Papers by Author: Jun Wang

Abstract: Based on a principle of laser drilling size and the roundness copied with respect of laser spatial mode, heat absorbing rate for laser drilling of YG8 is presented in theory and application. The mathematical models are then developed. The relationship of heat absorbing rate compared to the original absorbing rate is thus derived that is A = T +A0. It shows that heat absorbing rate to laser beam increases linearly with drilling temperature. The research outcome is used to optimize preheating process in which the novel method improves laser drilling precision from 0.03mm of primitive laser system to 0.01mm under the condition of heat absorbing.

Abstract: A study of the energy-mode adjustment and application was presented to investigate the effects of adjustable methods on energy mode. Three methods of energy-mode adjustment were used: by circular profile itself, by an optical scanning expander and deformable mirror. The circular profile naturally modifies energy density with the changes of incident angle. The optical scanning expander was used to turn a Gaussian beam into a uniform beam. Also a novel technique of deformable mirror was designed to obtain a more controllable energy mode for laser selective processing. Moreover, the models describing energy modes were developed to improve laser-processing performance. An experiment was arranged to simulate single-tip diamond truing and produced a result, as shown in the SEM photo, quite similar to a fine thread. The results were discussed to reveal the mechanism of laser processing.

Abstract: The recent investigations on spray formed ultrahigh-carbon steels (UHCSs) are reviewed. A satisfactory combination of strength and ductility in spray formed UHCSs can be obtained by hot rolling and annealing. The composition and hot rolling have a marked effect on the formation of graphite in UHCSs. The possibility of achieving high strain rate superplasticity in the spray formed UHCS was first revealed by very recent investigations in Shanghai Baosteel Research Institute. The UHCS processed by a combination of spray forming and hot rolling exhibited high strain rate superplasticity.

Abstract: Conventional strain-based mechanics theory does not account for contributions from strain gradients. Failure to include the strain gradient contributions can lead to underestimates of stresses and size-dependent behaviors in small-scaled structure [1]. This paper focus on the structural size effects on torsion of cylinders. The torsional stiffness of cylinders can be higher than conventional expectation when the cylinder size is in the nanometer - or micron-scale. Following the Saint-Venant theory of torsion, we established the equation of torsion in terms of the warping function on the basis of the nano-mechanical theory of elasticity. The torsional equations contain two higher order material length scale parameters and two conventional Lame constants. The equilibrium equation is a fourth order partial differential equation which can be reduced to two second order equations. Two formulations in terms of pseudo warping function and stress function are presented. Closed-form solutions for circular and thin wall section and series solutions for rectangular microbars have been obtained. The total torque depends only on the stresses conjugated to the strain and is only implicitly dependent on the higher order stress metrics. The solution reveals that the torsional rigidity is dependent on the higher order length scale parameters and strain gradients and increases asymptotically upward when the cylinder size is reduced to the size of the higher order length scale material parameters. The increase is most marked for thin walled cylinders, stiffening to more then 10 times the conventional value when the cylinder size is near that of the higher order length scaled parameters.