Fatigue crack growth through a residual stress field introduced by plastic beam bending

Abstract

A B S T R A C TWe present predictions and measurements of fatigue crack growth rates in plastically bent aluminium 2024-T351 beams. Beam bending and fatigue were carefully controlled to minimize factors other than residual stress that could affect the fatigue crack growth rate, such as large plastic strains or residual stress relaxation. The residual stress introduced by bending was characterized by a bending method and by the slitting method, with excellent agreement between the two methods. Crack growth rates were predicted by three linear elastic fracture mechanics (LEFM) superposition based methods and compared to experimental measurements. The prediction that included the effects of partial crack closure correlated with experimental data to within the variability normally observed in fatigue crack growth rate testing of nominally residual stress free material. Therefore, we conclude that crack growth through residual stress fields may be predicted using the concept of superposition as accurately as crack growth through residual stress free material, provided that the residual stress is accurately known, the residual stress remains stable during fatigue, the material properties are not changed by the introduction of residual stress, and that the effect, if any, of partial crack closure is taken into account. a = crack length B = specimen thickness da/dN = fatigue crack growth rate h(x,a) = weight function K A = stress intensity factor due to applied external forces K max = applied stress intensity factor at P max K min = applied stress intensity factor at P min K ssy = applied stress intensity factor at which small scale yield criteria is violated K open = the stress intensity factor due to P open K R = stress intensity factor due to residual stress K T = total stress intensity factor K T max = total stress intensity factor at P max K T min = total stress intensity factor at P min K T ssy = total stress intensity factor at which small scale yield criteria is violated

Effect of the amplitude loading on fatigue crack growth

“…Specimens are subjected to the bending fatigue tested used by many researcher [13][14][15]. Stress intensity factor for V-notch bent specimen is expressed by the following expression [16]:…”

A new experimental method to study the influence of welding residual stresses on fatigue crack propagation

“…The presence of RS in structures can have either beneficial or detrimental effects on FCPR. A number of studies have shown that compressive RS increase the fatigue life of cracked components (Beghini & Bertini, 1990;Fleck, Smith, & Smith, 1983;Ghidini, 2007;Itoh, Suruga, & Kashiwaya, 1989;Jones, 2008)while other studies have shown that tensile RS decrease it (Liljedahl, Zanellato, Fitzpatrick, Lin, & Edwards, 2010;Ohta, Maeda, Kosuge, Machida, & Yoshinari, 1989;Ohta, McEvily, & Suzuki, 1993;Trudel, Sabourin, Lévesque, & Brochu, 2014). Thus, there is a direct correlation between the orientation of the stress component normal to the propagation plane and its influence on FCPR.…”

Modeling of Residual Stress Fields and Their Effects on Fatigue Crack Growth

“…An intense debate is found in the literature between supporters of the elastic superposition method [32,57] and those who question its applicability for the prediction of FCG in RSF [5,6,7]. Moreover, other authors agree with the use of the elastic superposition method if the crack closure phenomenon is considered [58,59]. In the case of the specimens subjected to thermal or mechanical processes to relieve the RSF, the correlation between the stress intensity factor range and the FCG rate according to an empirical relationship has been successfully employed to predict FCG [4].…”

“…Jones and Dunn [59,56] employed the Finite Element Analysis (FEA) method to compute the total stress intensity factors and analyze the FCG in RSF according to the elastic superposition method. The specimens analyzed were the Single-Edge Bend (SE(B)) [59] and cold-hole expanded [56], and the material considered was a 2024-T351 aluminum alloy.…”

“…Jones and Dunn [59,56] employed the Finite Element Analysis (FEA) method to compute the total stress intensity factors and analyze the FCG in RSF according to the elastic superposition method. The specimens analyzed were the Single-Edge Bend (SE(B)) [59] and cold-hole expanded [56], and the material considered was a 2024-T351 aluminum alloy. The redistribution of RSF was not considered in the analysis and the pre-existing residual stresses in the uncracked specimens were employed as crack face pressures in the FEA models in order to compute K RS [59,56].…”