In order to improve the damage tolerance ability of aircraft skin, the superiority of laser cladding aluminum alloy structures for crack resistance is investigated by establishing a three-dimensional (3D) finite element simulation model based on the double ellipsoid heat source and sequentially coupled thermal-mechanical analysis (SCTMA) method. The temperature field and residual stress field under different laser power, laser scanning velocity, laser cladding length, laser cladding patterns and laser cladding angles are investigated to evaluate the effectiveness of fatigue life improvement. Stress intensity factors are calculated by M-integral method and fatigue life is estimated by Paris equation, respectively. The results show that the laser cladding samples achieve the best crack resistance performance at laser power of 1400 W and laser scanning velocity of 10 mm/s. The fatigue life for the sample of cladding coating length of 50 mm is 2.93 times than that of the untreated sample. The linear pattern shows a better crack resistance performance than other patterns and the best crack resistance performance is achieved when the cladding angle of linear pattern is “0”. The results demonstrate that the fatigue life of samples after being laser cladding treated is significantly higher than that of untreated samples, which benefits from the residual compressive stress induced by laser cladding process. The higher laser power or lower laser scanning velocity can improve the fatigue life of laser treated samples. The fatigue life of samples can be affected by laser parameters, laser cladding patterns and angles.

Effects of laser cladding on crack resistance improvement for aluminum alloy used in aircraft skin

A new parallel adaptive structural reliability analysis method based on importance sampling and K-medoids clustering

The force effect of the shockwave generated by the short-pulse and ultra-short-pulse laser enables the laser to enhance the mechanical properties of the material without ablating the material, improve the microstructure, change the shape of the material, and remove the tiny particles attached to the surface of the material, etc. Therefore, it is widely used in surface strengthening, surface cleaning, metal forming, etc. Laser shock peening (LSP) and laser shock cleaning (LSC) are two applications of laser shockwave in surface processing. The force effect of the laser shockwave allows non-thermal treatment has been used in aerospace, biomedical, semiconductor, etc. This paper reviews the principle of laser shockwave effects and the existing processing methods of short laser-included plasma shockwave; the numerical model of laser shock effects, including the laser–material interaction model and surface processing model; the effects of laser parameters on processing performance; the mechanical properties, the microstructure, and the surface features; finally, the future research and development of laser shock effect are prospected. 

Progress in applications of shockwave induced by short pulsed laser on surface processing

Adaptive structural reliability analysis method based on confidence interval squeezing

The aim of this paper is to research the effects of stop hole on crack turning, residual fatigue life and crack tip stress field, in which the location, size and shape of stop hole are considered. The numerical model is established according to M-integral technology, and crack turning angle is determined by maximum hoop stress criterion. The calculation results show that stop hole location has a significant effect on crack turning angle and residual fatigue life, and it should be drilled with a reasonable distance in vertical and horizontal direction around crack tip to achieve a better residual fatigue life retardation effect. The larger the stop hole size is, the wider effect range of stop hole on crack turning and residual fatigue life will be. The effects of elliptical stop hole on crack turning angle and residual fatigue life retardation are greater than that of round hole when the distance in vertical direction increases. Crack tip stress distribution is changed by increasing σy and decreasing σx, and the most dramatical changes occur at the circumferential direction of 90° and 270°.

Effects of stop hole on crack turning, residual fatigue life and crack tip stress field

To predict reliability for highly non-linear and complex model efficiently and accurately, an artificial neural network (ANN) based Monte Carlo method (MCM) is proposed. In this method, ANN trained by backpropagation (BP) algorithm is developed to establish the relationship between inputs and outputs. The trained ANN model is then connected to MCM to predict reliability and reliability sensitivity of structure. To examine the accuracy and efficiency of the proposed method, results obtained by polynomial-FOSM (first-order second moment) method and ANN-AFOSM (advanced first-order second moment) method are provided. Compared with the traditional Monte Carlo method, the time consumed by ANN-MCM, polynomial-FOSM and ANN-AFOSM methods only accounts for 0.14% of the traditional MCM. The reliability analysis and reliability sensitivity analysis results of ANN-MCM method are very close to traditional MCM, polynomial-FOSM method yields large errors, ANN-AFOSM is in between. It shows that the proposed method is of high accuracy and efficiency.

Yun Hu

Papers

Effects of stop hole on crack turning, residual fatigue life and crack tip stress field

Reliability analysis for highly non-linear and complex model using ANN-MCM simulation

Effects and optimization of biomimetic laser shock peening on residual fatigue life improvement of aluminum alloy used in aircraft skin