Ένα από τα κύρια προβλήματα που συναντώνται σε κτίρια ή γέφυρες που έχουν κατασκευασθεί πριν από το 1980, είναι η μειωμένη καμπτική αντοχή και πλαστιμότητα, το οποίο αρκετά συχνά οφείλεται στην έλλειψη περίσφιξης και στη παρουσία κοντών αναμονών που είχαν οι κατασκευές αυτές. Ο κύριος σκοπός της παρούσας διατριβής είναι να παρουσιάσει και να αξιολογήσει πέντε από τα διαθέσιμα στη βιβλιογραφία αναλυτικά μοντέλα προσδιορισμού του απαιτούμενου πάχους του εξωτερικά εφαρμοζόμενου μανδύα για την αποφυγή της αστοχίας των ματιζομένων οπλισμών των υποστυλωμάτων συμπεριλαμβανομένου και του αντίστοιχου μοντέλου το οποίο δίνεται στο Σχέδιο 1 και Σχέδιο 2 του ΚΑΝΕΠΕ. Τα αναλυτικά μοντέλα αξιολογούνται μέσω πειραματικών αποτελεσμάτων από τη βιβλιογραφία. Η αξιολόγηση γίνεται σε δύο επίπεδα. Στο πρώτο επίπεδο αξιολογείται η αξιοπιστία πρόβλεψης του απαιτούμενου πάχους του υλικού ενίσχυσης –χρησιμοποιώντας τις μέσες τιμές των υλικών- ενώ στο δεύτερο επίπεδο εξετάζεται η αντίστοιχη καταλληλότητα κάθε προσομοιώματος για το σχεδιασμό –χρησιμοποιώντας τις αντίστοιχες τιμές σχεδιασμού των υλικών-. Τροποποιημένες εξισώσεις βασιζόμενες στο προσομοίωμα του ΚΑΝΕΠΕ παρουσιάζονται. Η χρήση των τροποποιημένων εξισώσεων ελέγχεται μέσω διαθέσιμων πειραματικών αποτελεσμάτων και προκύπτει ικανοποιητική σύγκλιση με αυτά. / Reinforced concrete frames or bridges constructed in the early 80s or before, were usually designed and detailed to resist lower lateral forces than those required today. Building columns were commonly designed for compression only and as a result they do not have the adequate lateral strength to resist the imposed earthquake loads. One of the main deficiencies in these older structures is the limited flexural strength and ductility often due to short and lightly confined lap splices. The main aim of this thesis is to present and evaluate five of the proposed analytical models in order to rehabilitate reinforced concrete columns with short lap splices by external confinement, including and the confinement model given by the draft version of the Greek Retrofitting Code (GRECO). The above analytical models are validated against experimental results. The validation is performed in two levels. In the first level, the reliability of the prediction for the required jacket thickness given by the models, is examined, by using the average values of the materials. In the second level, the propriety for the design of each model is examined by using the design values of the materials. A modified equation based on the model given by GRECO is presented as well. By using the proposed modified equation a satisfactory agreement with the experimental results was accomplished.

Thesis (M.Soc.Sc.)--University of Hong Kong, 1984. / Also available in print.

Foi realizado um estudo comparativo da capacidade de duas variantes do método de radiografia por raios- X em detectar trincas de fadiga em juntas sobrepostas rebitadas de laminado híbrido metal-fibra Glare® de uso aeronáutico. Durante os ensaios mecânicos de fadiga sob amplitude constante de tensão, diversos corpos de prova rebitados foram periodicamente inspecionados por raios-X, em ambas as modalidades convencional e digital. Raios-X em filmes convencionais digital. Raios-X em filmes convencionais proporcionaram ótimo detalhamento de trincas nas juntas mecânicas, enquanto que as imagens geradas pela modalidade digital apresentaram qualidade muito inferior, prejudicando ou até mesmo impedindo a avaliação do grau de integridade estrutural das juntas rebitadas. / A comparison is performed on the ability of two modalities of nondestructive X-ray radiography method in detecting fatigue cracks in riveted lap joints of aeronautical grade fiber-metal laminate Glare™. During constant amplitude loading in fatigue testing riveted specimens were periodically inspected using both the conventional and digital X-ray methodology. Conventional film X-ray modality provided high quality images of growing cracks in the mechanical joints, whereas digital radiography generated faulty images, which impaired or even prevented the structural integrity assessment of the riveted joints.

Este trabalho objetivou a caracterização mecânica e a análise de falha de dois tipos de juntas compósitas através de ensaios mecânicos, em que uma das juntas era composta por dois laminados de fibras de carbono recoberto em ambas as faces por tecido de fibra de vidro reforçando uma matriz termoplástica (PPS-C) unidos via soldagem por resistência elétrica, e a outra confeccionada com dois laminados de fibras de carbono reforçando uma matriz de resina epóxi (EPX-C) unidos via colagem por filme de resina epoxídica. Os dois tipos de juntas foram submetidos a impacto único transversal de 10 J, condicionamento higrotérmico, além de carregamento em fadiga compressiva no plano nas mais diversas combinações destes processos degradativos de suas propriedades mecânicas. Observou-se, que a junta termorrígida colada de EPX-C apresentou a maior resistência mecânica em flexão em quatro pontos (F4P) na condição original (como-manufaturada), assim como os maiores valores de resistência residual para as várias condições de degradação mecânica e higrotérmica a que foi submetida. Por sua vez, a junta termoplástica soldada de PPS-C exibiu, em termos percentuais, menores reduções dos valores de resistência à flexão sob as condições avaliadas, relativamente às perdas apresentadas pela junta EPX-C em idênticas circunstâncias. A análise macroscópica da superfície de fratura de ambas as juntas indicou que o modo de falha predominante da junta termorrígida foi interfacial enquanto que, para a junta PPS-C, o modo de falha predominante foi o intralaminar. Análises fratográficas através da microscopia eletrônica de varredura (MEV) evidenciaram para a junta termorrígida EPX-C, uma alta adesão entre fibra/matriz, porém uma relativamente fraca interação entre os aderentes (laminado) e o filme adesivo de colagem, enquanto que, para a junta termoplástica PPS-C, reduzidas interações fibra/matriz forem inferidas na camada externa de PPS-V do aderente assim como entre a malha metálica resistiva e os filmes puros de PPS que a revestiam. Em ensaios de resistência ao cisalhamento interlaminar (ILSS), os espécimes retirados da junta EPX-C na condição virgem evidenciaram uma colagem uniforme/homogênea, enquanto que, para a junta PPS-C, os espécimes de ensaio usinados a partir da junta virgem indicaram a ocorrência de efeitos de degradação térmica altamente localizada nas bordas soldadas. / This study aimed to mechanical characterization and failure analysis of two kinds of composite single-lap joints by mechanical tests, in which a single-lap joint was made of two adherents of carbon fibers coated on both sides with glass fiber fabric reinforcing a thermoplastic matrix (PPS-C) welded via resistance welding, and the another type made of two adherents of carbon fibers reinforcing an epoxy matrix (EPX-C) bonded by epoxy adhesive film. The two types of single-lap joints were subjected to single transverse impact of 10 J, hygrothermal conditioning, and compressive fatigue loading in the plane in various combinations of these degradative processes of mechanical properties. It was observed that the thermosetting bonded joint EPX-C showed the highest strength in four point-flexure test in the original condition (as-manufactured), as well as greater residual strength values for the various conditions of mechanical and hygrothermal degradation which was subjected. In turn, the welded thermoplastic joint PPS-C exhibited, in percentage terms, smaller reductions in flexural strength values under the tested conditions, in respect of losses showed by EPX-C in similar circumstances. Macroscopic analysis of the fracture surfaces from both joints indicated that the predominant failure mode was interfacial to thermosetting while for PPS-C joint, the predominant failure mode was intralaminar. Analysis of fracture surfaces by scanning electron microscopy (SEM) showed, for thermosetting joints EPX-C, a high adhesion between fiber/matrix, but a relatively weak interaction between adherents and the bonding adhesive film, whereas for thermoplastic joint PPS-C, reduced interactions fiber/matrix are inferred in the outer layers of PPS-V and between metal mesh and the pure PPS films that coated it. In the interlaminar shear strength tests (ILSS), the specimens removed from the EPX-C joint in the pristine condition showed a uniform/homogeneous bonding along the joint area, while for PPS-C joint, coupons extracted from pristine condition joint indicated the occurrence of degradation caused by thermal effects localized in the welded edges.

This thesis is focused on defects occurring in products made by high pressure die casting of aluminum alloys. The theoretical part includes introduction to high pressure die casting technology and description of individual defects, causes and corrective procurations. The practical part focuses on the determination of the defect on the pre-selected casting, which is cast in the foundry ALW INDUSTRY, s.r.o. Based on the identification of the defect, there is a corrective procuration to reduce its occurrence.

No description available.

Für das Funktionieren von Verstärkungsschichten aus Textilbeton ist eine sichere Kraftübertragung zwischen den einzelnen Verbundbaustoffen sicherzustellen. Aufgrund der sehr hohen Garnzugfestigkeiten sind besonders bei Verwendung textiler Bewehrungen aus Carbon sehr effektive Verstärkungen herstellbar. In Textilbetonbauteilen sind hierbei im Regelfall Übergreifungsstöße der textilen Bewehrungslagen nicht zu vermeiden. Der vorliegende Beitrag befasst sich daher mit der experimentellen und analytischen Bestimmung der Übergreifungslängen textiler Bewehrungsstrukturen innerhalb von Textilbetonverstärkungsschichten. / A safe introduction and transmission of the acting forces is crucial for the functioning of composite materials. Because of the very high yarn tensile strengths of textile reinforcements made of carbon, the manufacturing of very effective TRC strengthening layers is possible. In TRC members, overlap joints within the textile layers usually cannot be avoided. This contribution deals with the experimental and analytical determination of the lap lengths of textile fabrics within a textile reinforced concrete strengthening layer.

<p>Twelve large-scale reinforced concrete (RC) specimens were tested at Purdue University’s Bowen Laboratory to evaluate the deformability of structural walls with longitudinal lap splices at their bases. Eight specimens were tested under four-point bending and four specimens were tested as cantilevers under constant axial force and cyclic reversals of lateral displacement. All specimens failed abruptly by disintegration of the lap splice, irrespective of what loading method was used or what splice details were chosen. Previous work on lap splices has focused mainly on splice strength. But, in consideration of demands requiring structural toughness (e.g. blast, earthquake, differential settlement), deformability is arguably more important than strength. </p> <p>Approximations of wall drift-strain relationships are presented in combination with estimates of splice strength and deformability to provide lower-bound drift capacity estimates for RC walls with lap splices at their bases. Deformations in slender structural walls (with aspect ratios larger than 3) are controlled by flexure. Shear deformations must be considered for walls with smaller aspect ratios. For slender walls with lap splices comparable to those tested, the observations collected suggest that drift capacities can be as low as 0.5%. That is: splices with minimum concrete cover, minimum transverse reinforcement (0.25% transverse reinforcement ratio) terminating in hooks, and lap splice lengths selected to reach yielding in the spliced bars (approximately 60 bar diameters for splices of Grade-60 reinforcement) can fail as yield is reached or soon after. For splices of the same length, doubling the amount of hooked transverse reinforcement increases deformation capacity by nearly 50%. By maintaining the same transverse reinforcement ratio but confining splices with closed hoops (instead of hooks), deformation capacity nearly doubles. Increasing splice length increases the expected splice strength but also increases the strain required to reach the same drift ratio. </p> <p>Evidence from this and similar experimental programs suggests that lap splices with minimum cover and confined only by minimum transverse reinforcement terminating in hooks should not be used in critical sections of structural walls when toughness is required. To prevent abrupt failure during events that demand structural toughness, it is recommended that lap splices be shifted away from locations where yielding in structural walls is expected.</p>

Fabric Reinforced Cementitious Matrix (FRCM) composites utilize a mineral mortar matrix as a substitute for epoxy resin that is used for Fibre Reinforced Polymer (FRP). This eliminates issues associated with the low thermal compatibility of FRP with concrete, susceptibility to UV radiation, and sensitivity to high temperatures in which organic polymers undergo vitrification. This study discussed the effect of varying parameters like the number of Carbon-FRCM (C-FRCM) layers (1, 2 and 3 layers), different anchorage configurations (non-anchored, spike anchor, wrap anchor and mechanical anchor), bond length (300 or 200 mm), and the fabric type (unidirectional and bidirectional) on the direct shear behaviour of C-FRCM composites bonded to a concrete substrate, especially the fibre-matrix bond which is the most common debonding interface of FRCM composites. Calibrated models of the bond – slip behaviour are provided based on the fabric type and number of fabric layers. The results indicate that the anchor type and the overall composite thickness are the main factors that control the failure mode of the composite. All properly anchored specimens using spike and wrap anchors failed due to fabric rupture. Moreover, a considerable number of the non-anchored specimens failed due to composite-substrate debonding, although premature fabric rupture was frequently observed. Furthermore, specimens with bidirectional fabric demonstrated shallower penetration of the strain into the composite which may be due to the horizontal fabric strands providing some anchorage for the longitudinal strands. They also exhibited slip initiation at a higher stress compared to unidirectional specimens. In addition, slip initiation stress of unidirectional specimens decreased with more fabric layers which may indicate that the additional layers have a lower bond efficiency. For the same reason, specimens with three layers of fabric generally experienced deeper strain penetration into the composite than one-layered or two-layered specimens regardless of the anchor type. The results also indicate that the use of bidirectional fabric and anchorage systems decreases the strain penetration into the composite and correspondingly, the effective length is shortened. Surface strain measurements captured using digital image correlation generally did not match the internal fabric strain values obtained from strain gauges.

The automotive industry is currently trying to replace the conventional steels to lightweight materials such as aluminum or carbon fiber to meet all stricter emission targets. When using such materials, traditional joining methods, such as spot welds, could be difficult to use. Therefore, more focus has been put on self-piercing rivets (SPR).In whole car models used in crash simulations, substitution models are used to model SPR joints. It is important to calibrate these models for different load cases. Volvo Cars Corporation (VCC) are currently calibrating using time-consuming physical tests where the SPR joint is subjected to loads in different directions. To save time, a way of virtually evaluating the SPR joint strength is therefore sought after. To do this, a method was developed using non-linear FEM in LS-DYNA. The method was then used to perform sensitivity studies concerning friction, sheet thickness and rivet geometry.The method developed can be divided into three parts. The process simulation, where the rivet insertion was simulated. A springback analysis, where the material is allowed to springback, closer resembling the real behaviour. Finally, the three destructive tests, lap-shear, cross-tension and KS2, were built using the geometry and initial values from the springback.For the process simulation, an explicit solution was used. To handle the large deformations present during the event, r-adaptivity was used together with a kill-element-method to describe failure, based on CrachFEM or Gissmo. The following springback analysis was then performed using one implicit step.For the destructive tests, a solid element representation of the SPR joint was created using the geometry and initial values from the springback. A shell-solid hybrid model was used to keep the computational time low.Using the method, a good correlation was found both for the process- and the destructive test simulations when compared to experiments. Furthermore, it could be concluded that friction, sheet thickness and rivet geometry affects the SPR joint strength and characteristics.