Abstract
A new criterion for hydrogen-induced cracking (HIC) that includes both the embrittlement effect and the loading effect of hydrogen was obtained theoretically. The surface cohesive energy and plastic deformation energy are reduced by hydrogen atoms at the interface; thus, the fracture toughness is reduced according to fracture mechanics theory. Both the pressure effect and the embrittlement effect mitigate the critical condition required for crack instability extension. During the crack instability expansion, the hydrogen in the material can be divided into two categories: hydrogen atoms surrounding the crack and hydrogen molecules in the crack cavity. The loading effect of hydrogen was verified by experiments, and the characterization methods for the stress intensity factor under hydrogen pressure in a linear elastic model and an elastoplastic model were analyzed using the finite-element simulation method. The hydrogen pressure due to the aggregation of hydrogen molecules inside the crack cavity regularly contributed to the stress intensity factor. The embrittlement of hydrogen was verified by electrolytic charging hydrogen experiments. According to the change in the atomic distribution during crack propagation in a molecular dynamics simulation, the transition from ductile to brittle fracture and the reduction in the fracture toughness were due to the formation of crack tip dislocation regions suppressed by hydrogen. The HIC formation mechanism is both the driving force of crack propagation due to the hydrogen gas pressure and the resisting force reduced by hydrogen atoms.
Highlights
The formation mechanism of hydrogen-induced cracking (HIC) has been extensively studied in numerous material systems [1,2,3,4,5,6]
As the HIC formation criterion proposed in this paper is based on the theory of stress intensity factor, the hydrogen pressure effect was characterized using the stress intensity factor (KIP (H2 )) via factor, the hydrogen pressure effect was characterized using the stress intensity factor (KIP(H2)) via finite element (FE) simulation
We proposed a new criteria through modifying the classic stress intensity factor criteria in the theory of fracture mechanics
Summary
The formation mechanism of hydrogen-induced cracking (HIC) has been extensively studied in numerous material systems [1,2,3,4,5,6]. The additional hydrogen gas pressure load promoting the material fracture. The hydrogen pressure in the crack cavity and on the outer surface significantly affect the crack propagation within the material [9,10,11]. An obvious increase in growth the fatigue crack growth in rate was observed inhigh experiments gaseous hydrogen action [10,11]. The equation of state for an ideal gas can be used to solve the under high pressure gaseous hydrogen action [10,11]. Due to theeffect stress-strain effect around hydrogen diffusion in the crack is affected [13,14,15]. A new criteria simultaneously loading effect of hydrogen pressure in the cavity.
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