Fatigue crack growth in Haynes 230 single crystals: an analysis with digital image correlation

Abstract

A B S T R A C T Fatigue crack growth was investigated in Haynes 230, a nickel-based superalloy. Anisotropic stress intensity factors were calculated with a least squares algorithm using the displacements obtained from digital image correlation. Crack opening/sliding levels were measured by analysing the relative displacement of crack flanks. Reversed crack tip plastic zones were calculated adopting an anisotropic yield criterion. The strains measured in the reversed plastic zone by digital image correlation showed a dependence on crystallographic orientation. Finally, a finite element model was adopted to examine plasticity around the crack tip. Results were compared with the experimentally observed strains.Keywords effective stress intensity factor range; fatigue crack growth; mixed-mode propagation; plastic zone; single crystal nickel-based alloy; single crystal plasticity. N O M E N C L A T U R Ea ij = Elastic constants A = Rigid body rotation B u = Horizontal rigid body translation B v = Vertical rigid body translation C = Paris law coefficient g = Slip system strength h 0 = Slip system initial hardening modulus h aβ = Single crystal hardening matrix K I = Mode I stress intensity factor K II = Mode II stress intensity factor n = Paris law exponent q = Latent hardening coefficient r = Radial distance from crack tip R = Load ratio S = Yield stress in the shear direction (Hill's criterion) t = ratio between ΔK II and ΔK I T = T-stress term u = Horizontal displacements v = Vertical displacements X, Y, Z = Yield stress in the principal directions (Hill's criterion) z = Rate sensitivity exponent α = Energy release rate ratio factor γ = Shear strain ΔK I = Mode I stress intensity factor range ΔK II = Mode II stress intensity factor range ΔK I,eff = Mode I effective stress intensity factor range ΔK II,eff = Mode II effective stress intensity factor range ΔK tot = Combined stress intensity factor range Correspondence: S. Rabbolini.

Multi-scale crack closure measurements with digital image correlation on Haynes 230

“…Moreover, taking several pictures of the defect during a load cycle, is it possible to evaluate the evolution of ∆K eff and to calculate crack opening levels. In this work, the procedure discussed in [7][8][9]11] is adopted. Since no mode II sliding was observed, since the crack propagated in a plane perpendicular to the loading direction, only ∆K I was considered in the calculations.…”

“…Recently, DIC was employed to analyse fatigue crack growth at high temperature in Haynes 230 [8]. In a study of fatigue crack growth in Haynes 230 single crystals [9], DIC was employed to extract effective stress intensity factor ranges during mixed mode propagation in an anisotropic body. An interesting feature of these techniques was that they allow the direct determination of the effective stress intensity factor range.…”

On higher order parameters in cracked composite plates under far‐field pure shear

“…The series expansions of the stress potentials in (30) do not include terms with even powers ( n 1 , n 2 , n = 1, 2, 3, … ). This requires all the coefficients of the even terms to vanish:…”

Full‐field characterisation of crack tip deformation and fatigue crack growth using digital image correlation—a review

“…One of the first applications of DIC technique in fracture mechanics studies is the estimation of SIF, K . Explicit stress and displacement fields near a crack tip may be derived from the Westergaard functions using the general Kolossov‐Muskhelishvili potentials .…”