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  • 1.
    Adolfsson, Robin
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Jönsson, Caroline
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Är SundaHus materialklassning kompatibel med Miljöbyggnads, BREEAMs och LEEDs materialkrav?: En studie om SundaHus miljöklassningar.2015Independent thesis Basic level (university diploma), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [en]

    We live in a society where there is a shortage of housing and the demand for new and sustainable buildings is growing. The houses that are being built today are focused on being energy efficient to save resources. Something that is forgotten is the choice of materials to house constructions. Materials can affect nature and people from the cradle to the grave by for example material hazardous components. The certification systems Miljöbyggnad, BREEAM and LEED have been checked and their material criteria have been defined. Through a selection of construction materials taken from SundaHus a review has been made of these materials towards the certification systems´ criteria on materials to see if they are compatible. The minority of the criteria were reviewed to separate materials and could be verified in SundaHus. Almost all materials passed the criteria that could be used of Miljöbyggnad and BREEAM regardless of classification in SundaHus. None of the LEED criteria were compatible with SundaHus for separate materials. The fact that the worse classifications in SundaHus could pass the criteria that were reviewed indicates that the requirements in environmental certification systems are too low. Higher and more demands should be made on individual materials and the hazardous substances in them.

  • 2.
    Arvidsson, Johan
    et al.
    Karlstad University, Faculty of Technology and Science.
    Leidefeldt, Marcus
    Karlstad University, Faculty of Technology and Science.
    Unosson, Tobias
    Karlstad University, Faculty of Technology and Science.
    Ergonomic Cabin Access: Utveckling av in- och ursteg till hög lastbilshytt2006Independent thesis Basic level (professional degree), 20 points / 30 hpStudent thesis
    Abstract [en]

    This degree project was performed by students of the Innovation and design engineering programme on Karlstad University, Sweden. Group members have been Johan Arvidsson, Marcus Leidefeldt and Tobias Unosson. The degree project consisted of 20 weeks of work of which 5 was an individual study in literature. The project carried out during the spring of 2006.

    Assigner for the project was Hedenberg Advanced Vehicle Design, HAVD, who is a development company serving the vehicle industry and specializing in interior parts and trim. Contacts were Björn Hedenberg and Ingemar Carlson, HAVD. Examiner at Karlstad University was Lennart Wihk. The project was also collaboration together with VOLVO Truck Car Corp in Gothenburg.

    The task the students were given was to improve and develop a new solution for truck drivers, getting in and out of high trucks. A goal with the project was to build a functioning prototype on a VOLVO truck to be shown at the exhibit for degree projects in Karlstad, May 2006.

    In this project the students participated in a project management course given by HAVD in their facilities. The group toke part of a new development method originated from the vehicle industry. This method was used as a frame for the entire project and consisted of three phases, the idea phase, research phase and the realization phase. Between each phase of the project there was a point called a gate, in which important decisions were maid in the group together with HAVD.

    The project resulted in a mechanical lift, mounted onto the side of the truck transporting the driver safely up and down. The solution was named ECA, Ergonomic Cabin Access. Drawings for the concept and its mounting were completed along with an economic calculation. The final result is developed with focus on the driver ergonomics with a sensible construction using available components. The core in the construction is the so called linear motion drive. This device transforms a rotating force into a linear motion. The concept was adapted to fit a VOLVO truck by replacing the trucks previous three footsteps.

    The final concept was presented at HAVD and Karlstad University at the exhibit for degree projects, 30 May 2006. The concept could not however be built into a prototype due to financial reasons. The degree project ECA resulted in drawings, renderings, animations and this academic report.

  • 3.
    Axelsson, Mikael
    et al.
    Karlstad University, Faculty of Technology and Science.
    Joelsson, David
    Karlstad University, Faculty of Technology and Science.
    Åkman, Karl
    Karlstad University, Faculty of Technology and Science.
    NEOS Office Workstation 2007: Daifukudesigns, Barcelona2008Independent thesis Basic level (professional degree), 15 points / 22,5 hpStudent thesis
    Abstract [en]

    The project consisted of developing an office workstation specially designed to compete at the Spanish market. The assignment was received from the Daifuku Designs, a design company in Barcelona, Spain. Daifuku Designs are well experienced in various kinds of product and interior design, but has not designed office furniture earlier. The project’s purpose was to introduce the company to the branch of office furniture.

    The research phase consisted in three different parts, a survey concerning office work that was handed out to Swedish and Spanish office workers and cleaning staff, studies of the world leading companies in the branch of office furniture and educational visits at different showrooms and offices.

    The project resulted in a desk that is offering a flexible space dividing system and a unique cord solution. The space dividers can be put anywhere along the desktop and are easily moved by hand. All the cords and cables are hidden in the desk and computers, phones, e.g. can be installed anywhere on the desk. The desk can be used both separately and in big office landscape. Flexibility is a common sales argument and the demand of this kind of flexibility is constantly growing. The trends to hire personnel and to work in temporary project groups are two reasons to the growing demand. The office furniture needs to be able to be used in different ways when the constellation of the project group is changing. It is a big advantage if the same desks can be used for different occasions.

  • 4.
    Cinca, Nuria
    et al.
    Univ Barcelona, Thermal Spray Ctr CPT, Dept Ciencia Mat & Engn Met, C Marti & Franques 1, E-08028 Barcelona, Spain..
    Vilardell, Anna M.
    Univ Barcelona, Thermal Spray Ctr CPT, Dept Ciencia Mat & Engn Met, C Marti & Franques 1, E-08028 Barcelona, Spain..
    Dosta, Sergi
    Univ Barcelona, Thermal Spray Ctr CPT, Dept Ciencia Mat & Engn Met, C Marti & Franques 1, E-08028 Barcelona, Spain..
    Concustell, Amadeu
    Univ Barcelona, Thermal Spray Ctr CPT, Dept Ciencia Mat & Engn Met, C Marti & Franques 1, E-08028 Barcelona, Spain..
    Garcia Cano, Irene
    Univ Barcelona, Thermal Spray Ctr CPT, Dept Ciencia Mat & Engn Met, C Marti & Franques 1, E-08028 Barcelona, Spain..
    Maria Guilemany, Josep
    Univ Barcelona, Thermal Spray Ctr CPT, Dept Ciencia Mat & Engn Met, C Marti & Franques 1, E-08028 Barcelona, Spain..
    Estrade, Sonia
    Univ Barcelona, Dept Elect, LENS MIND IN2UB, C Marti & Franques 1, E-08028 Barcelona, Spain..
    Ruiz, Alicia
    Univ Barcelona, Dept Elect, LENS MIND IN2UB, C Marti & Franques 1, E-08028 Barcelona, Spain..
    Peiro, Francesca
    Univ Barcelona, Dept Elect, LENS MIND IN2UB, C Marti & Franques 1, E-08028 Barcelona, Spain..
    A New Alternative for Obtaining Nanocrystalline Bioactive Coatings: Study of Hydroxyapatite Deposition Mechanisms by Cold Gas Spraying2016In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 99, no 4, p. 1420-1428Article in journal (Refereed)
    Abstract [en]

    The present article is intended to study the deposition mechanisms of bioactive hydroxyapatite (HA) particles by means of Cold Gas Spraying (CGS). A comparison of the deposition on two different substrates (Ti6Al4V and Al7075T6) and different particle sizes is presented. Although this is a more specific deposition technique for ductile materials, it is here shown that, in certain conditions, ceramic deposition is possible despite the inherent low ductility. The resulting internal structure and the features at the particle-substrate interface are discussed in view of Transmission Electron Microscopy examinations of a Focused Ion Beam lift-out prepared sample. Mainly, under shock compressive loading, the porous sintered powder proceeds through pore collapse, fragmentation and densification as well as grain refinement. The process is described through different plastic mechanisms in ceramics. This opens a new alternative route to produce nanocrystalline HA coatings through a cost-effective process.

  • 5.
    Doverholt, Therese
    Karlstad University, Faculty of Technology and Science.
    Slagseghet hos kalldragna sömlösa rör: Kartläggning av olika parametrars påverkan2007Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Slagsegheten hos stål är komplext beroende av ett antal olika parametrar, som i olika grad påverkar varandra.

    Många betydande och viktiga ledtrådar har hittats som förhoppningsvis kan ge en bredare förståelse varför slagsegheten varierar och varför den inte alltid uppnås i nuvarande process.

    Studien har utförts på kalldragna sömlösa rör, med stålsort EN 10305-1. Projektet innefattar ett antal olika produkt specifikationer med olika dimensioner, med lite olika kemiska sammansättning. På grund av slagseghetskraven på industriella produkter var det viktigt att utvärdera vilka parametrar som påverkar. En utvärdering gjordes dels av resultat från slagseghetsprovning efter påverkande processer, och dels från utvärdering av stålets mikrostruktur.

    Förutom dimension och kemisk sammansättning, varierar processlinjens faktorer. Den första processen som påverkar är kalldragningen som i denna studie har haft reduktioner mellan 15% och 31%. Avspänningsglödgningens temperatur påverkar även, där temperaturerna 525 oC, 575 oC och 600 oC är de som använts på produkterna i projektet. Vissa av projektets produkter har även normaliserats, och resultaten tyder på att detta är en mycket viktig process om man ser till slagseghet.

    Målsättningen var att får fram omslagskurvor vid olika tillstånd av stålet. Utifrån dessa tillsammans med utvärdering av stålets mikrostruktur och kemisk sammansättning kunde flera diskussioner föras.

    Den viktiga slutledningen som kunde dras var att inga faktorer är ensam avgörande för slagsegheten i den här studien. Den kemiska sammansättningen påverkar ihop med processlinjens olika faktorer. Man bör ligga på en temperatur för avspänningsglödgning över 550 oC. Projektet visar även på att större dimensioner påverkar slagsegheten negativt.

    Två viktiga felmarginaler kan ha påverkat resultaten i projektet, dels positionen för vart anvisningen görs på provstaven i förhållande till rören och dels användandet av en praxis som beräknar resultat från provning med reducerade provstavar. En undersökning av dessa felmarginaler gjordes, och resultaten var tydliga. En mer noggrann provuttagning bör göras, och man bör vara mer försiktig vid användandet av praxisen.

  • 6.
    Emanuelsson, Christian
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Scanning Electron Microscopy study of Macbat regeneration effect on lead-acid battery electrodes2013Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Electrodes from lead-acid batteries were studied using scanning electron microscopy and energy dispersive spectroscopy. This to observe the effects of cycling on the batteries and how a capacity recovery process, known as Macbat regeneration, affected the active material with focus on hard sulphation. First, two new batteries were cycled for two months and electrodes from them were studied when the batteries were new, cycled, fully charged after cycling and regenerated after cycling. Then electrodes from a separate battery that had been used in industry was studied prior to and after Macbat regeneration. On the cycled batteries it was found that after the cycling of the batteries no hard sulphation were present on the electrodes. The study of the separate battery showed that the battery had hard sulphation in its electrodes and that the Macbat regeneration was able to remove hard sulphation both on the surface of the electrodes and also inside the active material.

  • 7.
    Klevsäter, Anton
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Ytbehandling för att motverka uppbyggning: Undersökning av olika ytbehandlingsmetoder och material för applikation i en mjukpappersmaskin2017Independent thesis Basic level (university diploma), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [en]

    This exam report includes a survey of surface treatment materials and their associated surface treatment methods for application in a tissue machine commissioned by Valmet AB. The tissue machine produces 24 hours a day in a demanding environment consisting of water, heat, oils, glue, dust and various chemicals. The demanding environment makes it difficult to maintain the machine clean due to the limited access at various machine parts when the machine is operating, which can lead to both personal risks and risks for production stoppages. These factors form the basis for the build-ups that takes place at various machine parts. Mostly, it’s about paper fibres that either are loose and dry or clustered into lumps. They also appear as lumps of fibres held together by oil, glues or other chemicals. Over time, they can loosen and, in the worst case, are due to breakages and production failures. The build-ups can also destroy the function of moving machine parts or lead to corrosion.

    The commission was assigned by Bengt O Andersson and Mickey Lindevall at Valmet AB. The project was conducted as the examining part in the course Degree Project for the Bachelor of Science in Mechanical Engineering, MSGC17, at the faculty of health, science and technology at Karlstad university. The project was carried out individually by a student at the Bachelor of Science program in Mechanical Engineering at Karlstad university.

    This degree project has taken precedence where the previous degree project at Valmet AB completed its work. The previous degree project has served as a reference document in this report to work out a requirement specification and identifying machine parts that are desired to undergo some form of surface treatment. The acting environments that exist at the various machine parts that are desired to be surface treated have also been examined from the previous degree project. This report has taken a different approach compared to the previous thesis work and is instead directed towards finding suitable surface treatment materials and associated application methods using the material database, CES EduPack.

    The purpose of the degree project has been to present suitable surface treatment materials and associated surface treatment methods. These are to solve the existing problems, thus facilitating cleaning and maintenance of the tissue machine. To achieve this, a list of suitable materials and associated surface treatment methods has been presented. From this list, conclusions are drawn to find as good surface treatment materials and its associated application methods as possible. With these, the problem should be eliminated or reduced drastically for the number of build-ups regarding the treated machine parts.

    The objective for this project thesis has been to analyse and proposing suitable methods and materials for surface treatments. With the chosen method and material for the surface treatment, the surfaces upon application are to achieve such properties that build-ups do not adhere to them. The project also contains a requirement specification that has been translated into restriction terms that all investigated material candidates have had to fulfil to be classified as suitable material candidates. The report has also taken a stand to the literature and theory available in the subject area to further investigate what materials are currently used in similar industrial applications. The information that has been processed has, in a final phase, been used as a basis for the list of suitable surface treatment materials and their associated surface treatment methods presented in the report.

  • 8.
    Norrby, Alexander
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Nanotribological characterization of advanced tool steels2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

       Tribological  problems  of  tool–work  piece  interaction  is  a  key  aspect  influencing  product quality,  process  performance  and  tool  lifetime.  For  example,  in  sheet  metal  forming operations, sliding contact may cause adhesive wear of sheet materials with build up of worn material on the tool surface. This tribological problem often resulted in loss of tolerance and product quality and is called galling.  

       It  was  demonstrated  that  tendency  to  adhesive  wear  depends  on  the  steel  grade,  which means high importance of chemical- and phase-constitution of the tool steel. It was suggested that  adhesion  to  the  matrix  is  critical  due  to  metal  to  metal  contact  while  carbide  phase prevent adhesion of conterbody materials. Nevertheless, in macroscale tests it is difficult or even impossible to separate contribution of each phase into the wear mechanism.   

       In the present work, selected steels are to be investigated  at nanoscale by means of AFM facilities. Main attention will be paid on adhesion and frictional properties of steel matrix and primary  phase.  As  expected  and  reported  in  several  articles,  carbides,  carbonitrides  and nitrides   may   behave   differently,   contributing   into   the   final   performance   differently. Additional  attention  will  be  paid  on  phase  size  and  distribution,  meaning  they  are  also important parameters influencing tribological behaviour.

  • 9.
    Pettersson, Viktor
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Study of the effect of process parameters in laser blown powder with superalloys: Varying laser power and scanning speed, analyzing material properties2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Additive manufacturing (AM) is a growing process interesting many companies in many industries. Thereare multiple processes within the familty of AM, but this study focuses on laser blown powder (LBP). LBP involves a laser beam focused on the substrate with powder being blown into the laser beam. The laser beam melts both the powder and the surface of the substrate and as the laser beam moves and the melt pool solidies it leaves a bead of solid material behind. These beads are placed next to each other creating a layer which are then stacked, building the wanted geometry. As the method develops new materials are tested and this study analyses Haynes 282 powder onto Inconel 718 substrate. Multiple process parameters are involved in the LBP method and this study focuses on the impact of laser effect and scanning speed. Each value on the process parameters was inspired by previous reports with similar equipment and process. The laser effect ranges from 1600 W to 700 W, scanning speed ranges between 900 mm/min to 300 mm/min and the powder feeding rate was also varied from 4 g/min to 3 g/min. Each sample was built as a single bead and a multilayer specimen, which is ve layers and 16 beadswide at the bottom and 12 beads wide at the top. When analyzing the samples images from microscopes were mostly used for obtaining results. An image software called ImageJ allowed measurements in an image to obtain penetration depth or primary dendrite arm spacing. ImageJ also allowed measurements of porosity by turning the image binary and calculate the fraction of white and black. The results consists of numerical values and visual analysis of the bead geometry, minimum and maximum penetration, microstructure, porosity, hardness and cracks. The results show an increased bead width around 2 mm to 4 mm and decreased bead height around 0,2 mm to 0,7 mm of single beads with increased laser effect. Increased maximum penetration depth around, 200 μm to 500 μm, withincreased laser effect. More remelt between each deposited layer causing longer dendrites with increasinglaser effect. Porosity is decreased with an increased laser power, going from 0,04 % to 0,15 %. No distinct difference in hardness is observed between the samples, ranging between 255 HV to 310 HV. It is believed that aging causes the increased hardness right above the fusion zone. Cracks were found between dendrites and is believed to be caused by Laves-phases. Most results are comparable to previous similar studies, both as trends and numerical values. The statistics of the study is limited, meaning that all results should not be taken as granted but as a general guide line for more studies. The purpose and goals of the study has been met and completed.

  • 10.
    Rasmusson, Gunnar
    Karlstad University, Division for Engineering Sciences, Physics and Mathematics.
    Analys av tryckslag i rörsystem2006Independent thesis Basic level (professional degree), 15 points / 22,5 hpStudent thesis
    Abstract [sv]

    Sammanfattning

    När en rörledning skall dimensioneras måste den designas för att tåla de tryck som uppstår under stationära förhållanden. Ledningen måste också klara de tryck som kan uppstå under instationära förhållanden, t ex då en ventil stänger eller öppnas. Om en ventil stänger och flödet minskar så omvandlas vätskans rörelseenergi till tryckenergi. Om detta sker snabbt så kallas detta för tryckslag. De tryck som uppstår då kan leda till skador på rörledningar och annan utrustning i ett system.

    Dessa tryck kan simuleras med hjälp av datorprogram. Det finns också förenklade metoder för att beräkna dessa tryck. Dessa förenklade metoder är dock bara giltiga under speciella omständigheter.

    En ca 6000 m lång råvattenledning mellan sjön Hällungen i Stenungsunds kommun och en reservoar i Stenungsund har nyligen dimensionerats med hjälp av en förenklad beräkningsmetod för tryckslag. Det finns dock en misstanke att dessa metoder ger felaktiga resultat, vilket kan göra att ledningen blir över eller underdimensionerad.

    Studiens syfte är att ta reda på hur mycket resultaten från de förenklade beräkningsmetoderna skiljer sig från mer noggrannare simuleringar, samt under vilka förutsättningar dessa metoder gäller.

    Två förenklade metoder beskrivs i rapporten. Rapporten beskriver även en metod som kallas karakteristikmetoden, som är en metod som de flesta kommersiella programvaror använder.

    Dessa metoder tillämpas på det aktuella fallet och resultaten jämförs.

    Resultaten visar att de förenklade metoderna bara gäller under vissa speciella fall.

    Rapporten bekräftar att dessa ekvationer bara kan användas under speciella fall och med stor försiktighet. De kan dock ofta fungera som en första koll för att få reda på ungefärliga värden.

    När dessa förenklade metoder går att använda är bl a kopplad till hur fort en ventil stänger samt ledningens periodtid, d.v.s. den tid det tar för en tryckvåg att gå fram och tillbaka i en ledning.

  • 11.
    Sannemalm, Örjan
    et al.
    Karlstad University, Division for Engineering Sciences, Physics and Mathematics.
    Svensson, Magnus
    Karlstad University, Division for Engineering Sciences, Physics and Mathematics.
    Vibrationsanalys: Vibrationsproblem i travers2007Independent thesis Basic level (professional degree), 15 points / 22,5 hpStudent thesis
    Abstract [en]

    As a part of the Machine engineer-program at Karlstad University this dissertation has been in progress for 15 weeks. The principal is Scana Steel AB, a steelworks in Björneborg and the dissertation concerns one of their cranes. The task was to find sources to vibration and, if possible, eliminate the vibrations that the driver in the wheelhouse finds uncomfortable. To locate the source of the vibrations different analyses have been made with the help of SpectraPro and Vibshape, which are two softwares belonging to the measuring instrument Easy Viber. These two programs gave us the possibility to animate the movements of different components and they also gave us different spectra to analyze.

    The analyses show that the wheelhouse mainly vibrates in three different frequencies. These frequencies appear to be the same as the frequencies from the last cogwheel and the coupling. When determining the frequencies we have also taken some resonance phenomena into consideration.

    The methods how to avoid that the driver is uncomfortable due to the vibrations are numerous and require different sizes of operation. Some actions can, however, easily be tried without any bigger problems.

    Suggested actions are among others dynamic damper, frequency control and damping machine shoes.

  • 12.
    Tofique, Muhammad Waqas
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Initiation and early crack growth in VHCF of stainless steels: Experimental and theoretical analysis2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Mechanical fatigue is a failure phenomenon that occurs due to repeated application of mechanical loads. Very High Cycle Fatigue (VHCF) is considered as the domain of fatigue life greater than 10 million load cycles. Increasing numbers of structural components have service life in the VHCF regime, for instance in automotive and high speed train transportation, gas turbine disks, and components of paper production machinery. Safe and reliable operation of these components depends on the knowledge of their VHCF properties. In this thesis both experimental tools and theoretical modelling were utilized to develop better understanding of the VHCF phenomena.

    In the experimental part, ultrasonic fatigue testing at 20 kHz of cold rolled and hot rolled stainless steel grades was conducted and fatigue strengths in the VHCF regime were obtained. The mechanisms for fatigue crack initiation and short crack growth were investigated using electron microscopes. For the cold rolled stainless steels crack initiation and early growth occurred through the formation of the Fine Granular Area (FGA) observed on the fracture surface and in TEM observations of cross-sections. The crack growth in the FGA seems to control more than 90% of the total fatigue life. For the hot rolled duplex stainless steels fatigue crack initiation occurred due to accumulation of plastic fatigue damage at the external surface, and early crack growth proceeded through a crystallographic growth mechanism.

    Theoretical modelling of complex cracks involving kinks and branches in an elastic half-plane under static loading was carried out by using the Distributed Dislocation Dipole Technique (DDDT). The technique was implemented for 2D crack problems. Both fully open and partially closed crack cases were analyzed. The main aim of the development of the DDDT was to compute the stress intensity factors. Accuracy of 2% in the computations was attainable compared to the solutions obtained by the Finite Element Method.

  • 13.
    Tofique, Muhammad Waqas
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Review of VHCF studies, short crack models and theory of vibrationsManuscript (preprint) (Other academic)
    Abstract [en]

    This literature review loosely connects different concepts of very high cycle fatigue which are of significance within the scope of this thesis work. The ultrasonic fatigue testing equipment and its basic principle of operation is discussed in detail. The phenomenon of damping in the light of theory of vibrations is outlined. The significance of the understanding of damping phenomenon in the ultrasonic fatigue testing is highlighted. On the other hand, SN fatigue data obtained by several researchers for different materials are reviewed. In addition, the fundamental mechanisms responsible for fatigue crack initiation are also summarized.

     

    Considerable attention is focussed on the mathematical models developed for the prediction of growth behaviour of short fatigue cracks. The basic concepts, and models, which led to the development of the distributed dislocation dipole technique, have also been reviewed.

  • 14.
    Tofique, Muhammad Waqas
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Bergström, Jens
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Hallbäck, Nils
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Burman, Christer
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Fatigue initiation and strength of duplex stainless steel strip specimens in the very high cycle fatigue regime2014In: Very high cycle fatigue 6 (VHCF6), 2014Conference paper (Refereed)
    Abstract [en]

    Fatigue studies of cold-rolled duplex stainless strip steel were performed in the very high cycle fatigue life region. The duplex austenitic-ferritic microstructure gives this grade a combination of high mechanical strength and high corrosion resistance. Fatigue properties of thin steel strips are particular due to cold rolling introducing a very fine microstructure. Crack initiation and fatigue strength are controlled by steel microstructure and alloying. The initiation and growth of the very short initial fatigue crack in very high cycle fatigue are unclear and subject to different descriptions. Fatigue test data of thin strip specimens at very high fatigue lives are scarce due to testing difficulties. For practical reasons testing must be performed at ultrasound test frequencies which involves fixturing problems. A test setup including the load chain ultrasonic horn, fixture and specimen was designed for resonance with a horse-shoe design of a screw fixture. The design of the horse-shoe fixture and the specimens along with FEM calculation of eigenfrequency are presented. Fatigue testing was performed at 20 kHz in R=-1 conditions up to fatigue life of 107 to 5*109 cycles. Fatigue strength was tested and crack initiation was studied on the fracture surface using FEG-SEM at the initiation site.

  • 15.
    Tofique, Muhammad Waqas
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Bergström, Jens
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Karlstad University, Faculty of Technology and Science, Materials Science.
    Svensson, Krister
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Very High Cycle Fatigue of cold rolled stainless steels, crack initiation and formation of Fine Granular Area2017In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 100, no 1, p. 238-250Article in journal (Other academic)
    Abstract [en]

    Fatigue tests of cold rolled strip materials, a duplex stainless steel and a martensitic stainless steel, were performed using an ultrasonic fatigue test equipment operating at 20 kHz under a completely reversed tension compression load ratio R =-1. Fatigue test data (SN data) was generated in the VHCF regime and fracture surfaces of the failed specimens were investigated using a Scanning Electron Microscope (SEM). In the duple stainless steel grade, fatigue failures were found to be initiated at surface defects on the side surfaces or corners, created due to cold rolling, of the strip specimens. Features of a Fine Granular Area (FGA) were observed around the crack initiating surface defects on the fracture surfaces. In the martensitic stainless steel grade, fatigue crack initiation occurred due to aluminium-silicon oxide inclusions or surface defects created due to cold rolling of the material. In situ Focussed Ion Beam (FIB) technique was used to extract cross-sections from the FGA around the crack initiating defect on the fracture surface. Transmission Electron Microscope (TEM) investigations of the extracted cross-sections revealed FGAs in immediate vicinity of the crack initiating surface defects. The observed fine grained layers seemed to be composed of nano-sized grains and, thus, could be distinguished from the bulk material. The FGA around the surface crack initiating defects seems to have formed due to localized plastic deformation by stress concentration at the defects.

  • 16.
    Tofique, Muhammad Waqas
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Bergström, Jens
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Svensson, Krister
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Johansson, Sten
    Department of Materials Engineering, Linköping University, Sweden.
    Peng, Ru Lin
    Department of Materials Engineering, Linköping University, Sweden.
    EBSD and TEM analysis of plastic fatigue damage accumulation responsible for fatigue crack initiation and propagation in VHCF of duplex stainless steelsManuscript (preprint) (Other academic)
    Abstract [en]

    Fatigue test data (stress-life) of two duplex stainless steel grades, LDX 2101 and 2304 SRG, in the Very High Cycle Fatigue regime (VHCF) is presented. The fatigue testing is conducted using an ultrasonic fatigue testing equipment operating at 20 kHz under fully reversed tension-compression condition (R=-1). Scanning Electron Microscope (SEM) studies of the fracture surfaces and external surfaces of failed specimens is conducted. Electron Back Scattered Diffraction (EBSD) studies of the axially cut surface of the failed specimens is done to analyse grains near the external surface and crack initiation site. Analysis of accumulation of plastic fatigue damage and growth of cracks in the Crystallographic Growth Region (CGR) is carried out. Transmission Electron Microscope (TEM) analysis of thin foils cut from failed specimens of LDX 2101 is carried out to examine the effect of fatigue loading on dislocation structure. SEM studies of the CGR show features like grain boundaries and fatigue striations. The barrier effect of grain and phase boundaries on short fatigue crack propagation is observed. ECCI images and EBSD analysis show that Persistent Slip Bands (PSBs) are observed in ferrite grains in LDX 2101 grade. On the other hand, no PSBs are observed in any of the grains in 2304 SRG. The TEM observations in thin foils cut from the failed specimen of LDX 2101 show stacking faults in austenite grains. Stacking faults were observed to stop at the grain and phase boundaries.

  • 17.
    Tofique, Muhammad Waqas
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Hallbäck, Nils
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Development of the distributed dislocation dipole technique for the analysis of closure of complex fractures involving kinks and branchesManuscript (preprint) (Other academic)
    Abstract [en]

    This paper presents the development of the distributed dislocation dipole technique (DDDT) for the analysis of crack surface closure of crack cases involving kinks and branches. Crack cases in which closure occurs are analyzed by reformulating the Bueckner's principle taking the contact stresses at the contacting portions of the crack surfaces into account. Stress intensity factors corresponding to opening and sliding mode of deformation at the crack tips are computed. Three test cases involving kinked and/or branched cracks with at least one of the crack segments undergoing crack surface closure when subjected to remote tensile loading are analyzed. The results obtained from the DDDT are compared to those obtained from the Finite Element Method (FEM) analysis of the same crack cases. This comparison shows that the computation of stress intensity factors for the crack cases involving crack surface closure are less acurate compared to fully open crack cases. However, the stress intensity factors are still computed to an accuracy of within 2 percent if the Jacobi polynomial expansions of at least the sixth order are used to represent the crack surface opening and sliding displacements. Higher order Jacobi polynomials lead to increased accuracy.

  • 18.
    Tofique, Wagas
    et al.
    Karlstad Univ, Dept Phys & Engn Sci, S-65188 Karistad, Sweden..
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Karlstad Univ, Dept Phys & Engn Sci, S-65188 Karistad, Sweden..
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Karlstad Univ, Dept Phys & Engn Sci, S-65188 Karistad, Sweden..
    Johansson, S.
    Linkoping Univ, Dept Mat Engn, Linkoping, Sweden..
    Peng, R. L.
    Linkoping Univ, Dept Mat Engn, Linkoping, Sweden..
    ECCl/EBSD and TEM analysis of plastic fatigue damage accumulation responsible for fatigue crack initiation and propagation in VHCF of duplex stainless steels2017In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 100, p. 251-262Article in journal (Refereed)
    Abstract [en]

    Fatigue test data of duplex stainless steel grades, LDX 2101 and 2304 SRG, in the Very High Cycle Fatigue (VHCF) regime is presented. Fatigue testing was conducted using ultrasonic fatigue test equipment operating at 20 kHz under fully reversed tension-compression load condition. Scanning Electron Microscope (SEM) analysis of the fracture surfaces and external surfaces of failed specimens was conducted. Electron Channelling Contrast Imaging (ECCI) and Electron Back Scattered Diffraction (EBSD) studies of the axially cut surface of the failed specimens was done to analyse the accumulation of plastic fatigue damage and fatigue crack growth in the grains adjacent to the external surface and crack initiation site. Transmission Electron Microscope (TEM) analysis of thin foils cut from failed specimens of LDX 2101 was carried out to examine the effect of fatigue loading on dislocation structure. SEM studies of the Crystallographic Growth Region (CGR) showed features like grain boundaries and fatigue striations on the fracture surfaces. SEM analysis of the external surfaces of fatigue loaded specimens showed inhomogeneous accumulation of plastic fatigue damage. ECCl/EBSD analysis showed Persistent Slip Bands (PSBs) in ferrite grains in LDX 2101 grade but no PSBs were observed in any grains of 2304 SRG specimens. The barrier effect of grain and phase boundaries on short fatigue crack propagation was observed. TEM analysis of thin foils cut from the failed specimens of LDX 2101 showed stacking faults in austenite grains and they were seen to stop at the grain and phase boundaries. (C) 2017 Elsevier Ltd. All rights reserved.

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