Thesis (Ph.D.)--Drexel University, 2008. / Includes abstract and vita. Includes bibliographical references (leaves 175-184).

Thesis (Ph.D.)--Drexel University, 2008. / Includes abstract and vita. Includes bibliographical references (leaves 259-280).

Thesis (Ph. D.)--Drexel University, 2004. / Includes abstract and vita. Includes bibliographical references (leaves 114-122).

Thesis (Ph. D.)--Drexel University, 2004. / Includes abstract and vita. Includes bibliographical references (leaves 170-187).

Thesis (Ph.D.)--Drexel University, 2009. / Includes abstract and vita. Includes bibliographical references (leaves 163-178).

The thesis work was made in cooperation with the I-EDDA project who evaluates the drill equipment used in core drilling. The aim of this work was to determine how and why the drill bits are worn. The work consisted of two parts; investigate drill bits used in field tests and develop a lab scale method to be able to change one drill parameter at a time and see how it affects the wear. During the field tests the rotational speed and the pressure on the drill bits were changed between the three boreholes drilled. In the lab test one parameter at a time was changed; the rotational speed, the water flow and the load. The lab test was developed to attempt to replicate the core drilling and was performed by pressing a piece of a drill bit against a rotating stone cylinder. The drill bits from the field tests and lab test were analysed with the same methods on both macro- and microscale for easier comparison. The results indicate that the lab scale test can be used to evaluate the wear of drill bits. The analyses show rock present on the matrix of all the drill bits, in various amounts. The load has the largest impact on the wear of the drill bits and cause a change in mechanism. A high pressure leads to a higher amount of damaged diamonds and three body abrasive wear on the matrix. Lower pressure leads to polished diamonds and erosive wear on the matrix.

Infiltration is used in the production of several different material groups as electric contact materials, copper infiltrated sintered steels and metal matrix composites. The mechanism of infiltration causes also unwanted difficulties in processing as brazing of porous sintered compacts. The common question, in this work has been, how is it possible to control infiltration in different materials processing techniques? In joining of powder metallurgically (P/M) produced porous compacts, by brazing, the inherent porosity of the compacts causes the melt filler metal to infiltrate the interconnected pore channels of the P/M parts, by capillary forces. This will result in high penetration depths and filler metal consumption and a limited amount of filler metal will be available for the joint. In the production of metal matrix composites (MMC:s), the difference in surface energies between the metallic and ceramic components prohibits a spontaneous infiltration of the metallic phase into the ceramic porous body. This work includes a general analyse of the different physical and mechanical methods to control infiltration in brazing of porous compacts and processing of MMC:s respectively. The experimental part of the work concentrates on the study of physical methods for the infiltration control. Brazing of porous sintered compacts has been studied experimentally through different thermal treatments. A special (Cu-Ni-Mn-Si) filler-metal, developed by others in order to facilitate alloying between iron in P/M- compacts and the elements in the filler-metal, has been used and the results has been studied by optical and scanning electron microscopy and the mechanical strength and hardness has been measured. In the work on MMC:s a method for processing of aluminium matrix-alumina reinforced composites by spontaneous infiltration has been studied by wetting and in- situ high temperature X-ray experiments. The investigation of brazing shows that the filler metal starts to melt already at 930 oC and a two phase alloy is developed in the joint. The diffusion of elements from the filler metal and the sintered compact causes a development of an alloy with high melting temperature in the surface area of the sintered compact that blocks the surface pores from continued infiltration. The wetting experiments show that the spontaneous infiltration in production of MMC:s is enabled by chemical reactions in the system concerned. The in-situ X-ray experiments show that the formation of magnesium-nitride appears below 600 oC. The formation of AlN as a second reaction product in the spontaneous infiltration has been detected for compact tested after a processing cycle with increased pressure of nitrogen- gas in the processing furnace. The in-situ X-ray study of the spontaneous infiltration has shown that the formation of magnesium nitride could be detected. The results show also that it is possible to study chemical reactions at and above the melting temperature of the metallic constituent of the system. The results show also that it would be possible to create alumina-aluminium MMC with different hardness levels. / Godkänd; 2004; 20070116 (haneit)

The heavy plate rolling process needs accurate predictions of the process parameters. The plate thickness, flatness and rolling stability are of this direct influenced as well as the productivity. Therefore, careful calculation of the process parameters and pass schedules is necessary. The thesis is concerned with two aspects of controlling rolling; the choice of optimal pass schedules and roll wear. A software has been developed in Paper A to determine optimal pass schedules for thermomechanical rolling in order to obtain a fine microstructure. It includes models of the effect of strain, precipitates, static and dynamic recrystallization and austenite grain size on the final grain size. The predicted grain sizes for four different cases were compared with experimental results. It was also used to study the effect of different delay times during the pass schedule of rolling thermomechanical plate. The results shows that an increase in delay times results in finer ferrite grains are received. The refinement is however small for long delay times. Long delay times also affect the productivity negatively. A method for modeling of the work roll contour in a four high mill is presented in Paper B. The active parameters were found to be the plate length and the variations of the pressure from the plate and the back-up roll on the work roll along the work roll barrel. The method is build up with statistical methods. The bases for the statistics are simulations of different rolling cases and measurements from the production of heavy plates in Oxelösund. The proposed wear contour model was found to be in good agreement with the measurements from the production. / <p>Godkänd; 2006; 20061206 (pafi)</p>

The microstructure and consequently the mechanical properties of titanium alloys are highly dependent on the temperature history endured by the material. The manufacturing process of metal deposition induces repetitive cooling and heating in the material determining a specific microstructure. The presented study is devoted to developing and implementing a microstructure model for Ti-6Al-4V intended to be coupled to a thermo- mechanical model of the metal deposition process. Microstructural analysis of the metal deposited samples was first performed to understand the formed microstructure. A set of representative parameters for microstructure modelling were then selected as representative for the known impact of Ti-6Al-4V microstructure on mechanical properties. Evolution equations for these parameters were implemented for thermal finite element analysis of the process. Six representative state variables are modelled: the phase volume fraction of total alpha, beta, Widmanstätten alpha, grain boundary alpha, martensite alpha, and the alpha lath thickness. Heating, cooling and repeated re-heating involved in the process of metal deposition are taken into account in the model. The phase transformations were modelled based on a diffusionnal theory described by a Johnson-Mehl-Avrami formulation, as well as diffusionless transformations for the martensite alpha formation and the beta reformation during reheating. The Arrhenius equation is applied as a simplification to model temperature dependent alpha lath size calculation. Grain growth is not included in the present formulation, but would have to be added for capturing alpha lath coarsening during long term heat treatment. The temperature history during robotised tungsten inert gas deposition welding is simulated together with the microstructure. The implementation of the model handles well the complex cyclic thermal loading from the metal deposition process. A particular banded structure observed in the metal deposited microstructure is partially explained using the proposed microstructure model. It is concluded that although qualitatively interesting results have been achieved, further calibration testing over a wider range of temperature histories must be performed to improve the transformation kinetic parameters for reliable quantitative predictions of the microstructure. / <p>Godkänd; 2008; 20081128 (ysko)</p>

The simulation of hot extrusion processes is a difficult and challenging problem in process modeling. This is due to very large deformations, high strain rates and large temperature changes during the process. Computer models that with sufficient accuracy can describe the material behavior during extrusion can be very useful in process and product development. Today, the process development in industrial extrusion is to a great extent based on trial and error and often involves full size experiments. Numerical simulations can most likely replace many of these experiments, which are often both expensive and time consuming. The motivation for this research project is a request for accurate finite element models that can be used in process design and development of stainless steel tube extrusion. The models will be used to investigate the effect of different process parameters on the quality of the extruded tube. In the work presented in this thesis, thermo-mechanically coupled simulations of glass-lubricated tube extrusion were performed. Extrusion models in two and three dimensions were developed. Only extrusion problems with radial symmetry were considered. Simulations were carried out using the commercial code MSC.Marc, which is a Lagrangian finite element code. Frequent remeshing was therefore needed during the analyses. The models were validated by comparing predicted values of extrusion force and exit surface temperature with measurements from an industrial extrusion press. The two- dimensional model was shown to provide good and fast solutions to extrusion problems with radial symmetry. A two-dimensional model is sufficient for many applications and this model is planned to be used for solving process problems further on. For the three-dimensional model it was concluded that a very fine mesh would be needed to successfully predict the extrusion force using four-node tetrahedrons. This would result in unacceptably long computational times. The future work will be aiming at improving the three- dimensional model in order obtain accurate results within a reasonable time. To obtain reliable simulation results a good constitutive model is crucial. This work has focused on the use of physically based material models, which are based on the underlying physical processes that cause the deformation. It is expected that these models can be extrapolated to a wider range of strains, strain rates and temperatures than more commonly used empirical models, provided that the correct physical processes are described by the model and that no new phenomena occurs. Physically based models are of special interest for steel extrusion simulations since the process is carried out at higher strain rates than what are normally used in mechanical laboratory tests. A dislocation density-based material model for the AISI type 316L stainless steel was used in the finite element simulations included in this thesis. The material model was calibrated by data from compression tests performed at different temperatures and strain rates. / <p>Godkänd; 2006; 20070109 (haneit)</p>