Recent development of additive manufacturing technologies has led to lack of information on the base materials being used. A need arises to know the mechanical behaviors of these base materials so that it can be linked with macroscopic mechanical behaviors of 3D network structures manufactured from the 3D printer. The main objectives of my research are to characterize properties of a material for an additive manufacturing method (commonly referred to as 3D printing). Also, to model viscoelastic properties of Procast material that is obtained from 3D printer. For this purpose, a 3D CAD model is made using ProE and 3D printed using Projet HD3500. Series of uniaxial tensile tests, creep tests, and dynamic mechanical analysis are carried out to obtained viscoelastic behavior of Procast. Test data is fitted using various linear and nonlinear viscoelastic models. Validation of model is also carried out using tensile test data and frequency sweep data. Various other mechanical characterization have also been carried out in order to find density, melting temperature, glass transition temperature, and strain rate dependent elastic modulus of Procast material. It can be concluded that melting temperature of Procast material is around 337°C, the elastic modulus is around 0.7-0.8 GPa, and yield stress is around 16-19 MPa.

A obtenção de resultados de fluência em geossintéticos (isócronas e curva de ruptura por fluência) requer longo tempo de observação e rigoroso controle laboratorial. Dessa forma, muitos produtos disponíveis no mercado brasileiro não foram ensaiados quanto a este fenômeno dificultando sobremaneira a elaboração de projetos mais seguros e econômicos. Há, portanto, a necessidade de estudos não só do fenômeno da fluência em si, mas também de métodos de ensaio que facilitem e acelerem a obtenção das curvas de fluência. Este trabalho apresenta um estudo da fluência de dois geotêxteis não tecidos, um de polipropileno e outro de poliéster, através de ensaios acelerados, utilizando-se o processo denominado Stepped Isothermal Method (SIM). Os valores obtidos pelo método SIM foram comparados aos valores obtidos nos ensaios convencionais, realizados segundo a norma ISO 13431. Os resultados experimentais indicam que os ensaios acelerados, utilizando o método SIM, foram capazes de simular o fenômeno da fluência com boa precisão e, portanto, podem trazer uma grande economia de tempo, além de facilitar e agilizar a caracterização da fluência de geossintéticos. / Creep tests are time consuming and require rigorous laboratory testing control. Because of that many products commercially available in Brazil were not tested regarding this phenomenon. The absence of creep data is an obstacle to the design soil reinforced structures. It is therefore required continuous research effort not only to elucidate creep phenomenon but also to help in the development of test methods that ease and speed up the obtaining of creep curves. This paper presents a creep study carried out on two non-woven geotextiles (PP and PET) using temperature accelerated creep test, namely the Stepped Isothermal Method (SIM). The values obtained using the SIM method were compared to the ones obtained using conventional creep tests following the ISO 13431. The experimental results indicate that the accelerated creep tests, using the SIM method, were capable of simulating the creep phenomenon with good accuracy and, hence, they can bring a great deal of time saving to the characterization of creep in geosynthetics.

A obtenção de resultados de fluência em geossintéticos (isócronas e curva de ruptura por fluência) requer longo tempo de observação e rigoroso controle laboratorial. Dessa forma, muitos produtos disponíveis no mercado brasileiro não foram ensaiados quanto a este fenômeno dificultando sobremaneira a elaboração de projetos mais seguros e econômicos. Há, portanto, a necessidade de estudos não só do fenômeno da fluência em si, mas também de métodos de ensaio que facilitem e acelerem a obtenção das curvas de fluência. Este trabalho apresenta um estudo da fluência de dois geotêxteis não tecidos, um de polipropileno e outro de poliéster, através de ensaios acelerados, utilizando-se o processo denominado Stepped Isothermal Method (SIM). Os valores obtidos pelo método SIM foram comparados aos valores obtidos nos ensaios convencionais, realizados segundo a norma ISO 13431. Os resultados experimentais indicam que os ensaios acelerados, utilizando o método SIM, foram capazes de simular o fenômeno da fluência com boa precisão e, portanto, podem trazer uma grande economia de tempo, além de facilitar e agilizar a caracterização da fluência de geossintéticos. / Creep tests are time consuming and require rigorous laboratory testing control. Because of that many products commercially available in Brazil were not tested regarding this phenomenon. The absence of creep data is an obstacle to the design soil reinforced structures. It is therefore required continuous research effort not only to elucidate creep phenomenon but also to help in the development of test methods that ease and speed up the obtaining of creep curves. This paper presents a creep study carried out on two non-woven geotextiles (PP and PET) using temperature accelerated creep test, namely the Stepped Isothermal Method (SIM). The values obtained using the SIM method were compared to the ones obtained using conventional creep tests following the ISO 13431. The experimental results indicate that the accelerated creep tests, using the SIM method, were capable of simulating the creep phenomenon with good accuracy and, hence, they can bring a great deal of time saving to the characterization of creep in geosynthetics.

Disposed waste materials remained from demolished buildings have been an environmental problem especially for developing countries. Recycled Cement Concrete (RCC) is one of the abundant components of waste materials that include quality aggregates. Use of RCC in asphalt concrete pavements is economically a feasible option as it not only helps in recycling waste materials but also preserves natural resources by fulfilling the demand for quality aggregate in pavement constructions. However, due to variability in RCC characteristics, a detailed evaluation of its effect on asphalt concrete performance is required. In this study, effect of RCC content on rutting potential of asphalt concrete is investigated using laboratory prepared specimens. Rutting susceptibility of the specimens is determined using repeated creep tests performed in the uniaxial stress mode. Because of the aspect ratio requirements for the repeated creep test, the standard Marshall mix design procedures were modified based on the energy concept by changing the compactor device and the applied design number of blows. The modified specimens were tested to determine a number of parameters that can describe the rutting behavior of the tested mixes. The findings indicate that slope constant and flow number give relatively stronger relationships with rutting behavior as compared to the other rutting parameters. While increasing the RCC content yields improved rutting performance for coarse graded specimens, it dramatically reduces the performance for fine graded specimens.

Theoretical part of this thesis presents summary of material and testing parameters which influence SCG and consequently the duration of the FNCT test. The experimental part focuses on modification of testing conditions of FNCT test in order to minimize the test time. FNCT tests were performed for four types of surfactants: Arkopal N110, Sodium dodecylbenzensulfonate (NaDBS), Disponil LDBS55 and Simulsol SL8. The most pronounced accelerating effect was observed for NaDBS surfactant, which in comparsion with commonly used Arkopal N110 doubled the test speed at the same concentration (11 %) and other test conditions. The accelerating effect of NaDBS was also observed for two different PE grades: Liten VB85 and VL 20N. Under the test conditions 80 °C and 4 MPa, 5% NaDBS water solution caused for VL 20N almost 12,5-fold acceleration compared to conventional 2% Arkopal N110 and almost 8,5-fold acceleration for VB 85. The correlation between wettability of surfactant solution and FNCT time to fracture was found.

In Sweden spent nuclear fuel is planned to be placed 500 m down in the bedrock. The spent nuclear fuel will be contained in copper canisters. The reason behind the selection of copper is its thermodynamic stability against corrosion in the depository. The copper will be exposed to mechanical loading and will be plastically deformed due to creep. The canisters will be sealed by friction stir welding. Since the canisters have to survive intact for many thousands of years, the properties of the welds are critical. Oxygen free P-doped copper (Cu-OFP) is selected for its excellent creep ductility properties and corrosion resistance. In this thesis work creep ductility behavior of friction stir welded copper chosen at different areas of the weld is evaluated by using the test slow strain rate tensile test. Samples are chosen at different weld areas namely weld, cross weld and HAZ. A sum of 21 specimens is tested. These tests are achieved at three various strain rates and each rate are carried out at three different temperatures. The strain rates used for tests are 1e-4, 3e-6 and 1e-7 [1/s]. The samples are strained until rupture, 20% and 5% of the gauge length. Yield strength and tensile strength are usually decreasing with increasing temperature and at higher temperature the material can be easily deformed. Few strange behaviors are also observed for the samples from HAZ areas at strain rate 1e-7[1/s]. The experimental results are justified by using the Knock-Mecking model. The parametersand ω were evaluated by curve fitting method.

The objective of this study was to develop a model to predict the viscoelastic material functions of a vinyl ester (VE) polymer (Derakane 441-400, Ashland Co.,) with variations in its material properties. Short-term tensile creep/creep recovery experiments were conducted at two stress levels and at four temperatures below the glass transition temperature of the VE polymer, with 10 replicates for each test configuration. Experimental strains in both the longitudinal and transverse directions were measured using a digital image correlation technique. The measured creep strain versus time responses were subsequently used to determine the creep compliances using the generalized viscoelastic constitutive equation with a Prony series representation. The variation in the creep compliances of Derakane 441-400 was described by formulating the probability density functions (PDFs) and the corresponding cumulative distribution functions (CDFs) of the creep compliances using the two-parameter Weibull and log-normal distributions. The maximum likelihood estimation technique was used to obtain the Weibull shape and its scale parameters and the log-normal location and its scale parameters. The goodness-ofit of the distributions was determined by performing Kolmogorov-Smirnov (K-S) hypothesis tests. Based on the K-S test results, the Weibull distribution is a better representation of the creep compliances of Derakane 441-400 when compared to the log-normal distribution. Additionally, the Weibull scale and shape parameters of the creep compliance distributions were shown to be time and temperature dependent. Therefore, two-dimensional quadratic Lagrange interpolation functions were used to characterize the Weibull parameters to obtain the PDFs and subsequently the CDFs of the creep compliances for the complete design temperature range during steady state creep. At each test temperature, creep compliance curves were obtained for CDF values of 0.05, 0.50 and 0.95 and compared with the experimentally obtained lowest, mean and highest creep compliances, respectively. The predicted creep compliances of Derakane 441-400 in the design space are in good agreement with the experimental data.

Due to the cost and difficulty of conducting direct tensile and compression creep testing on engineering ceramics, four-point bending creep test methods are often used as an alternative. Stress distribution in the bending specimen is nonlinear, so a proper interpretation method is needed to get creep properties from data produced by four-point bending creep tests. The method of Hollenberg et al. and the method of Chuang are among the methods to predict the creep parameters from bending creep test data. However, bending creep test methods are often doubted for quantitative creep analysis with reasons like uncertainties from contact point shift or frictional effects in four-point bending creep tests. Finite element simulations of the four-point bending creep tests were performed to evaluate the limitations and abilities of four-point bending creep tests and the methods to predict creep parameters from bend test data. Material model for asymmetric creep behavior (different creep rate in tension and in compression) of ceramics material were developed by modifying the existing symmetric creep model and implemented in the inhouse non-linear finite element code. Explicit finite element method (dynamic relaxation) was successfully used to consider both, the frictional effects between loading rollers and specimen, and asymmetric creep properties of ceramics material. The developed asymmetric creep material model was verified by the simulation of C-ring compression creep test and comparison with published experimental data. It was found that when friction between loading rollers and specimen was not applied in the simulations, both Hollenberg’s and Chuang’s methods well predicted creep parameters from bend creep simulation data. But, when friction was high as in normal bend creep tests, the pre-exponent (A) was highly underestimated. Prediction of stress exponent (n) was not affected much by friction. Bend test set-up with rolling-pins in ASTM C 1211 was recommended to reduce the frictional effects in bend creep tests and a proof simulation was performed. The simulation showed that the test set-up in ASTM C 1211 effectively removed the frictional effect of the frequently used creep test set-up and the effect of bending moment increase due to the rolling of loading pin was minor. / Thesis / Master of Applied Science (MASc)

Les matériaux composites se caractérisent par une forte dispersion de leur durée de vie qui peut s'étendre de quelques minutes à plusieurs semaines lors d'un test de fluage. Lors d'un essai en fluage de ces matériaux nous distinguons trois phases de temps caractérisées chacune par une activité acoustique propre. Dans la première phase, le taux d'apparition des signaux d'EA est important, puis le taux diminue et atteint une valeur constante relativement faible durant la seconde phase, ensuite ce taux d'apparition s'accélère annonçant la troisième phase qui se termine par la rupture. Les caractéristiques des signaux d'émission acoustique (EA) émis dans la phase précédant la rupture sont différentes de celles des autres phases. Le premier volet de cette étude consiste à utiliser des méthodes d'apprentissage relevant de l'intelligence artificielle (réseaux de neurones, machines à vecteurs de support et classifieurs bayésiens) afin de prédire si les signaux recueillis à partir d'un matériau sous test se trouve dans la phase de pré-rupture ou non. Ce sont des méthodes qui, appliquées à l'émission acoustique, permettent d'identifier parmi un grand nombre de signaux, caractérisés par des paramètres principaux, des classes de signaux ayant des paramètres voisins et donc provenant probablement de la même phase. Ces méthodes se sont avérées très performantes en classification, nous atteignons avec les SVM une sensibilité de 82 % et une spécificité de 84% pour les résultats en validation croisée, et une sensibilité de 90 % et une spécificité de 94 % pour les résultats en test, avec un temps de calcul acceptable.Le deuxième volet de l'étude effectué dans le cadre de cette thèse concerne l'estimation de la durée de vie restante des les matériaux composites. La normalisation des courbes cumulées des signaux d'émission acoustique en fonction du temps prouve que les réponses en fluage des éprouvettes mises en test sont parfaitement ressemblantes. Un modèle a été établi pour caractériser le comportement de ce matériau lors de ce test. Deux approches sont utilisées pour déterminer le temps de rupture. Par rapport à la littérature, la première approche proposée améliore la détection des temps de transition des différentes phases. Cette approche fournit également une meilleure corrélation avec le temps de rupture. La deuxième approche est fondée sur la corrélation du temps de rupture avec le temps de référence correspondant à la diminution de la vitesse d'un certain pourcentage. Les résultats de cette dernière approche sont très intéressants : l'estimation du temps de rupture pour une éprouvette ayant une durée de vie de 1 heure peut être possible dès les 15 premières secondes, avec une erreur de l'ordre de 4 %. / The composite materials are characterized by a high dispersion of their lifetime, which may extend from several minutes to several weeks in a creep test. When tested in creep of these materials we distinguish three phases, each characterized by its own acoustic activity. In the first phase, the occurrence rate of the AE signals is important, and then the rate drops to a relatively low constant value during the second phase, then this occurrence rate accelerate announcing the third phase which ends by a rupture. The characteristics of the acoustic emission (AE) signals in the phase preceding the rupture are different from those of other phases.The first part of this study is to use learning methods from artificial intelligence (neural networks, support vector machines and Bayesian classifier) to predict if the signals collected from the material under test in the pre-rupture or not. These are methods which, when applied to acoustic emission, identify among a large number of signals, characterized by key parameters, classes of signals having similar parameters and thus probably from the same phase. These methods have proved highly effective in classification; we reach the SVM with a sensitivity of 82 % and a specificity of 84 % for cross-validation results, and a sensitivity of 90 % and a specificity of 94 % for test results, with an acceptable calculation time.The second part of the study in the framework of this thesis concerns the estimation of the remaining life of composites. Standardization of signals accumulated acoustic emission curves as a function proves that the responses of the creep test pieces are set perfectly similar. A model was developed to characterize the behavior of this material during this test. Two approaches are used to determine the time of rupture. Compared to the literature, the first proposed approach improves the detection time of transition phases. This approach also provides a better correlation with the rupture time. The second approach is based on the correlation of rupture time with the reference time corresponding to the decrease of the speed by a percentage. The results of this latter approach is very interesting : the estimation of the rupture time for a test piece having a life of one hour may be possible from the first 15 seconds, with an error of about 4 %.

Destructive testing of creep exposed components is a powerful tool for evaluation of remaining lifetime of high temperature pipe systems. The most common destructive evaluation method used today is uniaxial creep testing. Uniaxial creep tests can produce accurate creep curves but the test method has some drawbacks such as costliness and long testing times. It also demands large sample material outtake which often involve weld repair. Impression creep (IC) testing is a relatively new alternative test method for evaluating primary and secondary creep rates. The scope of this work is to evaluate the benefits and drawbacks of IC testing over uniaxial creep testing in order to determine its usefulness as a test method. A literature survey was carried out over the area creep testing of high temperature pipe systems, with particular focus on impression creep testing. The result of the literature survey clearly showed several benefits with impression creep testing. An IC test series was performed in order to determine the secondary creep rate of a service exposed 10CrMo9-10 high temperature pipe steel. The IC tests were performed by VTT in Finland, using the same test parameter and sample material as in previous projects where the creep properties of the test material were determined by uniaxial creep testing. The result of the predicted secondary creep rate obtained from the IC tests was compared with the secondary creep rates measured during the uniaxial tests. The IC tests results did not align satisfactory with the results from the uniaxial creep tests, which would have been expected. The reason for this may be due to sources of error during impression creep testing, since very small displacements due to creep have to be measured with high precision during the tests. Further testing of the impression creep test method is recommended as a result of this work, in order to evaluate the method.