Mechanical properties of terrestrial analogs to calcium sulfate veins on Gale crater, Mars

Abstract

The MSL (Mars Science Lab) Curiosity rover has documented the presence of natural fractures at the Gale crater on Mars. Through the utilization of the ChemCam instrument, the chemical composition of the veins on Mars has been analyzed, revealing their mineralogy as calcium sulfate. However, there is limited knowledge regarding the mechanical properties of these veins, which hinders a deeper understanding of their origin. This work aims to characterize the mechanical properties of gypsiferous Triassic Moenkopi mudrocks as the terrestrial rock analog to Mars. The Digital Image Correlation (DIC) technique was used in tandem with the Indirect Tensile Strength test to acquire the required spatial full-field strain maps for characterizing the fracture propagation with complex geometries in addition to the derived mechanical properties. The effect of the primary vein orientation on the exerted load on the load-strain profile, fracture initiation and propagation, and tensile strength was established. The dynamic spatial horizontal, vertical, and shear strains' progression was distinguished through DIC imaging. The key findings include: (1) Different failure modes were observed in samples with and without calcium sulfate veins, with higher tensile strength perpendicular to lamination; (2) Most samples with veins exhibited reduced tensile strength, except when oriented 90° to the load; (3) Fracture paths were influenced by the orientation angle, with irregular paths at certain angles and more regular paths for centrally located veins; (4) Digital image correlation revealed a fracture process zone before macro-crack initiation and subsequent shear crack propagation; (5) Shear strain accumulation preceded shear crack propagation, with potential initiation of tensile cracks.