Microstructure-sensitive estimation of small fatigue crack growth in bridge steel welds

Abstract

A probabilistic finite element model is implemented to estimate microstructurally small fatigue crack growth in bridge steel welds. Simulations are based on a microstructure-sensitive crystal plasticity model to quantify fatigue indicator parameters (FIPs) at the slip system level and a fatigue model that relates FIPs to fatigue lives of individual grains. Microstructures from three weld zones, namely, fusion zone (FZ), heat affected zone (HAZ), and base metal (BM), are constructed based on their microstructural attributes such as grain morphology, size, and orientation. Statistical volume elements (SVEs) are generated and meshed independently for the three welding zones. Each grain within the SVEs is divided into several slip bands parallel to crystallographic planes. During the loading process, cracks nucleate at the slip bands (SBs) with the largest FIP next to the free surface. The crack extension path is assumed to be transgranular along SBs and the number of cycles required to crack the neighbor grain is calculated by the corresponding FIP-based crack growth rate equation. The simulation process is carried out using ABAQUS with a user defined subroutine UMAT for crystal plasticity. After the calibration of the constitutive model and irreversibility parameters, numerical simulations for small crack growth in three zones are presented. The crack length vs. the predicted fatigue resistance shows significant differences in the mean values and variability among the three weld zones.

Effect of microstructure of simulated heat‐affected zone on low‐ to high‐cycle fatigue properties of low‐carbon steels

“…Hence, the very coarse grains that appear in the HAZ may have a greater‐than‐expected negative effect on fatigue life. In addition, numerical methods, such as crystal plasticity, are increasingly being applied to estimate the local fatigue behaviour of the HAZ 8,9 . Actual experimental data on HAZ microstructures are therefore also required to be able to validate this numerical approach.…”

Temperature‐dependent characteristics of DH36 steel fatigue crack propagation

“…18 Ferrite is a solid solution in which carbon and an alloying element are dissolved in α-Fe. The mass fraction of cementite to ferrite is 12% to 88%.…”

“…The plasticity and toughness properties are worse than ferrite but much better than cementite. 18 Ferrite is a solid solution in which carbon and an alloying element are dissolved in α-Fe. The ferrite has good ductility and toughness properties while it is also characterized by low strength and hardness.…”

The Influence of Rehabilitation Techniques on Static and Variabile Loads in Case of a HSLA Steel Samples

“…Also in the case of bridges welded structures we often meet static loads , as well as variable loads that cause fatigue failures [1][2][3][4][5][6][7]. In the case of static loads, things are simpler and clearer in the sense that structural failures occurs when the tear resistance of the base material is exceeded.…”