No description available.

No description available.

No description available.

No description available.

The R6 procedure is used for the prevention and prediction of crack behaviour and other defects in the reactor pressure vessel(RPV). The RPV material is an upper-bainitic, low alloy steel structure, which deforms inhomogeneously when yielding. The current codes that are used to design and calculate the fracture, within an RPV, assume that the material yields continuously as the size of the L¨uders strain is less than 2%. However, the work of Wenman et al[1] has shown that the inclusion of a L¨uders band during calculations can reduce the residual stress in a material, when compared to standard work-hardening models and, consequently, reduces the amount of conservatism. The objective of the research was to determine whether Wenman’s finding could be generalised and therefore initiate a re-evaluation of R6 procedure, when looking into materials that yield discontinuously. This required further investigation into L¨uders bands, such as using failure assessment diagrams (FADs). The findings from FADs showed that at the temperature range for an RPV steel at -155±C for different micro-structures (assuming that the material deforms homogeneously), this reduced the amount of conservatism. However, at fracture toughness values more representative of room temperature behaviour, the converse was true. That is, assuming a discontinuous yield point reduced the amount of conservatism. It was also shown that the tempered martensite structure could be used as an alternative to the current upper bainitic, low alloy steel that is used in RPVs. Further insight is gained into the nature of a L¨uders band, by developing a theoretical model that showed explicit relations between L¨uders strain and the mean free-path(ferrite path), dislocation density and the grain-size. It was also shown that an explicit relation between the L¨uders strain and carbon content was possible from known data, which a new parameter Á was derived, and is the derivative of the work-hardening exponent with respect to the lower yield stress.

我們主要研究了多孔體系在乾燥過程中的兩個現象: 一是裂縫行為，二是污染相在孔隙間的擴散特點、機理以及收集污染相、解決污染問题的方法。 / 在本文的第一部分中，我們用共聚焦顯微鏡觀察到了膠體懸浮體系在溶劑揮發時產生裂縫。我們尋找到一個可令裂縫完全消除的辦法：加入乳液到膠體體系後，裂縫的數量減少；當乳液達到一定濃度時，裂縫完全被消除。同時我們也發現加入乳液帶給體系的另一效應：空氣進入體系的速度也發生改變，從而實現了乾燥速度可控。通過用流變儀研究樣品的基本力學性質，我們找出了裂縫數量減少的根本原因。我們的方法可同時有效地控制裂縫數量和體系乾燥速度，因而在許多涉及到多孔體系乾燥或裂縫的工業過程中有潛在的應用。 / 在本文的第二部分中，我們受到石油洩漏污染海灘的啟發，研究了污染相在多孔體系里的擴散特點及機理，並在此基礎上設計了有效的處理方案。我們搭建了一個小尺度的系統來模擬石油滲入沙灘的過程，記錄了隨著海水沖洗次數的增加污染相在多孔體系里的分佈變化。我們發現不論是親水還是疏水的多孔體系，在幾次海水沖刷週期后，污染相都有了明顯的擴散；但是對於不同的體系，污染相呈現出不同的分佈和擴散特點。通過分析小孔尺度上體系內部的壓強分佈，我們很好地解釋了造成這種不同的基本原因。最後我們尋找到兩種可令污染相集中的方法，這對解決實際污染問题有一定的幫助。 / We study two interesting phenomena occurred during the evaporation of solvent in porous medium: first, the cracking behavior; and second, the expanding mechanism and the collecting methods of the non-evaporative phase. / In the first part of this thesis, we visualize the cracking behavior of colloidal suspensions during drying by a confocal microscope. We develop an effective method which can completely eliminate cracking during drying: by adding emulsion droplets into colloidal suspensions, we can systematically decrease the amount of cracking, and eliminate it completely above a critical droplet concentration. We also find another effect that the emulsion droplets can bring: it varies the speed of air invasion and provides a powerful method to adjust drying rate. Besides, we investigate the samples’ fundamental mechanical properties with a rheometer and clarify the underlying physical mechanism for the decreasing of crack amounts. With the effective control over cracking and drying rate, our study may find important applications in many drying and cracking related industrial processes. / In the second part of the thesis, we conduct a study on the expanding mechanism and collecting methods of the non-evaporative phase in porous medium, which is inspired by a practical pollution problem that occurs when oil spills to the sandy beach. We build a system in a smaller scale to mimic the practical pollution and investigate the distribution change of the polluting phase as the flushing cycle increases. We find an obvious expansion of the polluting phase after several flushing cycles in both hydrophilic and hydrophobic porous media, but with different distributions and expanding behaviors. We explained this difference by analyzing the pressure distribution in the system at the pore level. Finally, we develop two methods to concentrate the polluting phase in some particular regions, which is beneficial to collect and solve the practical pollution problem. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Jin, Qiu = Duo kong ti xi lie feng he you ru qin de yan jiu / Jin Qiu. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 62-67). / Abstracts also in Chinese.

published_or_final_version / Civil Engineering / Master / Master of Philosophy

This thesis deals with nonlinear analysis of reinforced concrete structures under monotonically increasing loads. Post-cracking behaviour of planar reinforced concrete structures is studied to investigate the tension stiffening phenomenon and the post-cracking shear resistance. The feasibility of using the available bond stress-slip relationships to model the steel-concrete interface behaviour is examined by incorporating these relationships in a three dimensional axisymmetric finite element model and analyzing several reinforced concrete tension specimens. / A finite element model which uses the advanced endochronic stress-strain relationship and incorporates the results of the investigation on post-cracking behaviour and steel-concrete interface behaviour is formulated and used in the analysis of several reinforced concrete members. Analysis results are compared with the available experimental data and with the results obtained by other researchers. Excellent correlation was obtained between the computed values and the experimental results.

No description available.

Master of Science / Department of Civil Engineering / Mustaque A. Hossain / The use of economical and environmentally friendly recycled asphalt materials has become increasingly popular for asphalt pavement construction. Although reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) are typically used in hot-mix asphalt, increasing the amount of RAP and RAS materials increases the potential for premature pavement distresses, especially cracking. This research evaluated four recycled Superpave mixtures with different RAP and RAS contents from Kansas Department of Transportation projects. Two of the mixtures contained 10% RAP and 5% RAS, while the other two mixtures contained 25% RAP but no RAS. Illinois semicircular bending and Florida indirect tension tests were performed to assess mixture cracking and fracture properties. Results showed that mixtures containing 10% RAP and 5% RAS have relatively low fracture energy, creep compliance, energy ratio, and flexibility index but high resilient modulus. These results indicate that mixtures containing 10% RAP and 5% RAS are stiffer, more prone to cracking, and tend to absorb less fracture energy. Mixtures with 25% RAP and no RAS showed the opposite behavior.