Combinations of different materials are increasingly used in the modern engineering structures. The driving forces of this trend are rising fuel costs, global warming, customer demands and strict emission standards. Engineers and industries are forced to improve fuel economy and cut emissions by introducing newly design engines and lightweighting of structural components. The use of lightweight materials in the structures has proved successful to solve these problems in many industries especially automobile and aerospace. However, industry still lacks knowledge how to manufacture components from polymeric materials in combination with metals where significant differences exist in properties. This thesis aims to demonstrate and generate the methodology and guidelines for hybrid joining of aluminium alloys to thermoplastics using friction stir welding. The developed technique was identified, optimized and evaluated from experimental data, metallography and mechanical characterization. The success of the technique is assessed by benchmarking with recent literatures. In this work, lap joints between aluminium alloys (AA5754, AA6111) and thermoplastics (PP, PPS) were produced by the friction stir welding technique. The specimens were joined with the friction stir welding tools under as-received conditions. Metallic chips were generated and merged with the molten thermoplastic to form a joint under the influence of the rotating and translating tool. The effects of process parameters such as rotational speed, translational speed and distance to backing were analyzed and discussed. The investigation found joint strength was dominated by mechanical interlocking between the stir zone and the aluminium sheet. The results also show that the joint strength is of the same order of magnitude as for other alternative joining techniques in the literature. / <p>QC 20150908</p>

This research work proposes a new methodology for implementing Value Stream Mapping, in processes that feature a High-Mix, Low-Volume product base.   The opportunity for adapting the methodology singularly for these types of environments was identified because implementing Value Stream Mapping as proposed in Learning to See features several drawbacks when implemented in High-Mix, Low-Volume.  Although Value Stream Mapping has been proven to enhance many types of processes, its advantages are shrunk if they are implemented in High-Mix, Low-Volume processes.   High-Mix, Low-Volume processes are types of processes in which a high variety of finished goods are produced in relatively low amounts.  The high variety of finished goods causes several complications for the implementation of flow.  The difficulties that prevent the flow are the following: The variance in the products: With hundreds, or sometimes thousands of possible finished goods, the number of products causes a non-repetitive process. The variance in the routings:  All of the products that are produced can have completely different process routings, or order of stations it has to visit.  This makes the application of production lines quite difficult. The variance in the cycle times for each process.  Each of the different products can have completely different capacity requirements at a specific machine, which limits the predictability of the process.   This purpose of the thesis is to gather the best practices for controlling and improving High-Mix, Low-Volume processes and merge them with some innovative ideas to create an inclusive Value Stream Mapping methodology which is better fitted with the types of complications in High-Mix, Low-Volume environments.  In parallel, the methodology is tested with the company: Boston Scientific, in their Ureteral Stents manufacturing process.   The real-life experimentation will allow for the fine-tuning of the methodology, in order to truly create impact in the process.

No description available.

DNA encodes the genetic instructions for the development and function of organisms and hence maintaining genomic integrity is essential for the propagation of life. However, DNA molecules are under constant threat of metabolic and environmental insults resulting in DNA damages including DNA double strand breaks (DSB), which are considered as a serious threat to cell survival. The majority of these DSB are repaired by Non-homologous end joining (NHEJ). Unrepaired DSB can lead to genomic instability resulting in cell cycle arrest, apoptosis, and mutations. Thus, delineating this DNA repair process is important in understanding the molecular mechanisms of aging and malignant progression. B lymphocytes undergo physiological DNA breaks and NHEJ-mediated DNA repair during their bone marrow differentiation and peripheral class switch recombination (CSR), thus lending them as a good model system in which to delineate the DNA repair mechanisms. To determine the effect of aging on NHEJ, B lymphocytes from old mice were analyzed. The results showed compromised DNA repair in cells from old mice compared to cells from adult mice. These results suggest that NHEJ is compromised during aging and might play critical roles in the aging process and age-associated conditions. To delineate the role of a CT in regulating the immune system, transgenic mice expressing NUP98-HOXD13 (NHD13) were analyzed for B lymphocyte differentiation, peripheral development, CSR, and antibody production. The results showed impaired B cell development and antibody production, which worsened with antigenic stimulation, suggesting the role of NHD13 in immune regulation. These studies explored the possibility of altered NHEJ-mediated DNA repair as a contributing reason for aging process and age-associated conditions. Also, the results from NHD13 study suggested that a primary CT can result in impaired NHEJ and regulate immune cell development and function. Furthermore, the results pointed to the possibility that a primary CT may lead to secondary mutations through altered NHEJ. Thus, these studies shed insight into the molecular mechanisms of altered NHEJ and may help in developing preventive or therapeutic strategies against accumulation of DNA damage, aging process and secondary mutations. / Ph. D.

Brazing and soldering, as advanced manufacturing processes, are of significant importance to industrial applications. It is widely accepted that joining by brazing or soldering is possible if a liquid metal wets the solids to be joined. Wetting, hence spreading and capillary action of liquid metal (often called filler) is of significant importance. Good wetting is required to distribute liquid metal over/between the substrate materials for a successful bonding. Topographically altered surfaces have been used to exploit novel wetting phenomena and associated capillary actions, such as imbibitions (a penetration of a liquid front over/through a rough, patterned surface). Modification of surface roughness may be considered as a venue to tune and control the spreading behavior of the liquids. Modeling of spreading of liquids on rough surface, in particular liquid metals is to a large extent unexplored and constitutes a cutting edge research topic. In this dissertation the imbibitions of liquid metal has been considered as pertained to the metal bonding processes involving brazing and soldering fillers. First, a detailed review of fundamentals and the recent progress in studies of non-reactive and reactive wetting/capillary phenomena has been provided. An imbibition phenomenon has been experimentally achieved for organic liquids and molten metals during spreading over topographically modified intermetallic surfaces. It is demonstrated that the kinetics of such an imbibition over rough surfaces follows the Washburn-type law during the main spreading stage. The Washburn-type theoretical modeling framework has been established for both isotropic and anisotropic non-reactive imbibition of liquid systems over rough surfaces. The rough surface domain is considered as a porous-like medium and the associated surface topographical features have been characterized either theoretically or experimentally through corresponding permeability, porosity and tortuosity. Phenomenological records and empirical data have been utilized to verify the constructed model. The agreement between predictions and empirical evidence appears to be good. Moreover, a reactive wetting in a high temperature brazing process has been studied for both polished and rough surfaces. A linear relation between the propagating triple line and the time has been established, with spreading dominated by a strong chemical reaction.

<div>Self-pierce riveting as a relative new technology has been used by automotive industry for decades. Because of the several benefits of the SPR technique, it has been widely used for joining the similar or dissimilar materials to satisfy the light-weighting requirements of automobile. There were many researchers and automotive manufacturers that had been investigated the SPR by experiments and applied this technique to their products. The SPR was designed for joining the materials with sufficient ductility because the joining process was going to introduce the large plastic deformation on the joint button area. Die casting aluminum alloy products became more and more popular to be used for structural components. However, the casting aluminum components have relative low ductility than the wrought alloy product. The cracking problems were easy to occur during the riveting process.</div><div><br></div><div>In terms of the cracking issues on die casting aluminum products, an analysis was conducted in this study to investigate the influence of composition on cracking problem. And the cracking mechanism was also analyzed and summarized. Corresponding to the influence of silicon content difference and silicon morphology, heat treatment was used to modify the eutectic silicon morphology of the casting aluminum alloys to improve the rivetability. Once the silicon network was broken by the heat treatment, the rivetability of die casting aluminum was drastically increased and the cracks on joint button were also suppressed. Under the effect of heat treatment, the joint performance was tightly related to the variation of the eutectic silicon phase and the cracks on the joint button. The joint strength was obtained by shear test to investigate the influence of heat treatment and die depth. A novel cracking statistics has been generated and used to calculate the cracks on the joint button. Eventually, a comprehensive joint performance was obtained by taking into consideration of joint strength, heat treatment and die depth.</div><div><br></div><div>Finally, the simulation of the SPR process was conducted and analyzed by FORGE. The die depth as the variable was used to investigate the strain and fracture distribution in</div><div>cross-section view of the joint. In terms of the initial results of the simulation, the die cavity with various sidewall incline angles was simulated to find the optimal die cavity geometry in order to improve the rivetability of the bottom material sheet.</div>

Advanced aluminum graphite composites have unique thermal properties due to opposing coefficients of thermal expansion of aluminum and graphite. The thermal and mechanical properties of such composites are anisotropic due to directional properties of graphite fibers and their designed orientation. A joint with different fiber orientations would theoretically produce an isotropic material for thermal management. This paper presents results for welding and brazing of the composite using different joining techniques. Laser welding of Al-Gr composite showed that a power density above 30kW/mm2 gives a weld with microstructure defects. Also the laser beam melts the matrix and delaminates the graphite fibers. The molten aluminum reacts with graphite to form aluminum carbide (Al4C3). The joint strength is compromised when laser welding at optimal conditions to minimize the carbide formation. Also porosity and redistribution of graphite fibers is seen during laser welding. These defects prompt us to consider a low temperature joining. Brazing is considered since the low melting temperature of a filler material suppresses the formation of Al4C3 while minimizing pores and microstructural defects in the joint. Microstructural study and shear test are performed to analyze the joints. Shear strengths of brazed joints are determined to be 20-21MPa which is comparable to the composite shear strength (46.5MPa in x-y plane and 19MPa in z plane). The fracture surface is found to be mostly on the composite rather than in brazed material or along the interface. Also, the microstructural study showed no Al4C3 formation and minimal porosity in the brazed region. These results show a successful joining of the composite using laser brazing and resistance brazing methods.

Wissenschaftliche Schriftenreihe, die Dissertationen der Professur Schweißtechnik beinhaltet.

APLF (Aprataxin and Polynucleotide kinase-Like Factor), a novel protein with a forkhead-associated (FHA) domain and two poly(ADP-ribose)-binding zinc fingers (PBZ), interacts with core non-homologous end-joining (NHEJ) repair factors, Ku and XRCC4-DNA ligase IV, and facilitates NHEJ. However, how APLF functions in NHEJ is undefined. This thesis demonstrates that the Ku-binding domain on APLF is mapped to amino acid residues 180-200, where conserved amino acid residue W189 strongly contributes to the APLF-Ku interaction. Remarkably, the APLF-Ku interaction is involved in the nuclear localization of APLF. Furthermore, we demonstrate that the N-terminal region (amino acids 1-200), containing the XRCC4-Ligase IV and Ku binding domains, is required for APLF- dependent NHEJ. Collectively, these findings suggest that Ku contributes to APLF nuclear localization, and that once APLF is retained in the nucleus, the N-terminal portion of APLF, which facilitates interactions with the core NHEJ proteins Ku and XRCC4-DNA ligase IV, is required for efficient NHEJ.

APLF (Aprataxin and Polynucleotide kinase-Like Factor), a novel protein with a forkhead-associated (FHA) domain and two poly(ADP-ribose)-binding zinc fingers (PBZ), interacts with core non-homologous end-joining (NHEJ) repair factors, Ku and XRCC4-DNA ligase IV, and facilitates NHEJ. However, how APLF functions in NHEJ is undefined. This thesis demonstrates that the Ku-binding domain on APLF is mapped to amino acid residues 180-200, where conserved amino acid residue W189 strongly contributes to the APLF-Ku interaction. Remarkably, the APLF-Ku interaction is involved in the nuclear localization of APLF. Furthermore, we demonstrate that the N-terminal region (amino acids 1-200), containing the XRCC4-Ligase IV and Ku binding domains, is required for APLF- dependent NHEJ. Collectively, these findings suggest that Ku contributes to APLF nuclear localization, and that once APLF is retained in the nucleus, the N-terminal portion of APLF, which facilitates interactions with the core NHEJ proteins Ku and XRCC4-DNA ligase IV, is required for efficient NHEJ.