Stress Corrosion Cracking of High Strength 18Ni-8Co-5Mo Maraging Steel Fasteners

Maraging steels have attractive combination of strength and toughness making them ideal choice for a number of structural applications. In one such application, this steel was used to fabricate shear bolts in an interstage of a satellite launch vehicle. Four numbers of these shear bolts were found to fail exactly at the head-shank interface under assembly condition. The failure has occurred when the structure was assembled with bolts to the specified torque of 43N-m. Detailed investigations revealed that the fasteners were under assembly loads and exposed to marine environment. The cracks initiated at the corrosion pits located at the head-shank interface propagated inwards in a transgranular mode. Fractography revealed brittle transgranular features with cleavage facets and corrosion products on the fracture surface. The EDS analysis at the corrosion pits near the fracture edge indicated the presence of chlorine. Based on detailed metallurgical analysis, it was concluded that the shear bolts failed due to the “Stress Corrosion Cracking”.

Video Segmentation Algorithm Based on Improved Kirsch Edge Operator and Three-Frame Difference

For the most commonly used method of are susceptible to noise, it is difficult to extract a complete moving target . Aiming at this problem, we propose a video segmentation algorithm through the combination of an improved Kirsch edge operator and the three-frame difference. Firstly, we got a moving region through a differential by the three consecutive image frames, and then got the edge on the current frame using an improved Kirsch edge detection operator, Synthesis of the two test results, we got a more accurate moving object edges. Then using the edge connector algorithm to complete the connection of the fracture edge, and finally, got moving target mask image through regional filling, thereby dividing the complete moving target, thus dividing the complete moving target. Experimental results show that the algorithm has a certain robustness, and can accurately detect moving targets.

Fenestrated vessels in human hemangioblastoma

✓ The capillaries in two cerebellar hemangioblastomas were studied by thin-section and freeze-fracture techniques. Fenestrae were found in the attenuated portions of the endothelium, and plasmalemmal vesicles in the nonfenestrated portions. In freeze-fracture preparations the fenestrae of the endothelial plasma membrane were about 450 to 550 A in diameter. They appeared as holes and “necks” in clusters of about 40 to 60 per µm2. When the fracture plane passed in a stepwise fashion from the luminal plasma membrane into the contraluminal plasma membrane, the fenestrae at the fracture edge involved both plasma membranes.

Interface Studies of Porcelain Enamel on Aluminum

Aluminum and aluminum alloys can be coated with porcelain enamel slip which is fired at 1000°F for approximately 10 minutes. This produces a material with a surface layer (about 0.1 mm thick) which has the properties of porcelain and the basic mechanical properties of a light ductile metal. A problem termed spalling may arise after weathering or exposure to a corrosive salt solution, if the base metal is not chosen carefully or pretreatment of the metal is not correct. A typical failure of this type on a test panel is illustrated in Fig. 1. The spalling failure initiates at pin holes, scratches and edges, then spreads laterally by attack at the interface between the enamel and base metal. An electron fractograph at the edge of a circular spalled area on a test panel of an improperly pretreated 6061 alloy is shown in Fig. 2. The corroded metal is on the bottom and the porcelain on the top. The narrow band through the center is the fracture edge of the porcelain enamel adjacent to the interface.