Abstract
Localized displacement measurements based on electronic speckle-pattern interferometry are used to obtain crack mouth opening displacement (CMOD), stress intensity factor (SIF) and T-stress values during crack growth around cold-expanded holes. The specimens with a central open hole are made from 2024 aluminium alloy. The expansion level is 5% of nominal interference. The results are obtained for the same stress range = 350 MPa, but different stress ratio R = –0.4 and R = –1.0. A sequence of narrow notches, inserted under the constant external load, serves for crack modelling at different stages of cyclic loading. Initial experimental data represent in-plane displacement component values measured in the vicinity of the crack tip. The transition from in-plane displacement components to SIF and T-stress values follows from the relationships of modified version of the crack compliance method. The crack length curves of CMOD, SIF and T-stress profiles are obtained for different stages of cyclic loading. These data provide the construction of dependencies of fracture mechanics parameters for cracks of fixed lengths from the loading cycle number.
Highlights
Present innovations in aircraft manufacture are based on advanced technologies
These data are essential for more realistic predictions of fatigue crack growth rates through the use of various models that are based on linear fracture mechanics and superposition principal [25,26,27]
The third remarkable capability resides in quantitative determination of fracture mechanics parameters for cracks of different lengths at different stages of cyclic loading under combined influence of remote and residual stresses. These data provide the construction of the dependencies of the fracture mechanics parameters for cracks of fixed lengths against of the loading cycle number, which reveal a process of fatigue damage accumulation
Summary
Present innovations in aircraft manufacture are based on advanced technologies. One of them is the cold expansion process that leads to enhance the fatigue life of structures with fastener holes [1]. A set of works is devoted to an accurate analysis of SIF values for cracks located in the vicinity of cold expanded holes [22,23,24] These data are essential for more realistic predictions of fatigue crack growth rates through the use of various models that are based on linear fracture mechanics and superposition principal [25,26,27]. It is established that residual stress variations must be taken into account in any potential model used for the prediction of fatigue life of cold-expanded holes This fact reveals the main problem inherent in reliable and accurate numerical estimations of SIF values for cracks propagating in residual stress field caused be cold expansion of holes. These data give us CMOD, SIF and T-stress curves for cracks of fixed lengths as a function of the number of cycles
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