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This study reports a novel and simple technique for successfully coating multi-walled carbon nanotubes (MWCNTs) on to the surface of carbon fibre (CF) fabric for the production of multi-scale CF-epoxy composites. Initially, epoxy composites with multi-scale reinforcement were produced by resin infusion (RI) using woven CF fabric coated with a dispersion of 1 wt. % MWCNTs in an epoxy binder of low molar mass. The effects of this reinforcement on the CF-epoxy interface with MWCNTs was studied in mode I and mode II interlaminar fracture toughness (ILFT) using double-cantilever beam (DCB) and 4 point end-notch flexure (4ENF) tests, respectively. Relative to an equivalent composite reinforced with non-coated CF reinforcement, the binder/MWCNTs coating increased significantly the ILFT of the CF-epoxy composite; in mode I by 105% and in mode II by 50%. This increase in ILFT was attributed to two main effects: Firstly, the binder alone (without MWCNTs), which has a much lower glass transition temperature (Tg) than that the matrix (45 vs. 140 °C), hindered crack propagation and increased the ILFT of the epoxy matrix by 25% for mode I and 15% for mode II; Secondly, the energy absorbing mechanisms of MWCNTs during fracture particularly pull-out and crack bridging. However the Tg of the matrix epoxy of the multi-scale composites was reduced to 118 °C compared to 140 °C, for the unmodified composite, due to phase mixing with the low Tg binder. For RI processing, the CF volume fraction of the composites prepared using coated CF was ≈50% compare to at ≈55% for the composite with non-coated CF. Curing agents were added to the binder, which not only increased the Tg from ≈50 °C to ≈100 °C, but also increased the Tg of the matrix epoxy of the multi-scale composites to 154 °C. Relative to an equivalent composite reinforced with non-coated CF reinforcement, the curable-binder/MWCNTs coating increased the ILFT of the CF-epoxy composite; in mode I by 120% and in mode II by 90%. A hybrid RI-hot press (HP) process was used to prepare CF-epoxy composites from coated fabrics with CF volume fractions of ≈55%. The damping curves for the HP-composites consisted of a β-peak, due to the formation of a third mixed phase, in addition to a γ-peak (assigned to the Tg of the binder) and an α-peak (assigned to the Tg of matrix epoxy). The β-peak, and the uniformly distributed nodular particles observed on the fracture surface of the matrix, by SEM, for HP-composites, are indicative of the formation of mixed-phase particles due to reaction induced phase separation (RIPS). Relative to an equivalent RI-composite, the curable-binder/MWCNTs treatment increased the ILFT of the CF-epoxy multi-scale composite; in mode I by 134% and in mode II by 15% for HP-composites. Impact test results showed that HP-composites absorbed more energy, due to CF fracture, compared to equivalent RI composites, which showed larger delamination areas after 5 J and 10 J impact. The out-of-plane electrical conductivity and thermal conductivity of the HP-composite with CF coated with curable-binder/MWCNTs was increased by ≈38% and ≈50%, respectively, compared to the composite with non-coated CF, indicating formation of MWCNTs networks in the matrix rich areas of the multi-scale composite.

The main aim of this work is to examine fracture toughness improvement mechanisms of a composite material containing tough interlayers modified with large thermoplastic particles. ¶ Various vinyl-ester (VE)/ poly(acrylonitrile-butadiene-styrene) (ABS) blends were used for the interlayer-toughening of a VE/glass fibre composite to increase delamination resistance of the material under mode I and mode II loading. Dry ABS powder was mixed with the liquid resin in four different weight ratios: 3.5, 7, 11 and 15 phr (parts per hundred parts of resin) while the layer thickness was varied from 150 to 500um. Firstly, the tensile and mode I fracture toughness properties of the VE/ABS blends were assessed, and, by using the Raman Spectroscopy technique, a chemical reaction was discovered which occurred during ABS/VE mixing. This reaction consisted of butadiene dissolution from the ABS particles into the VE. Also, butadiene saturation within the VE was achieved at a composition of around 7% ABS particle content. Both mode I and mode II fracture toughness of the composite were significantly improved with the application of interlayers. Mode I fracture toughness GIc was found to be a function of interlayer thickness and ABS particle content variations, with the latter dominating GIc after the saturation point. Mode II fracture toughness was found to be independent of interlayer thickness and only moderately influenced by particle content. The toughening mechanisms that were the most influential within this interlayered material were plastic deformation and micro-cracking of the layer materials. Evidence of both mechanisms was found using optical and scanning electron microscopy (SEM). ¶ A numerical analysis was conducted, using the experimental results from this study, to further explain the basic toughening mechanisms and fracture behaviour in the materials. The aim of the analysis was to examine the influence of the particles on the plastic zone size that develops in front of the crack tip, and the interaction between the particles and the crack tip. For this purpose FEA elastic-plastic crack propagation models were employed. Good agreement with the experimental data was found.

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No description available.

Bioactive glasses are a type of ceramic material designed to be used as bioresorbable therapeutic bone implants. Thermal treatment of bioactive glass ceramics dictates many important features such as microstructure, degree of crystallinity, mechanical properties, and mineralization. This study investigates the effects of temperature, time, and heating rates on the crystallization kinetics of melt cast bioactive glass 45S5. Bulk crystallization (three dimensional crystallite formation) was found to always occur in bulk bioactive glass 45S5 irrespective of the processing conditions. A comparative study of crack paths in amorphous and crystalline phases of bioactive glass 45S5 revealed crack deflections and higher fracture resistance in partially crystallized bioactive glass. Such toughening is likely attributed to different crystallographic orientations of crystals or residual thermal mismatch strains. Furthermore, in vitro immersion testing of partially crystalline glass ceramic revealed higher adhesion capabilities of the mineralized layer formed on amorphous regions as compared to its crystalline counterpart. / Materials Engineering

It is important to know the lifespan of a component, thus services can be planed. At Siemens Industrial Turbomachinery AB (SIT AB) develop and produce gas and steam turbines, the turbines are heavily strained by thermal and centrifugal forces during their life span which lead to cracking. Today there is no good crack propagation method for materials with large amount of plastic deformation and creep. At SIT a new method, ΔKBDCPP, has been developed that takes these phenomenon in consideration. It is assumed that the whole model has plastic material properties except circular elements at the crack front which have elastic properties. The new method is reviewed by doing simulations on a a specimen model in Franc3D together with the FE program Abaqus. There have been conducted thermo-mechanical fatigue (TMF) tests and 2D simulations on specimen to measure the crack propagation. The TMF tests where immitaded in new simulations with the method ΔKBDCPP. Forces, creep times, cycles and material data where emulated in the model and then simulated. The number of cycles per crack length for the isothermal simulations became higher then for the TMF tests. This is a expected result because the conditions are optimal during simulations, which they may not be during experimental test. The result of ΔKBDCPP are closer to the TMF test results then the 2D simulated ΔKeffective, another crack propagation calculation method. Additionally, out-of-phase (OP) simulations where carried out, in OP the maximum temperature and maximum stress do not coincide. When the temperature is at max the component is held in the minimum stress. For OP simulations the results became irregular, for one of the simulations the number of cycles per crack length became lower for the simulated specimen than for the TMF test, and contrariwise for the other OP simulation. However, it was concluded that the later was correct because the majority of the simulations, and all the isothermal simulations, gave this result. it also was the result for the isothermal simulations. One OP simulation was compared to a 2D simulation and here the method of ΔKBDCPP was also more accurate to the TMF tests. The method of ΔKBDCPP seem to function well however, the solving time for models with creep is long. A model with a small crack and creep is time consuming to simulate, which is a disadvantages. / Det är viktigt att veta livslängden på en komponent, då kan det planeras för en service. På Siemens Industrial Turbomachinery AB (SIT AB) utvecklas och produceras det gas- och ångturbiner, turbiner utsätts för höga temperaturer och krafter under dess livstid vilket resulterar i sprickor. Idag finns det inte en bra sprickpropageringsteori för material i ett stort plasticerat tillstånd och kryp, SIT har därför tagit fram en ny metod som ska ta hänsyn till dessa parametrar. I den nya beräkningsmetoden, ΔKBDCPP, antas det att hela modellen har en plastisk materialmodell förutom ett antal ringelement vid sprickspetsen som antas ha en elastisk materialmodell. Den nya metoden undersöks genom att provstavsmodell simuleras i programmet Franc3D tillsammans med Abaqus. Det har tidigare gjorts termodynamiska utmattningsprov (TMF), samt simuleringar i 2D, på provstavar för att mäta sprickpropageringen. Därför imiterades dessa TMF prov i nya simuleringar med metoden för ΔKBDCPP. Krafter, hålltider, cykler och materialdata efterliknades i modellen och sedan kördes simuleringarna. För de isoterma körningarna blev resultatet att antalet cykler per spricklängd är högre för simulerade värden än för TMF prover, vilket var väntat. Vid simulationer är det optimala förhållanden utan avvikelser, vilket kan finnas vid experimentella tester. De simulerade värdena för ΔKBDCPP stämmer bättre överens med TMF proverna än de 2D simulerade resultaten för ΔKeffective, en annan beräkningsmodell för sprickpropagering. Även out-of-phase (OP) simuleringar genomfördes, vid OP sker inte temperatur max och spännings max samtidigt. När det är max temperatur hålls komponenten i den minimala spänningen. För OP simuleringarna blev resultatet annorlunda, ena körningen blev antalet cykler per spricklängd lägre för de simulerade värden än för TMF prover och i den andra blev det tvärt om. Dock drogs slutsatsen att den senare stämde då majoriteten av körningarna, och alla isoterma körningar, gav det resultatet. En OP körning jämfördes med en 2D körning och även där var metoden för ΔKBDCPP närmare TMF provsresultatet. ΔKBDCPP metoden verkar fungera bra, dock är simuleringstiden för att lösa körningar med kryp väldigt lång. En modell med en liten spricka och kryp är mycket tidskrävande att lösa, vilket är en nackdel.

Made available in DSpace on 2014-10-09T12:42:56Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:25Z (GMT). No. of bitstreams: 1 05386.pdf: 22752594 bytes, checksum: 053f5623f341b18a8d0324e4a54de6de (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

abstract: Laboratory assessment of crack resistance and propagation in asphalt concrete is a difficult task that challenges researchers and engineers. Several fracture mechanics based laboratory tests currently exist; however, these tests and subsequent analysis methods rely on elastic behavior assumptions and do not consider the time-dependent nature of asphalt concrete. The C* Line Integral test has shown promise to capture crack resistance and propagation within asphalt concrete. In addition, the fracture mechanics based C* parameter considers the time-dependent creep behavior of the materials. However, previous research was limited and lacked standardized test procedure and detailed data analysis methods were not fully presented. This dissertation describes the development and refinement of the C* Fracture Test (CFT) based on concepts of the C* line integral test. The CFT is a promising test to assess crack propagation and fracture resistance especially in modified mixtures. A detailed CFT test protocol was developed based on a laboratory study of different specimen sizes and test conditions. CFT numerical simulations agreed with laboratory results and indicated that the maximum horizontal tensile stress (Mode I) occurs at the crack tip but diminishes at longer crack lengths when shear stress (Mode II) becomes present. Using CFT test results and the principles of time-temperature superposition, a crack growth rate master curve was successfully developed to describe crack growth over a range of test temperatures. This master curve can be applied to pavement design and analysis to describe crack propagation as a function of traffic conditions and pavement temperatures. Several plant mixtures were subjected to the CFT and results showed differences in resistance to crack propagation, especially when comparing an asphalt rubber mixture to a conventional one. Results indicated that crack propagation is ideally captured within a given range of dynamic modulus values. Crack growth rates and C* prediction models were successfully developed for all unmodified mixtures in the CFT database. These models can be used to predict creep crack propagation and the C* parameter when laboratory testing is not feasible. Finally, a conceptual approach to incorporate crack growth rate and the C* parameter into pavement design and analysis was presented. / Dissertation/Thesis / Ph.D. Civil and Environmental Engineering 2013

Made available in DSpace on 2014-10-09T12:42:56Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:25Z (GMT). No. of bitstreams: 1 05386.pdf: 22752594 bytes, checksum: 053f5623f341b18a8d0324e4a54de6de (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP