Papers by Author: Fu Ling Zhao

Abstract: Operating characteristics of small and medium tonnage lattice boom crane which withstand fatigue loads was analyzed in this paper. It showed that the lattice boom crane utilization level is in the overlap zone of low cycle fatigue and high cycle fatigue. There may be some plastic deformation in the structure. So the total damage calculated by the Palmgren-Miner rule had a large scatter. Typical operating conditions was analyzed that K-type welded joints of the boom is under axial load and in-plane bending loads. Several critical areas of K-type welded joints were determined by ANSYS finite element calculation software where the stress amplitude was larger on the single side of the lattice boom. A new stress spectrum acquisition method based on the “measured+statistics+compare+simulation” integrated strategy of crane K-type welded joints was proposed. Based on a simplified Huffman non-linear cumulative damage theory, fatigue life of crane K-type welded Joints were calculated based on the strain parameters. They were compared with Palmgren-Miner rule and together with fracture mechanics method. Results showed that although they were all conservative compared with test results, the new method can be applied easily in for engineering applications because it only need amplitude constant amplitude fatigue strain-life data.

Abstract: There were lots of distributed sources in the process of fatigue crack propagation of the lattice boom. Static evaluation of the reliability indicators couldnt be satisfied to solve practical engineering problems. The load and fatigue resistance were regarded as random processes and the fatigue failure of the randomness in a variety of factors, the concept of dynamic reliability of the weights index was proposed, models of dynamic reliability of the weights index were built based on the fatigue bearing capacity mode and limit damage degree mode. Fatigue stress experiments comparisons were done on a crawler crane according to the actual operating conditions with a K-type welded joints prototype. The results show that the dynamic reliability evaluation assessment model is more accurately in the fatigue life evaluation and the method can provide a new assessment method for engineering applications.

Abstract: The excessive tool wear always has a great influence on the machining accuracy in micro electrical discharge machining (micro EDM). According to the image processing on the image of tool electrodes, the contour information of the worn tools is obtained, and then the tool wear, especially the tool shape change in micro EDM is studied in this paper. Firstly, the Canny edge detection method is used to extract the outline image of the tool, the scatter points of outline image are curve fitted, and the mathematical description of the tool outline is presented. And then though the mathematical analysis of the fitting function, the tool shape change and tool wear law of micro EDM are analyzed. Finally, according to the curvature changes of fitting curves, the end wear, corner wear and side wear of cylindrical electrode in micro EDM drilling and micro EDM milling, respectively, are divided reasonably based on the analysis, and the amount of each kind of wear is quantitatively estimated.

Abstract: Lateral and edge wear of electrodes in micro-EDM affects workpiece shape accuracy. A method that change materials property of lateral side of electrode was put forward, based on discharge performance difference of different materials, and it was demonstrated with experiments. Results show that the method proposed is more effective and improves the precision of deep holes, compared with traditional sampling methods. The technology can provide reference to practicality of micro-EDM for 3D structure cavity and deep holes.

Abstract: Wear course was experimental analyzed and mechanism of electrode wear was discussed based on finite element analysis and electromagnetic theory. Cu–TiN nano composite electrode was prepared on Cu electrode by electro deposition and effects of the electrode on discharging were studied. It is shown that electric field distortion and skin effect are two of the basic reasons on electrode wear. Cu–TiN nano composite electrode is one of the the effective ways for uniform wear of electrode in EDM.

Abstract: In micro electrical discharge machining (micro-EDM) of deep holes, the debris dispersed in gap may increase the possibility of secondary discharge, resulting in electrode shape changing and low accuracy of machined hole. In this paper, the debris movement caused by flow fluid in the machining gap is analyzed to understand the mechanism of debris transport by using software, FLUENT. Comparison of debris movement calculated by the modified N-S equation and N-S equation is conducted. Debris movement calculated by the modified N-S equation is demonstrated to be correct by experiment. The simulation results can explain the phenomena such as subulate electrode and hole, unstable machining process and low machining speed in micro-EDM of deep holes. It is helpful to improve the process of micro-EDM.

Abstract: Effects of additive powders on the machining mechanism of powder mixed EDM were researched. The whole discharging process was discussed based on theory of plasma and dielectric. Experiments, oscillograms and energy spectrum analysis gotten in experiments were performed in order to examine the changes of discharge between EDM and powder mixed EDM.

Abstract: Powder mixed EDM can effectively improve the surface quality of a machined workpiece. In order to study the mechanism of powder mixed EDM process, particles’ activities in working conditions are simulated and corresponding experiments are done. A 3D electric fields model described by finite element method of the particles suspended in working fluid in the electric field is built, the generated field is computed and presented, and the activities of particles in the breakdown process are analyzed. The results show that this method can serve as a good way to learn the activities of particles in the breakdown of discharge.

Abstract: Grinding of single crystal silicon may be achieved by two modes of material removal: ductile mode and brittle mode. Knowing of the brittle to ductile transition point at which the grinding process changes from the brittle mode to ductile mode is critically important for the realization of ductile mode grinding. This paper uses a new single grain diamond grinding method developed recently by the authors to investigate the brittle to ductile transition during grinding of single crystal silicon in all around. The results indicate that there exist four stages of brittle to ductile transition as the depth of cut is reduced: firstly, the surface cracks outside the grinding groove disappeared, secondly
cracks on the bottom of the groove disappeared, then the lateral cracks ceased in the subsurface region, and finally the median crack is suppressed beneath the grooves. It is not until the depth of cut reaches the last transition point that a crack-free groove can be produced, therefore, the last transition stage is decisive. The critical depth of cut delineating the brittle to ductile transition point derived based on this criterion is 40 nanometers, which is much lower than that based on surface cracks.

Abstract: We have developed the laser nanoprocessing technique by the integration of the fs laser and near-field scanning microscopy (NSOM). The second harmonic femtosecond laser working in the optical near-field with the assistance of NSOM equipment was applied to expose the photosensitive polymer material. The nanopatterns with feature size smaller than the laser wavelength can be fabricated. The optical diffraction limitation is therefore broken through by the near-field nanoprocessing. It was found in our experiment that the nanofabrication feature size depends strongly on the gap between the fiber probe tip and the substrate surface, as well as the laser coupling efficiency. The approach offers the advantages of high precision, speed and selectivity in nanopatterning, and is promising to be used in data storage device manufacture for higher density recording.