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- Ghasemi, Rohollah, 1983-
(författare)
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Tribological and Mechanical Behaviour of Lamellar and Compacted Graphite Irons in Engine Applications
- 2015
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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.
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| 4. |
- Wiklund, Daniel, et al.
(författare)
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Evaluation of surface topography parameters for friction prediction in stamping
- 2004
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Ingår i: Wear. - Amsterdam : Elsevier. - 0043-1648 .- 1873-2577. ; 257:12, s. 1296-1300
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Tidskriftsartikel (refereegranskat)abstract
- The continued globalisation of the automotive industry, leading to increasing demands for competitiveness and escalating legislative requirements, is the main driving force of research activities of steel sheet surfaces. Recent studies on the stamping process have been carried out among others within AUTOsurf, a project funded by the European Community, and by Wihlborg and Crafoord. The purpose of this study was to evaluate the viability of the proposed parameters for friction prediction. Seventeen different surface topographies were investigated. The sheet materials were either, hot-dip galvanised, electrogalvanised or galvannealed, and electron beam or electric discharged textures. The frictional response was measured in a bending under tension (BUT) test under mixed lubricated conditions. This BUT test simulates the conditions of the die radius in a stamping tool. The laboratory test differs from the experimental work performed in AUTOsurf which simulated the conditions of the holding-down plate. In spite of the differences in test equipments in AUTOsurf, e.g. the rotational friction tester (RTF), on a comparison the correlation of frictional response was significant. But neither of the proposed parameters could predict the frictional response with sufficient accuracy in this study. In addition, the friction model in AUTOsurf describes peak lubrication as a dragging phenomenon on sliding surfaces. The movement eased friction in inverse proportion to the average peak area. However, the trend in this study showed the opposite, movement eased friction proportionally to the average peak area. The result indicates a switch of dominant friction mechanism when the sliding velocity is increased, i.e. from a dragging phenomenon at low velocities to micro-hydrodynamic wedge effects at high velocities.
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| 5. |
- Begovic, Ermina, et al.
(författare)
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Experimental modelling of local structure responses for high-speed planing craft in waves
- 2020
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Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 216
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Tidskriftsartikel (refereegranskat)abstract
- The modelling of planing craft dynamics in waves and related fluid-structure interaction is a hard challenge due to the highly nonlinear, transient and stochastic nature of the whole process. This paper explores the prospectives of detailed experimental modelling of the local structure responses for high-speed planing craft in waves. A novel experimental setup is presented where a well-defined model structure is integrated into the hull bottom of a typical planing craft model. The model is instrumented for measuring strains in the model structure, related slamming pressures, craft rigid body motions and accelerations. The experimental setup is thoroughly described and motivated and crucial aspects of the setup are verified through testing in idealized static loading conditions and by modal analysis. The capabilities of the experimental setup are demonstrated through systematic experiments in regular waves. The most indicative results are presented and discussed in relation to corresponding results from time-domain simulations The presented experimental modelling approach is concluded to enable uniquely detailed studies of the complete slamming related fluid-structure interaction process and provides a good tool for further research and development towards establishment of first principles-based methods for hydrodynamic and structure design of high-speed planing craft.
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| 6. |
- Manderbacka, Teemu, et al.
(författare)
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An overview of the current research on stability of ships and ocean vehicles: The STAB2018 perspective
- 2019
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 186
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Tidskriftsartikel (refereegranskat)abstract
- The paper provides an insight into contemporary research on ship stability and identifies the possible directions for future research by reviewing a selection of papers published in STAB 2015, ISSW 2016 & 2017. These works have been organized in different sections, according to the main thematic areas of research, covering intact and damage stability, regulatory issues including probabilistic approaches, advanced numerical methods for ship motion and stability failure prediction including roll damping, operational issues related to ship stability and environmental modelling. Furthermore, the educational potential of STAB/ISSW is exemplified. This review paper is a joint effort within the SRDC (Stability R&D Committee).
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| 7. |
- de Alwis, Pahansen, 1980-
(författare)
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On Evaluation of Working Conditions aboard High-Performance Marine Craft
- 2018
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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.
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| 9. |
- Zu, Marion, et al.
(författare)
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Specifying Seakeeping Criteria for Efficient Task Performance
- 2022
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Ingår i: Proceedings 15th International Symposium on Practical Design of Ships and Other Floating Structures PRADS 2022.
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Konferensbidrag (refereegranskat)abstract
- Determining the operability of a vessel is a critical task for the naval architect since it provides valuable information for vessel owners and operators on the vessel’s performance. This task requires a seakeeping analysis and a set of seakeeping criteria to evaluate predicted vessel motions. These seakeeping criteria link the performance and safety of the crew and vessel to operability. Existing seakeeping criteria (e.g., NORDFORSK, NATO STANAG 4154) are specified for certain vessel types and not applicable to different tasks and operational activities aboard work vessels such as pilot boats, ocean research vessels, dredgers, pipe laying crane vessels. Being relatively small in size, these work vessels are susceptible to the perils of waves, yielding motion responses that can degrade crew performance. This paper proposes a framework for specifying seakeeping criteria for efficient task performance, focusing primarily on the effects of motions on the crew and system performance. Findings from preliminary interviews with some crew at the Swedish Maritime Administration and the Swedish Sea Rescue Society align with the literature on the effects of motions on crew performance, including motion-induced interruptions, motion-induced fatigue, motion sickness, and effects on motor skills and perception. These findings from the interviews are used in a case study to demonstrate the approach of the proposed framework. The proposed framework refines further and adds to the established structure of the traditional seakeeping assessment since it captures, in addition, the effect of motions on crew performance.
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| 10. |
- Malmqvist, Johan, 1964, et al.
(författare)
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Optional CDIO Standards : Sustainable development, Simulation-based mathematics, Engineering entrepreneurship, Internationalisation & mobility
- 2020
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Ingår i: 16th International CDIO Conference, CDIO 2020 - Proceedings. - : Chalmers University of Technology. ; 1, s. 48-59
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Konferensbidrag (refereegranskat)abstract
- An effort to update the CDIO Standards from version 2.1 to 3.0 was started in 2017 (Malmqvist et al., 2017) and further outlined in 2019 (Malmqvist et at., 2019). The aims were to incorporate external changes to the context of engineering education, to address criticism that had been raised against earlier versions of the standards, and to establish an extendable CDIO framework architecture. The work has resulted in that the original twelve CDIO standards, from now on named “core” CDIO standards, will be complemented by “optional” CDIO standards, that codify additional educational best practices that have been developed within the CDIO community in the same format as the original CDIO standards. Eleven optional standards have been proposed (Malmqvist et al., 2019). This paper accounts for the elaboration of the subset of the proposed optional standards that were recommended for further development by the CDIO Council in November 2019. These recommended optional standards are presented as full texts, i.e., including descriptions, rationale and rubrics. The described optional standards are: Sustainable development, Simulation-based mathematics, Engineering entrepreneurship and Internationalization & mobility.
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