Papers by Author: Lei Fang

Abstract: Laser shock processing is a technique similar to shot peening that imparts compressive residual stresses in materials for improved fatigue resistance. Finite element analysis techniques have been applied to predict the residual stresses from Laser shock processing. The purpose of this paper is to investigate of the different sheet thickness interactions on the stress distribution during the laser shock processing of 7050-T7451 aluminum alloy by using the finite element software. The results indicate that the sheet thickness has little effects on the compression stress in the depth of sheet, but great impacts on the reserve side.

Abstract: Laser shock processing (LSP) is a new technique for surface strengthening of fastener holes. The process of LSP before hole-drilling was adopted. A finite element model was established to study the effects of laser shock parameters on the residual stress field of aluminum alloy7050T7451 with Fastener Holes. The results indicate that increasing the laser power density until a fixed value results in a large peak in the hole-edge surface residual compressive stress. The hole-edge surface residual compressive stress and the depth of residual compressive stress are both increased with the increase of laser pulse width. Multiple laser shock processing can improve the residual compressive stress greatly, and with the increasing number of shot, the strengthening effect is gradually diminished.

Abstract: Laser shock forming (LSF) is characterized in non-contact load, high pressure and high strain ratio. It has many promising applications in aerospace, automotive, metal and many other industries. However, despite the extensive experimental and modeling study in literature, seldom investigations are about the effect of laser parameters on strain rates. With the variation of strain rates in LSF, the failure mechanism and plastic instability theory are different. Therefore, the variation of strain rates should be considered in the process of establishing LSF theory. Based on this, the article discussed the effect of laser shock parameters on the strain rates. Taken the 3003-H16 aluminum alloy as the specimen, the finite element (FE) analysis for LSF was performed.

Abstract: As a new lightweight structural sheet metal, tailor rolled blanks has a good prospect in the future development of the automobile industry, and its formability is the current research focus. We use ABAQUS software to analyze the impacts of blank holder force, thickness ratio, die radius, shape and size of sheet metal on the movement of the transition zone and thickness direction strain on the formability of square box of tailor rolled blanks in deep drawing. The results show that, generally, in the punch and side wall corner, where thinning is more serious is a dangerous rupture area, while the inner edge of flange part is prone to wrinkle. When the BHF is 140kN, the connection between the thin side and the transition zone where thinning is severe is also a dangerous area, and even more serious, likewise when the blank thickness ratio arrives at 1.4mm/0.8mm, or the blank size 260mm*260mm, thinning is very serious at the connection between the thin side and the transition zone which is a dangerous rupture area.

Abstract: With more and more attention to the technology of tailor welded blanks (TWBs), it is vital to study the springback of TWBs. In this paper, the springback law of parallel and perpendicular to the weld of TWBs hyperboloid shallow shell affected by blank holder force, punch string height, and the difference of blank thickness was researched by finite element software. The results show that: by means of drawing and trimming, the springback of TWBs can be reduced, and the curvature of TWBs is less parallel to the weld, but the curvature is larger perpendicular to the weld. The effect of blank holder force on the trimming springback is relatively small in the range of experimental date. With the punch string height increasing, the drawing and the trimming springback are both increased firstly and then gradually decreased perpendicular to the weld, and the drawing and the trimming springback are both decreased parallel to the welding. And perpendicular to the weld, with the increase of the quadratic difference of thickness, the drawing springback of the thinner side is gradully decreased, and the drawing springback of the thicker side is gradually increased, after trimming, the springback of the thinner and the thicker side are both less than the drawing springback, and parallel to the weld, the drawing and the trimming springback are decreased firstly and then increased with the increase of the quadratic difference of thickness.

Abstract: Laser shock forming (LSF) of sheet metal is a novel technology in plastic deformation. It is necessary to correctly predict the Forming Limit Diagram (FLD) based on LSF. New failure maximum thickness reduction rate criterion is used to determine the forming limit based on the numerical system during LSF. The relationship model between maximum thickness reduction rate and the strain path is built. In addition, the effects of strain path and strain-hardening exponent on forming limit are considered. The maximum thickness reduction rate under equi-biaxial tensile strain path can be determined easily during LSF and the expression of the criterion is determined finally. Then the limit strains under other strain paths between uniaxial tension to equi-biaxial tension can be determined by the criterion combined with numerical simulation of forming process. The criterion can predict forming limits for sheet metal exactly and makes it possible to determine forming limit strains under different strain paths only through equi-biaxial tensile test during LSF.

Abstract: In this study, the springback law of generatrix direction, circumferential direction of tailor welded blanks (TWBs) cylinder shallow shell impact from blank holder force, punch profile radius and sheet thickness was researched by finite element analysis, which was compared with non-welded blanks. The results show that: in the circumferential direction, with the increase of blank holder force, the trimming springback of the tailor welded blank of the thickness combination of 1.2mm and 0.8mm (TWB1208) is decreased firstly and then increased, which is larger than that of the non-welded blanks of 0.8mm and 1.2mm. With the increase of punch profile radius, the drawing and the trimming springback of TWB1208 are both increased, and after trimming, the both springback are greater than that of the non-welded blanks. With the increase of the quadratic difference of thickness, TWB1208, TWB1612 and TWB1608, the drawing springback is decreased, and the trimming springback is gradually increased. In the generatrix direction, when blank holder force is less, the distortion deformation of TWBs is serious, and after the trimming, it is decreased according to the increasing blank holder force. With the increase of punch profile radius, the distortion deformation is larger. The greater the difference of thickness is, the more serious the distortion deformation is.

Abstract: As a new lightweight material and new technique,Tailor Rolled Blanks has a good prospect in energy-saving environmental protection and the future development of the automobile industry, formability window of Tailor Rolled Blanks at blank-holder force has important practical significance. Based on the research of a square box TRB, the paper proposes a theory of TRB’ formability window, also with the usage of an ABACUS finite element software to simulate the TRB sheet in the course of the critical wrinkling BHF curve and critical fracture BHF curve, to establish TRB formability window under the condition of blank holder force. The results not only show that the square box of TRB has the security zone in the deep drawing process, but also has got the wrinkling and fracture areas of the square box.