A technique for identifying and characterizing the microcracks produced in machined surfaces

Abstract

Microcrack formation constitutes an mportant feature of the machining process and a undamental component of the surface integrity of machined components. Microcracks have been observed inside the shear zone and their presence used to explain some aspects of the chip formation process. A preliminary investigation conducted on a number of materials machined under various cutting conditions has confirmed microcrack formation on machined surfaces as a result of machining. There has been, however, no systematic study of these microcracks and their extent, dimensions and the conditions in which they are produced are not well known yet. Bearing in mind that surface microcracks can affect the fatigue, corrosion and other properties of machined components, it is important to devise some means of quantifying this microcrack formation. A technique of microcrack identification and measurement based on Transmission Electron Microscopy (TEM) is described in this paper along with its application. Two new parameters, namely the Microcrack Area Ratio (MAR) and the Microcrack Density (MD) are introduced and defined. The extent of microcrack formation on the surface of three different materials machined in the same cutting conditions is examined in the light of this technique. The results show that this technique seems promising and may be adopted in future investigations of microcrack formation on machined surfaces and the factors of influence