Examination of fatigue crack driving force parameter

Abstract

A B S T R A C T Most of the previous parameters that utilized as a crack driving force were established in modifying the parameter K op in Elber's effective SIF range K eff ( = K max − K op ). However, the parameters that replaced the traditional parameter K op were based on different measurements or theoretical calculations, so it is difficult to distinguish their differences. This paper focuses on the physical meaning of compliance changes caused by plastic deformation at the crack tip; the tests were carried out under different amplitude loading for structural steel. Based on these test results, differences of several parameter K eff in literature are analysed and an improved two-parameter driving force K drive ( =(K max ) n ( K ∧ ) 1−n ) has been proposed. Experimental data for several different types of materials taken from literature were used in the analyses. Presented results indicate that the K drive parameter was equally effective or better than K(=K max − K min ), K eff (=K max − K op ) and K * ( = (K max ) α ( K + ) 1−α ) in correlating and predicting the R-ratio effects on fatigue crack growth rate. BCAL = block constant amplitude loading BFS = back face strain CAL = constant amplitude loading CPLM = crack growth load measurement K * = two-parameter crack driving force k = unified two-parameter crack driving force K + = tensile part of the stress intensity range K = applied SIF range K appl = applied stress intensity range K CF = stress intensity factor range corresponding to P CF ( = P max − P CF ) K CF , P CF = stress intensity factor corresponding to P CF , crack flanks contact load K cl , P cl = closure stress intensity factor, closure load K drive = improved two-parameter crack driving force K eff,th , K th = the effective or threshold stress intensity factor range K max,appl = applied maximum stress intensity factor K max,tot = resultant maximum stress intensity factor K max , P max = maximum stress intensity factor, maximum load K min,act = actual stress intensity transmitted to the crack tip at externally applied stress 754

Fatigue crack growth behavior of beta-annealed Ti–6Al–2Sn–4Zr–xMo (x= 2, 4 and 6) alloys: Influence of microstructure and stress ratio

“…Many researchers have pointed out that stress ratio (R, ratio of minimum to maximum stress) had a direct relationship with RICC where a higher stress ratio would make fracture surfaces avoid contact. Until now, most of the research related to stress ratio effect (also called mean stress effect) was based on the mathematical expression descriptions about FCG rates [12,13,16,[32][33][34][35], where stress ratio effect has been taken into account (basically make an amendment to the classic Paris equation [36]). Although crack closure, which induces enhanced shielding effect on FCG, can be rationalized by the effective (∆Keff) rather than by the applied stress intensity factor range (∆K) to some extent, the specific mechanism of stress ratio acting on FCG behavior is complicated [8] and still not fully understood.…”

A Novel Methodology for Calculating Crack Opening Stress under Tension‐Compression Cyclic Load

“…In order to improve the accuracy of life calculation for engineering structure subjected to compression load, damage tolerance and durability design are proposed, in which the calculation of fatigue crack growth rate is one of the key contents [10,11]. Due to the fact that the effective driving force directly reflects the fatigue crack growth rate, it is necessary to establish an effective driving force model for crack growth [12][13][14].…”

A quantitatively accurate theory of stable crack growth in single phase ductile metal alloys under the influence of cyclic loading

“…Multiple parameter crack growth models that have recently been developed using a less mechanistic approach have been more successful than previous work in capturing the stress ratio effect. Noroozi et al (2005); Xiong and et al (2008); Kujawski (2001); Kwofie and Rahbar (2011); Lu and Liu (2012) In some of these models, parameters are often combined to form a so called "crack growth driving force". Noroozi et al (2005); Xiong and et al (2008); Kujawski (2001); Kwofie and Rahbar (2011); Lu and Liu (2012) Although there are numerous ways to interpret multi-parameter crack growth driving forces, it is taken here that they imply multiple mechanism crack growth.…”

“…Methods by which scientists and engineers have attempted to characterize or predict the stress ratio effect have also involved multi-parameter crack growth driving forces, instead of extra fitting parameters Noroozi et al (2005)Lu and Liu (2012);Xiong and et al (2008);Kwofie and Rahbar (2011);Kujawski (2001) Noroozi, Glinka, and Lambert use a two parameter…”