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Selected AbstractsOn the mechanism of fatigue failure in the superlong life regime (N>107 cycles).FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2000Part 1: influence of hydrogen trapped by inclusions The fracture surfaces of specimens of a heat-treated hard steel, namely Cr,Mo steel SCM435, which failed in the regime of N,=,105 to 5,×,108 cycles, were investigated by optical microscopy and scanning electron microscopy (SEM). Specimens having a longer fatigue life had a particular morphology beside the inclusion at the fracture origin. The particular morphology looked optically dark when observed by an optical microscope and it was named the optically dark area (ODA). The ODA looks a rough area when observed by SEM and atomic force microscope (AFM). The relative size of the ODA to the size of the inclusion at the fracture origin increases with increase in fatigue life. Thus, the ODA is considered to have a crucial role in the mechanism of superlong fatigue failure. It has been assumed that the ODA is made by the cyclic fatigue stress and the synergetic effect of the hydrogen which is trapped by the inclusion at the fracture origin. To verify this hypothesis, in addition to conventionally heat-treated specimens (specimen QT, i.e. quenched and tempered), specimens annealed at 300 °C in a vacuum (specimen VA) and the specimens quenched in a vacuum (specimen VQ) were prepared to remove the hydrogen trapped by inclusions. The specimens VA and VQ, had a much smaller ODA than the specimen QT. Some other evidence of the influence of hydrogen on superlong fatigue failure are also presented. Thus, it is concluded that the hydrogen trapped by inclusions is a crucial factor which causes the superlong fatigue failure of high strength steels. [source] On the mechanism of fatigue failure in the superlong life regime (N>107 cycles).FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2000Part II: influence of hydrogen trapped by inclusions High cycle fatigue fracture surfaces of specimens in which failure was initiated at a subsurface inclusion were investigated by atomic force microscopy and by scanning electron microscopy. The surface roughness Ra increased with radial distance from the fracture origin (inclusion) under constant amplitude tension,compression fatigue, and the approximate relationship: Ra,,,C,K,2I holds. At the border of a fish-eye there is a stretched zone. Dimple patterns and intergranular fracture morphologies are present outside the border of the fish-eye. The height of the stretch zone is approximately a constant value around the periphery of the fish-eye. If we assume that a fatigue crack grows cycle-by-cycle from the edge of the optically dark area (ODA) outside the inclusion at the fracture origin to the border of the fish-eye, we can correlate the crack growth rate da/dN, stress intensity factor range ,KI and Ra for SCM435 steel by the equation and by da/dN proportional to the parameter Ra,. Integrating the crack growth rate equation, the crack propagation period Np2 consumed from the edge of the ODA to the border of the fish-eye can be estimated for the specimens which failed at Nf,>,107. Values of Np2 were estimated to be ,1.0,×,106 for the specimens which failed at Nf,,,5,×,108. It follows that the fatigue life in the regime of Nf >107 is mostly spent in crack initiation and discrete crack growth inside the ODA. [source] Photografting of unable-to-be-irradiated surfaces.JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Abstract In this article, a batch liquid-phase process was reported, by which the photo-initiated grafting polymerization could be carried out on the dark surfaces that were not directly irradiated by UV light. In the reaction system, an aluminum foil was placed horizontally to reflect UV light back and form a dark area underneath where the grafting polymerization took place. The occurrence of the polymerization was demonstrated by gravitational analyses and XPS spectra. The factors affecting the grafting reaction have been studied and the results showed that increasing irradiation time, reaction temperature, and benzophenone concentration and decreasing distance (D) between the light area and the place where grafting reaction took place were beneficial to the grafting reaction. The highest grafting density was obtained at a acrylic acid concentration of 15 vol %. Moreover, some further investigations were also made. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 118,124, 2007 [source] Stroma remodelling during healing of corneal surface irregularities induced by PTKACTA OPHTHALMOLOGICA, Issue 4 2007Marios Panagiotopoulos Abstract. Purpose:, To study the histopathology of the remodelling process in the stroma after excimer-laser-induced corneal irregular injuries. Methods:, Seven New Zealand white rabbits received in one eye a transepithelial plano photoablation (60 µm) and an additional plano ablation (25 µm). On the denuded stroma, an electron microscopy specimen grid was placed and another 25 µm ablation was applied to produce surface irregularities. Dichlorotriazinyl aminofluorescein (DTAF) was then applied for 45 seconds. Another seven right eyes of seven rabbits were ablated the same way but without using the grid, resulting in a plano ablation. All the rabbits were killed at weekly intervals after treatment. The harvested corneas from both eyes were further processed for haematoxylin-eosin staining and were also stained with monoclonal antibodies directed against Ki-67 antigen and ,-smooth muscle actin (,-SMA). All specimens were examined under light and fluorescence microscope. Results:, The corneal wounds were covered by epithelium during the first week. The 25 µm × 25 µm × 25 µm stromal irregularities were clearly discernible up to 3 weeks after treatment, during which time they melted and disappeared. A homogeneous zone was formed in which stroma cells laid down an initially disorganized stroma. This was sharply visible under a fluorescence microscope as a dark area between the dichlorotriazinyl aminofluorescein (DTAF) fluorescent stroma and autofluorescent epithelium. Very little response was seen in the plano-ablated wound microscopically and in terms of positive stained cells. Conclusion:, As the irregularities are flattened and the homogenous zone becomes repopulated with keratocytes forming extracellular matrix material (ECM), the cornea regains its previous architecture in both groups. The irregular wound surface promotes wound-healing reactivity, a process that allows the cornea to compensate for the irregularities and heal to a functional state. [source] CD34+ Pigmented Fibrous Proliferations: The Morphologic Overlap Between Pigmented Dermatofibromas and Bednar TumorsJOURNAL OF CUTANEOUS PATHOLOGY, Issue 1 2005J. Chu McAllister Pigmented dermatofibrosarcoma protuberans (Bednar tumor) constitute 5,10% of all cases of dermatofibrosarcoma protuberans, and are usually considered mimics of melanocytic proliferations rather than fibrous lesions. We report two cases of pigmented fibrous proliferations that demonstrate features of both dermatofibromas and DFSP. The first case is a 19-year-old man with a three year history of a slowly growing pigmented lesion on the right arm. On clinical exam the lesion was a 7 mm firm pigmented papulonodular lesion. The second case is a 31-year-old woman with a 4,5 year history of a slowly enlarging, asymptomatic ,dark area' on the right buttock. On clinical exam the lesion is a 2 cm darkly pigmented flat nodule. Morphologically both lesions are primarily dermal proliferations of spindled cells admixed with pigmented dendritic melanocytes. The lesional cells trap collagen fibers at the periphery and there is basal cell hyperpigmentation. Adnexal structures are effaced but significant trapping of subcutaneous fat is not present. By immunohistochemistry both lesions show focal CD34 positivity but are negative for Factor XIIIa and melanocytic markers. Although overlap between dermatofibromas and DFSP is well documented in the literature, pigmented fibrous lesions with features of both entities are not well described. [source] Adaptive Logarithmic Mapping For Displaying High Contrast ScenesCOMPUTER GRAPHICS FORUM, Issue 3 2003F. Drago We propose a fast, high quality tone mapping technique to display high contrast images on devices with limited dynamicrange of luminance values. The method is based on logarithmic compression of luminance values, imitatingthe human response to light. A bias power function is introduced to adaptively vary logarithmic bases, resultingin good preservation of details and contrast. To improve contrast in dark areas, changes to the gamma correctionprocedure are proposed. Our adaptive logarithmic mapping technique is capable of producing perceptually tunedimages with high dynamic content and works at interactive speed. We demonstrate a successful application of ourtone mapping technique with a high dynamic range video player enabling to adjust optimal viewing conditions forany kind of display while taking into account user preference concerning brightness, contrast compression, anddetail reproduction. Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Image Processing and Computer Vision]: Image Representation [source] | |||||||||||||