Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
Cite this article:
ZHOU Tingting, ZHAO Fuqi, ZHOU Hongqiang, ZHANG Fengguo, YIN Jianwei. Mechanism and Damage Model for the Dynamic Tensile Fracture of Liquid Aluminum Containing He Bubbles. Acta Metall Sin, 2025, 61(4): 643-652.
The dynamic fracture of metals in liquid state has become a subject of considerable interest in current times because of its observation in various physical and technological processes such as inertial confinement fusion and high-power laser-driven surface micromachining. In addition, it has been found that the fractures at elevated temperature are highly correlated with the microstructure of materials. He bubbles are frequently observed in many metals exposed to irradiation environments as a result of radioactive or self-irradiation. Both experimental and theoretical studies have indicated that He bubbles can substantially affect the mechanical properties of irradiated metals, resulting in hardening, swelling, and embrittlement. In recent years, attention has been drawn to understand the effects of He bubbles on the dynamic properties of materials, including shock compression, dynamic fracture, and surface ejection. This study examines the dynamic tensile fracture behavior of liquid aluminum containing He bubbles across a wide range of strain rates by utilizing molecular dynamics (MD) simulations and continuum modeling. The physical mechanism leading to the dynamic fracture is revealed to be predominated by the growth of He bubble. Under strain rates ranging from 3.0 × 106 s-1 to 3.0 × 109 s-1, tension primarily induces bubble growth. At higher strain rates, such as 3.0 × 1010 s-1, both bubble growth and void nucleation-growth are observed, although bubble growth remains the dominant factor. The growth of He bubbles unfolds in two distinct phases: rapid growth followed by slower growth. These staged evolutionary characteristics appear to be consistent across strain rates, but the growth rate of helium bubbles markedly increases with increasing strain rates. Furthermore, the dynamic tensile strength at varying strain rates indicates a significant reduction for the metal containing He bubbles compared to the pure metal. However, this discrepancy decreases at extremely high strain rates, such as 3.0 × 1010 s-1. In addition, a continuum damage model is constructed based on the insights obtained from MD simulations to describe the dynamic tensile fracture of liquid metal containing He bubbles. This model accounts for external tensile stress, internal pressure of He bubbles, inertia, viscosity, and surface tension. Theoretical calculations using the damage model and the binomial equation of state, which depict the pressure-volume relationship of the metal substrate, exhibit excellent agreement with MD data over a wide range of strain rates. This includes the evolution of the tensile stress and He bubble radius. The self-consistent MD-continuum model proposed in this study has the potential to be applied in macroscopic hydrodynamic simulations, to depict the dynamic tensile fracture behavior of liquid metal with He bubbles.
Fig.1 Initial configuration of the liquid Al sample with He Bubbles (Al-He sample) (a) and the optimized configuration (by molecular dynamics (MD) simulation) at 1100 K (b) (The sample is cut through the center to show the central He bubble)
Fig.2 Evolutions of He bubble/voids during the dynamic tension process at the strain rate () of 3.0 × 108 s-1 (a) Al-He sample (b) pure Al
Fig.3 Time (t) evolutions of tensile stress (P) (a), He bubble radius (R) (b), and the internal pressure of He bubble (Pg) (c) of Al-He sample during the dynamic tension process at = 3.0 × 108 s-1 (In Fig.3b, the black curve represents the fast growth of He bubble and the blue curve shows the slower growth of He bubble; the same in Fig.6)
Fig.4 Time evolutions of P (a) and volume of voids/He bubble (b) during the dynamic tension process at = 3.0 × 108 s-1 for pure Al sample and Al-He sample
Fig.5 Evolutions of He bubble during the dynamic tension process at = 3.0 × 109 s-1 (a) and = 3.0 × 107 s-1 (b) for Al-He sample
Fig.7 Variations of dynamic tensile strength with for pure Al sample and Al-He sample
Fig.8 Microstructure evolutions for the sample with He bubble during the dynamic tension process at = 3.0 × 1010 s-1 (The central large pore is He bubble, and the other small pores are new nucleated voids)
/ s-1
R0 / nm
/ GPa
γ / (J·m-2)
n
K1 / GPa
K2 / GPa
η / (Pa·s)
3.0 × 106
1.868
0.632
0.59
4.6
51
130
0.03
3.0 × 107
1.868
0.632
0.59
4.6
51
130
0.006
3.0 × 108
1.868
0.632
0.59
4.6
51
130
0.0025
3.0 × 109
1.868
0.632
0.59
4.6
51
130
0.0012
Table 1 Parameters in the present damage model
Fig.9 Time evolutions of P (a) and R (b), and dynamic tensile strength (c) at various strain rates obtained from MD simulations and the present continuum model
Fig.10 Viscosity coefficients at different used in the present continuum model (dots) and the fitting curve using Eq.(7)
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