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Laser-induced forward transfer (LIFT) is proposed as a highly efficient and high-resolution printing technique. Tilting of the microjet in the LIFT process affects the deposition deviation, lowering the printing resolution. In this paper, the tilting behaviors of the metal microjet in the nanosecond LIFT process are investigated based on a high-speed observation. Experiments were conducted on the copper film under different laser fluences. Observations based on the pump-probe method were performed to capture the ejection behavior of microjets. It is found that the tilting direction is isotropic, and the tilting angle follows Gaussian distribution. The tilting behavior originates from the disturbance of residual stress within the film during jet generation because the statistical result of the tilting angle hardly varies with the propagation time. In addition, the tilting angle is found to decrease linearly with the laser fluence due to the ejection velocity increasing at a higher rate than the lateral velocity. The lateral offset of the tilting microjet at different flight distances matches well with the position deviations, verifying the tilting behavior of the microjet. This study provides essential comprehension of the tilting behavior of metal microjet in the LIFT process. [ABSTRACT FROM AUTHOR]

Laser peen forming (LPF) is a promising method to fabricate fiber metal laminates (FMLs) with its design flexibility to produce complex shapes. Eigenstrain-based modeling is a helpful method to predict deformation after LPF, while determining eigenstrain is very difficult because of its complex constituents and high-dynamic loading of process. An effective experiment-based method is proposed in this work to obtain eigenstrain induced by LPF in metal layers of FMLs. An analytical beam model is developed to relate the deflection profile generated by specific scanning strategy to equivalent bending moment. Based on the determined bending moment from the measured deflection profiles, the generated eigenstrain can be inversely calculated by the proposed beam model describing the relationship between the eigenstrain and the bending moment. Chemical etching to remove sheets layer by layer is used to obtain the relaxed deflection profile to calculate the eigenstrain in each metal layer. Furthermore, an approximate model of plate is established to predict deformation after LPF based on determined eigenstrain. The results show that the predictive deformed shape agrees very well with both experiments and finite model prediction. [ABSTRACT FROM AUTHOR]

Accurate numerical modeling of laser shock processing, a typical complex physical process, is very difficult because several input parameters in the model are uncertain in a range. And numerical simulation of this high dynamic process is very computational expensive. The Bayesian Gaussian process method dealing with multivariate output is introduced to overcome these difficulties by constructing a predictive model. Experiments are performed to collect the physical data of shock indentation profiles by varying laser power densities and spot sizes. A two-dimensional finite element model combined with an analytical shock pressure model is constructed to obtain the data from numerical simulation. By combining observations from experiments and numerical simulation of laser shock process, Bayesian inference for the Gaussian model is completed by sampling from the posterior distribution using Morkov chain Monte Carlo. Sensitivities of input parameters are analyzed by the hyperparameters of Gaussian process model to understand their relative importance. The calibration of uncertain parameters is provided with posterior distributions to obtain concentration of values. The constructed predictive model can be computed efficiently to provide an accurate prediction with uncertainty quantification for indentation profile by comparing with experimental data. [ABSTRACT FROM AUTHOR]

Laser shock peening (LSP) is an innovative surface treatment technique similar to shot peening. An analytical model to predict the residual stress field can obtain the impact effect much quickly, and will be invaluable in enabling a close-loop process control in production, saving time and cost of processing. A complete analytical model of LSP with some reasonable simplification is proposed to predict residual stresses in depth by a sequential application of a confined plasma development model and a residual stress model. The spatial distribution of the shock pressure and the high strain rate effect are considered in the model. Good agreements have been shown with several experimental measured results for various laser conditions and target materials, thus proving the validity of the proposed model. [ABSTRACT FROM AUTHOR]