Thesis (Professional Degree)--University of Missouri, School of Mines and Metallurgy, 1921. / The entire thesis text is included in file. Typescript. Illustrated by author, except for photographs. Title from title screen of thesis/dissertation PDF file (viewed May 29, 2009)

This thesis presents the development and validation of a high ductility seismic resistant steel brace connector called the Yielding Brace System (YBS) that improves the earthquake performance of steel braced frame buildings. The connector is comprised of two steel castings which dissipate seismic energy through flexural yielding of specially designed triangular yielding fingers. In this body of work, the need for such a system is presented along with a summary of previously developed steel castings for enhanced earthquake performance of building structures. The development of the YBS concept is then discussed in detail and equations are developed to predict the elastic and plastic response of a YBS connector based on the geometry of the yielding fingers. The low-cycle fatigue life of the cast steel material used for the yielding elements of the YBS is characterized based on the results of several cyclic, small-scale yielding fingers tests and a low-cycle fatigue life prediction model is derived. Following this, the design of a prototype connector for the second storey brace of a fictitious six storey sample building located in Los Angeles is presented. This design is conducted using the low-cycle fatigue prediction model, the response prediction equations and non-linear finite element analysis. Results of four full-scale prototype tests are then presented. Two of the tests are axial tests of the device alone, while the other two are full-scale braced frame tests. Finally, the design of a 12-storey sample building is presented. This building design is then evaluated via non-linear time-history analysis using the FEMA P-695 methodology. The results from these analyses are then discussed and compared to a similar study conducted on the same building designed with buckling restrained braces. This work shows that the Yielding Brace System is a highly ductile, seismic resistant brace that can be used as an alternative to the buckling restrained brace with the potential to provide a stiffer structure with increased ductility.

This thesis presents the development and validation of a high ductility seismic resistant steel brace connector called the Yielding Brace System (YBS) that improves the earthquake performance of steel braced frame buildings. The connector is comprised of two steel castings which dissipate seismic energy through flexural yielding of specially designed triangular yielding fingers. In this body of work, the need for such a system is presented along with a summary of previously developed steel castings for enhanced earthquake performance of building structures. The development of the YBS concept is then discussed in detail and equations are developed to predict the elastic and plastic response of a YBS connector based on the geometry of the yielding fingers. The low-cycle fatigue life of the cast steel material used for the yielding elements of the YBS is characterized based on the results of several cyclic, small-scale yielding fingers tests and a low-cycle fatigue life prediction model is derived. Following this, the design of a prototype connector for the second storey brace of a fictitious six storey sample building located in Los Angeles is presented. This design is conducted using the low-cycle fatigue prediction model, the response prediction equations and non-linear finite element analysis. Results of four full-scale prototype tests are then presented. Two of the tests are axial tests of the device alone, while the other two are full-scale braced frame tests. Finally, the design of a 12-storey sample building is presented. This building design is then evaluated via non-linear time-history analysis using the FEMA P-695 methodology. The results from these analyses are then discussed and compared to a similar study conducted on the same building designed with buckling restrained braces. This work shows that the Yielding Brace System is a highly ductile, seismic resistant brace that can be used as an alternative to the buckling restrained brace with the potential to provide a stiffer structure with increased ductility.

The present work was conducted at Scania CV AB and has as main goal to produce a cast steel guideline. There is a great need to conduct a cast steel guideline, in order to help designers in their process to choose suitable materials and methods to produce lightweight components with higher performance. This work contains information related to mechanical properties, casting processes, castability, machinability, defect characterization, heat treatments, weldability and surface treatments of cast steels. This work was limited to cast steels which could be applied on two specific components of the truck, a bracket which is a structural component of chassis subjected to fatigue and a turbo manifold which is subjected to creep, oxidation, corrosion-, thermal- and mechanical- fatigue. A benchmark search was performed focused on these two components. A characterization of a cast stainless steel turbo manifold prototype was performed in the as-cast state, which included microstructural analyzes and hardness measurements. Besides this initial characterization, a set of heat treatments were conducted, in order to study the possibility to eliminate the initial grain boundary carbides. The main conclusions of this work are that cast steel has potential to be a material choice in many applications due to its wide range of properties. For structural parts, cast steel is advantageous compared with cast iron when for instance welding and high strength combined with high fracture toughness are requirements. For high temperature resistance components, cast steel or more precisely cast stainless steel, is advantageous for service at temperatures >750 ºC,besides its higher price. The annealing heat treatment followed by an aging treatment eliminated most of the grain boundary carbides and increase the hardness through a fine dispersion of carbides in matrix, which can also increase the creep resistance. / Examensarbetet utfördes på Scania CV AB med främsta målet att utarbeta en vägledande guide för gjutstål. Det finns ett stort behov av att sammanställa en guideline för gjutstål, med syfte att hjälpa konstruktörer i deras process att välja lämpliga material och metoder för att producera lättviktskomponenter med högre prestanda. Arbetet innehåller information om mekaniska egenskaper, gjutningsprocesser, gjutbarhet, skärbarhet, defektkarakterisering, värmebehandlingar, svetsbarhet, ytbehandling och mycket annat gällande gjutstål. Detta arbete var begränsat till gjutstål som kan tillämpas för två specifika komponenter i lastbilen, en konsol som är en strukturell komponent i chassit som utsätts för utmattning och ett turbogrenrör vilket är en komponent som utsätts för högtemperaturcykler. En benchmark utfördes med fokus på dessa två komponenter. Slutligen gjordes en karakterisering av turbogrenrörsprototypen i rostfritt stål, i det gjutnatillståndet, vilket inkluderade mikroanalyser och hårdhetsmätningar. Förutom den förstakarakteriseringen, utfördes en uppsättning värmebehandlingar för att undersöka möjligheten att eliminera de initiala korngräns-karbiderna. De viktigaste slutsatserna av detta arbete är att gjutstål har potential att bli ett materialval i många applikationer på grund dess breda egenskaper. Konstruktionsdelar i gjutstål är fördelaktiga jämfört med gjutjärn, till exempel vid svetsning och när hög hållfasthet i kombination med hög brottseghet är nödvändigt. För högtemperaturs-komponenter är gjutstål, eller mer exakt, gjutna rostfria stål fördelaktiga för service vid temperaturer >750 ºC, med undantag för dess högre pris. Glödgningsvärmebehandling följt av åldringsbehandling eliminerar de flesta av korngräns-karbiderna och ökar hårdheten genom en fin dispersion av karbider i matrisen, vilket också kan öka krypmotståndet.

Increasing awareness of environmental protection has made both governments and the industry aim for lowering carbon dioxide emissions. For the transport industry this means increasing engine efficiency, replacing fossil fuels with bio-based fuels or full electrification. For heavy-duty trucks, the first two options are currently the paths taken as short and mid-term solutions. These alternatives introduce new service conditions to the engines; namely higher combustion temperature and pressure, which will impose increased thermal and mechanical loads on the engine parts. In particular, the exhaust system parts must withstand constant thermal cycles in their normal operation. In heavy-duty trucks, exhaust systems are mostly manufactured from cast iron or cast steel. The usual materials, such as cast iron SiMo51 are reaching their maximum operating temperature, therefore new materials must come forward to fulfill new challenges. These materials oxidize at high temperatures forming different types of scales, which sometimes can act as protective barriers preventing their degradation. However, thermal cycles in the engine can impose new stresses and strains in these newly formed oxide scales, sometimes leading to spallation. A continuous spallation behavior in the exhaust systems is deleterious for the system, and the debris could also affect the downstream engine parts. This investigation focuses on the study of high temperature oxidation behavior of four iron-based candidate materials. Samples of two ductile cast irons and two austenitic stainless steels were exposed to thermal cycling in a simulated exhaust gas atmosphere at 850 °C, and to isothermal experiments at 850 °C and 900 °C in a stagnant air atmosphere. Additionally, the thermodynamics and kinetics were simulated using Thermo-Calc and Dictra software, respectively.  The results show that SiMo1000 grows a relatively thick iron-rich oxide layer with evidence of internal oxidation aided by the graphite shape exhibited by the alloy. The other cast iron Ni-Resist behaves better than SiMo1000, forming chromia and silica layers that prevent internal oxidation from occurring, although some spallation did occur in water containing atmospheres. 1.4832 behaved poorly compared to the other materials, entering into breakaway oxidation mode throughout all the exposures; therefore, it is not a material suited for high temperature service. HK30 was susceptible to water aided chromium evaporation but had a comparatively small mass change throughout the experiments; nonetheless, there was evidence of internal oxidation following interdendritic zones. Also casting defects were observed in these areas. Both might affect mechanical properties at high temperature. / Ökad miljömedvetenhet har gjort att både industri och politiker har satt upp mål för att sänka koldioxidutsläppen. För transportbranschen innebär detta till exempel ökad motoreffektivitet, att fossila bränslen ersätts med biobaserade bränslen eller full elektrifiering. För tunga lastbilar är de två första alternativen de som är aktuella på kort och medellång sikt. Dessa alternativ innebär nya förhållanden för motorn; nämligen högre förbränningstemperatur och -tryck, vilket kommer att öka termisk och mekanisk last på motorn. Detta är särskilt tydligt för avgassystemet, eftersom det utsätts för termisk cykling vid normal drift. Avgassystemet i en tung lastbil är oftast gjort i gjutjärn och ibland i gjutstål. Gjutjärnen, t ex segjärn SiMo51, börjar nu närma sig sin maximala driftstemperatur och nya material behöver introduceras. Vid höga temperaturer oxiderar dessa metalliska material och bildar olika typer av oxidskal. Beroende på sammansättningen på oxidskalet, kan det fungera som skydd för underliggande material. Termisk cykling kan ge spänningar i oxidskiktet som i sin tur kan ge flagning av skiktet. Om flagningen fortsätter kontinuerligt, förbrukas dels material, men flagorna kan också ge skador nedströms i avgassystemet. I detta arbete undersöks fyra järnbaserade kandidatmaterial avseende högtemperaturkorrosion. Prover av två gjutjärn och två austenitiska rostfria gjutstål exponerades dels isotermt vid 850 °C och 900 °C i stillastående luft, dels i experiment med termisk cykling i en simulerad flödande avgasatmosfär och varm temperatur 850 °C. Dessutom användes termodynamisk programvara (Thermo-Calc/DICTRA) för att simulera termodynamik och kinetik. Resultaten visar att SiMo1000 bildar ett relativt tjockt, järnrikt oxidskikt med viss inre oxidation som verkar följa grafitstråk i materialet. Det andra gjutjärnet, segjärnet Ni-Resist, beter sig bättre än SiMo1000 och bildar krom och kiseldioxidlager som förhindrar intern oxidation. Viss flagning observerades i den cykliska exponeringen. 1.4832 visade ett sämre beteende än de andra materialen och bildade inget skyddande oxidskikt, utan visade kontinuerlig massförlust i samtliga exponeringar. Detta material är därför inte lämpligt för de undersökta högtemperaturmiljöerna. HK30 visade låg massförlust i samtliga undersökningar med oxidation i interdendritiska områden. Även gjutfel som t ex porer observerades idessa områden. Båda kan påverka materialets mekaniska egenskaper vid dessa temperaturer.