Papers by Author: De Jun Kong

Abstract: The X70 pipeline steel welded joint was processed to strengthen with laser shock wave, the structures of welded joint by laser shock wave were observed with Scanning Electric Microscope (SEM), and its surface residual stresses was analyzed with X-ray diffraction (XRD), the residual stress distributions of welded joint by laser shock processing were discussed, and the strengthened mechanism of X70 pipeline welded joint by laser shock processing was investigated. The experimental results shown that the phenomenon of grain fine is produced in the surface of X70 pipeline steel welded joint by laser shock processing, and compressive residual stress is formed in its surface layer, and improves the distribution of residual stress, which is benefit to increasing the capability of stress corrosion resistance for X70 pipeline steel welded joint.

Abstract: To widespread six-dimensional spatial vibration and shock in engineering, a novel device is present in which Hexapod platform is used as the main body and Magneto–rheological(MR) damper is used as a vibration control units installed at six branch chain. But the mathematics model for controlling is very complex because the multi-DOF model is highly coupling. In this paper, owing to the six chain vectors of the Hexapod mechanism are linear independence, which shows every branch of the system can be controlled by independent controlling algorithm. A neutral-fuzzy control algorithm is designed to achieve active vibration control a 2-DOF model. The results indicate that the effect of isolation after active control is obvious comparing passive control.

Abstract: A six dimensional vibration damping device is introduced which is composed of Hexapod parallel mechanism and six controllable damp units fixed on driving pairs. Firstly, the structure of the system is designed according to theory of the Hexapod mechanism. Then, Jacobian matrix and dynamics model are discussed successively. Lastly, a six dimensional vibration model is found by using ADAMS software. Through theory and simulation analysis, it has been approved that the system can be used to control six dimensional vibrations.

Abstract: VC coating was prepared on the surface of Cr12MoV cold working die steel by TD process, and its friction and wear properties were researched with HSR-2M type high-speed reciprocating friction and wear tester, the effects of load on friction and wear properties were discussed, and the wear surface morphologies were observed with SEM. The experimental results shown that fatigue wear and adhesive wear are mainly wear mechanism of VC coating, and the different parts have an influence on wear mechanism; When cracks occurs, the crack growth is the combined result of mutual influence of elastic-plastic crack growth and fatigue crack growth; There is no relationship between friction coefficient and load, and the wear rate increases with the load.

Abstract: The surface of Al2O3 coating sprayed on 40Cr substrate was re-melted with high power continuous CO2 laser, and its micro-hardness and residual stresses were measured, respectively. The strengthening mechanism of Al2O3 coating by laser re-melting was analyzed and discussed. The experimental results shown that the surface of Al2O3 coating by laser re-melting is neat and smooth, and its compositions are even, its structures are compact, and Al2O3 coating is evenly distributed in its surface with grain forms, and its micro-hardness increases about 200%; Residual stress of Al2O3 coating by laser re-melting is changed into compressive stress from tensile stress, which is benefit to improving bonding strength of coating-substrate interface.

Abstract: Thermally induced errors can contribute as much as 70% of the final error of the part dimensions produced on machine tools [1-5]. Thermal errors of machine tools can be treated as the superposition of a series of the errors coming from different heat source. 4 key temperature points of a turning lathe were obtained based on the temperature field analysis. A novel thermal error model on the basis of grey system theory was proposed. The basic principle and method of grey system model and its application in thermal error modeling on machine tools had been presented briefly.

Abstract: Based on the fact that symmetric coupler curve can have three different tangent points with given straight-line, the three symmetric points of coupler locus was specified, and they was made into symmetric tangent points to determine the position of instant centre method. The size of the hinged four-bar linkage straight-line mechanism is determined using the position of instant centre method. The results were shown that coupler locus curve is obtained with this approach that is approximated with the intended straight-line precisely, and the basis of this approach is simpler than other analytic approaches.

Abstract: The surface of 304 stainless steel was processed by laser shock wave, its surface micro-structures were observed with SEM, and residual stresses on its surface were measured with X-ray diffraction (XRD) stress tester, and the production mechanism of residual stress was analyzed. The experiment of stress corrosion in 25% NaCl aqueous solution was finished, the crack sensitivity of stress corrosion in NaCl aqueous solution was researched, and the effects of LSP on stress corrosion resistance were analyzed. The results shown that the refined hardened-layer is acquired on the surface of 304 stainless steel by LSP, and compressive residual stress has greatly increased, which improve availably the performances of stress corrosion resistant. The time of appearing cracks is inverse ratio with compressive residual stress, and LSP decreases effectively its stress corrosion cracks.

Abstract: The residual stresses of WC coating prepared by flame spraying and laser re-melting were measured quantitatively with X-ray diffraction (XRD) stress tester, and its micro-structures were observed with SEM, and the effects of residual stress on bonding strength of coating interface were analyzed. The experimental results are shown that residual stresses of WC coating are all tensile, and the effects of coating thickness on its residual stress is obvious, and residual stress is verse ratio with its thickness; Coating stress influences its cracking, tensile stress speeds its cracking, which causes its bonding strength decrease; The stress state is improved by decreasing its thickness, and its bonding strength can be increased.

Abstract: Residual stresses of model S1100 of crankshaft chamfer were measured by the technology of XRD. The distributions of residual stresses under mechanical peening, mechanical rolling and isothermal quenching are measured, and the tests of fatigue life were conducted. The results showed that the distribution of residual stress by machining in the crankshaft chamfer is complicated, which is at the tensile-compressive status, and it is one of the main factors to affect fatigue life of the crankshaft; isothermal quenching improves the distribution of residual stress, and tensile stress of the crankshaft chamfer is changed into the compressive stress, which may satisfy the requests of fatigue testing for 5 × 106 cycles. Although the mechanical rolling improved the residual stress distribution in the chamfer linked with the crank, tensile stresses in the chamfer connected with the linkage also increase, which influences the service life of the crankshaft.