CRACK INITIATION IN CRYSTALLINE MATERIALS.
Interim technical rept. no. 1,
SYRACUSE UNIV RESEARCH INST N Y
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The influence of several macroscopic and microscopic parameters on the fracture of crystalline materials was studied on commercially pure tungsten, 2.5Al-16V titanium alloy and LiF single crystal specimens. Test results showed that the continuum mechanical maximum stress theory predicts the correct behavior of these materials when surface preparation techniques are identical. Microplasticity at the surface seems to influence the mode and stress for crack initiation and fracture. Bend test results on LiF showed that small cleavage cracks at the surface are not necessarily responsible for crack initiation. The actual dislocation process occuring at or near the surface was strongly dependent on the condition of the surface. Based on the equations of Neuber, the position of the maximum stress for an elliptical crack inclined at an arbitrary angle to the applied load was calculated. Author