With the advent of technology, manufacturing of bulk materials from nano particles has been made possible. As a result, there has been an increased interest in modeling the mechanical behavior of ultra fine grain and nano scale materials. But their behavior differs markedly from that of coarse grain materials as their volume fraction of grain boundaries is inherently high. Conventional models of both phenomenological and physical character fail to give a satisfactory description of their behavior in a generic nature. In this paper, the reason for this is traced through the history of mechanics briefly and shortcomings of both the phenomenological approach and physical models are discussed. Need for a modified approach is emphasized and as a way of example, one such approach adopted by us, for describing near superplastic deformation of fine grained alloys, is discussed.

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