부산대학교 도서관

In this series of papers, we investigate the mechanics and physics of necking and fragmentation in ductile materials. The behavior of ductile metals at strain rates of about 4,000–15,000 per second is considered. The expanding ring experiment is used as the vehicle for examining the material behavior in this range of strain rates. In Part I, the details of the experiment and the experimental observations on Al 6061-O were reported. Statistics of necking and fragmentation were evaluated and the process was modeled through the idea of the Mott release waves both from necking and fragmentation. Finally, it was shown that the strain in the ring never exceeded the necking strain in regions that strained uniformly. In Part II, we addressed the issues of strain hardening, ductility, geometry and size. Specifically, we examined different materials—Al 1100-H14, and Cu 101—and concluded that geometric constraint influences the strain at onset of localization significantly. The time taken for the localization to propagate across the cross-section and begin to unload its neighborhood was shown to control the amount of strain that can be experienced by the material; this also influences the statistics of localization and fragmentation. In the present paper, Part III, we examine the influence of compliant polymeric claddings on the localization and fragmentation response of metallic materials. Thin aluminum rings were coated with a layer of polyurea, with the thickness being an important parameter in the study. The onset of necking localization is shown not to be influenced by the coating; however, the propagation of unloading or release waves is shown to be significantly impeded by the cladding and therefore, further straining and fragmentation of the rings is affected. This result is of great importance in determining the impact resistance of elastomer-clad metallic structures. In future contributions as part of this sequel, we will explore the effect the development of localization and fragmentation in tubes and sheets where the geometric constraint can be varied over an even larger range. [ABSTRACT FROM AUTHOR]