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Plastics fuel tanks have been used successfully abroad ; metal counterparts are still predominant in this country plastics tanks have to satisfy stringent performance regulations : low temperature impact tests ; permeability ; and fire resistance. Blow moulded high density polyethylene (HDPE) fuel tanks have superior strength to mass ratio compared with metal equivalents (the density of steel is about 8000 kg/m3 compared with HDPE, which has a density of under 1000 kg/m3 ). HDPE will tend to drip in a fire situation, thus reducing explosion risk. HDPE is the chosen material because it possesses inherent properties suitable for the blow moulding process : it has a high viscosity at low stresses ; and is highly inert. Rotational moulded HDPE fuel tanks can also be considered. However, these are shown to have inferior properties when compared with blow moulded tanks ; attraction of rotational moulding is the cheapness of equipment. Petrol immersion was found to enhance impact properties of HDPE, although yield stresses were lowered slightly. The thickness distributions of blow moulded fuel tanks were found to vary ; this is because of the present difficulty of predicting parison behaviour with respect to time. Thickness is important because of impact strength and permeation considerations. Impact properties of fuel tanks were assessed ; peak force of impact was found to be heavily dependent on thickness (raised to the power 1.1) and temperature of mould in the blow moulding process (a low mould temperature led to inferior properties). Pinch-offs were found to be particularly detrimental to impact properties. Cooling behaviour was investigated. With the aid of a cooling model for blow mouldings, it was found that a warm mould (40·C) could be used with internal air circulation to obtain a cooling time the same as that with a cold mould and no air circulation. Thus optimising mechanical strength and maintaining economic viability. Welding of injection moulded fittings to the main blow moulded body of the fuel tank was found to be faulty, in all of the tanks examined ; many weld failures have been reported in use. This work determines optimum welding conditions for HDPE grades, these are Rigidex H060-45P and Lupolen 426l-A.

Indiana University-Purdue University Indianapolis (IUPUI) / Since the conception of three dimensional (3D) printing circa 40 years ago, there has been the proliferation of several additive manufacturing (AM) technologies that enable its use in everyday applications such as aerospace, medicine, military, oil and gas and infrastructure. In order to improve its applicability and growth, 3D printed materials are subjected to the same or even higher levels of scrutiny for its mechanical behavior as its conventionally manufactured counterpart. One of the most important mechanical properties is toughness or the ability of a material to undergo large strain prior to fracture when loaded. The toughness of a material can be correlated to its impact energy or the increase in internal energy due to impact. In this study, the impact properties, including the toughness of 3D printed 15-5 stainless steel were investigated at low temperature (77 K), room temperature (298 K) and high temperature (723 K) using experimental and numerical modeling of the Charpy impact test. In addition, ballistic impact simulations were performed to determine the applicability of 3D printed 15-5 stainless steel in the defense industry. The 15-5 stainless steel specimens were printed (horizontal-build) using the direct metal laser sintering (DMLS) technique, cooled or heated to the specified temperature, then tested in accordance with the ASTM E23-2016b [1] standard. The Johnson-Cook (J-C) phenomenological material model and fracture parameters were used in the numerical modeling. The cross-sectional microstructures of surfaces and impact energies of the Charpy impact test were examined. For the ballistic impact simulations, a 3D printed 15-5 stainless steel typical plate was investigated at the same temperatures as the Charpy impact test. A typical missile using the J-C properties at room temperature (298 K) was assigned an initial velocity of 300 ms-1 for each plate temperature. The fracture surface investigation (microsurface analysis as well as visual inspection) and impact energy values of the Charpy impact test show that the 3D printed 15-5 stainless steel exhibited brittle behavior at low and room temperatures, but transitioned into a more ductile behavior at high temperature. At 77 K, 298 K and 723 K, the experimental Charpy impact test results were 0.00 J/cm2, 6.78±4.07 J/cm2 and 50.84±3.39 J/cm2 respectively; whereas the simulated impact energy were 1.05 J/cm2, 10.46 J/cm2 and 47.07 J/cm2 respectively. Hence, the impact energy for the experimental and numerical simulations were in good agreement; especially at higher temperatures. Consistent with the results from the Charpy impact test, the ballistic impact simulations show an increase in the impact energy, elastic plastic strain and deflection of the plate with an increase in temperature indicating brittle-to-ductile behavior. The high exit velocity at low and room temperature may not make the plate attractive in defense in its current configuration; however, at the high temperature, the exit velocity reduction was significant.

The aim of the work reported here was to determine the influence of an amine curing agent, and postcure cycle on the mechanical and thermal properties of diglycidyl ether of bisphenol A (DGEBA) epoxy resin. The results of this initial study were then used as the basis for selecting material to obtain optimum toughness in epoxy/glass fibre systems. These basic materials were further used to make comparisons with the properties of modified resin systems which contained commercial elastomers. Differential Scanning Calorimetry (DSC), Dynamic Mechanical Thermal Analysis (DMTA), Fourier Transform Infrared Spectroscopy (FTIR), flexural and interlaminar shear tests, Instrumented Falling Weight Impact (IFWI), visual observation, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) were all used to investigate various properties and the structures which gave rise to them. The properties of cured products were found to be affected by the amounts of curing agent, curing times and temperatures, and the structure of the elastomers. Not surprisingly the maximum thermal and mechanical properties tended to be found in the stoichiometric (standard) mix systems. However, postcuring at higher than room temperature, which was used as the basic curing temperature, led to more conversion. This effect improved the thermal and mechanical properties of both the unmodified and modified resin systems. The maximum flexural strength of 104 MPa of the unreinforced resins was found in the stoichiometric mix ratio after postcure at 150°C for 4 hr. However, the maximum flexural modulus and glass transition temperature (Tg) were found after postcuring at the same temperature for 48 hr. This was believed to be due to increased crosslinking, but unfortunately the longer curing time led to degradation of the resins. In the systems modified with -20 phr of polyetheramine elastomers, the one modified with the lowest molecular weight (2000) was found to have the highest flexural strength (85.8 MPa) and modulus (2.5 GPa). The impact properties of all the composites with modified resin matrices were found to be higher than the unmodified resin matrix composites. The best impact properties were, however, obtained with the elastomer modifier with a molecular weight of 4000. The impact energy at maximum force increased from 11.9 to 16.4 J, and energy at failure increased from 18.7 to 21.6 J. This increase in impact properties was due to the increase in areas of phase separated elastomer particles over similar systems with lower molecular weight modifier.

The thesis describes effect of long-time ageing on the microstructure and properties of the Eurofer´97 steel. The ferritic-martensitic reduced activation steel Eurofer´97 is candidate structural material for in-core components of proposed fusion reactors. Thesis is focused on examination and description of brittle-fracture behaviour of the steel. Properties of the steel were investigated in as-received state and state after long-time ageing. Detailed microstructure studies were carried out by means of optical and electron microscopy and also by means of quantitative electron microscopy. Mechanical properties were evaluated also in both states by means of hardness tetsing, tensile testing and Charpy impact testing. Fractography analysis of fracture surfaces was carried out on samples after Charpy impact testing.

Wood is a widely used construction material that has many advantageous properties, and some drawbacks. These drawbacks are mainly associated with the porous vascular structure of wood that makes it a high water-absorbent material. In addition, wood’s properties alter substantially with respect to the moisture content. Amongst the treatment techniques that limit the water uptake capacity of wood, vacuum-aided impregnation has exhibited promising results. However, little research has explored the effect of key parameters (such as the vacuum pressure) on the effectiveness of the impregnation. This study aims to optimize the performance of SiO2 impregnation of spruce wood under vacuum pressures. The main objective of this research is to overcome wood’s weakness by reducing its water uptake capacity through a vacuum-aided impregnation technique and study its effect on the physico-mechanical properties of wood under dry and saturated conditions. The study was conducted in two parts. In the first part, wood samples underwent impregnation under atmospheric and three vacuum pressures. Density measurements, water uptake tests, microscopy examination, thermogravimetric analysis, and dynamic mechanical analysis were conducted on non-treated and SiO2-treated samples. Quantitative and qualitative analyses demonstrated that SiO2 impregnation performed under -90 kPa was able to effectively enhance the wood’s properties compared to the other conditions. The SiO2 impregnation under high vacuum pressure demonstrated an effective increase in the density of the wood and achieved a significant reduction in the water uptake capacity. The analysis of the wood’s viscoelastic properties revealed that SiO2 impregnation under atmospheric and vacuum conditions triggered two different reinforcing mechanisms: a solid film, causing stick-slip oscillation, and particle diffusion, causing particle-particle and particle-lumen wall friction, respectively. For the second part, characterization methods such as Impact test, DMA, SEM, EDS, Porosity, and SAXS tests were conducted on non-treated and -90 kPa treated spruce wood samples in dry, saturated, and submerged states in order to reveal the synergistic effect of the SiO2 impregnation pressure and water uptake on the wood’s properties. The results showed that high vacuum impregnation pressure has a significant positive reinforcing effect on the wood’s properties. It increased the impact resistance of wood in dry and saturated conditions. A high vacuum impregnation was able to overcome the softening effect of water and caused a significant increase in the Storage modulus by strengthening the wood’s vascular structure, which accordingly increased the wood’s capacity to absorb energy. High vacuum impregnation was also able to counteract the plasticizing effect of water and significantly increased the Loss modulus by increasing the internal friction in the wood with the diffusion of the nanoparticles in the wood’s cell walls and vascular structure. This phenomenon increased the wood's capacity to absorb and dissipate energy under dry and submerged conditions.

Este trabalho consiste no estudo das propriedades mecânicas de tração e impacto do aço Hadfield refinado com Hf em relação ao aço Hadfield sem refino. Foram realizadas simulações no software Thermo-Calc para caracterizar o caminho de solidificação e a evolução microestrutural do aço Hadfield (composição química de 13% de Mn, 1,2% de C e 0,65% de Si). Foram fundidos os corpos de prova de aço Hadfield sem refino e refinado pela adição de Hf, ambos com a composição química de acordo com a norma ASTM A128 - grau B2. Os corpos de prova foram submetidos ao tratamento térmico de solubilização à temperatura de 1120oC por 10 horas. A caracterização macroestrutural mostrou que o aço Hadfield com adição de Hf apresenta tamanho do grão austenítico cinco vezes menor (600 µm) do que o aço Hadfield sem refino (de 3000 µm para 600 µm), sendo que este resultado foi confirmado pela técnica de EBSD (Electron backscatter diffraction). Os resultados do ensaio de tração dos corpos de prova para as duas condições mostraram que as propriedades de limite de escoamento (6%), tenacidade (88%), resistência à tração (37%), e do coeficiente de encruamento (30%) do aço Hadfield refinado aumentaram em relação ao aço Hadfield sem refino. A energia absorvida no impacto aumentou de 156 J/cm2 para 179 J/cm2 com o refino do tamanho de grão austenítico. A lei de Hall-Petch foi utilizada para explicar o efeito do refino de grão no limite de escoamento, mas não pode ser usada para explicar o aumento na resistência a tração, tenacidade, e as mudanças no coeficiente de encruamento. A caracterização microestrutural das amostras rompidas em tração e impacto mostrou que a fração de maclas aumentou em 46% (em tração) e 45% (no impacto) para o aço Hadfield refinado em comparação com o aço Hadfield sem refino. Os resultados da caracterização microestrutural dos corpos de prova rompidos no ensaio de tração e impacto indicam que o mecanismo de deformação plástica por maclação foi mais atuante com o refino do grão austenítico. / The tensile and impact properties of Hf-refined Hadfield steel were compared to the properties of non-refined Hadfield steel. Simulations in Thermo-Calc software were made in order to study the solidification and microstructural evolution of a Hadfield steel (13% Mn, 1.2% C and 0.65% Si). Samples of non-refined and refined Hadfield steel (with addition of 0.1% of H), both with chemical composition as described in ASTM A128- grade B2, were cast and subjected to a solution heat treatment at 1100oC for 10 hours, followed by water quenching. Macrostructural characterization showed that the refined Hadfield steel featured an austenitic grain size equal to 600 ?m, five times smaller than the grain size of the non-refined Hadfield steel (3000 µm). These results were confirmed by EBSD (Electron backscatter diffraction) analysis. The tensile test results showed an increase in the values of the yield stress (6%), the fracture toughness (88%), the tensile strength (37%) and the strain hardening coefficient (30%) with the reduction on the austenitic grain size from 3000 µm to 600 µm. Additionally, the value of the absorbed energy of the impact test was improved from 156 J/cm2 to 179J/cm2 with reduction on the grain size. The Hall-Petch law was used to explain the small increase of 8% in the value of the yield stress with the grain refinement, but this law could not be used to explain the increase in the values of the fracture toughness, the tensile strength and the strain hardening coefficient. The microstructural characterization of the fractured test-pieces after tensile and impact testing showed that the values of the fraction of mechanical twins (definer) in the plastically deformed microstructure near the fracture surfaces of the refined condition increased by 45% when compared to the non-refined condition. These results indicated that the austenitic grain refinement of the Hadfield steel changed the plastic deformation mechanism, favoring the activation of the plastic deformation by twinning mechanism and, therefore, increasing the values of the fracture toughness (~88%), the ultimate tensile strength (~30%), the strain-hardening coefficient (~30%) and the absorbed energy during Charpy-test (~15%).

Este trabalho consiste no estudo das propriedades mecânicas de tração e impacto do aço Hadfield refinado com Hf em relação ao aço Hadfield sem refino. Foram realizadas simulações no software Thermo-Calc para caracterizar o caminho de solidificação e a evolução microestrutural do aço Hadfield (composição química de 13% de Mn, 1,2% de C e 0,65% de Si). Foram fundidos os corpos de prova de aço Hadfield sem refino e refinado pela adição de Hf, ambos com a composição química de acordo com a norma ASTM A128 - grau B2. Os corpos de prova foram submetidos ao tratamento térmico de solubilização à temperatura de 1120oC por 10 horas. A caracterização macroestrutural mostrou que o aço Hadfield com adição de Hf apresenta tamanho do grão austenítico cinco vezes menor (600 µm) do que o aço Hadfield sem refino (de 3000 µm para 600 µm), sendo que este resultado foi confirmado pela técnica de EBSD (Electron backscatter diffraction). Os resultados do ensaio de tração dos corpos de prova para as duas condições mostraram que as propriedades de limite de escoamento (6%), tenacidade (88%), resistência à tração (37%), e do coeficiente de encruamento (30%) do aço Hadfield refinado aumentaram em relação ao aço Hadfield sem refino. A energia absorvida no impacto aumentou de 156 J/cm2 para 179 J/cm2 com o refino do tamanho de grão austenítico. A lei de Hall-Petch foi utilizada para explicar o efeito do refino de grão no limite de escoamento, mas não pode ser usada para explicar o aumento na resistência a tração, tenacidade, e as mudanças no coeficiente de encruamento. A caracterização microestrutural das amostras rompidas em tração e impacto mostrou que a fração de maclas aumentou em 46% (em tração) e 45% (no impacto) para o aço Hadfield refinado em comparação com o aço Hadfield sem refino. Os resultados da caracterização microestrutural dos corpos de prova rompidos no ensaio de tração e impacto indicam que o mecanismo de deformação plástica por maclação foi mais atuante com o refino do grão austenítico. / The tensile and impact properties of Hf-refined Hadfield steel were compared to the properties of non-refined Hadfield steel. Simulations in Thermo-Calc software were made in order to study the solidification and microstructural evolution of a Hadfield steel (13% Mn, 1.2% C and 0.65% Si). Samples of non-refined and refined Hadfield steel (with addition of 0.1% of H), both with chemical composition as described in ASTM A128- grade B2, were cast and subjected to a solution heat treatment at 1100oC for 10 hours, followed by water quenching. Macrostructural characterization showed that the refined Hadfield steel featured an austenitic grain size equal to 600 ?m, five times smaller than the grain size of the non-refined Hadfield steel (3000 µm). These results were confirmed by EBSD (Electron backscatter diffraction) analysis. The tensile test results showed an increase in the values of the yield stress (6%), the fracture toughness (88%), the tensile strength (37%) and the strain hardening coefficient (30%) with the reduction on the austenitic grain size from 3000 µm to 600 µm. Additionally, the value of the absorbed energy of the impact test was improved from 156 J/cm2 to 179J/cm2 with reduction on the grain size. The Hall-Petch law was used to explain the small increase of 8% in the value of the yield stress with the grain refinement, but this law could not be used to explain the increase in the values of the fracture toughness, the tensile strength and the strain hardening coefficient. The microstructural characterization of the fractured test-pieces after tensile and impact testing showed that the values of the fraction of mechanical twins (definer) in the plastically deformed microstructure near the fracture surfaces of the refined condition increased by 45% when compared to the non-refined condition. These results indicated that the austenitic grain refinement of the Hadfield steel changed the plastic deformation mechanism, favoring the activation of the plastic deformation by twinning mechanism and, therefore, increasing the values of the fracture toughness (~88%), the ultimate tensile strength (~30%), the strain-hardening coefficient (~30%) and the absorbed energy during Charpy-test (~15%).