Orowan problem

The value of w may be higher than the true value of o by several orders of magnitude. This is the so-called Orowan problem [32], However, for a correct understanding of the aforementioned relationship, one needs to realize that the work w changes symbatically with the value of a and consequently plummets with a significant drop in o. The latter constitutes the embrittlement due to the action of a surface-active medium. The work w itself corresponds to the degree of distortion in the vicinity of the fracture surface that one needs to introduce in order to achieve a critical state. The Griffith equation can also be applied to the case of fractures of plastic bodies in which the microcrack nuclei are formed as a result of plastic strain. 

In drawn metal wires the fibre axis is usually not a crystal axis. The problem of the determination of crystal orientation in such specimens (and in rolled metal sheets), though closely related to those dealt with here, is outside the scope of this book. (The unit cell dimensions, and indeed the complete structures of such crystals, are usually known, and the problems that arise are questions of correlation of physical properties with orientation.) See Schmid and Boas, 1935 Orowan, 1942. 

Two methods have been adopted to overcome this problem. In the first, due to Orowan and others the term S is generalized to include dissipative energy contributions which are thus, somewhat arbitrarily, assigned to the new crack surfaces although they actually occur over a volume dhtribution around the crack tip and even throughout the stressed body. In this paper we shall use the expression J to represent this modified surface energy and we shall call it the surface work . 

Orowan, E. (1940), Problems in plastic gliding, Philosophical Transactions of the Royal Society (London) 52, 8-22. 

E. Orowan, Die Zugfestigkeit von Glimmer und das Problem der technischen Festigkeit. Z. fflr Phys. A Hadrons Nuclei 82(3), 235-266 (1933). doi 10.1007/bf01341490... 

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