Micro-structure of damage in thermally activated fracture of Lennard-Jones systems

TL;DR

This study uses molecular dynamics simulations to analyze how thermal fluctuations influence damage micro-structure and fracture behavior in Lennard-Jones solids, revealing temperature-dependent damage localization and its impact on macroscopic failure.

Contribution

It provides new insights into the temperature-dependent damage profiles and the micro-structural evolution leading to fracture in Lennard-Jones systems, combining simulation data with damage characterization.

Findings

Damage profile follows an exponential distribution with a temperature-dependent length scale.

Higher temperatures lead to more extended damage zones and reduced stress intensity factors.

Final failure is sudden, initiated by vacancy and void formation, with creep strength scaling inversely with the square root of notch size.

Abstract

We investigate the effect of thermal fluctuations on the critical stress and the micro-structure of damage preceding macroscopic fracture of Lennard-Jones solids under a constant external load. Based on molecular dynamics simulations of notched specimens at finite temperature, we show that the crystalline structure gets distorted ahead of the crack in the secondary creep regime. The damage profile characterizing the spatial distribution of lattice distortions is well described by an exponential form. The characteristic length of the exponential form provides the scale of damage which is found to be an increasing function of the temperature: At low temperature damage is strongly localized to the crack tip, while at high temperature damage extends to a broader range leading to more efficient relaxation of overloads. As a consequence, the stress intensity factor decreases with increasing temperature. The final macroscopic failure of the system occurs suddenly which is initiated by the creation of vacancies and voids. The creep strength exhibits the inverse square root scaling with the notch size corrected by the extension of the process zone.