THE THEORY OF MICROTOME SECTIONING WITH AN INFINITELY SHARP CUTTING EDGE
AEON LABS EGHAM (ENGLAND)
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A variety of metallurgical and other specimens sectioned on a diamond knife ultra microtome were studied by means of light and electron microscope techniques in an investigation of the mechanisms involved in the machining of metals. It was observed 1 that, when elastic properties were maintained under the highest strains applied during cutting, the sections were not deformed, and 2 that for plastically deforming materials the simple plastic shear may be accompanied by plastic shear on another system in the relief of compressive stresses, causing curvature of the section. A model for this composite stress-relieving mechanism is described. Factors determing the propagation of slip in ductile metals may cause either homogeneous shear with successive slip planes activated or a discrete step slip pattern. Section formation in brittle materials or under conditions with knife edge defects occurs as a series of fractures in the plane of maximum shear stress. Special apparatus was designed to facilitate crystal preorientation for transmission electron microscopy and electron diffraction and replication studies.