruppe und von den Testgruppen zeigte. 6- Untersucht wurden die Auswirkungen der oralen Applikation von E. coli Stamm Nissle 1917 mit und ohne Plasmid auf die Konzentrationen von Serum-Avidin, IgY gegen S. Enteritidis und IgY gegen E. coli Nissle 1917 bei experimentell mit S. Enteritidis-infizierten SPF-Hühnern. Bei der Serum-Avidin-Konzentration konnte kein Unterschied zwischen Testgruppen und positiver Kontrollgruppe festgestellt werden. Die Testgruppen zeigten ihrerseits im Vergleich zur positiven Kontrollgruppe eine signifikante Erhöhung der Konzentration von IgY gegen S. Enteritidis, vor allem an den Tagen 21 und 28. Ein signifikanter Anstieg der Konzentration von IgY gegen E. coli Nissle 1917 konnte in allen Testgruppen im Vergleich zur positiven Kontrollgruppe, vor allem an den Tagen sieben und vierzehn festgestellt werden. 7- Aus den Resultaten des ersten und des zweiten Versuchs schließen wir, dass der probiotische Stamm E. coli Nissle 1917 das Caecum von 7 bis 28 Tage alten Hühnern erfolgreich kolonialisieren kann. Orale Applikation des Stammes kann die Ansiedlung von S. Enteritidis, aerobe und Gram-negative Gesamtkeimzahl, Mortalitätsrate, Reisolationsrate von S. Enteritidis in Organen und im Intestinaltrakt (mit Ausnahme des Caecums im ersten Versuch) deutlich reduzieren. Die Kombination von E. coli Nissle 1917 und Bdellovibrio bacteriovorus hatte nicht den gewünschten Effekt, der auch von mehreren Autoren in-vitro beobachtet wurde. Bdellovibrionen waren in den Testgruppen des ersten Versuchs im Vergleich zu denen im zweiten deutlich erhöht. Beim durchschnittlichen Körpergewicht konnte kein signifikanter Unterschied zwischen beiden Versuchen festgestellt werden. Der Serum-Avidin-Spiegel war im ersten Versuch in der Testgruppe deutlich reduziert, im zweiten dagegen nicht. Dies ist möglicherweise auf den Effekt von Bdellovibrionen zurückzuführen, bedarf allerdings noch der weiteren Bestätigung. Im Allgemeinen konnten wir eine signifikante Verbesserung des Immunsystems der Vögel als Resultat der oralen Applikation von E. coli Nissle 1917 feststellen. 8- Untersucht wurden die antagonistischen Effekte von E. coli Stamm Nissle 1917 mit und ohne Plasmid auf die in-vitro-Wachstumsrate von S. Enteritidis PT4. Wir konnten feststellen, dass E. coli Nissle 1917 sowohl mit als auch ohne Plasmid die Wachstumsrate von S. Enteritidis erfolgreich reduzieren konnte. / Summary Influence of the probiotic strain Escherichia coli Nissle 1917 on experimental infections with Salmonella Enteritidis PT4 in chickens Imad Azmi Awadein Mohamed Institute of Bacteriology and Mycology, Faculty of Veterinary Medicine, University of Leipzig and Institute of Poultry Diseases, Faculty of Veterinary Medicine, Free University Berlin Submitted in January, 2004 Keywords: (E. coli strain Nissle 1917, chickens, S. Enteritidis, Probiotics, Bdellovibrios) (94 pages, 48 figures, 16 tables and 150 references) 1- The effect of oral application of E. coli strain Nissle 1917 with Bdellovibrio bacteriovorus on the colonization of S. Enteritidis PT4, reduction of the mortality rate, total aerobic bacterial counts, Gram negative bacterial counts, bdellovibrio bacterial counts and body weight of Specific Pathogen Free chickens were investigated. A significant reduction in the colonization of S. Enteritidis PT4 in the caecum of trial groups at 14, 21 and 28 days old in comparison to the positive control group was observed. A reduction in mortality rate in the trial groups was seen in comparison to the positive control group which had 10 %. The total aerobic and Gram negative bacterial counts were significantly decreased in the trial groups at 28 days old in comparison to the positive control group. Bdellovibrio bacterial counts were significantly increased in the trial groups in comparison to the control groups. No significant difference was seen in the mean body weight of the trial groups in comparison to control groups. 2- The effect of oral application of E. coli strain Nissle 1917 with Bdellovibrio bacteriovorus on reisolation rate of S. Enteritidis from different parts of the intestinal tract and organs of SPF chickens was investigated. A reduction in the S. Enteritidis reisolation rate was seen from crop, proventriculus, duodenum, heart blood, lungs, livers and spleens of the trial groups in comparison to the positive control group but not from the caecum. 3- The effect of oral application of E. coli strain Nissle 1917 and Bdellovibrio bacteriovorus on the serum avidin levels, IgY against S. Enteritidis and IgY against E. coli strain Nissle 1917 levels of SPF chickens experimentally infected with S. Enteritidis was investigated. A significant reduction in the serum avidin levels was observed in the trial groups at 7 days old in comparison to the positive control group. The antibody levels against S. Enteritidis was significantly increased in the trial group at 7 days old in comparison to the positive control group. A significant increase at day 7 in the antibody levels against E. coli strain Nissle 1917 was seen in the trial group in comparison to the positive control group. 4- The effect of oral application E. coli Nissle 1917 with and without plasmid on reduction on the colonization of S. Enteritidis PT4, reduction of the mortality rate, total aerobic bacterial counts, Gram negative bacterial counts, bdellovibrio bacterial counts, Lactobacillus-Bifidobacterium counts, C. perfringens bacterial counts and body weight of SPF chickens were investigated. A significant reduction in the colonization of S. Enteritidis PT4 in the caecum of trial groups at 7, 21 and 28 days old in comparison to the positive control group was observed. No mortalities were seen in the both trial groups in comparison to the positive control group which had 15 % mortalities. The total aerobic and Gram negative bacterial counts were significantly decreased in the trial groups at 21 and 28 days respectively old in comparison to the positive control group. No significant difference was observed in bdellovibrio isolation from the trial groups in comparison to the control group. Lactobacillus-Bifidobacterium bacterial counts were significantly increased in the trial groups at 7, 14 and 21 days old in comparison to the positive control group. A significant reduction in C. perfringens bacterial counts were seen in the trial groups at 7 and 14 days old in comparison to positive control group. No significant difference was observed in the mean body weight of the trial groups in comparison to control groups. 5- The effect of oral application E. coli Nissle 1917 with and without plasmid on the reisolation of S. Enteritidis from different parts of intestinal tract and organs of SPF chickens was investigated. A reduction in the S. Enteritidis reisolation rate was seen from crop, proventriculus, duodenum, caecum, heart blood, lungs, livers and spleens of the trial groups in comparison to the positive control group. 6- The effect of oral application E. coli Nissle 1917 with and without plasmid on the serum avidin levels, IgY against S. Enteritidis and IgY against E. coli strain Nissle 1917 levels of SPF chickens experimentally infected with S. Enteritidis were investigated. No significant reduction in the serum avidin levels were seen in the trial groups in comparison to the positive control group. The antibody levels against S. Enteritidis were significantly increased in the trial groups at 21 and 28 days old in comparison to the positive control group. A significant increase in the antibody levels against E. coli strain Nissle 1917 were seen in the trial groups in comparison to the positive control group. 7- From the results observed in the first and second experiments we concluded that probiotic strain E. coli Nissle 1917 can successfully colonize the caecum of SPF chickens from 7 to 28 days old. Oral appliction of probiotic strain E. coli Nissle 1917 has significantly reduced the S. Enteritidis colonization, total and Gram negative bacterial counts, mortality rate, reisolation rate of S. Enteritidis in organs and the intestinal tract except the caecum in first experiment in the trial groups in comparison to positive control. The combination between E. coli strain Nissle 1917 and B. bacteriovorus had not achieved the desirable effects in the first experiment which observed by many authors in vitro. Bdellovibrio was significantly increased in the trial groups of the first experiment in comparison to the second experiment. This may be a possible effect of Bdellovibrio which is yet to be confirmed. No significant difference was observed in the mean body weight in both experiment. A significant reduction of serum avidin levels were observed in the trial groups of the first experiment but not in the second experiment. We have observed a significant improvement in the immune system of the birds as a results of oral application of E. coli strain Nissle 1917. 8- Antagonistic effect of E. coli Nissle 1917 with and without plasmid on the growth rate of the S. Enteritidis PT4 in vitro was investigated. We concluded that E. coli Nissle 1917 with and without plasmid successfully reduced the growth rate of S. Enteritidis in comparison to the control one.
910

Durability of Embedded Fibre Optic Sensors in Composites

Levin, Klas January 2001 (has links)
<p>This thesis concerns various aspects of the durability offibre optic sensors embedded in composite. Since repair orreplacement of embedded sensors is not generally possible, thefunctional reliability of embedded sensors is one of the mostimportant prerequisites for successful use. The main researchobjective was to investigate the interaction between the sensorand the composite, and how this is affecting the mechanical andoptical sensor response. Fibre optic sensors embedded incomposite structures induce local stress concentrations whenthe composite is subjected to mechanical loads andenvironmental changes such as temperature and moisture. Acomplex transfer of stresses through the interfaces between theembedded sensor and the composite occurs and can result inlarge local stresses in the composite and a significant changein the response of the embedded sensor. These stressconcentrations make the interfaces susceptible todebonding.</p><p>The sensor performance was studied experimentally andnumerically. Some basic results were generated for the EFPI andBragg grating sensors. The phase-strain response was determinedduring static and fatigue loading. The results showed that thesensors were more reliable in compression than in tensilestatic and fatigue loading. Generally, the sensor reliabilityduring loading was significantly improved for the Bragg gratingsensors over that of the EFPI sensor, as an effect of thesensor geometry. This was also demonstrated in theinvestigations on impacts. Impacts do not necessarily result indamage in the composite, but might cause debonding or otherfailure modes in the sensor area. Large, local stressconcentrations occur at several positions in the EFPI sensor,which pointed out that this sensor type was not suitable forembedded applications.</p><p>The shift in focus from the sensor concept based on the EFPIsensor to that based on the Bragg grating sensor manifesteditself in several studies. The calculated deformation fieldaround an embedded optical fibre was verified in experimentsusing a high-resolution moiré interferometric technique.Furthermore, the improvement in the coating technology wasverified. A significant higher interfacial strength wasobtained with the silane-treated glass surface. The resultsindicated that at least a twofold improvement of the shearstrength was obtained.</p><p>To simultaneously measure the in-plane strain components andthe temperature change, embedded Bragg grating sensors werearranged in a rosette configuration. The relationship betweenthe optical response from each sensor and the strains in thelaminate was numerically and analytically established.</p><p>Damage lead to stress redistribution in the sensor region,which may influence the output from the embedded Bragg gratingsensor. The effect was numerically evaluated for interfacialdamage, and was compared to that of a sensor with undamagedinterface. The results showed that debonding might have asignificant influence, in particular for combined thermal andmechanical loading.</p><p><b>Keywords</b>: composites, fibre optic sensor, embedded, EFPIsensor, Bragg grating sensor, durability, fatigue, impact,strain measurement, interface, stress analysis</p>

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