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The paper describes the experiments aimed at the extension of the method early proposed for the uniaxial fatigue monitoring to the multiaxial modes of loading. The common denominator for both methods approach is based on the possibility of computer‐aided optical analysis of extrusion/intrusion structure, called often surface deformation relief, to be used for quantitative assessment of accumulated fatigue damage and remaining life. Experimental data obtained under the different modes of loading are presented and described as well as some objectives for the future activities are outlined.
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and T. P MaslakWe present the results of our study aimed at development of a computerized optical method of evaluation of the accumulated fatigue damage. We show a possibility of predicting the residual resource of aircraft components made from clad aluminum alloys by the deformation relief of their surface near stress concentrators. For the quantitative estimation of deformation relief we use the parameters which characterize its saturation and fractal dimension.
The characteristic informative parameters for defect detection to be used in fatigue sensors have been established. Their development is interpreted in terms of scale levels of deformation and fracture. Damage accumulation of the sensor's surface tends to exhibit the self-organization nature. It is accompanied by formation of "folded" strain-induced relief on the surface. The mechanisms of damage accumulation under cyclic deformation were analyzed with the use of the multiscale approach.
The possibility of atomic force microscopy application for the investigation of fatigue damage process of aluminum alloy D16AT has been substantiated. It
IntroductionFatigue damage analysis of aviation structures becomes more required because of damage tolerance principal is practiced at a large scale in aircraft designing, because of increasing operation time and number of flights during the aircraft life span. At the same time the requirement of minimum mass for aircraft is actual also.The aluminum alloys like D16AT, V95, 2024 T3, 7075 T6 are widely use for the production of main structural components of the wing, empennage and fuselage of the aircraft.They are covered by pure aluminum for the corrosion protection.The deformation relief is formed on the surface of these aluminum alloys under cyclic loading.Deformation relief is external feature of local micro plastic deformation formed by the dislocation motion and dislocation transformation.As a result of these we can watch the extrusions, intrusions and persistent slip bands on the surface of material.The results of deformation relief investigations [1] show that deformation relief parameters (damage parameter D and fractal dimension Dp/s) have close correlations with cyclic loading and can be used for the models of fatigue life prediction for the structural components and for the aircraft in general. It has been shown [2; 3] the sensitiveness of the deformation relief parameters to the maximum stress level and to the stress ratio.The main aim of this work is to show the possibility of atomic force microscopy application for the quantitative analysis of the deformation relief formation.
The paper describes the key principles and results of preliminary experiments aimed at the development of new technique for the fatigue life prediction under conditions of biaxial cyclic tension. The foundations of the method were developed early by the numerous tests with monitoring the process of surface deformation relief formation, which is proved to be an indicator of accumulated fatigue damage under uniaxial fatigue. The employed phenomenon was early applied for the development of a family of uniaxial loading fatigue sensors. The formation of strain induced relief has been recently taken into consideration as a part of damage accumulation criteria under biaxial fatigue as well. The home-made testing machine has been designed to implement combined bending and torsion loading that simulates loads experienced by an aircraft wing skin. The experimental evidences on formation and evolution of the deformation relief revealed under conditions of combined loading, supports the proposed concept of biaxial fatigue sensor.
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