ABSTRACT
Early in the 20th century, a number of scientists tried to predict the theoretical strength of a crystalline solid by estimating the shear stress required to move one plane of atoms over another (Fig. 6.1). They found that the predicted theoretical strengths were much greater than the measured strengths of crystalline solids. The large discrepancy (an order of magnitude or two) between the theoretical and measured shear strengths puzzled many scientists until Orowan, Polanyi, and Taylor (1934) independently published their separate classical papers on dislocations (line defects).
