Granitic rocks usually exhibit strongly anisotropy due to pre-existing microcracks induced by long-term geological loadings. The understanding of anisotropy in mechanical properties of rocks is critical to a variety of rock engineering applications. In this thesis, the anisotropy of tension-related failure parameters involving tensile strength, flexural strength and Mode-I fracture toughness/fracture energy of Barre granite is investigated under a wide range of loading rates. Three sets of dynamic experimental methodologies have been developed using the modified split Hopkinson pressure bar system; Brazilian test to determine the tensile strength; semi-circular bend method to determine the flexural strength; and notched semi-circular bend method to determine the Mode-I fracture toughness and fracture energy. For all three tests, a simple quasi-static data analysis is employed to deduce the mechanical properties; the methodology is assessed critically against the isotropic Laurentian granite. It is shown that if dynamic force balance is achieved in SHPB, it is reasonable to use quasi-static formulas. The dynamic force balance is obtained by the pulse shaper technique. To study the anisotropy of these properties, rock blocks are cored and labeled using the three principal directions of Barre granite to form six sample groups. For samples in the same orientation group, the measured strengths/toughness shows clear loading rate dependence. More importantly, a loading rate dependence of the strengths/toughness anisotropy of Barre granite has been first observed: the anisotropy diminishes with the increase of loading rate. The reason for the strengths/toughness anisotropy can be understood with reference to the preferentially oriented microcracks sets; and the rate dependence of this anisotropy is qualitatively explained with the microcracks interaction. Two models abstracted from microscopic photographs are constructed to interpret the rate dependence of the fracture toughness anisotropy in terms of the crack/microcracks interaction. The experimentally observed rate dependence of the anisotropy is successfully reproduced.

Granitic rocks usually exhibit strongly anisotropy due to pre-existing microcracks induced by long-term geological loadings. The understanding of anisotropy in mechanical properties of rocks is critical to a variety of rock engineering applications. In this thesis, the anisotropy of tension-related failure parameters involving tensile strength, flexural strength and Mode-I fracture toughness/fracture energy of Barre granite is investigated under a wide range of loading rates. Three sets of dynamic experimental methodologies have been developed using the modified split Hopkinson pressure bar system; Brazilian test to determine the tensile strength; semi-circular bend method to determine the flexural strength; and notched semi-circular bend method to determine the Mode-I fracture toughness and fracture energy. For all three tests, a simple quasi-static data analysis is employed to deduce the mechanical properties; the methodology is assessed critically against the isotropic Laurentian granite. It is shown that if dynamic force balance is achieved in SHPB, it is reasonable to use quasi-static formulas. The dynamic force balance is obtained by the pulse shaper technique. To study the anisotropy of these properties, rock blocks are cored and labeled using the three principal directions of Barre granite to form six sample groups. For samples in the same orientation group, the measured strengths/toughness shows clear loading rate dependence. More importantly, a loading rate dependence of the strengths/toughness anisotropy of Barre granite has been first observed: the anisotropy diminishes with the increase of loading rate. The reason for the strengths/toughness anisotropy can be understood with reference to the preferentially oriented microcracks sets; and the rate dependence of this anisotropy is qualitatively explained with the microcracks interaction. Two models abstracted from microscopic photographs are constructed to interpret the rate dependence of the fracture toughness anisotropy in terms of the crack/microcracks interaction. The experimentally observed rate dependence of the anisotropy is successfully reproduced.

Hollow glass microspheres have been used extensively in the automotive and marine industries as an additive for reducing weight and saving material costs. They are also added to paints and other materials for their reflective properties. They have shown promise for weight critical applications, but have thus far resulted in materials with low fracture toughness and impact resistance when combined with thermosetting resins in syntactic foam. The advent of commercially available microspheres with a wide range of crushing strengths, densities and adhesive properties has given new impetus to research into syntactic foam with better fracture behaviour. Current research suggests that the beneficial effects on fracture and impact resistance gained by the addition of solid reinforcements such as rubber and ceramic particles are not seen with the addition of hollow glass microspheres. The research presented in this paper has examined the mechanisms for fracture resistance in glass microsphere filled epoxy (GMFE) syntactic foams, as well as determined the effect microsphere crushing strength and adhesion strength has on the material???s fracture toughness. The flexural properties of various GMFE have also been determined. GMFE were manufactured with varying microsphere volume fraction up to 50%, and with variances in microsphere crushing strength and adhesion. The specimens were tested for Mode I fracture toughness in a three point single edge notched bending setup as described in ASTM D5045 as well as a three point flexural setup as described in ASTM D790-3. Fracture surfaces were inspected using scanning electron microscope imaging to identify the fracture mechanisms in the presence of microspheres. Results indicate a positive effect on fracture toughness resulting from new fracture areas created as tails in the wake of the microspheres in the fracture plane. Results also indicate a negative effect on fracture toughness resulting from weak microspheres or from interfacial disbonding at the fracture plane. These two effects combine to show an increase in GMFE fracture toughness as the volume fraction of microspheres is increased to between 10 ??? 20% volume fraction (where the positive effect dominates), with a reduction in fracture toughness as microspheres are added further (where the negative effect dominates).

OBJECTIVES: To test and compare the effects of static and cyclic loading on fracture toughness (K1C) and microhardness of dental restorative CAD/CAM materials. MATERIAL AND METHODS: Five commercially available CAD/CAM restorative materials were included in this study: Lava™ Ultimate Restorative (3M ESPE), IPS Empress® CAD (Ivoclar Vivadent), Enamic® (VITA), IPS e.max® CAD (Ivoclar Vivadent), and CERASMART™ (GC Dental). Polished rectangular bars 4×2×14 mm (n=30) were prepared from mill blocks for each material. Single notch of 0.5-1 mm in depth was made on the center of one length edge. Ten specimens per group for each material were randomly selected for 1) static mode, 2) after 100k cyclic loads, and 3) after 200k cyclic loads. The survival bars after the fatigue test were then subjected to a three-point flexural test. K1C values were determined on ‘single-edge-pre-crack-beams’ (SEPB) method. In addition, random specimens after the flexural test were selected for Vickers microhardness test from each group. Additionally indentation fracture method (IF) was used to determine surface fracture toughness for e.max CAD and Empress CAD. All the results were analyzed via ANOVA with Tukey’s HSD test or least square regression model using JMP Pro 12.0. RESULTS: The mean fracture toughness (K1C) of the material tested in static mode (3.2 MPa.m1/2 for e.max CAD, 2 MPa.m1/2 for Lava Ult, 1.95 MPa.m1/2 for Empress CAD, 1.92 MPa.m1/2 for Enamic, and 1.65 MPa.m1/2 for Cerasmart). The 100k fatigue group (4.02 MPa.m1/2 for e.max CAD, 3.06 MPa.m1/2 for Cerasmart, 2.55 MPa.m1/2 for Lava Ult, 2.01 MPa.m1/2 for Enamic, 1.94 MPa.m1/2 for Empress CAD) The 200k fatigue group (3.14 MPa.m1/2 for Cerasmart, 2.83 MPa.m1/2 for Lava Ult, 2.68 MPa.m1/2 for e.max CAD, 2.01 MPa.m1/2 for Enamic, 1.72 MPa.m1/2 for Empress CAD). While there was a significant difference in the mean fracture toughness (K1C) and (VHN) after fatigue of material tested (p<0.05). CONCLUSION: The CAD/CAM materials tested exhibited a higher K1C values after cyclic loading, along with lower K1C compared to the static group. In addition, K1C values by IF method exhibit lower K1C values after fatigue that was not a good way to test the fracture toughness value. / 2018-09-28T00:00:00Z

Resumo: Neste trabalho foi feita uma análise detalhada dos micromecanismos de iniciação da fratura em amostras entalhadas para cinco aços e duas ligas de alumínio. Com esse objetivo foram obtidas curvas de transição frágil-dúctil e de tenacidade à fratura em função do raio da raiz do entalhe, e realizados ensaios interrompidos antes da fratura da amostra. Análises fractográficas e micrográficas das regiões de iniciação das fraturas foram realizadas por microscopia eletrônica de varredura. A variação dos micromecanismos de iniciação em função da variação da capacidade plástica local na raiz dos entalhes, como induzida pela variação da temperatura de ensaio e pela variação do raio da raiz, foi analisada. De um modo geral, três tipos de micromecanismos de iniciação foram observados. Um frágil, em que a iniciação envolve a nucleação de uma microtrinca à frente do entalhe e sua subsequente propagação instável. Dois dúcteis, um pela ruptura por cisalhamento localizado ao longo de linhas de cisalhamento máximo formadas na raiz do entalhe, e outro pela formação de microcavidades cuja ligação entre si e a ponta do entalhe envolve um processo misto de cisalhamento localizado e de coalescência de microcavidades. Aspectos de modelos que relacionam tenacidade com a microestrutura foram discutidos com base nos micromecanismos observados. / Abstract: In this study a detailed analysis of the micromechanisms of the fracture initiation in notched specimens was made, for five steels and two aluminum alloys. With that purpose brittle/ductile transition and fracture toughness x r1/2 curves were obtained, and interrupted tests before the fracture of the sample were used. Fractographic and micrographic analysis of the fracture initiation areas were accomplished by scanning electron microscopy. The variation of the initiation micromechanisms in function of the variation of the local plastic capacity in the notch root, as induced by the variation of the test temperature and by the variation of the notch root radius, was analyzed. In a general way, three types of initiation micromechanisms were observed. A brittle one, where the initiation involves the microcrack nucleation ahead of the notch and its subsequent unstable propagation. Two ductile, one by localized shear rupture along the maximum shear lines formed in the notch root, and other by microvoids nucleation whose link to each other and the notch tip involves a mixed process of localized shear and microcavoid coalescence. Aspects of relating models of fracture toughness with microstructure were discussed, based in the observed micromechanisms. / Orientador: Fathi Aref Ibrahim Darwish / Coorientador: Luís Rogério de Oliveira Hein / Banca: Valdir Alves Guimarães / Banca: Marcelo dos Santos Pereira / Banca: Luiz Carlos Pereira / Banca: Marcos Venicius Soares Pereira / Doutor

Carbon capture and storage (CCTS) is a transitional technology offering a nearterm method of mitigating climate change. Pipelines are considered to be the most suitable systems for CCTS; however, structural integrity of pipeline has to be guaranteed in order for this technology to become a practical technical solution. The investigation detailed here is based on a systematic experimental approach to investigate the structural integrity of API X100, X60 and X70 steels exposed in simulated flue-gas under dynamic conditions. A core of the structured experiments through some methods such as aging test, tensile properties, fracture toughness, residual stress and engineering critical assessment was accomplished in parent material and exposed samples on flue-gas. The temperature range of evaluation for tensile test covers -70C to 21C while fracture toughness was over the range -196C to 21C. Tensile properties of virgin material show that steels meet standard specification while aging samples do not show significant scatter compared with parent steels. Ovalisation of the fracture surface and splitting phenomenon was observed which is related with steel anisotropy. Fracture toughness obtained from experiment was compared with that calculate by two existing correlations. However both correlations did not predict the level of fracture toughness expected indicating the methods used in this work has limited applicability under the test conditions used here. Residual stress (RS) induced in API X100 steel by cold rolling method was characterised using two complementary techniques known as Neutron Diffraction (ND) and Incremental Hole Drilling (IHD). The RS distribution shows good agreement for both techniques used but reproducibility of them depends on their own inaccuracies. An Engineering Criticality Assessment (ECA) was performed based in Failure Assessment Diagram (FAD) approach using all the experimental data obtained by a leak-before-break method under three operational pressures. The results showed the effect on the integrity of material under the presence of a flaw length assessed. Overall, the thesis presents a combined engineering critical assessment which involved the examination of materials used to transport flue-gas and established a methodology to determine fracture toughness alongside with the FAD to assess the integrity of pipelines.

To fully exploit the strengths of La2Zr2O7 pyroclores and promote them as a next-generation thermal barrier coating (TBC), the improvements of their thermally insulating property and fracture toughness are studied in this thesis. A strong phonon scattering source, rattlers, is found in Y3+-doped La2Zr2O7 pyrochlores. Rattlers dramatically flatten k (thermal conductivity)-T curves, or even make k approach the amorphous limit. The presence of rattlers is strongly dependent on (1) oversized atomic cages that are formed in pyrochlores; and (2) the occupation of smaller guest ions in those oversized cages. To maximize the rattling effect, In3+/Sc3+ ions that are much smaller than Y3+ are introduced to the La2Zr2O7 lattice. As envisaged, the smaller ions in the oversized lattice voids make k glass-like at a much lower doping content. Nevertheless, they are still not effective in reducing the high temperature plateau kmin. Instead, oxygen vacancies are very effective in reducing kmin, because they generate an electrostatic repulsion force among cations surrounding them, resulting in stronger lattice anharmonicity and weaker bonds. The plateau kmin is reduced dramatically by the filling of the B-sites in La2Zr2O7 with a 21% larger (and 50% heavier) Ce4+ guest ion rather than a 96% heavier (but similar-sized) Hf4+ ion, suggesting that a large absolute size of substitutional atoms is more effective in reducing kmin than a heavy absolute mass. This is because: (1) kmin is proportional to (E/M)0.5 (where E is the elastic modulus and M is the average atomic mass); (2) a larger size of guest ions tends to produce a weaker ionic bond and consequently, a lower E; and (3) the changing extent of E by introducing larger guest ions is much greater than that of M induced by adding heavier ones. Lastly, the fracture toughness (KIc) has been increased by dispersing the tetragonal 3 mol% Y2O3-stabilized zirconia (t-3YSZ) particulates in the La2Zr2O7 (LZ) matrix. The tendency of the dispersive t-3YSZ second phases transforming to monoclinic (m) phases strongly depends on the volume fraction introduced. For samples made from equilibrium route, they are toughened by phase transformations within the dispersive t-3YSZ second phases and a crack shielding effect arising from the residual compressive stress within the LZ matrix. An anticipated increase of KIc from ferroelastic toughening together with the residual compressive stress toughening highlights a potential to improve coating durability by depositing t’-3YSZ/LZ composite TBCs by the non-equilibrium route.

Durante os anos desde 1910, diversos trabalhos científicos foram desenvolvidos, tornando o processo de têmpera bem estabelecido nas plantas industriais. Atualmente, existem diferentes tipos de têmpera e mais técnicas estão sendo desenvolvidas para aumentar as propriedades de componentes de aço. Um deles é o de têmpera intensiva, que pode ser considerado como um processo relativamente novo. O método de têmpera intensiva visa otimizar o processo produtivo, ao mesmo tempo em que diminui consideravelmente o custo da etapa de tratamento térmico. Além disso, atualmente o uso de soluções ambientalmente amigáveis torna este processo bem menos agressivo ao planeta. Neste trabalho realizou-se a têmpera intensiva e a têmpera convencional em corpos de prova preparados para teste de tenacidade à fratura. Trata-se, porém, de um método alternativo de teste, relativamente recente, no qual são considerados parâmetros de fratura dúctil e fratura frágil para o cálculo de K1C. Estes ensaios de tenacidade foram feitos a partir de ensaios de tração em corpos de prova com pré-trinca. Embora as tensões residuais compressivas tenham atingido os valores mais altos na têmpera intensiva, os resultados de tenacidade à fratura foram mais positivos para as amostras com têmpera convencional. A junção e aplicação desses métodos pode trazer um novo parâmetro de fabricação e análise de materiais metálicos, em especial aços-mola, que foi o objeto de estudo deste trabalho. / Since the beginning of 20th Century, several scientific works were developed and conventional quenching process became well established into the industrial area. Nowadays new quenching process were introduced increasing mechanical properties of the heat treated components. Intensive quenching is one of these process which optimize the heat treatment process using also quenchants considered nontoxic to the environment. In this work it was made comparative studies in the SAE 5160 samples which were submitted to conventional quenching and intensive quenching. Toughness fracture were evaluated using an alternative test where are analyzed ductile fracture and brittle fracture parameters to calculate KIC. In this method tensile test are performed in pre-cracked samples. Residual stresses were also measured and although intensive quenching promoted highest compressive stresses in the surface, KIC obtained in such samples presented low values compared with conventional quenching. The presented method of analysis will bring a new parameter for production and analysis for metallic materials, particularly spring steel, where compressive stress and toughness are important as properties for suspension components.

Raloxifene is an FDA-approved selective estrogen receptor modulator (SERM) that improves tissue quality by binding to collagen and increasing the bound water content in the bone matrix in a cell-independent manner. In this thesis, active tissue formation was induced by non-invasive external tibial loading in female mice and combined with raloxifene treatment to assess their combined effect on bone morphology and mechanical properties. Thermoregulation is an important factor that could have physiological consequences on research outcomes, and was introduced as an additional experimental factor in this study. We hypothesized that by removing the mild cold stress under which normal lab animals are housed, a metabolic boost would allow for further architectural and mechanical improvements as a result of the combination of tibial loading and raloxifene treatment. Ten week old female C57BL/6J mice were treated with raloxifene, underwent tibial loading to a strain level of 2050με and were housed in thermoneutral conditions (32°C) for 6 weeks. We investigated bone morphology through microcomputed tomography (μCT) and mechanical properties via four-point bending and fracture toughness testing. Results indicated a combined improvement by external loading and raloxifene on geometry, particularly in the cancellous region of the bone, and also in bone mechanics leading to greater improvements than either treatment individually. Temperature did not have a robust impact on either bone architecture or mechanical integrity.

This diploma thesis deals with short-fibre reinforced composites for dental applications. Particulate barium filler, short polyacrylonitryle fibres or short glass fibres were added to the dimethacrylate matrix to study their effect on the composite material properties. Methods used for this study were thermogravimetric analysis (TGA), differential compensation photocalorimetry (DPC), dynamic mechanical analysis (DMA), three point bending, scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). The matrix curing was defined by heat of polymerisation, degree of conversion and polymerisation rate. Composite materials were characterized by the glass transition temperature, storage moduli at 35 °C and 100 °C, elastic modulus, strength, the critical value of stress intensity factor and the critical value of energy release rate. Fracture surface investigation is also included in this thesis.