• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 51
  • 37
  • 9
  • 8
  • 8
  • 7
  • 4
  • 2
  • 1
  • Tagged with
  • 162
  • 53
  • 29
  • 27
  • 25
  • 25
  • 23
  • 22
  • 20
  • 19
  • 19
  • 16
  • 15
  • 14
  • 14
  • 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.
21

Environmental impact of textile barriers : A comparative study of coated and laminated textile

Wickman, Clara, Kloth, Rebecka January 2019 (has links)
This thesis examined how the sustainability of laminated and coated textile barriers can be compared by analysing them through an environmental and functional perspective. This was done by building an evaluation model in which an analysis of the functional performance and an analysis of the environmental performance was combined and applied on a case study of a laminated and a coated material used for workwear. A Life Cycle Assessment (LCA) was used to evaluate the environmental impact. To evaluate the functional performance a series of material testing was made for tear strength, waterproofness and permeability. The LCA measured the environmental impact in terms of water use, climate change, and human toxicity. The results showed a similar impact on climate change and water use for both barriers. The assessment of human toxicity showed that the solvent dimethylformamide, used in the coating paste, meant a potential risk for human health. From the material testing it could be stated that the coating performed better in terms of tear resistance and waterproofness, but that the laminate showed more even results and higher breathability. To conclude, the study showed that the production of the coated textile barrier had the largest environmental impact due to the use of a toxic solvent, but that the functional performance generally was better for this coated material. The use of an evaluation model to compare coated and laminated textiles demanded knowledge and experience of LCA to be used. Though with the right LCA knowledge, the combined methods of functional testing and environmental impact may lead to conclusions which would otherwise go unnoticed. / I den här rapporten undersöktes hur hållbarheten hos laminerade och textila barriärer kan jämföras genom både ett funktionellt och ett miljömässigt perspektiv. Det gjordes genom att bygga en utvärderingsmodell inom vilken en analys av den funktionella prestandan och en analys av den miljömässiga prestandan kombinerades för att appliceras på en fallstudie av ett laminat och en beläggning som används för arbetskläder. En livscykelanalys (LCA) användes för att analysera den miljömässiga prestandan. För att analysera den funktionell prestandan utfördes en serie materialtester i rivstyrka, vattentäthet och permeabilitet.LCAn mätte miljömässig prestanda genom påverkanskategorierna klimatförändring, vattenanvändning och humantoxicitet. Resultaten visade liknande påverkan avseende klimatförändring och vattenanvändning för materialen. Utvärdering av påverkan gällande humantoxicitet visade att lösningsmedlet dimetylformamid, som används i beläggningspastan, innebär en risk för människors hälsa. I materialtesterna gav beläggning bättre resultat i rivstyrka och vattentäthet, men laminatet visade en mindre spridning i resultaten och en högre permeabilitet. Efter viss förslitning och tvätt uppvisade materialen dock mer liknande värden.Sammanfattningsvis visade studien att det belagda materialet hade störst miljöpåverkan på grund av utsläpp av det toxiska lösningsmedlet, men att det belagda materialet generellt hade bättre funktionell prestanda. Nackdelen med utvärderingsmodellen som togs fram för jämförelsen av materialen, var att den krävde kunskap och erfarenhet av LCA för att kunna användas. Med det sagt är en LCA det bästa verktyget tillgängligt för att mäta miljöpåverkan, och med den rätta kunskapen om LCA kan den kombinerade modellen leda till insikter som annars skulle missas. Därför kan utvärderingsmodellen vara ett framgångsrikt verktyg för att jämföra textila barriärer, och även utgöra ett steg på vägen i arbetet mot att kunna mäta hållbarhet.
22

Characterization of carbon fiber polymer matrix composites subjected to simultaneous application of electric current pulse and low velocity impact

Hart, Robert James 01 July 2011 (has links)
The use of composite materials in aerospace, electronics, and wind industries has become increasingly common, and these composite components are required to carry mechanical, electrical, and thermal loads simultaneously. A unique property of carbon fiber composites is that when an electric current is applied to the specimen, the mechanical strength of the specimen increases. Previous studies have shown that the higher the electric current, the greater the increase in impact strength. However, as current passes through the composite, heat is generated through Joule heating. This Joule heating can cause degradation of the composite and thus a loss in strength. In order to minimize the negative effects of heating, it is desired to apply a very high current for a very short duration of time. This thesis investigated the material responses of carbon fiber composite plates subjected to electrical current pulse loads of up to 1700 Amps. For 32 ply unidirectional IM7/977-3 specimens, the peak impact load and absorbed energy increased slightly with the addition of a current pulse at the time of an impact event. In 16 ply cross-ply IM7/977-2 specimens, the addition of the current pulse caused detrimental effects due to electrical arcing at the interface between the composite and electrodes. Further refinement of the experimental setup should minimize the risk of electrical arcing and should better elucidate the effects of a current pulse on the impact strength of the specimens.
23

Experimental Evaluation of Full Scale I-Section Reinforced Concrete Beams with CFRP-Shear Reinforcement

Aquino, Christian 01 January 2008 (has links)
Fiber reinforced polymer (FRP) systems have shown great promise in strengthening reinforced concrete structures. These systems are a viable option for use as external reinforcement because of their light weight, resistance to corrosion, and high strength. These systems, externally bonded in the form of sheets or laminates, have shown to increase the flexural and more recently the shear capacity of members. Major concerns of the system are issues related to the bond strength and premature peeling especially when reentrant corners are present. The objectives of this study were to verify the effectiveness of carbon FRP (CFRP) laminates on an I-section beam with no anchorage and to determine the feasibility of using an anchorage system to prevent premature debonding. The two types of anchorage systems used were a horizontal CFRP laminate and glass FRP (GFRP) spikes. These anchorage systems verified that the use of anchorage on I-shaped beams can prevent premature debonding of the laminate and allow the specimens to achieve a higher shear capacity. Recommendations for future research of such systems are also presented.
24

Fabrication of Carbon/Silicon Carbide Laminate Composites by Laser Chemical Vapor Deposition and their Microstructural Characterization

Gillespie, Joshua Robert 09 January 2004 (has links)
Laser Chemical Vapor Deposition (LCVD) is a process by which reagent gases are thermally activated to react by means of a laser focused on a substrate. The reaction produces a ceramic or metallic deposit. This investigation focuses on the use of LCVD as a method for producing laminated composites, specifically carbon/silicon carbide laminates. The laminates that were produced were examined using scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS) to determine composition. Deposit geometrical characteristics such as laminate thickness and volcano depth as well as deposit morphology were also determined using SEM. Another subset of experiments was performed for the purpose of simultaneously depositing carbon and silicon carbide, ie., codeposition.
25

Manufacturing and Mechanical Properties of Centrally NotchedAL/APC-2 Nanocomposite Laminates

Liu, Chun-Kan 26 July 2010 (has links)
The purpose of thesis aims to investigate the mechanical behavior and properties of a centrally notched hybrid Al alloy/Carbon-Fiber/PEEK(APC-2) laminate at elevated temperature. The high performance hybrid composite laminates of 0.5mm Aluminum alloy sheets sandwiched by APC-2 cross-ply and guasi-isotropic laminates were fabricated. The prepregs of APC-2 were stacked into cross-ply [0/90]s and quasi-isotropic [0/45/90/-45] laminates spread uniformly with nanoparticles SiO2. The sheet surface was treated by chromic acid anodic method to achieve perfectly bonding with matrix PEEK. The modified diaphragm curing process was adopted to fabricate Al/APC-2 hybrid nanocomposite laminates. The panels were cut into the specimens and then drilled an diameter hole in the center with diameters of 1,2,4,6 mm. The MTS 810 material testing machine was used to conduct the tension and fatigue tests. In addition, the MTS 651 environmental chamber was installed to control and keep the specific testing temperatures, such as ,25¢XC(RT), 75¢XC, 100¢XC, 125¢XC and 150¢XC. At first, the nominal stress(£mnom) and stress-strain diagram were obtained due to static tension tests at elevated temperature. The constant stress amplitude tension-tension cyclic tests were carried out by using load-control mode at a sinusoidal loading with frequency of 5Hz and stress ratio R=0.1. The received fatigue data were plotted in normalized S-N curves at variously elevated temperature. For the tensile tests, at the same temperature the nominal stress of cross-ply specimens was higher than that of quasi-isotropic specimens. Comparing with the notched and unnotched of cross-ply specimens, the nominal stress of notched specimens was about 60% to 80% that of unnotched specimens. Besides, as for the notched and unnotched quasi-isotropic specimens, the nominal stress of notched specimens was about 75% to 85% that of unnotched specimens. Then, the fatigue life and stress-cycles (S-N) curves of notched specimens were obtained often tension-tension fatigue tests. In the case of the same loading, notched specimens possess worse fatigue behavior, but in the same normalized stress ratio, the S-N curves of the unnotched were below the notched ones. The fatigue resistance of notched samples decrease as the temperature rising.
26

Manufacturing and Mechanical Properties of Ti/APC-2 Nanocomposite Laminates

Chang, Che-kai 23 August 2010 (has links)
The aims of this thesis are fabrication of Ti/APC-2 hybrid nanocomposite laminates and investigation of their mechanical properties at elevated temperature. The prepregs of APC-2 were stacked into cross-ply [0/90]s and quasi-isotropic [0/45/90/-45] laminates spread uniformly with nanoparticles SiO2. The sheet surface was treated by chromic acid anodic method to achieve perfectly bonding with matrix PEEK. The prepregs were sandwiched with the Ti alloy sheets. The modified diaphragm curing process was adopted to produce Ti/APC-2 hybrid nanocomposite laminates. The nanocomposite laminates were a five-layer composite with two 0.55 mm thick APC-2 layers sandwiched by three 0.5 mm thick Gr.1 titanium alloy sheets. The MTS 810 material testing machine was used to conduct the tension and fatigue tests. In addition, the MTS 651 environmental chamber was installed to control and keep the experimental temperature, such as 25¢XC, 75¢XC, 100¢XC, 125¢XC and 150¢XC. The mechanical proper¬ties, such as ultimate tensile strength, longitudinal stiffness of cross-ply and quasi-isotropic nanocomposite laminates, were obtained from the static tensile test. The stress-strain diagrams were plotted in the corresponding temperature. The constant stress amplitude tension-tension cyclic tests were carried out by using load-control mode at a sinusoidal loading with frequency of 5Hz and stress ratio R=0.1. The received fatigue data were plotted in normalized S-N curves at variously elevated temperature. From the summarized results, some conclusions were made. First, the ultimate strength of Ti/APC-2 nanocomposits was better than Ti/APC-2 composites at room temperature; Second, Both two type nanocomposite laminates¡¦ ultimate strength and S-N curves go downwards as temperature rising, especially at 150¢XC; Third, The fatigue tensile strength of both hybrid composite laminates was the lowest at 150¢XC. Fourth, Ti/APC-2 quasi-isotropic nanocomposite laminates had better fatigue resistance than Ti/APC-2 cross-ply nanocomposite laminates. Finally,The longitudinal stiffness was in good agreement with prediction by using the modified ROM because of the changed curve fitting ranges.
27

Fatigue Response of Centrally Notched Ti/APC-2 Nanocomposite Laminates by Two-Step Loading Cyclic Tests

Lee, Huei-Shiun 27 July 2011 (has links)
The aims of this thesis to investigate the two step loading of Ti/APC-2 hybrid nanocomposite laminates and their notched effect. Ti/APC-2 laminates were composed of three layers of titanium sheets and two layers of APC-2. Nanoparticles SiO2 were dispersed uniformly on the interfaces of APC-2 with the optimal amount of 1 wt %. Then, APC-2 was stacked according to cross-ply [0/90]s and quasi-isotropic [0/45/90/-45] sequences. The modified diaphragm curing process was adopted to fabricate the hybrid panels for minimal impact of production. The panels were cur into samples and drilled an diameter hole in the center with diameters of 4 or 6 mm. Both tension and fatigue tests were carried out with MTS 810 universal testing machine at room temperature. Also, two-step loading tests include high¡÷low and low¡÷high tests, were conducted. 0.9£mnom is denoted as high load and 0.7£mnom low load for two-step loading spectrum. In both high¡÷low and low¡÷high step loadings the first step is to do cyclic tests at a half life of the corresponding load, and then finish it due to last step load. From the received results, some conclusions were made. First, the ultimate load of notched cross-ply samples was reduced about 50% and the notched quasi-isotropic samples reduced about 30% compared to their unnotched counterparts. Second, the S-N curves are very close for both centrally notched samples of diameters 4 mm and 6 mm in cross-ply and quasi-isotropic samples. Third, quasi-isotropic samples had higher average values of cumulative damage than cross-ply samples. Because of notched effect centrally notched samples of diameters 4 mm had higher average values of cumulative damage than centrally notched samples of diameters 6 mm.
28

Mechanical and Fatigue Behavior of Al/APC-2 Nanocomposite Laminates at Elevated Temperature

Sung, Yi-Chun 21 August 2012 (has links)
The innovative Al/APC-2 hybrid nanocomposite fiber metal laminates (FMLs) were successfully fabricated. To overcome the usual problem of delamination, the Al alloy 2024-T3 thin sheets were treated by chromic acid anodic (CAA) method to achieve perfectly bonding with matrix PEEK eventually. It was found much better than the previously surface treatment method of CrO3-based chemical etching. A systematic study of hybrid specimens subjected to both static tensile and fatigue tests was conducted at elevated temperatures to obtain their mechanical properties, fatigue lives and failure mechanisms. From the tensile tests, the mechanical properties of Al/APC-2 hybrid cross-ply and quasi-isotropic nanocomposite FLMs at elevated temperatures were received, such as ultimate tensile strength and longitudinal stiffness. Also, the predicted stress-strain curves was proposed and in good agreement with experimental data. The average values of received notched strength were affected significantly by stress concentration and high temperature. The modified point stress criterion (PSC) was used with the varied characteristic length dependent on nature of material and specimen geometry. The predicted notched strengths by the modified PSC model were not only precisely validated, but extended to the application at elevated temperatures. The received fatigue data were plotted in S-N curves at variously elevated temperatures. The predictions of fatigue life curves were also presented and verified. The predicted S-N curves were compared with experimental data and found quite accurate.
29

Manufacturing and Mechanical Properties of AS4/PEEK Nanocomposite Laminates

Wu, Chun-Hsien 07 July 2004 (has links)
The work aims to manufacture AS-4/PEEK APC-2 nano-composite laminates first. We used the prepreg form of AS-4 Graphite/PEEK laminae to make APC-2 laminates of 2 mm thick with two lay-ups of cross-ply and quasi-isotropic totally 16 plies by a hot press via the modified diaphragm curing. The nano-particles SiO2 with the average diameter of 15¡Ó5 nm were uniformly spread in the specific interfaces of laminate. From mechanical testing it is found that the nanocomposite specimens of spreading 10 plies nanoparticles (3% by wt. of matrix) possesses the highest mechanical properties. we see that in cross-ply specimens the ultimate strength increases 10.91 % and stiffness 6.7 %; while in quasi-isotropic specimens the ultimate strength increases 12.48 % and stiffness 19.93 %. Second, repeat the tensile tests at 50, 75, 100, 125, 150¢J to receive respective stress-strain curve , strength and stiffness. At elevated temperatures the ultimate strength decreases slightly below 75¢J and the elastic modulus reduces slightly below 125¢J, however, both properties degrade highly at 150¢J ( Tg) for two layups generally. Finally, the constant stress amplitude tension-tension cyclic testing was conducted. It is found that both the stress-cycles (S-N) curves are very close below 104 cycles for cross-ply laminates w/wo nanoparticles, and the S-N curve of nano-laminate slightly bent down after 105 cycles. Whilst in quasi-isotropic laminates, the S-N curve of nano-laminate is always slightly below that of APC-2 laminate through the life.
30

Manufacturing and Mechanical Properties of AL/APC-2 Nanocomposite Laminates

Lai, Ying-da 08 July 2008 (has links)
The thesis is to fabricate Al/APC-2 hybrid nanocomposite laminates and investigate their mechanical properties at elevated temperature. The prepregs of Carbon /PEEK were stacked into cross-ply [0/90]s and quasi-isotropic [0/45/90/-45] laminates spread uniformly with nanoparticles SiO2. The sheet surface was treated by chromic acid anodic method to achieve perfectly bonding with matrix PEEK. The prepregs were sandwiched with the Al alloy sheets. The modified diaphragm curing process was adopted to produce Al/APC-2 hybrid nanocomposite laminates. The hybrid nanocomposite laminates were a five-layer composite with two 0.55 mm thick Carbon/PEEK layers sandwiched by three 0.5 mm thick 2024-T3 Aluminum alloy sheets. The MTS 810 material testing machine was used to conduct the tension and fatigue tests. In addition, the MTS 651 environmental chamber was installed to control and keep the specific testing temperature, which was room temperature, 75¢XC, 100¢XC, 125¢XC and 150¢XC. The mechanical proper¬ties, such as ultimate tensile strength and longitudinal stiffness of hybrid cross-ply and quasi-isotropic nanocomposite laminates, were obtained from the static tensile test, and the stress-strain diagrams were plotted in the corresponding temperature. The constant stress amplitude tension-tension cyclic tests were carried out by using load-control mode at a sinusoidal loading with frequency of 5Hz and stress ratio R=0.1. The received fatigue data were plotted in normalized S-N curves at variously elevated temperature. In order to observe the failure mechanism of samples, the scanning electron microscope was used. From the summarized results, some conclusions were made. First, the slope changed at strain=0.1% in the stress-strain diagram, and led to a noticeable error between the experimental data and ones calculated according to Rule of Mixtures. Second, the Al/APC-2 cross-ply nanocomposite laminates were less resistant to fatigue than quasi-isotropic. Third, the ultimate tensile strength of both hybrid composite laminates was the lowest at 150¢XC. Fourth, the Al/APC-2 quasi-isotropic nanocomposite laminates were more resistant to the temperature effect. Finally, The mechanical proper¬ties were better for the surface treated by chromic acid anodic method than chemical etching.

Page generated in 0.0342 seconds