The tensile strength of compressed dust samples and the catastrophic disruption threshold of pre-planetary matter

ABSTRACT During the planetary formation process, mutual collisions among planetesimals take place, impacting on their porosities. The outcome of these collisions depends, among other parameters, on the tensile strength of the colliding objects. In the first stage of this work, we performed impact experiments into dust samples, assembled with material analogous to that of the primitive Solar System, to obtain highly compressed samples that represent the porosities measured in chondritic meteorites. In the second stage, we obtained the tensile strengths of the compressed dust samples by the Brazilian Disc Test. We found a correlation between the tensile strength and the volume filling factor of the compressed dust samples and obtained the corresponding critical fragmentation strength in mutual collisions and its dependence on the volume filling factor. Finally, we give prescriptions for the catastrophic disruption threshold as a function of the object size, for different values of the volume filling factor.

Energy Dissipation Characteristic of Red Sandstone in the Dynamic Brazilian Disc Test with SHPB Setup

In order to quantitatively investigate the energy dissipation characteristic during the dynamic tension failure of rock materials, the dynamic Brazilian disc tests on red sandstone were conducted using the split Hopkinson pressure bar (SHPB) setup. The states of the specimens after different incident energies can be divided into three forms (i.e., the unruptured state, the ruptured state, and the broken state), and the failure processes of the specimens were recorded by using a high-speed camera. The results show that the ruptured state of the specimen corresponds to the critical failure strain. Taking the critical incident energy as a turning point, two positive linear fitting relations between the dissipated energy and incident energy before and after the point are obtained, and the dynamic linear dissipation law is found. When the incident energy is less than the critical energy, specimens were unruptured after impact. When the incident energy is greater than the critical energy, specimens will be broken after impact. According to the obtained linear energy dissipation law, the dynamic tensile energy dissipation coefficient (DTEDC) was introduced for quantitatively describing the dynamic energy dissipation capacity of rock materials in the dynamic Brazilian disc test. When the specimen is in the unruptured state, the ideal DTEDC is a constant value. When the specimen is in a broken state, the DTEDC increases with the increase of incident energy.

Comparative Study on the Test Method for Tensile Elastic Modulus of Rock Materials

Rock material has different mechanical behaviors under compressive and tensile loading. Correspondingly, there are two types of elastic modulus: compressive elastic modulus Ec and tensile elastic modulus Et, respectively. To distinguish which indirect test methodology, including three-points bending test and Brazilian disc test, is more suitable to measure the tensile elastic modulus Et of rock materials, a series of uniaxial compressive test (UCT), direct tensile test (DTT), three-points bending test, and Brazilian disc test are performed for three typical types of rock: marble, granite, and sandstone. Comparative investigation on the reliability of measurement results of tensile elastic modulus Et is systematically conducted. Finally, it is found that Brazilian disc test could be a suitable method to measure tensile elastic modulus of rock materials, due to the excellent agreement with that measured by DTT and the simplicity of sample preparation, as well as test operation.