Fatigue tests and estimation of crack initiation and propagation lives in AISI 304L butt-welds with reinforcement intact

Abstract

The crack process in a fatigue failure initiating at the toe of a butt weld with reinforcement intact normally comprises two major stages: (1) the crack initiation life ( N i): and (2) the crack propagation life ( N p). The initiation period was found to occupy approximately two-thirds of the total fatigue life and consists of the cycles necessary to shake down the residual stresses in the weld. The crack propagation stage consists of two paths: (1) through thickness ( N p x ): and (2) along width direction ( N p y ). This model considers the influence of crack propagation direction in estimating the propagation life. The notch-root stress approach is used to estimate the crack initiation life, while the fatigue crack propagation lives were estimated using fracture mechanics concepts. A test method is evaluated to estimate the fatigue crack propagation life using fracture mechanics concepts. The experimental part consists of fatigue tests for gas metal arc welded (GMAW) butt joints of AISI 304L stainless steel with reinforcement intact. Constant amplitude fatigue tests with stress ratio, R=0 were carried out using a 100 kN servo-hydraulic DARTEC universal testing machine with a frequency of 30 Hz. The predicted lives were compared with the experimental values. This study suggests that the crack growth parameters are dependent on the crack propagation directions for the same material.