This paper aims to study the effects of biomimetic laser shock peening (BLSP) on crack resistance ability of aluminum alloy aircraft skin. The extracted feature parameters obtained from cherry leaves obey normal distribution. Based on the extracted biomimetic parameters, a 3D finite element model (FEM) is developed to study the effects of BLSP treatment on the residual stress distribution, stress intensity factors and residual fatigue life of specimens. Results show that BLSP treatment contributes to form leaf-shaped residual stress distribution. Indepth residual stress field is divided into three layers of compressive residual stress at both surfaces and tensile stress in the middle. Since the compressive residual stress generated by BLSP balances the load applied on specimens, stress intensity factors of treated specimens are reduced effectively, greatly increasing residual fatigue life. The asymmetry of residual stress distribution facilitates crack turning to prolong the crack path. An artificial neural network (ANN) with three layers is established to predict the optimal structure by linking with MonteCarlo method (MCM). The relative error of the ANN-MCM prediction, merely 3.26%, indicates that the proposed method is able to employed to save design time and computation resource.

Fatigue & Fracture of Engineering Materials & StructuresVolume 43, Issue 11 p. 2756-2760 LETTER TO THE EDITOR Crack resistance behaviour of aluminium alloy for aircraft skin with bionic coupling units processed by laser cladding Jiaming Liu, Jiaming Liu orcid.org/0000-0001-6242-7198 School of Mechatronics Engineering, Nanchang University, Nanchang, ChinaSearch for more papers by this authorLushen Wu, Lushen Wu School of Mechatronics Engineering, Nanchang University, Nanchang, ChinaSearch for more papers by this authorMinjie Song, Minjie Song School of Mechatronics Engineering, Nanchang University, Nanchang, ChinaSearch for more papers by this authorYun Hu, Corresponding Author Yun Hu hyfatigue@163.com orcid.org/0000-0003-2267-0155 School of Mechatronics Engineering, Nanchang University, Nanchang, China Correspondence Y. Hu, School of Mechatronics Engineering, Nanchang University, Nanchang 330031, China. Email: hyfatigue@163.comSearch for more papers by this authorMin Lei, Min Lei School of Mechatronics Engineering, Nanchang University, Nanchang, ChinaSearch for more papers by this authorFilippo Berto, Filippo Berto orcid.org/0000-0001-9676-9970 Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology, Trondheim, NorwaySearch for more papers by this author Jiaming Liu, Jiaming Liu orcid.org/0000-0001-6242-7198 School of Mechatronics Engineering, Nanchang University, Nanchang, ChinaSearch for more papers by this authorLushen Wu, Lushen Wu School of Mechatronics Engineering, Nanchang University, Nanchang, ChinaSearch for more papers by this authorMinjie Song, Minjie Song School of Mechatronics Engineering, Nanchang University, Nanchang, ChinaSearch for more papers by this authorYun Hu, Corresponding Author Yun Hu hyfatigue@163.com orcid.org/0000-0003-2267-0155 School of Mechatronics Engineering, Nanchang University, Nanchang, China Correspondence Y. Hu, School of Mechatronics Engineering, Nanchang University, Nanchang 330031, China. Email: hyfatigue@163.comSearch for more papers by this authorMin Lei, Min Lei School of Mechatronics Engineering, Nanchang University, Nanchang, ChinaSearch for more papers by this authorFilippo Berto, Filippo Berto orcid.org/0000-0001-9676-9970 Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology, Trondheim, NorwaySearch for more papers by this author First published: 02 August 2020 https://doi.org/10.1111/ffe.13315Citations: 1Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume43, Issue11November 2020Pages 2756-2760 RelatedInformation

Aircraft skins are likely to experience cracks and fracture failure due to the combined action of shear, bending, and torsional load. Inspired by the crack resistance exhibited by plant leaf, a method is proposed to improve the crack resistance of aluminum alloy aircraft skin. The characteristic parameters of main and secondary leaf veins are extracted by image edge detection and analysis methods. According to a constructed collection of self-similar fractal sets, a bio-inspired residual stress field with fractal characteristics extracted from leaf veins is applied to specimens ahead of crack tip by using laser peening. The effects of fractal parameters on crack retardation are analyzed using interaction integral. The results show that the stress intensity factor ahead of crack tip is reduced by applying a bio-inspired residual stress field, whereas the plastic zone area ahead of crack tip is enlarged. The correlation between these two trends reveals the mechanism of stress intensity decrease after the introduction of bio-inspired residual stress field. The optimal crack retardation effect is achieved at a fractal angle of 55 degrees, at which the residual fatigue life is increased by up to 203.0%. Compared with square-shaped laser peening, full-coverage laser peening, square criss-cross pattern method, and single-edge notched tensile (SENT) specimen repair method, the proposed method achieves the longest residual fatigue life, which is almost three times that of the square-shaped laser peening method. Therefore, this theoretical study presents a potential method for improving the crack resistance of aluminum alloy aircraft skin.

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°.