Papers by Keyword: Propagation

Abstract: Titanium alloy Ti6Al4V was oxidation annealed in the beta-phase region (1050 °C/3 hours + WQ) in a furnace under a non-protective atmosphere. The above treatment caused the formation of an alpha-case layer on the surface. The above layer, because of its high hardness and strength, has a significant effect on the surface properties of the alloy. However, undesirable effects include the formation of cracks in this layer and a change in the mechanism of initiation and propagation of fatigue cracks. Based on the above findings, it is also very complicated to predict the fatigue life of Ti alloys processed in this way because of the presence of cracks in the alpha-case layer and the varying thickness of this layer. From the fractography and microstructural point of view, the initiation of fatigue cracks in the heat-treated alloy is realized by transcrystalline cleavage and the formation of pronounced fracture facets as a consequence of surface cracks in the alpha-case layer. Fatigue crack propagation (in the alpha-case layer region) is realized along the interface of the alpha-phase needles and the beta-phase primer grain without the significant presence of so-called fatigue striations.

Abstract: Desiccation is the process of extreme drying that results in cracking in materials such as soils. Cracking is a complex process that has the potential to spread and penetrate deeper into the soil, which could lead to instability in earth structures like embankments. A number of desiccation tests were conducted to observe the crack behaviour of manufactured kaolin clay at laboratory scale. All samples were prepared at variation of initial water content and desiccation tests carried out using aluminium desiccation trays. Their crack behaviour was monitored at different thickness and comparison made to the samples tested on different base materials such as ceramic, steel and wood plates. The drying process, crack propagation and pattern were measured and observed daily. A digital image is captured and the crack intensity factor (CIF) calculated manually using a grid system. It was found that a sample of kaolin clay that was 5 mm thick had the highest CIF with rapid propagation and produced non-orthogonal patterns. It also discovered that the thickness of the samples, type of plates utilised and soil state at the start of the test have an impact on the formation and propagation of cracks.

Abstract: Mechanical failure of zeolite-high density polyethylene (HDPE) material applied to skull bone implants is a material fracture that cannot be controlled. An important step to minimize failure due to fracture is to understand the fracture characteristics indicated by the propagation path pattern. This study aimed to investigate the fracture propagation pathways of zeolite-HDPE composites in quasi-static conditions. UV-irradiated Double-edge cracked zeolite-HDPE composite was tested in mode I (a stress perpendicular to the plane of the crack) in a universal testing machine (UTM) with a crosshead speed of 2 mm/min at a constant room temperature of approximately 25°C. The stress and elongation were registered by the UTM. During loading, the evolution of cracks in the ligament length region was recorded with the camera so that the crack propagation pathway until the total fracture occurs can be clearly observed. The results show that the crack propagation pathway patterns were not all straight and parallel to the ligament length. They are also found in a deviant state of the ligament length line by forming an angle α. created between the ligament length line and the fracture propagation deviation direction. This deviation occurs after the crack propagates straight away from the initial-cracks.

Abstract: The receiving of plain problem by analytical appearance with horizontal edges on the endless layer of propagation of the vertical crack and the dependence of the inner pressure of crack is observed. It supposed that the bottom edge of the layer is fixed to absolutely hard semi-flatness, but the upper edge is free. In this respect, we have tried to get the propagation measure of the opening and the analytical aspect of pressure change dependence acting inside it, by method of local modifications using the received solutions. The corresponding methods of approximate illustration of functional dependence are used. In the environment of the opening and the received measure of crack propagation the analytical expressions of distribution of stresses give the full image of peculiarities of those dependences for that immeasurable domain and correspond to the received results by method of modifications. The received formulas may be applied by solving concrete applicable problems and in studies of opportunities of cracks’ propagation for environment of fragile material. Those opportunities are increasing moreover if we take into account that the solutions are received for immeasurable environment.

Abstract: The prediction of a crack initiation and propagation occurring on the microstructural level of heterogeneous materials can be a very demanding problem. According to the results of recent investigations, the emerging phase field approach to fracture has a strong potential in modelling the complex crack behaviour in a simple manner. In this study, recently developed phase field staggered solution scheme with the residual norm stopping criterion has been employed for the fracture analysis of heterogeneous microstructure exhibiting complex crack phenomena. The microstructural geometries based on the metallographic images of the nodular cast iron and the material properties of an academic brittle material have been used in numerical simulations where the graphite nodules have been considered as porosities. Two commonly used energy decomposition models, the spectral decomposition and the spherical-deviatoric split, and their effects on the results of the phase field modelling are investigated. Numerical results show that the proposed algorithm recovers the complicated crack path driven by the complex microstructural topology.

Abstract: Phenomenological ductile fracture criteria represent, among others, one of powerful tools for prediction of ductile fracture. These criteria are based on evaluating damage throughout the solid body as a response to straining. The damage is influenced by plasticity but not vice versa. Therefore, these criteria are often called uncoupled as they do not mutually couple the damage and plasticity. One of immense advantages of such criteria is a possibility not only to predict the crack initiation but also to follow the propagation based on the damage. Moreover, it is not restricted for one specific locus but the damage is evaluated in the entire solid body and one or more cracks can be tracked simultaneously or sequentially. Ductile fracture criteria are calibrated on the basis of several independent calibration tests under various stress states. One way how to verify calibrated model is to simulate numerically an experimental tests and follow the crack initiation and propagation. In the present study, selected phenomenological criteria were calibrated using various calibration tests. Then, selected calibration tests were simulated together with implemented ductile fracture criteria. In our case, the verification is carried out on tensile cylindrical specimens. Finally, computationally obtained results were compared to the experimentally observed ones and the prediction ability and reliability of selected phenomenological criteria is discussed.

Abstract: The presented article deals generally with the use of architecture to the propagation of the ideas and the use of structure of space for propagation of power influences of one group at the expense of another group. The use of architecture to the propagation of ideology lies in the tendency to shape ideologically acceptable space. Space is shaped so the world should be seen in accordance to the ideology and not to the reality. Architectural styles are specific for certain communities that are separated by land, culture, and time. Morphology is associated in architecture with a certain cultural epoch. The article focuses on the use of architecture in propaganda of one totalitarian system - socialist realism, which is typical in the Czech cultural environment in 1948 – 1958. The architecture of socialist realism should promote sociability of people. The aim was to demonstrate the power of unity of collective and nothingness of human individuality. A few examples of basic elements and characters in the architecture of real socialism in Ostrava are mentioned in the conclusion of the article.

Abstract: This paper analyzes the factors, which causes the no-linear of the ultrasonic in the processing system, and the reasons of the ultrasonic reflection and transmission at the contact interface according to the wave theory. In this paper, the ultrasonic displacement coefficient, the pressure reflection coefficient, the displacement transmission coefficient and the pressure transmission coefficient are deduced. The relation among the x-axis and included angle, the incident wave, reflected transmitted waves. The relationship between the preload of the piezoelectric ceramics and the ultrasonic propagation is established, and the best of the bolt preload is investigated. The experiment is done to verify the relationship between the amplitude-frequency characteristics and the ultrasonic transducer at different preload, which provides a reliable basis for the ultrasonic system design, installation and maintenance.

Abstract: Submarine landslide is the most serious threat on both local and regional scales. Tsunami phenomenon induced by submarine slide has put us on the challenge in understanding from generation mechanism to propagation and coastal inundation and mitigating the risk from it. Submarine slides can trigger tsunamis with high run-up affecting offshore structures, subsea facilities and human lives along the shoreline. Unfortunately, there are no effective numerical models that could simulate simultaneously all stages of generation, propagation and run-up of tsunamis phenomena. This paper presents a comprehensive review on the landslide tsunami phenomenon.

Abstract: Most of the engineering failures especially in mechanical and aerospace industry are due to the fatigue. Fatigue cracks and their propagation can be monitored by observing changes in the structural stiffness resulting from strength reduction as a function of the number of loading cycles. This monitoring can be observed using piezoceramic (PZT) transducer based electromechanical impedance (EMI) technique, and digital image correlation (DIC) system which uses variations on structural surface. The fatigue load usually aggravates the fracture if any defects pre-exist in the structure. The present work monitors multiple-crack emanating from electrode sparked multiple plane defects which are induced in to the specimens prior to the fatigue test, using EMI technique and DIC system. The fracture occurs much below the ultimate stress for the structures which already have defects as in the present case. EMI technique uses signature comparison of healthy and cracked state of the structure to depict crack growth. Initial detection of surface hair-line cracks from the corners of induced defects and their propagation till merging and subsequent failure were explained by signature variations and DIC techniques. Thus, a signal processing technique EMI, and image processing technology DIC were found to complement each other in prediction of early crack and their appearance on surface of the specimens.