Over the past decades, bulk metallic glasses (BMGs) have attracted extensive interests because of their unique properties such as good corrosion resistance, large elastic limit, as well as high strength and hardness. However, with the advent of micro-electro-mechanical systems (MEMS) and other microscaled devices, the fundamental properties of micrometer-sized BMGs have become increasingly more important. Thus, in this study, a methodology for performing uniaxial compression tests on BMGs having micron-sized dimensions is presented. Micropillar with diameters of 3.8, 1 and 0.7 £gm are fabricated successfully from the Mg65Cu25Gd10 and Zr63.8Ni16.2Cu15Al5 BMGs using focus ion beam, and then tested in microcompression at room temperature and strain rates from 1 x 10-4 to 1 x 10-2 s-1. Microcompression tests on the Mg- and Zr-based BMG pillar samples have shown an obvious sample size effect, with the yield strength increasing with decreasing sample diameter. The strength increase can be rationalized by the Weibull statistics for brittle materials, and the Weibull moduli of the Mg- and Zr-based BMGs are estimated to be about 35 and 60, respectively. The higher Weibull modulus of the Zr-based BMG is consistent with the more ductile nature of this system. In additions, high temperature microcompression tests are performed to investigate the deformation behavior of micron-sized Au49Ag5.5Pd2.3Cu26.9Si16.3 BMG pillar samples from room to their glass transition temperature (~400 K). For the 1 £gm Au-based BMG pillars, a transition from inhomogeneous flow to homogeneous flow is clearly observed at or near the glass transition temperature. Specifically, the flow transition temperature is about 393 K atthe strain rate of 1 x 10-2 s-1. For the 3.8 £gm Au-based BMG pillars, in order to investigate the homogeneous deformation behavior, microcompression tests are performed at 395.9-401.2 K. The strength is observed to decrease with increasing temperature and decreasing strain rate. Plastic flow behavior can be described by a shear transition zone model. The activation energy and the size of the basic flow unit are deduced and compared favorably with the theory.

Bitumen acts as a binding agent in asphalt mixtures where it binds the aggregates together. It is known for its potential to heal small cracks and recover its mechanical properties under the right conditions. Though this self-healing property is known, there is currently a lack of knowledge about the mechanisms that drive the process. To optimize the use of this material for pavement design, the healing ability should be better understood and controlled. In this work, it is investigated how neutron imaging can be used to increase the understanding of the mechanisms behind the self-healing in bitumen. As a first step, the sample size requirement set by the measurement technique was determined. In order to detect micro cracks in bitumen by using this technique, the sample must be sufficiently small to allow neutron transmission. On the other hand, too small samples would complicate the structural analysis of the material since less information would be possible to obtain. Bitumen with different dimensions were scanned with neutrons to determine the maximum sample thickness. This work was followed by evaluating the healing capability of fractured bitumen and mastic samples, by using time series neutron tomography. The studied samples had a varying combination of hydrated lime (HL) filler concentration, crack volume, and contact area between the broken pieces. The data acquired from the time series tomography scans was analyzed using a three-dimensional analysis procedure including denoising, segmentation and volume measurements. From the volumetric analysis, it appeared that the initial crack size and crack shape have a large impact on the healing rate. It was found that bitumen, mastic with 20%, and 30% filler content had a similar healing behavior for relatively small crack volumes. When increasing the content of HL in the mastic, the healing rate decreases exponentially, with a drastic decrease after reaching a filler content of about 30%. / Bitumen fungerar som bindemedel i asfaltsblandningar där det binder ihop stenaggregaten. Bitumen är känd för sin förmåga att läka små sprickor och återfå sina mekaniska egenskaper under rätt förutsättningar. Trots att den självläkande egenskapen är välkänd, råder det idag en brist på kunskap om de mekanismer som ligger bakom denna process. För att optimera användandet av bitumen för vägbeläggningar behövs en bättre förståelse kring denna läkande egenskap. I detta projekt undersöks det hur neutronavbildning kan användas för att öka förståelsen kring de mekanismer som ligger bakom den självläkande egenskapen hos bitumen. Som ett första steg bestämdes provstorlekskravet för denna analysteknik. För att möjliggöra detekteringen av små sprickor i bitumen genom att använda denna teknik måste provmaterialet vara tillräckligt tunt för att neutronerna ska kunna transmitteras genom materialet. Allt för små provstorlekar skulle, å andra sidan, försvåra analysen av materialets struktur då informationen man kan erhålla blir mer begränsad. Bitumen med olika provstorlekar skannades med neutroner för att bestämma den maximala provtjockleken. Därefter analyserades den självläkande förmågan hos brutna bitumen- och bitumenmastixprover med tidsserie neutrontomografi. Prover med olika mängder av kalciumhydroxidfiller i bitumenblandningen, olika storlek på sprickvolymen och kontaktytan mellan de brutna provdelarna studerades. Data erhållna från experimenten användes för att göra en 3-dimensionell analys som inkluderade brusreducering av bilder, segmentering och volymmätningar. Från volymanalyserna konstaterades det att den initiala sprickstorleken och sprickformen har en stor inverkan på läkningstakten. Bitumen, mastix med 20%, och 30% filler-additiv uppvisade liknande läkningsegenskaper för relativt små sprickstorlekar. Vid en ökning av mängden filler material i mastixen minskar läkningstakten exponentiellt, med en drastisk minskning när man passerar en filler-koncentration på runt 30%. / <p>QC 210303</p>