| 1. |
- Ghasemi, Rohollah, 1983-
(författare)
-
Tribological and Mechanical Behaviour of Lamellar and Compacted Graphite Irons in Engine Applications
- 2015
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There has been much discussion about the beneficial uses of lamellar graphite iron in piston rings–cylinder liner systems, where a good combinations of both thermal and tribological properties are essential. The excellent tribological performance of lamellar iron under such sliding conditions is principally associated with lubrication behaviour of the graphite particles which are distributed as lamellas throughout the matrix. During sliding, graphite particles are extruded and smeared onto the counterfaces, act as solid lubricating agents and form a thin graphite film between the sliding surfaces. Although this process especially, during the running-in period significantly changes the sliding wear response of the components, the exact mechanism behind of this phenomenon has rarely been discussed in previous studies.It is tribologically beneficial to keep the graphite open, particularly in applications where the scuffing issues do matter. In this thesis, the main causes involved in closing the graphite lamellas are discussed, with a focus on matrix plastic deformation that occurs during sliding. In first step, the relationship between graphite lamellae orientation and plastic deformation was investigated. To do so, two piston rings, belonging to the same two-stroke marine engine operated for different periods of time, were selected and compared to the unworn sample. The worn piston rings displayed a substantial decrease in both frequency and area fraction of the graphite lamellas. Most of the lamellas were closed as a result of plastic deformation of matrix. This happening was caused mainly by the interaction between abrasive particles and metallic matrix. Additionally, it was found that graphite lamellas parallel or near-parallel to the sliding direction exhibited maximum closing tendency under sliding condition.In next step, to have a better understanding of the graphite film formation mechanism and matrix deformation role in closing the graphite lamellas, microindentation and microscratch testing were performed on typical lamellar iron. The qualitative results showed a similar mechanism involving in graphite contribution to lubricate the sliding surfaces. Moreover, microindentations made nearby the graphite lamellas demonstrated that the deformation of the matrix causes the formation of cracks in the centre of the graphite lamellas, compressing and then extruding the graphite from its natural position, irrespective of the lamellas′ size. Furthermore, it was found that subsurface graphite orientation had a large influence on the extrusion behaviour, in that, for graphite lamellas oriented towards the indenter, the effect was observed more pronounced.Furthermore, an improved fully ferritic solution strengthened compacted graphite iron was produced for future wear studies. The effects of different Si levels and section thicknesses on tensile properties and hardness were investigated as well. The influence of Si content and section thickness on mechanical properties was revealed by improving the materials strength and slightly enhancing the hardness through increasing Si content. Besides, Si addition up to 4.5 wt% significantly affected the strength and elongation to failure of cast samples.
|
|
| 2. |
- de Alwis, Pahansen, 1980-
(författare)
-
On Evaluation of Working Conditions aboard High-Performance Marine Craft
- 2018
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High-Performance Marine Craft (HPMC) is a complex system confronted by the stochastic nature of the waves challenging the safety of life at sea. The personnel aboard these craft are vulnerable to detrimental conditions, in fact, limiting the system’s performance evoking the significance of the Human Factors Integration (HFI) in the design and operation of these craft. The risks related to the work environments at sea have inadequately been investigated. A consistently identified fact is that the exposure to work environments containing vibration and repeated shock elevates the risk of adverse effects on human health and performance. In the event that the exposure risk is known, the situation can be managed by the operators and the legislated health and safety demands can be achieved by the employer. Moreover, when quantification of the exposure-effect relationships is potential, human factors, in terms of health and performance, can be integrated into HPMC design and operation. However, the knowledge is limited about the adverse health and performance effects among the High-Performance Marine Craft Personnel (HPMCP), the factors causing theses effects and their relationships.The thesis presents a holistic approach for the integration of human factors, in terms of health and performance, into HPMC design and operation. A research program has been designed branching the design and operational requirements of HPMC concerning HFI. A method is introduced for a real-time crew feedback system, which monitors and characterizes vibration and shock conditions aboard HPMC, enabling determination of the risk of acute injuries due to the high-intensity instantaneous impact exposure and the acquired risk of adverse health and performance effects due to the accumulated vibration exposure. This brings forth the requirement of epidemiological studies in order to strengthen the exposure-effect relationships. Therefore, web-based questionnaire tools are developed, validated and pilot tested for cross-sectional and longitudinal investigation of health and performance in HPMCP. The work exposure is measured aboard HPMC in terms of vibration and investigated in relation to the adverse health and performance event onsets, and the ride perception of the personnel aboard.The introduced method for the real-time crew feedback is capable of informing the exposure risk in terms of human health and performance. The questionnaire tools are feasible for epidemiologically surveying HPMCP and similar populations providing data for investigating adverse health and performance effects, risk factors and their relationships. Promising trends are observed between the quantified work exposure and the health and performance onsets, and the human perception.The work will be continued to identify the exposure-effect relationships facilitating better use of the existing standards, supporting ongoing development of the existing standards and providing information to draw appropriate design and operational limits in rules and regulations.
|
|
| 3. |
- Eriksson, Anders
(författare)
-
Cathodic Arc Synthesis of Ti-Si-C-N Thin Films from Ternary Cathodes
- 2010
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cathodic arc deposition is a powerful technique for thin film synthesis, associated with explosive phase transformations resulting in an energetic and highly ionized plasma. This Thesis presents film growth through arc deposition from compound cathodes of Ti3SiC2, providing source material for plasma and films rich in Si and C. The interest for the resulting Ti-Si-C-N films is inspired by the two ternaries Ti-Si-N and Ti-C-N, both successfully applied as corrosion and wear resistant films, with a potential for synergistic effects in the quarternary system.When using a rotating substrate fixture setup, which is common in high capacity commercial deposition systems, the repeated passage though the plasma zone results in growth layers in the films. This effect has been observed in several coating systems, in deposition of various materials, but has not been explained in detail. The here investigated layers are characterized by a compositional modulation in Si and Ti content, which is attributed primarily to preferential resputtering in segments of rotation when the plasma has high incidence angle towards the substrate normal. For depositions in a non-reactive environment, the films consist of primarily understoichiometric TiCx, Ti, and silicide phases, and display a modest hardness (20-30 GPa) slightly improved by a decreasing layer thickness. Hence, the side effects of artificial layering from substrate rotation in deposition systems should be recognized.Adding N2 to the deposition process results in reactive growth of nitride material, formed in a wide range of compositions, and thereby enabling investigation of films in little explored parts of the Ti-Si-C-N system. The structure and properties of such films, comprising up to 12 at% Si and 16 at% C, is highly dependent on the supply of N2 during deposition. Superhard (45-50 GPa) cubic-phase (Ti,Si)(C,N) films with a nanocrystalline feathered structure is formed at N-content of 25-30 at%. At higher N2 deposition pressure, C and Si segregate to column and grain boundaries and the cubic phase assumes a more pronounced nitride character. This transformation is accompanied by substantially reduced film hardness to 20 GPa. Ti-Si-C-N films thus display a rich variety of structures with favorable mechanical properties, but in the regime of high Si and C content, the amount of N must be carefully controlled to avoid undesirable formation of weak grain boundary phases based on Si, C and N.
|
|
| 4. |
- Lanemo Myhrinder, Anna, 1975-
(författare)
-
Restricted antigen recognition in B cell chronic lymphocytic leukemia
- 2009
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Chronic lymphocytic leukemia (CLL) cells are considered to be derived from antigen-exposed B cells. To further explore the antigen-driven selection behind the leukemogenesis of CLL, we performed immunoglobulin (Ig) specificity screening of 7 CLL cell lines and 23 primary CLL clones from patient peripheral blood. We also included a recombinant monovalent monoclonal antibody (mAb) belonging to a subset of CLL cases with identical or semiidentical heavy chain complementarity determining region 3 (HCDR3) of the IGHV3-21 gene rearrangement. We found CLL mAb specificities against vimentin, filamin B, cofilin-1, proline-rich acidic protein 1, cardiolipin, oxidized low density lipoprotein and Streptococcus pneumoniae polysaccarides. These molecules are functionally associated with microbial infection and/or apoptotic cell removal. An antigen-driven selection would therefore imply that CLL B cell precursors are involved in the elimination and scavenging of pathogens and apoptotic cells, which could trigger the development of the disease.The limited in vitro survival of CLL cells makes Epstein-Barr virus (EBV) immortalization of CLL cells a useful experimental model for studies on antibody-specificity screening. Considering the intricate procedure of EBV transformation of CLL cells and the many false cell lines used worldwide, we also wanted to characterize and evaluate the authentic origin of several previously established CLL cell lines and their normal lymphoblastoid counterparts. Three of the CLL cell lines tested were truly authentic (I83-E95, CLL-HG3 and CII), two had features of a biclonal Ig expression (232B4 and WaC3CD5+), one was only tentatively verified (PGA-1), whereas one cell line could not be verified (EHEB) due to lack of original patient cells for comparison. Two of the presumed normal lymphoblastoid cell lines tested were shown to be a neoplastic CLL clone. This study emphasizes the importance of proper cell line authentication and we will continue to verify additional cell lines not yet proven authentic.In conclusion, we provide evidence for natural Ab production by CLL cells and suggest that these cells might be derived from B cell precursors involved in the innate immunity and, thus, providing a first-line-defence against pathogens and in elimination of apoptotic cells.
|
|
| 5. |
- Razola, Mikael, 1984-
(författare)
-
On Structural Design of High-Speed Craft
- 2013
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development in structural design and construction of high-speed craft has been extensive during the last decades. Environmental and economical issues have increased the need to develop more optimized structures, using new material concepts, to reduce weight and increase performance efficiency. However, both lack of, and limitations in design methodology, makes this a difficult task.In this thesis a methodological framework which enables detailed studies of the slamming loads and associated responses for high-speed planing craft in irregular waves is established. The slamming loads can either be formulated based on numerical simulations, or on experimental measurements and pressure distribution reconstruction. Structure responses are derived in the time-domain using finite element analysis. Statistical methods are used to determine design loads and lifetime extreme responses.The framework is applied to perform phenomenological studies of the slamming loading conditions for high-speed craft, and used to highlight and quantify the limitations in the prevailing semi-empirical method for design load determination with respect to slamming. A number of clarifications regarding the original derivation and the applicability of the prevailing semi-empirical method are presented. Finally, several potential improvements to the method are presented and the associated implications discussed.The long-term goal of the research project is to establish a method for direct calculation of loads and response for high-speed planing craft, which can enable design of truly efficient craft structures. The methodology and the results presented in this thesis are concluded to be important stepping-stones towards this goal.
|
|
| 6. |
|
|
| 7. |
- Skoglund, Lukas, 1988-
(författare)
-
Optimal weather routing using ensemble weather forecasts
- 2015
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ships small and large all battle the elements when crossing the worlds oceans. As such, ships are designed to operate in situations with high speed winds and heavy waves. There are however limits to what any ship can handle safely and it is thus important to avoid the worst weather systems as much as possible. To do this ships are routed using weather data, gathered as statistical seasonal averages or numerical forecasts, in a process called weather routing. With increased capabilities to model ship performance and seakeeping numerically, using computers, weather routing evolved to what is usually called route optimization. In route optimization weather forecasts are used to compute the most ecient route. How to determine which route is most ecient is up to the ship operator, usually some combination of fuel consumption and sailing time is used together with constraints related to safety. This thesis explores the implications of unreliability in weather forecasts on route optimization and howensemble weather forecastsmay be used to improve route optimization.In paper A a route optimization method that uses the ensemble weather forecast to compute routes is developed and tested against standard route optimization methods. The results show that routes optimized using the ensemble weather forecasts are more reliable in their predictions of fuel consumption and arrival time at the destination.In paper B the relationship between forecast reliability and the risk of late arrival is explored through the use of arobustnessmeasure based on the ensemble weather forecast.In paper C the research presented inpaper Bis continued and extended. The relationship between therobustnessof a route and the likelihood of late arrival is investigated. The eect of seakeeping constraints on the robustnessmeasure is explored. Finally a method of using the robustnessmeasure for route optimization is developed and tested. The results show that this method can reduce the risk of late arrival without increasing fuel consumption on average.
|
|
