Multiscale fatigue crack growth modelling for welded stiffened panels

Abstract

A B S T R A C T The influence of welding residual stresses in stiffened panels on effective stress intensity factor (SIF) values and fatigue crack growth rate is studied in this paper. Interpretation of relevant effects on different length scales such as dislocation appearance and microstructural crack nucleation and propagation is taken into account using molecular dynamics simulations as well as a Tanaka-Mura approach for the analysis of the problem. Mode I SIFs, K I , were calculated by the finite element method using shell elements and the crack tip displacement extrapolation technique. The total SIF value, K tot , is derived by a part due to the applied load, K appl , and by a part due to welding residual stresses, K res . Fatigue crack propagation simulations based on power law models showed that high tensile residual stresses in the vicinity of a stiffener significantly increase the crack growth rate, which is in good agreement with experimental results.Keywords dislocation; fatigue crack growth rate; microstructurally small cracks; residual stress. N O M E N C L A T U R Ea = half crack length a 0 = initial crack length a fin = final crack length C = material constant of the Paris equation CRSS = critical resolved shear stress d = slip band length da/dN = crack growth rate E = Young's modulus F → r; t ð Þ = interatomic force F max = maximum applied force F min = minimum applied force G = shear modulus K = stress intensity factor (SIF) K appl = stress intensity factor due to the applied load K res = stress intensity factor due to weld residual stresses K th = stress intensity factor threshold K tot = total stress intensity factor m = atomic mass m = material constant of the Paris equation N = number of stress cycles for the fatigue crack propagation N f = number of stress cycles for fatigue failure N g = number of stress cycles required for crack nucleation in a single grain N ini = number of stress cycles needed for the initiation of a small crack R = stress ratio R eff = effective stress intensity factor ratio U → r ; t ð Þ = interatomic embedded atom method pair potential W c = specific fracture energy per unit area Correspondence: Ž. Božić.

Modelling of overload effects on fatigue crack initiation in case of carbon steel

“…Multiscale approach – schematic description of bridging between scales and the outputs (O/P) (CRSS – critical resolved shear stress, a ini – initiation crack length, N ini – number of stress cycles for crack initiation, N prop – number of stress cycles for crack propagation) from each of the scales . [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…The relevant material parameter from the atomistic (nano‐)scale needed for the micromechanics simulation of fatigue crack initiation process is the CRSS on the relevant, most active slip line. The CRSS is calculated from MD simulation and is later used in the micromechanical model based on the TM equation, which provides the cycles required to initiate a PSC together with its size. This information is finally used as an input for the macroscale modelling of the fatigue crack growth on the basis of power law equations (e.g.…”

Correlation of Pipe Ring Notched Bend (PRNB) specimen and Single Edge Notch Bend (SENB) specimen in determination of fracture toughness of pipe material

“…Results of numerical modelling show that the elastic–plastic behaviour of notched pipe ring specimens is similar as at standard three‐point bending specimens with fatigue pre‐crack. However, fatigue crack behaviour in real welded joint can make difference even if some procedure for automatic control and simulation of loading process will be applied …”

Determination of Stresses in the Axle Pin Based on the Wind Model in the Wind Turbine

“…The mesh is created with Curvature-Based Mesh 2 and with Mesh Control 3 in the area of point E. Element size is 72.31 mm and the tolerance is 2.47 mm. In area E, at the point of determining the stress, the finite element size is 8.23.…”

“…Changes in wall thicknesses and a reduction in diameters can cause defects in the material, such as pores, flaws or slag. Therefore, for reliable use, it is necessary to perform structural integrity assessment of the axle pin for flaws, such as cracks [1,2].…”