Abstract
Stress corrosion cracking (SCC) of metals is an issue of major concern in engineering since this phenomenon causes many catastrophic failures of structural components in aggressive environments. SCC is even more harmful under cathodic conditions promoting the phenomenon known as hydrogen assisted cracking (HAC), hydrogen assisted fracture (HAF) or hydrogen embrittlement (HE). A common way to assess the susceptibility of a given material to HAC, HAF or HE is to subject a cracked rod to a constant extension rate tension (CERT) test until it fractures in this harsh environment. This paper analyzes the influence of a residual stress field generated by fatigue precracking on the sample’s posterior susceptibility to HAC. To achieve this goal, numerical simulations were carried out of hydrogen diffusion assisted by the stress field. Firstly, a mechanical simulation of the fatigue precracking was developed for revealing the residual stress field after diverse cyclic loading scenarios and posterior stress field evolution during CERT loading. Afterwards, a simulation of hydrogen diffusion assisted by stress was carried out considering the residual stresses after fatigue and the superposed rising stresses caused by CERT loading. Results reveal the key role of the residual stress field after fatigue precracking in the HAC phenomena in cracked steel rods as well as the beneficial effect of compressive residual stress.
Highlights
Stress corrosion cracking (SCC) is one of the most frequent causes of failure of structural components in aggressive environments [1]
Assuming quick mass exchange between the metal and the environment on the hydrogen entry surface, hydrogen distribution coincides with the steady state solution of the diffusion Equation (4) at time t the equilibrium concentration value given by the expression (5) may be used as a boundary condition for the specimen immersed in the hydrogenating environment and subjected to sustained load
From the stress states that appear in the simulated samples after the precracking process and their subsequent loading during constant extension rate tension (CERT) tests in cathodic conditions, the hydrogen accumulation was obtained by means of numerical simulation of the hydrogen diffusion assisted by stress
Summary
Stress corrosion cracking (SCC) is one of the most frequent causes of failure of structural components in aggressive environments [1]. In the case of cathodic conditions (beneath the hydrogen discharge line of H2 O in a Pourbaix diagram) the damage appears in a quite different way as the so-called hydrogen assisted cracking (HAC) [3] In this case, the environment promotes the creation of atomic hydrogen that is adsorbed at the metal surface and later absorbed into the material. It accumulates to a critical concentration associated with hydrogen assisted damage at the microstructural level This process is influenced by the stress state of the material. 10, 485 final stage of fatigue precracking This residual stress state influences hydrogen diffusion and ,. Stress field appears in the vicinity of the crack tip (CT), depending on the maximum level and the (Kmax) applied during theCERT final test stageinofthe fatigue precracking. The numerical simulations of the fatigue precracking and posterior CERT loading of a cracked pearlitic steel rod by using a
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