Local Strain Measurement for Prediction of Fatigue Macrocrack Initiation in Notched Specimens

Abstract

On the basis of direct measurement of the opening displacement of the notch contour the procedure of the evaluation of local elastoplastic strains range, De à , is developed. The experimental values of De à are compared with the calculational data using known equations by Neuber, Glinka, etc. It is shown that for De à < 2% the experimental and calculational values are in good agreement but only in the case when the gradient of strains near the notch tip is taken into account. The proposed experimental method is used for the prediction of period N i to fatigue macrocrack initiation in specimens of a complicated shape.

Driving forces for localized corrosion-to-fatigue crack transition in Al-Zn-Mg-Cu

“…The large, consistent deviation observed for the elongated pit data suggests that, as pit‐surface area increases, crack formation is less likely to occur at macroscopic‐high stress areas. The lack of consistent crack formation at locations of high macro‐stress concentration is consistent with prior analyses, 22,32,91 as well as the expectation that fatigue crack formation is driven by local plastic deformation, 14,39 , 93–98 which concentrates at micro‐topographic features about the pit surface 33,34,88 …”

“…The results shown in Figs 10 and 11 suggest an important role for plastic strain concentration from local geometry and perhaps microstructure. Cyclic plastic strain accumulation is necessary for fatigue crack formation 14,23,34,39,93–96 . Elastic and elastic–plastic FEA analyses reported in literature show significant elastic stress ( k t ‐ e between 2 and 6) 33,34,88 and plastic strain (up to 10‐fold) 33 concentrations at the base of 10 to 20 μm‐scale pit‐like features.…”

Effect of chloride concentration on the corrosion–fatigue crack behavior of an age-hardenable martensitic stainless steel

“…Computationally intensive and mechanistically rigorous efforts have been put forth to model the crack formation life from fixed local defects [174]. However, empirically-based stress/strain life models of crack formation [175] that capture the effects of local defect geometry on the stress/strain inputs have been demonstrated to be accurate and are likely more feasible for engineering applications [42,170,[176][177][178]. Specifically, a mean stress modified Smith-Watson-Topper [175] based approach was highly accurate in predicting the crack formation life from pre-corrosion damage in aerospace Al-alloys [42].…”

The effect of pit size and density on the fatigue behaviour of a pre‐corroded martensitic stainless steel

“…3,15,26,27 Two engineering considerations motivate the investigation of the factors that govern the crack formation Nomenclature: CL1, Corrosion level 1 (severe corrosion); CL2, Corrosion level 2 (moderate corrosion); UNS S17400, 17-4 martensitic steel process from a broadly corroded surface. 15 Various modelling approaches have been proposed to quantitatively calculate the crack formation life [46][47][48][49][50][51][52][53][54] ; however, these methods typically only consider an isolated corrosion damage location. [28][29][30][31][32][33][34][35][36][37] Generally, these approaches use the pit size as an initial flaw size in LEFM calculations of the initial crack tip driving force and assume that the crack progresses as a periphery crack about the initial flaw size.…”

“…Second, by definition, LEFM estimates of fatigue life only consider the crack propagation stage; however, for relatively low loading levels and smooth pit morphologies, it has been observed that the crack initiation life can be significant. 15 Various modelling approaches have been proposed to quantitatively calculate the crack formation life [46][47][48][49][50][51][52][53][54] ; however, these methods typically only consider an isolated corrosion damage location. A critical knowledge gap is to understand how the crack formation process is dependent on the characteristics of the global pit damage distribution.…”