Terms of acoustic emission (AE) and electromagnetic emission (EME) designated physical effects and also as diagnostic methods based on these effects. These effects are caused by generated cracks in materials that rank among non-destructive techniques of material diagnostics. The advantage of them is that they do not affect the measured object and give us information about the current dynamic state of a tested material. One disadvantage of these effects is that they provide very low energy of signal emissions and make it difficult for broader usage. It is expected better localization of cracks in non-conductive materials by connecting of these two techniques (diagnostics). There are designed and described new methods for crack detection with usage of AE and EME signals in this work. Also there is description of measuring arrangement intended of crack detection and experimental sample for checking accuracy of methods for crack detection. There was performed comparison of accuracy of methods in crack detection.

Master's thesis deal with the design and static analysis of supporting structures of main underground reinforced concrete tank located in Combined cast-in-place structure of WTP in Kořenec. The tank has dimensions of 9.5 x 9.5 m and the is divided into four sub-tanks by internal walls. Supporting structures, foundation slab, external and internal walls and ceiling slab, were verified for limit state design requirements for concrete members. Verification of serviceability limit state and crack control of width was made.

The fatigue life and the kinetics of short crack growth in specimen of austenitic-ferritic duplex steel cycled with constant stress amplitude and different mean stresses is studied. Fatigue life was determined on smooth cylindrical specimens. Strain amplitude and mean strain were recorded. Short crack growth was studied in cylindrical specimens with a shallow notch. Cyclic straining was interrupted and crack length was measured using an optical microscope mounted on the testing machine. Crack length and crack growth rates were evaluated. The effect of the mean stress on the rate of short cracks and fatigue life were discussed.

Bewehrungen mit einer hochmoduligen Polymertränkung erreichen im Betonbauteil Textilspannungen von über 1200 N/mm². Ab diesem Niveau wurden in Dehnkörperversuchen Längsrisse und Betonabplatzungen beobachtet. Für die Eingrenzung und Identifikation der elementaren, verantwortlichen Mechanismen weisen großformatige Dehnkörper störende Einflüsse von Randeffekten und Imperfektionen auf. Daher wurde ein neuer Versuchsaufbau entwickelt, bestehend aus einem in einen Betonquader eingebetteten Einzelroving. Die simple Herstellung und die Verlässlichkeit dieser Kategorie von Experimenten in Bezug auf die Reproduzierbarkeit und der geringen Streuung der Resultate machen sie zu einer robusten Grundlage für experimentelle Untersuchungen des Verhaltens von TRC. Die experimentell ermittelten Bruchlasten werden zunächst bezüglich ihrer Leistung diskutiert und dann die beobachteten Bruchvorgänge kategorisiert hinsichtlich kompatibler mechanischer Hypothesen für die Initiierung von Längsrissen und des Spaltversagen. / Reinforcements with a high-modulus, polymeric impregnation achieve textile tensions of 1200 N/mm² and more in concrete parts. Starting at this level longitudinal cracks and splitting were observed in tests. In order to isolate and identify the fundamental, responsible mechanisms large-scale specimen show an interfering impact of boundary effects and imperfections. Therefore a new test set-up was developed, consisting of a single roving embedded in a single concrete cuboid. The simplicity of production and reliability of this class of experiments in terms of repeatability and low scatter of results makes them a robust basis for experimental investigation of TRC behavior. The experimentally obtained strengths are discussed in terms of the performance, followed by the categorization of observed failure patterns with respect to the available mechanical hypotheses of the longitudinal crack initiation and splitting failure.

Cracks in the concrete slab of continuous composite bridges are common due to the tensile stresses at the supports. These bridges are allowed to crack as long as the cracking is controlled and not exceeding the design crack width (according to Bro 94 the crack should be injected if they are bigger than 0.2 mm). The Ångermanälven Bridge (railway bridge part of the Bothnia line project) was designed with big edge beams of width 1.2 m, 40 % of the total area of the concrete deck cross-section. During the final inspection cracks larger than the design crack width (0.3 mm according to Bro 94) were observed over the supports.In this thesis the design and the construction procedure of the bridge is studied to clarify the causes of the cracking in the edge beam. The objectives of this thesis were addressed through a literature study of the different types of cracks and the Swedish bridge codes. The expected crack width was calculate according to the same code, using a 2-D FEM model for the moment calculation, and compared with the crack width measured at the bridge.The result of the calculations shows that tensile stress due to ballast and only restraining moment due to shrinkage is not big enough to cause the measured crack width. Shrinkage force and temperature variation effects may have contributed to the concrete cracking in the edge beams. The large cross-section area of the edge beams indicates that it should be designed as part of the slab, taking that into consideration, 1.1 % reinforcement ratio in the edge beams is believed to limit the crack width to the code limits (0.3 mm).

Increasing the use of Ultra High Strength Steels (UHSS) in vehicle bodystructures is important for reducing weight and cutting CO2 emissions. This thesis investigates challenges in resistance welding that can be a barrier to implementing UHSS as a replacement for low strength steels in vehicle structures. Empirical research has been performed to offer new approaches for improved joint strength and to increase knowledge on cracking mechanisms in resistance projection welding and resistance spot welding of UHSS. By optimising the current build-up phase and peak current during the first milliseconds of weld time, it was shown that the strength could be improved by up to two-fold for projection welded joints. An approach to improve the ductility and strength of resistance spotwelds in UHSS using reduced cooling time was unsuccessful. The reduced cooling rate after weld metal solidification did not fully create the desired softened microstructure. The study on the surface cracking mechanism in resistance spot welded dual-phase UHSS showed that cracking is linked to the galvanization method. It is proposed that formation of aluminium oxide layers on the electrode tips increases the surface temperature and thereby increases the probability for liquid metal embrittlement and surface cracking. / <p>QC 20150526</p>

The steel quality is deteriorated at a continuous casting start. Therefore, material from the first cast slab is cut off and re-melted in the melt shop. If too little is discarded, the inferior quality in the retained length can cause defects like edge cracks during subsequent hot rolling. This means that manufacturing resources are wasted on processing inferior material which has to be re-melted anyways at a later stage. On the other hand, if an excessive length of the first slab is re-melted, good material is wasted. In either case, optimizing the length of the start-scrap material is both economically and environmentally beneficial. Edge cracks are more common in the beginning of the first slab, even though a part is cut off. It is likely that the edge cracks arise due to reduced hot ductility in the first cast material. The purpose of this project is to optimize where the cut should be made in order to achieve the best yield. The hot ductility was investigated by performing hot tensile- and bending tests. The hot tensile tests indicate high hot ductility for the investigated specimens. The area reduction, which is correlated to the hot ductility, is above 70 % for all the investigated specimens. When considering the average area reduction while neglecting possible differences between the heats, the specimens from one meter tend to have a lower hot ductility compared to the other specimens. However, the differences are small. No difference can be seen between edge and middle specimens when only looking at the tensile tests. The bending tests did not crack without notches, even though the maximum load and a test temperature of 750 °C was used. That strongly indicates high hot ductility as well. By using notches, the bending tests cracked and it was shown that edge specimens and specimens from one meter cracked the most. No edge cracks were found, after hot rolling, on the first cast slabs from the investigated heats. / Vid en stränggjutstart är kvalitén på första slaben sämre. På grund av detta så skärs en bit, av det först gjutna slabet av och smälts om i stålverket. Om för lite material kapas av kan det leda till defekter, såsom kantbrakor, under den efterföljande varmvalsningen. Detta innebär att resurser används i onödan för att tillverka material av otillräcklig kvalitet som sedan ändå måste smältas om i ett senare steg. Skärs istället för mycket material bort så smälts prima material om i onödan. Att optimera startskrotlängden är följaktligen positivt både för miljön och rent ekonomiskt. Under varmvalsningen kan defekten kantbrakor, det vill säga sprickor vid kanterna, uppstå. Trots att en bit av det första gjutna slabet skärs av, så är det första slabet fortfarande mest utsatt för kantbrakor. Detta tros bero på nedsatt varmduktilitet i det första gjutna materialet. Syftet med detta projekt är att optimera längden på startskrotet för att spara så mycket användbart material som möjligt. Varmduktiliteten undersöktes genom drag- och bockprovning. Dragproven indikerar hög varmduktilitet för de undersökta proven. Areakontraktionen, som är ett mått på varmduktiliteten, är över 70 % för alla undersökta prov. Medelareakontraktionen, när man bortser från eventuella skillnader mellan chargerna, visar att prov från en meter generellt har något lägre varmduktilitet än de övriga proven. Det är endast små skillnader som uppfattas. Ingen skillnad kan ses mellan kant- och mittenprov när man enbart tittar på dragprovsresultaten. Bockproven sprack inte trots att maximal last användes och att testtemperaturen var 750 °C. Detta tyder också på hög varmduktilitet. Genom att skapa anvisningar kunde man få bockproven att spricka och det visade sig att kantprov och prov från en meter sprack mest. Inga kantbrakor hade uppstått på de första gjutna slabsen under varmvalsningen av försökschargerna.

The report contains three parts. The first part is a summary and overall presentation of thermal cracks and preventing measures against such cracks. This is a theoretical part where the interested designer can get acquainted with various alternatives, be guided to more detailed literature, and receive some practical information regarding the design of the respective measures. The second part deals with calculation of the risk for thermal cracks and design of water cooling as a limiting measure. Two complementary methods are reviewed for efficient calculation: • the handbook method CraX1 (by Lulea University of Technology) is used for quick verification • finite differential analysis in the calculation tool ConTeSt Pro for more precise projecting Here is also presented a development of existing standards through design of the cooling system by means of the Bernoulli equation. Comparison is made with the approximation with Manning’s formula, which occurs in the field today. The calculation part is concluded with a calculation example. In addition to prescribing good project planning, the example also highlights some of the calculation programs’ possibilities and limitations. The third part of the report evaluates the current calculation of the risk for thermal cracking in young concrete, as well as the design and implementation of thereto related measures. This is done through studies of reference objects and interviews with all parts involved, i.e. clients, consultants, contractors and suppliers. The report aims to a compilation and transfer of skill and experience, so that potential for improvement in the prevention of thermal cracking can be identified, and the design can be improved with regard to the conditions of the construction phase. / Rapporten innehaller tre delar. Den forsta delen utgor en sammanstallning och oversiktlig presentation av temperatursprickor samt forebyggande atgarder mot sadana sprickor. Det ar en teoretisk del dar den intresserade projektoren kan satta sig in i olika alternativ, vagledas till utforligare litteratur, samt fa en del praktisk information infor projekteringen av respektive atgard. Den andra delen avhandlar berakning av risk for temperatursprickor samt projektering av vattenkylning som sprickbegransande atgard. Tva kompletterande metoder gas igenom for effektiv berakning: • handboksmetoden CraX1 (fran Lulea tekniska universitet) for snabbare kontroller • finita differensanalyser i berakningsprogrammet ConTeSt Pro for noggrannare projektering Har presenteras aven en utveckling av nuvarande standarder via dimensionering av kylsystem for vatskekylning med hjalp av Bernoullis ekvation. Jamforelse gors med approximationen med Mannings formel, vilken i dagslaget forekommer i branschen. Berakningsdelen avslutas med ett berakningsexempel. Forutom att foreskriva god projektering, belyser exemplet dessutom nagra av berakningsprogrammens mojligheter och begransningar. Rapportens tredje del utvarderar den nuvarande berakningen av risk for temperatursprickor i ung betong, samt projekteringen och genomforandet av tillhorande atgarder. Detta gors via studier av referensobjekt och intervjuer med samtliga involverade aktorer, d.v.s. bestallare, konstruktorer, entreprenorer och leverantorer. Rapporten syftar till en sammanstallning och aterforing av kompetens och erfarenhet, sa att forbattringspotential i forebyggandet av temperatursprickor kan identifieras, och projekteringen kan forbattras med hansyn till produktionens forutsattningar.

Rolling contact fatigue is a problem encountered with many machine elements.In the current report a numerical study has been performed in order to predictthe crack path and crack propagation cycles of a surface initiated rolling contactfatigue crack. The implementation of the contact problem is based on theasperity point load mechanism for rolling contact fatigue. The practical studiedproblem is gear contact. Different loading types and models are studied andcompared to an experimental spall profile. Good agreement has been observedconsidering short crack lengths with a distributed loading model using normalloads on the asperity and for the cylindrical contact and a tangential load on theasperity. Several different crack propagation criteria have been implemented inorder to verify the validity of the dominant mode I crack propagation assumption.Some general characteristics of rolling contact fatigue cracks have beenhighlighted. A quantitative parameter study of the implemented model hasbeen performed. / Utmattning med rullande kontakter är ett ofta förekommande problem för många maskinelement. I den aktuella rapporten utfördes en numerisk studieför att förutsäga sprickvägen hos utmattningssprickor som initierats i ytan vidrullande kontakter. Implementeringen av kontaktproblemet bygger på asperitpunktlastmekanismen för rullande kontakter. Studien av kontaktproblemetär tillämpad till kugghjul. Olika belastningstyper och modeller studeradesoch jämfördes med profilen hos en experimentell spall. Bra överensstämmelseobserverades för korta spricklängder när en modell med fördelad belastninganvänds för en belastningstyp där en normalbelastning agerar på asperiten ochvid cylindriska kontakten och en tangentialbelastning införs på asperiten. Olikakriterier för spricktillväxt implementerades för att verifiera giltigheten av antagandetatt mode I spricktillväxt är dominant. Några generella kännetecken avutmattningssprickor med rullande kontakter framhävdes. En kvantitativ parameterstudie för den implementerade modellen utfördes.

Establishing dynamic characteristics of structures is a challenging area of research. The dynamic characteristics of structures, such as natural frequencies, modeshapes, response levels and damping characteristics play an important role in identifying the condition of the structures. The assumed modes method is a particular analytical method used to estimate the dynamic characteristics of a structure. However, the eigenfunctions used in the assumed mode method often led to ill-conditioning due to the presence of hyperbolic functions. Furthermore, a change in the boundary conditions of the system usually necessitates a change in the choice of assumed mode. In this thesis, a set of Alternative Admissible Functions (AAF), along with penalty functions, are used to obtain closed form solutions for an Euler-Bernoulli beam with various boundary conditions. A key advantage of the proposed approach is that the choice of AAF does not depend on the boundary conditions since the boundary conditions are modelled via penalty functions. The mathematical formulation is validated with different boundary conditions, Clamped-Free (CF), Simply-Supported (SS), and Clamped-Clamped (CC). A specific relation between the penalty function and the system parameters are established for CF, SS and CC boundary conditions to obtain appropriate values of penalties. Validation of results with the reported literature indicates excellent agreement when compared with closed-form Euler-Bernoulli beam values. The AAF approach with penalties is extended to a beam with a shallow crack to estimate the dynamic characteristics. The crack is modelled as a penalty function via a massless rotational spring. This model has the advantage of simplifying parametric studies, because of its discrete nature, allowing easy modification in the crack position and depth of the crack. Therefore, once the model is established, various practical applications may be performed without reformulation of the problem. Validation of results with the reported literature on beams with shallow cracks indicates the suitability of the proposed approach.