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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Implementering av höghållfast stål i byggbranschen : Analys av hur höghållfasta stålkonstruktioner kan appliceras för byggnadstekniska verk: fördelar, risker och användningsområden

Mansour, Masis, Frid, Alexander, Bakr, Souzan January 2020 (has links)
Purpose: The purpose of this study has been to investigate the essentials of being able to incorporate high-strength steels (460 MPa and beyond) for structural elements in buildings. As of late, structural steels with a yield point of 355 MPa have been considered standard and have been for the past decade. One of the problems that occur with an increased yield point, is that deflection of structural elements increases, as the Young’s modulus does not increase with increasing yield point. Welding, stability, behavior during fire, and fatigue are also subjects of interest. Method: The study was conducted through several courses of action: a literature review covering the latest research of high-strength steels within the sought-after area of interest, followed by calculations of a truss resting on two columns, being subject to bending moment and compressive force, in both 355 MPa and 700 MPa, in order to review the differences that occur and how they can be counteracted. Lastly, interviews were carried out, where structural engineers gave their thoughts and experiences on the matter at hand. Results: The results show that welding is one of the largest hurdles with being able to utilize high-strength structural steels, though there are newer, more promising methods of welding which can be used, such as electron beam welding. Regarding structural integrity and buckling of structural elements, high-strength steel can be used for trusses, where the structural members are mainly being pulled, opposed to being subject to compressive force. This was shown with the performed calculations, during the interviews, and by the literature overview. Conclusions: The general conclusions of the study is that for welding, further research, education, and training is required for all concerned parts, such as the structural engineers and the on-site welders, which will increase the knowledge regarding how welding of high-strength steels should be performed, but also raise awareness about newer and more modern methods. Fire behavior for high-strength steels are a higher risk factor that should be treated and executed with higher degrees of caution by engineers. Reduction factors for fire affected steel construction elements should be corrected to fit the behavior for high-strength steels as well, as they differ from the current Eurocode 3 for lower class steels. Problems with instability can be counteracted by utilizing the steel in pulled structural members, such as trusses and struts. Lastly, for high-strength steels to be used more widely, structural engineers and manufacturers need to work together for any of the two to profit, as low production rates are costly.
42

Residual stresses in Ti-6Al-4V from low energy laser repair welding / Restspänningar i Ti-6Al-4V av lågenergetisk laserreparationssvetsning

Ericson, Peter January 2018 (has links)
Millimeterstora och svårupptäckta defekter kan uppstå internt i stora och komplexa gjutgods av Ti-6Al-4V, ibland går dessa oupptäckta tills detaljen genomgått mekanisk bearbetning och en stor kostnad redan har gått in i den. Dessa defekter och andra industriella olyckshändelser leder till ett behov av additiva reparationsmetoder där den för tillfället rådande metoden är TIG-svetsning. Denna metod reparerar defekterna men leder till oacceptabla restspänningar vilka kan åtgärdas med värmebehandling som i sin tur kan orsaka ytdefekten alpha case. Därav finns ett industriellt behov av reparationsmetoder som leder till mindre eller negligerbara restspänningsnivåer i reparerad detalj. Detta arbete utfört hos GKN Aerospace – Engine Products Sweden i Trollhättan analyserar eventuella förhållanden mellan parametrarna Effekt, Spot size, och Svetshastighet och de resulterande restspänningarna i ett lågparameterområde på materialet Ti-6Al-4V. En parameterrymd uppspänd av 17 parameteruppsättningar etablerades, svetsades och analyserades med mikrografi. Ur denna rymd simulerades de 8 yttre parametrarna med hjälpa av Finita Elementmetoden i svetssimuleringsmjukvaran MARC och ett förhållande mellan ingående parametrar och resulterande restspänningar undersöktes. En statistiskt säkerställd trend erhölls för att en minskad Svetshastighet leder till minskade tvärspänningar i mitten på en 20mm lång svetssträng. Detta är applicerbart för svetsar nyttjande start och stopplåtar. Det noterades även att en ökning i Effekt eller Spot size, eller en minskning utav svetshastigheten leder till att det av restspänningar utsatta området ökar i storlek. Detta är har implikationer för efterföljande värmebehandling i avgörandet av form och storlek på området som skall värmebehandlas. / Minute defects may occur in large complex Ti-6Al-4V castings, sometimes these are unnoticed until after machining and a high cost has been sunk into the part. These defect and other potential manufacturing mishaps render a need for additive repair methods. The state of the art method TIG welding can repair the parts but may leave unacceptable residual stresses, where the state of the art solution of Post Weld Heat Treatment might create a surface defect known as alpha case. Therefore there is a need for a repair weld method that results in lesser or negligible residual stresses. This thesis, carried out at GKN Aerospace – Engine Products Sweden, Trollhättan analyses the potential relationships between the laser welding parameters Power, Spot size, and Weld speed and the resulting residual stresses in a low energy parameter area on the material Ti-6Al-4V. A parameter box of 17 parameter sets was established, laid down and analyzed under micrograph, of this box the outer 8 parameter sets were simulated via the Finite Element Analysis welding simulation software MARC and a relationship between the input parameters and their resulting residual stresses was analyzed. A statistically significant trend was found supporting the claim that a decrease in transversal stresses in the center of a 20mm weld line is caused by an increase in Weld speed. This has implications for welds using run-on & run-of plates. It was also noted that an increase in Power or Spot size, or a decrease in Weld speed increases the area under residual stress; both as individual parameters and in synergy. This has implications for Post Weld Heat Treatment in determining the size and shape of the area in need of treatment.
43

Projection Nut Welding to High- and Ultra-high Strength Steels / Muttersvetsning av hög- och ultrahöghållfast stål

Englund, Love January 2023 (has links)
In an effort to increase the fuel efficiency of cars more widespread use of higher strength steels is seen for their high strength-to-weight ratio. Thesesteels are more limited in their formability and tendency to harden than conventional steels, complicating manufacturing. This thesis summarizes the available research on resistance projection nut welding to higher strength steels and investigates the accuracy of the simulation program SORPAS when simulating projection nut welds to AlSi-coated Boron steel. It was found that the greatest difficulties in welding coated ultra high strength steels were the metallurgical effects of both the high alloying content of the steel and the coatings interacting with the weld when melting. Although SORPAS was an intuitive program to use for resistance welding and had a wide library of materials available, it was not found to be able to predict the resistance characteristics or results of projection nut welds to coated Boron steel without significant changes to default material parameters. The biggest issue was the delaying effect the coating layer had on the peak resistance, something not observed experimentally. Better results are suggested to be possible after experimentally ensuring the properties of the materials used and importing those values into SORPAS. / I ett försök att öka bilars bränsleeffektivitet används i allt större utsträckning stål med högre hållfasthet på grund av deras goda förhållande mellan styrka och vikt. Dessa stål är mer begränsade i sin formbarhet och tendens att härda än konventionella stål, vilket försvårar tillverkning. Denna uppsats sammanfattar den tillgängliga forskningen om motståndssvetsning med projektionsmutter i höghållfasta stål och undersöker noggrannheten hos simuleringsprogrammet SORPAS vid simulering av projektionsmuttersvetsar i AlSi-belagt borstål. Det konstaterades att de största svårigheterna vid svetsning av belagda ultrahöghållfasta stål var de metallurgiska effekterna av både stålets höga legeringsinnehåll och beläggningarnas interaktion med svetsen vid smältning. Trots att SORPAS var ett intuitivt program att använda för motståndssvetsning och hade ett brett bibliotek av tillgängliga material kunde det inte förutsäga motståndsegenskaperna eller resultaten av projektionsmuttersvetsar mot belagt borstål utan betydande förändringar av standardmaterialparametrarna. Det största problemet var den fördröjande effekt som beläggningsskiktet hade på maximala resistansen, något som inte observerades experimentellt. Bättre överenstämmelse föreslås vara möjlig efter att experimentellt säkerställa egenskaperna hos de material som används och importera dessa värden till SORPAS.
44

Manufacturing Effects on Iron Losses in Electrical Machines

Bourchas, Konstantinos January 2015 (has links)
In this master thesis, the magnetic properties of SiFe laminations after cutting and welding are studied. The permeability and the iron loss density are investigated since they are critical characteristics for the performance of electrical machines. The magnetic measurements are conducted on an Epstein frame for sinusoidal variations of the magnetic ux density at frequencies of 50, 100 and 200 Hz, according to IEC 404-2. Mechanical cutting with guillotine and cutting by means of ber and CO2 laser are performed. The inuence of the ber laser settings is also investigated. Especially the assisting gas pressure and the power, speed and frequency of the laser beam are considered. In order to increase the cutting e ect, the specimens include Epstein strips with 1, 2 and 3 additional cutting edges along their length. It is found that mechanical cutting degrades the magnetic properties of the material less than laser cutting. For 1.8% Si laminations, mechanical cutting causes up to 35% higher iron loss density and 63% lower permeability, compared to standard Epstein strips (30 mm wide). The corresponding degradation for laser cut laminations is 65% iron loss density increase and 65% permeability drop. Material of lower thickness but with the same Si-content shows lower magnetic deterioration. Additionally, laser cutting with high-power/high-speed characteristics leads to the best magnetic characteristics among 15 laser settings. High speed settings have positive impact on productivity, since the cutting time decreases. The inuence of welding is investigated by means of Epstein measurements. The test specimens include strips with 1, 3, 5 and 10 welding points. Experiments show an iron loss increase up to 50% with a corresponding 62% reduction in the permeability. A model that incorporates the cutting e ect is developed and implemented in a FEMbased motor design software. Simulations are made for a reference induction motor. The results indicate a 30% increase in the iron losses compared to a model that does not consider the cutting e ect. In case of laser cut core laminations, this increase reaches 50%. The degradation prole considers also the deteriorated magnetizing properties. This leads to increased nominal current up to 1.7% for mechanically cut laminations and 3.4% for laser cut la / I detta examensarbete studeras hur de magnetiska egenskaperna hos SiFe-plat paverkas av skarning och svetsning. Permeabilitet och jarnforlustdensitet undersoks eftersom de ar kritiska variabler for elektriska maskiners prestanda. De magnetiska matningarna genomfordes pa en Epstein ram med en odesfrekvens pa 50, 100 och 200 Hz, enligt IEC 404-2. E ekterna av mekanisk skarning med giljotin samt skarning med ber- och CO2-laser studerades. Inverkan av olika berlaserinstallningar undersoktes ocksa genom att variera gastrycket, skarhastigheten samt frekvensen och e ekten av laserstralen. For att oka skare ekten inkluderades Epsteinremsor med ytterligare 1, 2 och 3 langsgaende skarsnitt. Det visas att mekanisk skarning har en mindre paverkan pa de magnetiska egenskaperna hos materialet an vad laserskarning har. Matningar pa plat med 1.8% Si visar att da prov med tre extra langsgaende giljotinklipp anvands kan permeabiliteten reduceras med upp till 63% och jarnforlusterna kan oka med upp till 35%. Motsvarande resultat for laserskurna platar visar en permeabilitetsreduktion pa upp till 65% och en jarnforlustokning pa upp till 65%. Ur studien av de tva studerade skarprocesserna framkommer aven att tunnare plat paverkas mindre negativt an tjockare plat. Ett antal olika installningar har provats for att utreda hur olika parametrar paverkar e ekterna av laserskarning. Studien indikerar att skarning med hog e ekt och hog hastighet ger den minsta paverkan pa materialets magnetiska egenskaper. Vilket aven har en positiv inverkan pa produktiviteten vid laserskarning. Epsteinprover har aven utforts for att undersoka vilka e ekter som introduceras da SiFe-plat svetsas. Provstyckena bestod av remsor med en, tre, fem och 10 svetspunkter. Experimenten visar en jarnforlustokning med upp till 50% samt en permeabilitetsreduktion upp till 62% da platarna svetsats samman tva och tva. En modell for att studera e ekterna av de forandrade materialegenskaperna vid skarning pa en induktionsmotor utvecklas och implementeras i en FEM-baserad mjukvara. Resultaten tyder pa en jarnforlustokning med 30% da skare ekten orsakad av giljotin beaktas. Vid simulering av laserskuren plat kan denna okning vara sa stor som 50%. Det framkommer aven att laserskarningen kan reducera e ektfaktorn sa mycket som 2.6%.

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