Research On Shot Peening Strengthening Mechanism Of Civil Aircraft Structural Parts With Corrosion Damage

Aircraft structural parts have been working under the condition of load and all kinds ofcorrosive environments, some corrosion damage phenomenons will occur frequently, such ascorrosion fatigue and stress corrosion etc. Aging trend of existing civil aircraft such as Boeing,Airbus ect is growing with the increase of service time (fatigue, corrosion and wear are themain problems of the aging aricraft to face). A large number of existing corrosion damagescan not be ignored in the repair process of civil aircraft structural parts.The research of this thesis was financially corporately supported by National NaturalScience Foundation of China and Civil Aviation Administration of China (Subject title:Research on Shot peening Strengthening Mechanism of Civil Aircraft Structures withCorrosion Damage; Subject No.:61179051), civil aircraft structural parts with corrosiondamage were selected as the object of study, a integrated method of combining theoreticalanalysis and experimental study was employed, shot peening strengthening mechanism ofcivil aircraft structural parts with corrosion damage were studied deeply.For the excessive computation problem of multi-shots random finite element model,model simplified method based on automatic transmitting of the historical information, rapidmodeling method based on movement vector, solving scheme of stabilized residual stresswere put forward, a series of key issues were worked out; Calculation method of surfacecoverage was put forward, which implemented the quantitative analysis of influence ofsurface coverage on distribution rule of residual stress; Some subprograms abaqus-orientedwere developed by employing Python language for estalishing random-shots geometricalmodel, autocommitting job files and rapid modelling based on movement vector; Nonlinearfinite element numerical models for shot peening were established based on Abaqus; And theinfluence of different friction coefficient μ and the hourglass stiffness coefficient on theresults of finite element simulation were analyzed. The research results guarantee theaccomplishment of the study about shot peening strengthening mechanism.Mechanism and type of corrosion damage and the topography of corrosion damage areaswere concluded and summarized for aluminum alloy aircraft structural parts (AAASP),geometrical features located in grinding area of AAASP were classified; Residual stress fielddistribution for different geometrical features (including different shape of surface and filletradius rd) were studied by employing shot peening method with fixed angle based onrandom-shots shot peening FEM. Residual stress field distribution rule for differentgeometrical features were revealed "the order from big to small of surface residual compressive stress srsand the max residual compressive stress mcrsis concave arc surface,convex-concave surface, bi-concave surface, flat surface, convex arc surface, bi-convexsurface. For convex arc surface, and increase with the increment of fillet radiusrd; For concave arc surface, and decrease with the increment of fillet radius rd.the variation of the corresponding depthz mwith and the total depthz0of residualcompressive stress are not obvious ".Residual stress field distribution rule for different geometrical features located intransition region of structural parts were analyzed deeply, with the identical shot peeningstrengthening process parameters and different shot peening strengthening method, based onlocal coordinate transformation method of stress; A analytic calculating model of Almenintensity AHsatwith different shot peening strengthening process parameters was obtained;The required number of shots for achieving100%surface coverage of structural parts werecalculated; Taking concave arc surface for example, residual stress field distribution of whichwas discussed with different shot peening strengthening process parameters; And takinggrinding area of two sides with open mouth for example, the influence of residual stress field,organization structure and surface topography characteristics for structural parts after shotpeening strengthening on effect of shot peening strengthening were analyzed in detail. Theresults have higher theory and engineering application value, which establish a soundfoundation for the practical application of shot peening strengthening process in aircraftstructural parts repair with corrosion damage.Almen intensity AHsatfor different injection pressure Psand shot diameter Dswerestudied based on novel experiment scheme; Required cycle number of shot peening forachieving100%surface coverage were obtained with different Psand Dsbased on digitalimage processing method, the distance between adjacent two passes of shot peeningstrengthening was optimized combined with normal distribution; Surface roughness Raandsurface residual stress of structural parts were measured and analyzed; The fatigueperformances of structural parts after shot peening strengthening were studied. And theexperimental results of AHsat, Ra, and fatigue test were used to compare with thetheoretical analytical results in chapter3and4. which show that the theoretical analyticalresults are accurate and reliable.