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Circular ring is the most useful specimen in industry. However, any small crack exists on it will cause some damage about the equipment and even more some serious disaster. As we understand plastic hinge will appear if we increase the load of the ring. The ring will collapse when there are four plastic hinges. The sequence of formation of these hinges is also depended on the location of the crack of the ring. In this paper three different approaches i.e., theoretical, numerical, and experimental will be presented. The theoretical approach is based on the linear elastic fracture mechanics (LEFM) and the method of superposition. The boundary element method (BEM) will be employed in the numerical approach. Finally, the cracked ring specimen was made of Aluminum 6061-T6 whose property is close to the ideally elastic-plastic material property in the experimental approach. The results show the consistency of these three different approaches and provide reasonable information to inspect the circular ring used in daily life.

A novel bactericidal material, Ag@rGO-Fe3O4-PEI composite is prepared by in situ growth of silver nanoparticles onto the polyethylenimine (PEI)-mediated magnetic reduced graphene oxide (GO). The antibacterial performances of the composite are investigated by using the gram-negative bacteria Escherichia coli O157:H7 (E. coli O157:H7) as a model. The results indicate that the Ag@rGO-Fe3O4-PEI composite exhibits excellent antibacterial performance against E. coli O157:H7, with an antibacterial performance superior to those for the ever-reported photothermal materials. The bactericidal capability or the inhibition capability for bacteria growth is found to depend on the dosage of the Ag@rGO-Fe3O4-PEI and Ag/rGO-Fe3O4-PEI mass ratio within a certain range. By using a dosage of 0.1 μg mL(-1), a killing rate of 99.9% is achieved for the E. coli O157:H7 (1 × 10(7) cfu mL(-1)) under a 0.5 min NIR laser irradiation (785 nm/50 mW cm(-2)). In addition, a minimum bactericidal concentration (MBC) of 0.100 μg mL(-1) is achieved under near infrared (NIR) laser irradiation for 10 min, for which case there is absolutely no colony of E. coli O157:H7 found in the broth agar plate.