Sir Alan Cottrell and the Dislocation Mechanics of Fracturing R.W. Armstrong Center for Energetic Concepts Development, Department of Mechanical Engineering, University of Maryland, College Park, MD 20742, U.S.A. Abstract. Sir Alan Cottrell led the transformation of metallurgy from an observational science to analytical description. The following ditty, written for an analysis of the influence of polycrystal grain size on mechanical strength properties, could very well have been inspired by subliminal guidance from Cottrell: The physically-weaker mortals are supported With stronger materials, needfully, more so every day. How so, you say – by brain power exhorted To restrict the role that cracks and dislocations play! The following account is an honoring contribution in recognition of the great man’s leading researches on one of several materials-based topics that he led: the dislocation mechanics of fracturing. 1. Introduction A previous festschrift for the 70th birthday celebration meeting in honor of Sir Alan Cottrell [1] may be compared with related recognitions given some years previously for Professors Egon Orowan [2], Norman Petch [3], and Takeo Yokobori [4], and a few years afterward, for Professor George Irwin [5]. The fracture-related research accomplishments of Cottrell were intimately connected with those of the persons who are referenced. Cottrell made quantitative use in a real sense of the dislocations figuratively invented by Orowan [6], and are also credited to Polanyi [7] and Taylor [8]. With Norman Petch, Cottrell developed the ductile-brittle transition theory for understanding the onset at lower temperatures or higher applied loading rates of brittleness in steel and related metals [9, 10]. Cottrell and Yokobori shared the vision of producing an understanding of fracturing on a combined microscopic and macroscopic level, this relating to encouragement from Cottrell for the founding by Yokobori of the International Congress on Fracture (ICF) [11]. Among Yokobori’s earliest research articles is one on the Cottrell-Bilby theory of yielding of iron [12]. And, the later Bilby, Cottrell and Swinden [13] model of crack propagation with an attendant localized plastic zone at the crack tip provided a breakthrough example of fracturing at macroscopic dimensions, as pioneered also by George Irwin [14]. Four sub-topics among Cottrell’s notable contributions to fracturing are to be covered: (1) the ductile-brittle transition temperature (dbtt); (2) the dislocation reaction mechanism for crack initiation; (3) the limiting theoretical strength of metals; and (4) the dislocation mechanisms of slip intrusions and extrusions involved in fatigue cracking. The following descriptions are intended to build onto the recent memorial articles honoring Cottrell by J.F. Knott [15], L.M. Brown [16] and D. Hull [17]. 2. Dislocation mechanics of the ductile-brittle transition temperature
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