FUNDAMENTAL STUDIES OF FRACTURE.
Final rept. 7 May 65-6 May 69,
COLUMBIA UNIV NEW YORK HENRY KRUMB SCHOOL OF MINES
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The investingation of fracture focused on elucidating the mechanisms by which strain becomes so concentrated that the work of deformation, limited to a small volume becomes little. The research concerned primarily with engineering materials consisted of the following phases 1 A theoretical study of the elastic contribution to the surface energy controlling final separation of the material embrittled by plastic deformation. 2 An experimental study of how to reveal the plastic zone and measure its size in materials of interest. 3 A study of strain hardening, which controls the plastic zone size, by studying the effects of prior strain on the operation of latent slip systems. 4 A study of strain hardening by calculating the stress at a point due to pile-up complete dislocation loops. 5 A study of the process of fracture in fatigue, both experimental by optical and electron microscopy, and theoretical by applying dislocation dynamics. 6 An experimental and theoretical study of plastic zone strain distribution, controlling fracture toughness, and propagation velocity controlling crack speed, in iron and an iron-silicon alloy. 7 A similar study of brass, involving stacking-fault energy as a variable. 8 A study of creep, relating to the slow growth of cracks preceeding rapid crack propagation, by applying the theory of thermally and stress activated rate processes to dislocation movements. Author