For TIG welding of transformer fame is important enough weld root fusion, however exposed surfaces must remain unaffected. Three types of test were made to determine properties of welds under different conditions. Tests were macroscopic inspection, tensile test and fracture test. Next was economic evaluation of different methods. Best results were for single layer weld with pre-heated material.

Z důvodu rozdílných koeficientů délkové teplotní roztažnosti jednotlivých vrstev vzniká ve vrstvách keramického vrstevnatého kompozitního materiálů reziduální napětí. V průběhu chladnutí vrstevnatého kompozitu ze slinovací teploty jednotlivé vrstvy smršťují různými rychlostmi v závislosti na velikosti koeficientu délkové teplotní roztažnosti. Jestliže jsou tyto vrstvy spolu pevně spojeny vzniká v jednotlivých vrstvách různě velké trvalé zbytkové napětí. Velikost residuálního napětí je dána objemovým podílem obou složek v kompozitu. Tato práce byla zaměřena na přípravu a popis 7-mi a 9-ti vrstevných keramických laminátů složených ze střídajících se vrstev dvou rozdílných materiálů. Keramické lamináty byly připraveny pomocí metody suspenzního lití a elektroforetické depozice. U připravených laminátu byl sledován vznik tzv. hranových trhlin (edge cracks) ve vrstvách obsahujících tlaková zbytková pnutí. Výsledky pozorování přítomnosti hranových trhlin pro různou konfiguraci velikosti zbytkových napětí a tloušťky vrstev byly srovnány s teoretickou předpovědí vytvořenou pomocí parametrického 2D modelu. Vliv vzniklých hranových trhlin na průběh lomu byl studován pomocí 3D rekonstrukce lomového povrchu po ohybové zkoušce připravených vrstevnatých kompozitů.

Cette thèse traite des effets de pré-écrouissage, monotone ou cyclique, sur le comportement cyclique et la durée de vie en fatigue (traction-compression à température ambiante). Les matériaux utilisés sont un alliage de nickel-chrome (80-20%), un acier inoxydable austénitique 316L et du cuivre pur. Ils présentent une aisance croissante au glissement dévié ; un paramètre considéré comme majeur pour expliquer les écarts de sensibilité aux effets de mémoire de pré-écrouissage existants entre ces matériaux.Des courbes d'écrouissage cyclique obtenues suite à des chargements multi-paliers sur des échantillons pré-écrouis sont comparées à celles des matériaux vierges. Cette comparaison permet de tracer des cartographies d'effet mémoire. Différents effets y sont observés et leurs origines discutées via une approche par partition de contrainte. Enfin, des essais de fatigue sont effectués pour chaque domaine de mémoire de pré-écrouissage et leurs conséquences sur la durée de vie sont discutées / This work focuses on the effect of a pre-hardening, either monotonic or cyclic, on the cyclic behavior and the fatigue life during tension-compression tests at room temperature. Materials used are a nickel-chromium alloy (80-20%), a 316L austenitic stainless steel and OFHC pure copper. They present an increasing ease to the cross-slip : a deformation mechanism identified as a key parameter to understand the distinct memory effect sensibilities existing between materials.Cyclic stress-strain curves obtained from sequential loadings on prestrained samples are compared to the ones of virgin materials. Such comparison allows plotting memory effect maps. According to these memory plots, different pre-hardening effects exist and their origins are discussed through a stress-partition analysis. Finally, fatigue tests are carried out for each domain of the prestrain memory and their consequences on fatigue life are discussed

<div>Due to the inherent dangers associated with handling high explosive materials, it is often useful to have access to inert simulant materials that mimic certain physical or mechanical properties, called "mock" materials. Mock materials can take the place of explosives in experiments, allowing experimental results to be obtained with less difficulty and risk. Recently there has been an interest in identifying new mechanical mock materials for the explosives HMX and PETN. These energetic materials and their prospective mocks are often used and tested in the form of small submillimeter crystals, with which typical size and geometry make many mechanical tests difficult or impossible. Additionally, these materials are typically prone to brittle fracture, which can further limit the usage conditions of the material as well as the range of conditions in which mechanical testing results are valid. Nanoindentation is a useful technique to measure mechanical properties in particulate form without the need to grow large single crystals or do additional processing on existing crystals.</div><div><br></div><div>Here, nanoindentation tests were performed on PETN, HMX, and several inert molecular crystals selected as potential mocks based on density, crystal structure, and previous thermal testing results. Comparisons were made on the basis of hardness, elastic modulus, yield point behavior, indentation fracture response, and sensitivity to non-uniform indenter orientation. Based on the results of these experiments, the inert material idoxuridine was selected for further consideration as an HMX mock, and the inert materials meso-erythritol and 2,4,6 trifluorobenzoic acid were selected for further consideration as PETN mocks.</div><div><br></div><div>As a result of this study, potential mechanical mocks were selected for two energetic materials, nanomechanical properties were reported for the first time ever for 6 inert molecular crystals, and nanoindentation was shown to be a versatile tool for rapid initial screening of materials as well as detailed investigations of materials of interest. <br></div>

La combinaison de la tomographie à rayons X comme technique d’imagerie 3D non destructive, et de la corrélation d’images numériques (DVC) qui permet de mesurer les champs de déplacements à partir de paires de telles images, a ouvert la voie à l’exploitation quantitative d’expérimentations mécaniques in situ. Cette thèse contribue à élargir le champ d’application de ces techniques en développant deux axes :- d’une part la régularisation mécanique qui permet de pallier le manque de contraste microstructurale en compensant ce déficit par une connaissance a priori sur le comportement mécanique du matériau. Initialement destinée à rendre compte d’un comportement élastique linéaire, nous avons étendu cette stratégie à des essais montrant une propension à la localisation de la déformation plastique dans deux directions tout en préservant le caractère isochore de la transformation. Cette technique a été testée sur des images de laminographie de tôle d’un alliage d’Aluminium pour montrer que la déformation plastique localisée précède très sensiblement l’endommagement plastique (au sens de l’apparition et la croissance de cavités plastiques).- d’autre part, à partir d’un volume de référence reconstruit, nous avons développé une technique de corrélation d’images volumiques qui apprécie la cinématique de l’objet étudié directement sur les projections (radiographies). Cette stratégie permet de diminuer très fortement le nombre de projections nécessaires à chaque instant du chargement, et donc d’augmenter très fortement la résolution temporelle de la technique en minimisant le temps d’acquisition. Cette technique a été utilisée sur un exemple de propagation de fissure de fatigue dans une fonte à graphite sphéroïdal.- enfin l’utilisation conjointe de ces deux stratégies ouvre des perspectives séduisantes d’essais rapides avec suivi cinématique 4D où la résolution temporelle peut être augmentée de plus de deux ordres de grandeur sans compromission sur la qualité de la mesure. Enfin, il est à noter que les données expérimentales restent redondantes, si bien que la validation (ou non) des hypothèses utilisées est naturellement obtenu à l’issue du traitement. Ces deux axes soulignent le bénéfice engendré par l’infusion d’une pré-connaissance, que ce soit sur le comportement mécanique ou sur la microstructure de l’éprouvette, dans la résolution du problème inverse des mesures cinématiques. / The combination of X-Ray Tomography as a 3D nondestructive imaging technic and the digital volume correlation (DVC) which uses two images to measure displacement fields, paved the way to the quantitative exploitation of in situ mechanical testing.This thesis has contributed to broaden the scope of these technics by developing two axes :- On one hand the mechanical regularization which overcomes the lack of microstructural contrast by adding an a priori knowledge of the material’s mechanical behavior. Initially designed for and linear elastic behavior, this strategy has been extended to tests where plastic strain occurs in two directions while preserving the isochoric characteristic of the deformation. This technic has been tested on images of Aluminum plates obtained by laminography to show that localized plastic strain occurs way before plastic damage (i.e. germination and growth of plastic cavities).- On the other hand, from a reconstructed volume, a DVC technic has been developed which measure the kinematic of a sampled on the radios. This strategy allows to reduce greatly the number of necessary projections à each loading step, and therefore to improve greatly the temporal resolution by minimizing acquisition time. This technic has been used on an example of fatigue crack propagation of a cast iron.- At last, the combine use of these two strategies pave the way to appealing perspectives of fast mechanical test with 4D kinematics measurements, where the temporal resolution can be improve by more than two order of magnitude without any loss in the quality of the measure. One can realized that experimental data are redundant, so the validation (or not) of the hypotheses used is obtained at the end of the procedure.These two axes show the gain of using pre-knowledge, either on mechanical behavior, either on the microstructure o the sample, in the resolution of inverse problem for kinematics measurements.

PhD Thesis / Cardiac surgeons rely on simulation training to improve their surgical skills. The focus of this research was on creating a 3D aortic valve model for cardiac surgical skills training. The research was divided into four different stages including CAD model development, tissue testing using surgical tools, aortic valve model manufacturing and model evaluation. First, the development of a patient-specific aortic valve model was carried out. The process involved heavily processing CT scanned data of the aortic valve to extract the geometric information via segmentation. Patient-specific models are critical for pre-operative planning and training. However, those models are not ideal for large volume quantities due to the high production costs and the extensive manual labour required to process the models. Therefore, another approach was chosen to produce a generic model that was more suitable for large volume quantities. The generic aortic valve model was developed using data obtained from the literature. The contribution in this stage was developing the methodology to reverse engineer patient-specific cardiac tissues. Additionally, a generic CAD model of the aortic valve was developed. Second, to select suitable materials for the model, samples from biological tissues and polymers were tested using a surgical tool. The contribution in this stage was documenting the forces and displacements obtained from puncturing and cutting the samples using suturing needles and scalpel blades. Third, the aortic valve model was manufactured using two approaches including AM and casting. The contribution in this stage revolved around the development of several moulds for casting. Finally, evaluation of the model was done via an initial assessment session with surgical residents. Although the model was not evaluated in extensive training sessions, a plan highlighting the important elements to do that was included in this research. Thus, the contribution in this stage was developing the model testing plan. / Thesis / Doctor of Philosophy (PhD) / Typically, surgeons use post-mortem human tissues (cadavers) and animal tissues for surgical skills training. However, those methods can be both expensive and limited in availability. Therefore, other non-biological methods are introduced constantly to provide viable alternatives. Those methods include producing models using 3D printing, virtual reality (VR) simulation and even using household items to create training models. However, to date, there is a lack of highly accurate representation of real tissues (fidelity) of most models for cardiac surgical training. The purpose of this research was to develop and manufacture surgical skill training tools for cardiac surgeons focusing on the aortic valve cardiac tissues. The research was divided into several parts including developing computer models using patient-specific medical imaging, developing a general training model and training models manufacturing. Also, the research included manufacturing materials selection process as well as plans for testing the training models in training sessions.

Syftet med rapporten är att redovisa en studie där val av utskrivningsmetod samt passande material inom additiv tillverkning ska motiveras, för att tillverka kalibreringsformar till Bucher Emhart glass glasmaskiner. Målet med studien är att tillverka kalibreringsformarna som väger mindre än stålformarna som används idag i glasmaskinerna, detta för att minska arbetsbelastningen på personalen. Stålformarna väger ca 9kg i dagsläget. För att utesluta material och utskriftmetoder användes i första steget kravspecifikationen, och sedan användes pughs matris för att väga de material och utskrivningsmetoder som klarar kraven som ställs. För att validera materialen gjordes även en FEM analys samt en analytisk beräkning på spänningarna. Utifrån Pughs matrisen kunde det konstateras att med den data som givits att en FDM skrivare med ASA som material är mest lämpat för detta projekt. Med denna 3D-skrivare och tillhörande material fick en formhalva en vikt på ca 700g, vilket minskar avsevärt vikten som måste lyftas och således minskar arbetsbelastningen hos arbetarna.

The applications of Li-ion batteries in the electronics and vehicle industry is increasing at a very rapid pace. This is primarily due to superior properties such as high specific energy storage and power as well as wider operation temperature ranges. Additional potential for improved properties is connected to capacity losses with time and the thereby resulting limitations of lifetime of batteries. The lifetime of a battery is strongly related to the mechanical and chemical degradation of the active material of electrodes during repeated electrochemical reactions at charging and discharging. To identify this phenomenon from a mechanical perspective, the mechanical properties of the electrode active layers should be characterized. Additionally, with the aid of mechanical properties, realistic electro-chemo-mechanical models should be developed to comprehend the mechanisms causing capacity fade. In the first part of this thesis, macroscopic material properties of the active layers of Li-ion battery electrodes were measured with a unique bending test technique. Contrary to methods previously used; it is capable to overcome the challenges that were encountered in other traditional testing techniques. In papers 1 and 2 this bending test technique (U-shaped bending test), is used to characterize the elastic and viscoelastic behavior of NMC cathodic and graphite anodic active layers, respectively. By using single-sided thin electrode specimens in U-shape bending tests, it was possible to distinguish tensile and compressive elastic and viscoelastic behavior of the electrode active materials. The tensile Young’s moduli of cathodic and anodic active layers are found as 0.73 GPa and 1 GPa, respectively. On the other hand, the compressive Young’s moduli show a stiffening behavior at increasing strains. Stiffnesses between 1.3 GPa and 2.8 GPa for the cathodic active layer, and between 1 GPa and 3.8 GPa for the anodic active layer were recorded. This compressive behavior of the electrode active layers is expected as a result of the porous nature of the materials. In addition, the viscoelastic behavior of the electrode active layers is expressed through Prony series. It was observed that the behavior can be described by a short term (minutes) and a long term (hours, days) relaxation. In paper 3, a statistical representative volume element is introduced to predict the elastic properties of a dry cathodic electrode active layer. A porous cathodic electrode active layer that is composed of NMC active particles and polymeric binder material with conductive carbon additives is modeled as a face-centered-cubic structure. Several particle-binder and particle-particle interaction conditions are repeated 50 times with random orientations. Based on the statistics for each interaction case, Young’s modulus is estimated. The results show a good agreement with the experimental findings from Paper 1. Furthermore, particle-particle and particle-binder contact force distributions are calculated for 3% of particle swelling. The characteristics of the force distributions are correlated with the typical material failures in the active layer such as particle cracking and binder debonding. The statistical data obtained here are also used to improve an analytical model that was previously derived to estimate the elastic properties of active porous layers. The analytical model, complemented by the statistical results, showed an excellent agreement with the finite element simulations. / <p>QC 230124</p>

UV-LIGA is a microfabrication process realzed by material deposition through microfabricated molds. UV photolithography is conducted to pattern precise thick micro molds using UV light sensitive materials, mostly SU-8, and electroforming is performed to fabricate micro metallic structures defined by the micro molds. Therefore, UV-LIGA is a bottom-up in situ material-addition process. UV-LIGA has received broad attention recently than LIGA – a micro molding fabrication process using X-ray to pattern the micro molds. LIGA is an expansive and is limited in access. In comparing to LIGA, the UV-LIGA is a cost effective process, and is widely accessible and safe. Therefore, it has been extensively used for the fabrication of metallic micro-electro-mechanical-systems (MEMS). The motivation of this research was to study micro mechanical systems fabricated with nano-structured metallic materials via UV-LIGA process. Various micro mechanical systems with high-aspect-ratio and thick metallic structures have been developed and are presented in this desertation. A novel micro mechanical valve has been developed with nano-structured nickel realized with UV-LIGA fabrication technique. Robust compact valves are crucial for space applications where payload and rubstaness are critically concerned. Two types of large flow rate robust passive micro check valve arrays have been designed, fabricated and tested for robust hydraulic actuators. The first such micro valve developed employs nanostructured nickel as the valve flap and single-crystal silicon as the substrates to house inlet and outlet channels. The Nano-structured nickel valve flap was fabricated using the UV-LIGA process developed and the microchannels were fabricated by deep reactive etching (DRIE) method. The valves were designed to operate under a high pressure (>10MPa), able to operate at high frequencies (>10kHz) in cooperating with the PZT actuator to produce large flow rates (>10 cc/s). The fabricated microvalves weigh 0.2 gram, after packing with a novel designated valve stopper. The tested results showed that the micro valve was able to operate at up to 14kHz. This is a great difference in comparison to traditional mechanical valves whose operations are limited to 500 Hz or less. The advantages of micro machined valves attribute to the scaling laws. The second type of micro mechanical valves developed is a in situ assembled solid metallic (nickel) valves. Both the valve substrates for inlet and outlet channels and the valve flap, as well as the valve stopper were made by nickel through a UV-LIGA fabrication process developed. Continuous multiple micro molds fabrication and molding processes were performed. Final micro mechanical valves were received after removing the micro molds used to define the strutures. There is no any additional machining process, such as cutting or packaging. The alignment for laminated fabrication was realized under microscope, therefore it is a highly precise in situ fabrication process. Testing results show the valve has a forward flow rate of19 cc/s under a pressure difference of 90 psi. The backward flow rate of 0.023 cc/s, which is negligible (0.13%). Nano-structured nickel has also been used to develop laminated (sandwiched) micro cryogenic heater exchanger with the UV-LIGA process. Even though nickel is apparently not a good thermal conductor at room temperature, it is a good conductor at cryogentic temerpature since its thermal conductivity increases to 1250 W/k·m at 77K. Micro patterned SU-8 molds and electroformed nickel have been developed to realize the sandwiched heat exchanger. The SU-8 mold (200mm x 200mm x50mm) array was successfully removed after completing the nickel electroforming. The second layer of patterned SU-8 layer (200mm x 200mm x50mm, as a thermal insulating layer) was patterned and aligned on the top of the electroformed nickel structure to form the laminated (sandwiched) micro heat exchanger. The fabricated sandwiched structure can withstand cryogenic temperature (77K) without any damages (cracks or delaminations). A study on nanocomposite for micro mechanical systems using UV-LIGA compatible electroforming process has been performed. Single-walled carbon nanotubes (SWNTs) have been proven excellent mechanical properties and thermal conductive properties, such as high strength and elastic modulus, negative coefficient of thermal expansion (CTE) and a high thermal conductivity. These properties make SWNT an excellent reinforcement in nanocomposite for various applications. However, there has been a challenge of utilizing SWNTs for engineering applications due to difficulties in quality control and handling – too small (1-2nm in diameter). A novel copper/SWNT nanocomposite has been developed during this dissertational research. The goal of this research was to develop a heat spreader for high power electronics (HPE). Semiconductors for HPE, such as AlGaN/GaN high electron mobility transistors grown on SiC dies have a typical CTE about 4~6x10-6/k while most metallic heat spreaders such as copper have a CTE of more than 10x10-6/k. The SWNTs were successfully dispersed in the copper matrix to form the SWNT/Cu nano composite. The tested composite density is about 7.54 g/cm3, which indicating the SWNT volumetric fraction of 18%. SEM pictures show copper univformly coated on SWNT (worm-shaped structure). The measured CTE of the nanocomposite is 4.7 x 10-6/°C, perfectly matching that of SiC die (3.8 x 10-6/°C). The thermal conductivity derived by Wiedemann-Franz law after measuring composit's electrical conductivity, is 588 W/m-K, which is 40% better than that of pure copper. These properties are extremely important for the heat spreader/exchanger to remove the heat from HPE devices (SiC dies). Meanwhile, the matched CTE will reduce the resulted stress in the interface to prevent delaminations. Therefore, the naocomposite developed will be an excellent replacement material for the CuMo currently used in high power radar, and other HPE devices under developing. The mechanical performance and reliability of micro mechanical devices are critical for their application. In order to validate the design & simulation results, a direct (tensile) test method was developed to test the mechanical properties of the materials involved in this research, including nickel and SU-8. Micro machined specimens were fabricated and tested on a MTS Tytron Micro Force Tester with specially designed gripers. The tested fracture strength of nanostructured nickel is 900±70 MPa and of 50MPa for SU-8, resepctively which are much higher than published values.

yes / This paper presents test results of six concrete beams reinforced with longitudinal carbon fiber reinforced polymer (CFRP) bars and without vertical shear reinforcement. All beams were tested under a two-point loading system to investigate shear behavior of CFRP reinforced concrete beams. Beam depth and amount of CFRP reinforcement were the main parameters investigated. All beams failed due to a sudden diagonal shear crack at almost 45°. A simplified, empirical expression for the shear capacity of FRP reinforced concrete members accounting for most influential parameters is developed based on the design-by-testing approach using a large database of 134 specimens collected from the literature including the beams tested in this study. The equations of six existing design standards for shear capacity of FRP reinforced concrete beams have also been evaluated using the large database collected. The existing shear design methods for FRP reinforced concrete beams give either conservative or unsafe predictions for many specimens in the database and their accuracy are mostly dependent on the effective depth and type of FRP reinforcement. On the other hand, the proposed equation provides reasonably accurate shear capacity predictions for a wide range of FRP reinforced concrete beams.