Mr. Jiancheng Jiang Profile

Jiancheng Jiang

at Shanghai Jiao Tong Univ.

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Proceedings Article | 9 October 2021 Paper

Improvement of numerical instabilities in laser peen forming process planning based on perimeter constraint

Jiancheng Jiang, Yongxiang Hu, Maziar Toursangsaraki

Proceedings Volume 11892, 118920O (2021) https://doi.org/10.1117/12.2601462

KEYWORDS: Process modeling, Numerical stability, Optimization (mathematics), Metals, Laser processing, Laser energy, Error analysis

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Laser peen forming (LPF) is a novel flexible forming process with remarkable advantages in complex shape forming. The distributed process planning model, which applies eigen-moment as the intermediate design variable, is an effective way to realize the process planning for complex shape forming. Due to the immaturity of the model, numerical instabilities such as checkerboards and intermediate densities commonly occurring in process planning. Therefore, it is difficult to apply the planning results as a forming scheme directly. This study utilizes the perimeter constraint method, re-drives the process planning model's mathematical expression to realize the aggregation control of the eigen-moment field. Effects of perimeter constraint and Tikhonov regularization term are verified and compared through the numerical method. Results show that perimeter constraint is more effective in preventing numerical instabilities. Then the improved model is applied to the LPF process planning of cylinder, saddle, and wave surface. LPF experiments are carried out based on the process planning results. Experimental surfaces are measured and compared with objective surfaces to verified the improved model. Because there still exists a specific error between the experimental surfaces and the objective surfaces. Reasons for the error are analyzed and discussed, and methods to improve the precision of LPF technology are further proposed.

Proceedings Article | 9 October 2021 Paper

Experimental investigation of laser peening effects on tensile properties of AA2195-T6 friction stir welded joints

Maziar Toursangsaraki, Yongxiang Hu, Jiancheng Jiang

Proceedings Volume 11892, 118920J (2021) https://doi.org/10.1117/12.2599515

KEYWORDS: Digital image correlation, Image processing, Laser welding, Homogenization, Heat treatments, Aluminum, X-rays, X-ray diffraction, Distortion, YAG lasers

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The considerable local dissolution of strengthening phases under gradient thermo-mechanical effects of friction stir welding leads to a noticeable decrease in material local hardness and tensile properties in friction stir welded Al-Li joints at the joint central area, known as the thermo-mechanical coupling zone, compared to its surrounding regions. Consequently, the resulting high gradient in joint local properties at borders of the joint center leads to high local stress concentration and tensile failure under relatively low loading values at this region. In this study, firstly, effects of joint center laser-peening-induced local compressive residual stresses evolution and work hardening are investigated on the enhancement in local hardness and tensile properties of AA2195-T6 friction stir welded joints. Then overall induced joint mechanical property homogeneity effects from these effects are evaluated on the improvement in joint global tensile properties. LP-induced local residual stresses are measured through the depth using the X-ray diffraction method. X-ray diffraction pattern peak broadening analysis is utilized to measure dislocation density local variations after LP which represent plastic work hardening effects. Local tensile properties are characterized by the digital image correlation technique with the corporation of the monotonic tensile test approach. Considerable increments in local material properties lead to the enhancement of overall joint tensile yield strength up to about 31% and ultimate tensile strength to 11% as a result of LP-induced compressive residual stresses, surface work hardening and joint tensile homogenization effects.

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