Study on the fatigue crack growth behavior behavior of 30CrMnSiA 30CrMnSiA Straight Attachment Attachment Lugs LiMingWu1,YuTingHe1,*, HaiWei Zhang1, Teng Zhang1,QingShao1 1 Aeronautics and Astronautics Engineering College, Air Force Engineering University, 710038, China * Corresponding author: hyt666@tom.com Abstract The finite element model of straight attachment lug subjected to axial or oblique loading is built by using finite element software, a cosine pin-bearing pressure distribution is applied on the pin-hole squeeze surface as a boundary condition. The stress intensity factor (SIF) expressions for single through-the-thickness crack in straight attachment lug that subjected to axial or oblique pin-load less than 45 degrees are determined and validated. The fatigue crack growth rate da/dNand the stress intensity factor range ΔKare obtained by using the fatigue crack growth test data and the SIF expressions. The fatigue crack growth model of the typical straight lugs is established by using the Paris law, offering an analytical as well as experimental method for assessing and designing damage tolerant attachment lugs. Keywords attachment lug, finite element method, fatigue crack growth, stress intensity factor, the Paris law 1. Introduction Attachment lugs are one of the most fatigue-and fracture-critical components in modern engineering structures[1]. In aircraft structures, lug-type joints are frequently used to connect major structural components or in linkage structure, theirs failure can result in disastrous accidents. In the study of fatigue crack growth and fracture behavior of attachment lugs, an accurate calculation of the stress intensity factor is essential. There are a number of different methods for determining SIF, K, for crack in aircraft attachment lug. Over the years, several extensive studies have been made on lug fatigue performance, involving both experimental and analytical means. Liu and Kan[2] and Kirkby and Rooke[3] used the simple compounded solution method which involves superimposing known solutions, such as in Reference [4] to estimate the stress intensity factors. Schijve and Hoeymakers[5] and Wanhill[6] derived empirical K-solutions from the growth rate data for through cracks under constant amplitude loading using a backtracking method such as that proposed by James and Anderson[7]. Pian, et al[8], used the hybrid finite element method to compute the K-values for cracks oriented in various angles from the axial direction of straight lugs. Aberson and Anderson[9] used a special crack-tip singularity element to compute the stress intensity factors for a crack in a nonsymmetrical aircraft lug of an engine pylon. Impellizzeri and Rich[10] modified the exact weight function derived by Bueckner[11], for an edge crack in a semi-infinite plate, to include a series of geometry correction factors. Then they computed the K-values using the weight function method. However, at the aspect of damage tolerance design and analysis, only the situation of straight lug subjected to axial pin loading can be solved. For the straight lug and symmetric tapered lug, which are subjected to axial, oblique and transverse pin loadings, there is a lack of methods for ascertaining the crack propagation characteristics and residual strength. So, it is important to develop analytical as well as experimental procedures for assessing and designing damage tolerant attachment lugs to ensure the operational safety of aircraft[12], and to calculate the stress intensity factors (SIFs) in different geometric parameters and load conditions. Most of the researches made the assumption that the assumed or computed pin-bearing pressure distribution for an uncracked case remains unchanged even after the crack has initiated and propagated. Based on the parametric study conducted in Reference [8], it was found that, for any given crack length, the difference in the SIF computed using the uniform and cosine pin-bearing pressure distributions was as much as 30 percent. Therefore, it is salient that the correct representation of the pin-bearing pressure distribution during the crack growth process is essential to the calculation of accurate stress intensity factors. This paper presents a systemic study of the 30CrMnSiA straight attachment lug’s fatigue crack growth behavior using the finite element software ANSYS. The finite element model of the lug is established
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