Diurnal temperature variation as the source of the preferential direction of fractures on asteroids: theoretical model for the case of Bennu

TL;DR

This study models how diurnal temperature cycles induce fractures on asteroid Bennu, revealing preferential crack propagation directions and matching thermal fatigue growth rates with experimental data.

Contribution

It introduces a combined thermoelasticity and fracture mechanics model to predict fracture directions caused by thermal gradients on asteroids.

Findings

Cracks tend to propagate in N-S, NE-SW, NW-SE directions.

The model's crack growth rate aligns with experimental observations.

Thermal fatigue analysis supports the fracture propagation predictions.

Abstract

It has been shown that temperature cycles on airless bodies of our Solar System can cause damaging of surface materials. Nevertheless, propagation mechanisms in the case of space objects are still poorly understood. Present work combines a thermoelasticity model together with linear elastic fracture mechanics theory to predict fracture propagation in the presence of thermal gradients generated by diurnal temperature cycling and under conditions similar to those existing on the asteroid Bennu. The crack direction is computed using the maximal strain energy release rate criterion, which is implemented using finite elements and the so-called G$\theta$ method (Uribe-Su\'arez et al. 2020. Eng. Fracture Mech. 227:106918). Using the implemented methodology, crack propagation direction for an initial crack tip in different positions and for different orientations is computed. It is found that cracks preferentially propagate in the North to South (N-S), in the North-East to South-West (NE-SW) and in the North-West to South-East (NW-SE) directions. Finally, thermal fatigue analysis was performed in order to estimate the crack growth rate. Computed value is in good agreement with available experimental evidence.