The Relaxation of Residual Stresses During Fatigue

300

181

A B S T R A C T Many manufacturing processes can induce residual stresses in components. These residual stresses influence the mean stress during cyclic loading and so can influence the fatigue life. However, the initial residual stresses induced during manufacturing may not remain stable during the fatigue life. This paper provides a broad and extensive literature survey addressing the stability of surface and near-surface residual stress fields during fatigue, including redistribution and relaxation due to static mechanical load, repeated cyclic loads, thermal exposure and crack extension. The implications of the initial and evolving residual stress state for fatigue behaviour and life prediction are addressed, with special attention to fatigue crack growth. This survey is not a critical analysis; no detailed attempt is made to evaluate the relative merits of the different explanations and models proposed, to propose new explanations or models or to provide quantitative conclusions. Primary attention is given to the residual stresses resulting from four major classes of manufacturing operations: shot peening and related surface treatments, cold expansion of holes, welding and machining. A = function of material and temperature C = empirical constant CX = cold expansion DOD = Department of Defence DR = deep rolling EP = electropolished FAA = Federal Aviation Administration FCG = fatigue crack growth FE = finite element FTI = Fatigue Technology, Inc. GBP = glass bead peening GP = gravity peening JSSG = Joint Service Specification Guide k = Boltzmann's constant LBP = low plasticity burnishing LCF = low-cycle fatigue LSP = laser shock peening m = empirical constant Correspondence: R. C. McClung. Fatigue Fract Engng Mater Struct 30, 173-205 173 174 R. C. McCLUNG Q = effective activation energy for residual stress relaxation R = stress ratio S-N = Stress-Life SP = shot peening SR = stress relieved t = time T = Temperature USAF = United States Air Force WP = water peening σ RS = residual stress 3D = three-dimensional

“…The most extensive work on the stability of residual stresses induced by machining was performed by James; 223 see also Ref. [224].…”

Section: Machiningmentioning

confidence: 99%

Section: Machiningmentioning

confidence: 99%

A literature survey on the stability and significance of residual stresses during fatigue

McClung

2007

300

181

“…Furthermore, only about 0.5% plastic strain is needed to introduce the residual stress field which is significantly smaller than the 3% plastic strain for which Schijve 43 noted a crack growth rate acceleration factor of 2 in aluminium 2024‐T351. Lastly, the cyclic stress amplitudes in these experiments are less than the fatigue endurance limit of the material, implying that little to no residual stress relaxation will occur 46 . Therefore, this specimen offers an opportunity to evaluate the accuracy of superposition based predictions and partial crack closure corrections in a well characterized residual stress field largely free from other complicating factors.…”

Section: Introductionmentioning

confidence: 99%

“…Lastly, the cyclic stress amplitudes in these experiments are less than the fatigue endurance limit of the material, implying that little to no residual stress relaxation will occur. 46 Therefore, this specimen offers an opportunity to evaluate the accuracy of superposition based predictions and partial crack closure corrections in a well characterized residual stress field largely free from other complicating factors.…”

mentioning

confidence: 99%

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

Jones

Dunn

2008

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

“…A number of combinations of load and material have been investigated and some relaxation models have been put forward. James [9] proposed a model for relaxation based on an effective shear stress acting on primary slip planes oriented at an angle to the surface. Nevertheless, more knowledge is required to understand the mechanisms of relaxation and to acquire data on materials for design use and predictive models.…”

Section: Introductionmentioning

confidence: 99%

Effect of Shot Peening on Residual Stress and Fatigue Life of a Spring Steel

Farrahi

Lebrijn

Couratin

1995

162

This study describes shot peening effects such as shot hardness, shot size and shot projection pressure, on the residual stress distribution and fatigue life in reversed torsion of a 60SC7 spring steel. There appears to be a correlation between the fatigue strength and the area under the residual stress distribution curve. The biggest shot shows the best fatigue lie improvement. However, for a shorter time of shot peening, small hard shot showed the best performance. Moreover, the superficial residual stresses and the amount of work hardening (characterised by the width of the X-ray diffraction line) do not remain stable during fatigue cycling. Indeed they decrease and their reduction rate is a function of the cyclic stress level and an inverse function of the depth of the plastically deformed surface layer.