Papers by Author: Jin Zhon Lu

Abstract: The strain-rate sensitivity of LY2 aluminum (Al) alloy subjected to laser shock processing (LSP) was investigated according to the fracture morphology at strain-rates ranging from 0.00001 s-1 to 0.1 s-1. The fracture morphology was observed by the scanning electron microscopy (SEM). Fracture morphology at different strain-rates suggested that LY2 Al alloy after LSP seemed to evolve towards a more ductile dimple fracture mode with increasing the strain-rates. The relations underlying the fracture morphology and strain-rate sensitivity were also addressed.

Abstract: The marking system by laser shock wave (LSW) based on liquid crystal mask, which differs entirely from marking by laser ablation (or laser thermal effect), was established. Two-dimension (2D) nondestructive markings based on liquid crystal mask were prepared by LSW, and the distribution of residual stresses in laser-shocked region was measured and analyzed. The results showed that tensile residual stresses of sample surface were converted into compressive residual stresses by LSW, which is a nondestructive marking for aviation key parts.

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.

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.

Abstract: The diesel engine cylinder was processed by laser honing (LH) device, the structure morphology was observed with scanning electric mirror (SEM), and lubricant consumes and wear performances were measured, at the same time the mechanism of LH and effects of laser parameters on LH results were analyzed. The experimental results are shown that LH is a kind of phase transformation treatment by laser, which processes a hardening belt in the certain distributing form on the work-piece surface, and forms the hardness distribution of soft and hard material alternatively; LH may lower the engine oil consumes 30%-60%, and reduce the pollution of the catalyst machine, and lower the grain let of the engine oil 25%-30%. LH intentionally machines the grain cave, which has the certain angle, depth, and width etc.. The surface microcosmic sculpting has the lubricating function for usage process, and storage and transport lubricant, which improves the rubbing condition, then lower the part wear and increase the other performances. The short-wave laser is more applicable to the LH process, which improves the lubrication condition, and increases the service life of the engine and the efficiency, and lowers the engine oil consumes.

Abstract: The theoretical researches on fabrication, measurement and identification of laser marking system of 3D(three-dimension) anti-counterfeiting identifiers have been done in this paper. 3D identifiers were fabricated and 3D identifiers’ modelings were reconstructed, and binary coding of gray images were encoded by programmable control of liquid crystal mask, spatial modulating of laser beam and photolithography fabrication technics. We regarded the depth of 3D identifiers as anti-counterfeiting information, and the original marking data and anti-counterfeiting information are saved in remote database server by database technology and computer network technology，so true produces can be distinguished from fake through network. The basic theory of 3D nondestructive anti-counterfeiting identifiers based on liquid crystal mask was built, and a new technology of creating 3D anti-counterfeiting identifiers by laser shock wave was set up, which differs entirely from marking by laser ablation (or laser thermal effect). A new high-efficiency theory of detecting and identifying on 3D anti-counterfeiting identifiers by 3D identifiers’ reconstruction and binary coding was set up. The study enriches dynamic plastic deformation theory of partial high-strain-rate and anti-counterfeiting design & manufacturing theory which is also a highlight based on advanced manufacturing theory of mechanical effect on laser shock wave.

Abstract: For the characteristics of soft X-ray stress testing technology, a formula to resolve main residual stress is deduced based on analyzing the relationship between main residual stress and normal stress of different sections. The distribution of main stress of laser shock forming TA2 metal sheet is studied combined with the experimental study on the determining residual stress with soft X ray diffraction analyzer. The result shows that testing and calculating main residual stress is an important approach to study the deformation law of sheet metal material.

Abstract: With the advent of high-power pulsed lasers, laser peening has emerged as a new and very promising technique to improve the resistance properties of materials to fatigue, wear and corrosion. In this paper, the effect of laser peening on the surface performance of QT700-2 materials was investigated, the parameters of laser peening were optimized by an artificial neural network (ANN) method. A series of experiments was carried out by using a high-power, Q-Switched, pulsed neodymium-glass laser. The microstructure features were analyzed with SEM and the hardness and residual stresses at the surface and in-depth were measured. The results indicate that the depth of hardened layer was about 0.31ı1.40mm for a different shot number of 1-4 times and the compressive residual stress at the surface increases with increasing laser pulse energy, from -165MPa for the low energy 12J to -410MPa for the higher energy 20J. Laser peening can restrain nucleation of fatigue cracks and improve the fatigue life of nodular cast iron materials.