The topographies of various surfaces have been studied in many fields due to the significant influence that surfaces have on the practical performance of a given sample. A comprehensive evaluation requires the assistance of fractal analysis, which is of significant importance for modern science and technology. Due to the deep insights of fractal theory, fractal analysis on surface topographies has been widely applied and recommended. In this paper, the remarkable uprising in recent decades of fractal analysis on the surfaces of thin films, an essential domain of surface engineering, is reviewed. By summarizing the methods used to calculate fractal dimension and the deposition techniques of thin films, the results and trends of fractal analysis are associated with the microstructure, deposition parameters, etc. and this contributes profoundly to exploring the mechanism of film growth under different conditions. Choosing appropriate methods of surface characterization and calculation methods to study diverse surfaces is the main challenge of current research on thin film surface topography by using fractal theory. Prospective developing trends are proposed based on the data extraction and statistics of the published literature in this field.

Rotary ultrasonic machining (RUM) is a mechanical type of nontraditional hybrid machining process that combining the material removal regime of both ultrasonic machining and conventional grinding. By utilizing the RUM of hard and brittle materials, superior processing outcomes can be realized, such as improved material removal rate, reduced cutting force, improved machining accuracy and surface integrity. Since the invention of the RUM, a large number of researches on RUM equipment and processing technology have been carried out. And now, it has been widely used in the machining of nearly all leading hard and brittle materials. The basic principles and development process of RUM are briefly summarized. This research works about the material removal mechanism, the processing characteristics, the novel application type, and the development of equipment are presented. Furthermore, the development trends and the noteworthy issues of RUM are prospected. © 2017 Journal of Mechanical Engineering.