Papers by Author: Yong Kang Zhang

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Authors: Ai Xin Feng, Yong Kang Zhang, H.K. Xie, Lan Cai
Abstract: The interfacial adhesion between thin film and substrate is often the predominant factor and chief target in determining the performance and reliability of thin film/substrate system. A new technique of laser scratch testing technique has been presented by the authors of the article to characterize the interfacial adhesion between film and substrate, which synthesizes the advantages of traditional scratching technique and laser measure technique. The failure procedure is studied detailedly in the article. On different failure step of the film/substrate system, there are different characteristic s of stress and strain, as well as the characteristic of thermal lensing effect, which can be used as the distinguishing rule of the bonding state of the film/substrate system.
Authors: Yong Kang Zhang, Yu Long Li
Abstract: The 3-D finite element analysis model of beam-edge structure with spaced multiple layers under bird impact is established. Numerical simulations are implemented by using the non-linear contact-impact code ANSYS/LS-DYNA when the birds collide at three locations of the structure respectively. The failure process of the structure and the equivalent plastic strain at supports are obtained. The residual strength of the structure after impact is predicted. The results show that the front spars are penetrated or cracked after the leading edge is perforated. The equivalent plastic strain at the support is much higher when the bird impacts the structure at the central location. Both the structure deformation and failure mode from the simulation are consistent with the results of full scale test, which proves the validity of the method proposed in this paper.
Authors: Yong Kang Zhang, Xu Dong Ren, Jian Zhong Zhou, Ai Xin Feng
Abstract: Laser shock processing (LSP) employs high-energy laser pulses from a solid-state laser to create intense shock waves into a material, which can induce compressive residual stresses in the target surface and improve its mechanical property efficiency. Three different ablative, sacrificial coating were chosen to protect the 6061-T651 alloys from surface melting by laser pulse. This paper analyzes the effect of the paint and foil coatings on the shock wave propagation into the 6061-T651 alloys and the resulting change in mechanical properties. The depths of hardening by laser processing of 6061-T651 alloys up to 1 mm, and the surface hardness reach to 138HV. When the laser pulse energy density increase from 2.8 GW/cm2 to 3.6 GW/cm2, the surface hardness of the black paint, aluminum foil and silica acid black paint samples increase to 19, 27, 36 respectively.
Authors: Y.Y. Xu, Xu Dong Ren, Yong Kang Zhang, Jian Zhong Zhou, Xing Quan Zhang
Abstract: Laser shock processing is an important surface treatment that induces compressive residual stress to components, where the coating plays an important role. This paper deduce a general formula of the optimum thickness of coating according to the law of energy conservation and analysis the influence of coating on residual stress of the titanium alloy in laser shock processing. Titanium alloy with black paint, silica acid black paint and without coating were shocked by laser system respectively. It was found that coating could increase shock pressure amplitude and laser density absorption. Compressive residual stresses at the surface of the sample with the black paint and silica acid black paint are about -212.2MPa and -264.2MPa respectively, while the surface stress on the uncoated specimen is very high tensile stress. The bare surface due to melting and vaporization, leads to a very rough surface. The depth of induced compressive stress could reduce stress corrosion cracking in titanium alloy and improve fatigue lifetime.
Authors: Chao Jun Yang, Yong Kang Zhang, Jian Zhong Zhou, Ming Yong Ni, Jian Jun Du, Xing Quan Zhang, Jun Zhou, Xiang Guang Cao
Abstract: Laser shot peen-forming of sheet metal(or LasershotSM Peening) is a new plastic forming technique for metallic materials, which uses high-power pulsed laser replacing the tiny balls to peen the surface of sheet metal. When the pressure of shock waves induced by laser impresses an inhomogeneous residual stresses distribution in a given depth on the surface of sheet, it responds to the stress by elongating at the peened surface and effectively bending the sheet. In order to investigate the mechanism of laser shot peen-forming, the narrow strip peen-forming experimental of aluminum alloy 6061-T6 was carried out by using a pulsed Nd:glass laser with 0.5Hz repetition-rate. Here, under some given laser energy, laser pulse width, laser beam diameter and pulse repetition frequency and so on, the influence of shot strip interval and shot times on surface residual stresses and the deformation of the sheet is analyzed. The results show that the bending forming of the sheet metal can be found, and the peened surface of sheet metal becomes convex. That the bending increases with shot strip interval increase is not obvious, but it increases with the shot times increase in a proper range of shot times. Besides, because laser shot peen-forming generates compressive residual stresses on the surface, it offers many desirable characteristics in shaped metals and is a valuable technique for producing components for a range of industries.
Authors: Yong Kang Zhang, De Jun Kong, Jin Zhon Lu, Ai Xin Feng, Xu Dong Ren, Xing Quan Zhang
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.
Authors: Jin Zhon Lu, Yong Kang Zhang, Y.Y. Xu, De Jun Kong, H.B. Yao, Xu Dong Ren
Abstract: The surface of K24 superalloy was processed with laser cladding & LSP (laser shock processing). Residual stress in the laser cladding zone by LSP was measured with X-ray stress tester X-350A, and the variational rule of residual stress in the cladding zone by tempering treatment of 8 hours and 16 hours was measured, respectively. The experimental results show that compressive residual stress of K24 superalloy surface by laser cladding & laser shock processing is above -600MPa, which exceeds residual stress by mechanical peening treatment; and there is no clear effect on residual stress by tempering treatment at 600°C for 8 hours and 16 hours, respectively, which can improve fatigue life of K24 superalloy.
Authors: Xu Dong Ren, Yong Kang Zhang, Jian Zhong Zhou, Yong Yu Gu, Y.Y. Xu, Xing Quan Zhang
Abstract: Laser shock processing (LSP) employs high-energy laser pulses from a solid-state laser system to create intense shock waves into a material, which can induce compressive residual stresses in the target surface and improve its mechanical property efficiency. Residual stress of Ti6Al4V alloy both before and after LSP with multishocks was analysised. The depth of compressive residual stress was found to have a dependence on the number of shocking layers and a slight dependence on the level of irradiance. Surface stress improvements of more than 50% increases are possible after laser shock processing with either large spot or small spot patterns. The large spot gave a surface stress of 432MPa and a depth of over 1mm. The low intensity small spot gave a surface stress of 285MPa with a depth comparable to the large spot. Laser shock processing induces a compressive residual stress field, which increases fatigue crack initiation life and reduces fatigue crack growth rate.
Authors: Jian Zhong Zhou, Y.H. Fu, H.Y. Xu, Yong Kang Zhang, Judith C. Yang, Yun Zhang
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