Dynamic strength, fragmentation, and the impact cratering process

Abstract: Introduction: During impact cratering, target materials are subjected to extreme deformation conditions. Brittle deformation under these conditions, where strain rates can exceed 101 to 102 s­­-1, is rate-sensitive. Typically, rocks are stronger when deformed at high strain-rate conditions [1]. This occurs because fracture propagation has a limited velocity; at high loading rates, the weakest flaws in a material are not able to cause failure before other, increasingly strong flaws are activated. This results in significant changes to mechanical properties and causes fragmentation of the target material [2, 3]. Dynamic compressive strength and fragmentation in brittle materials is not currently implemented in numerical impact simulations.

In this study, we present results of high strain rate mechanical tests to determine the characteristic strain rate for rate-dependent brittle failure and dynamic strength increase, and the fragment size and shape distributions that result from failure at these conditions. We investigated a variety of rock types and considered whether the fragment characteristics can be used as diagnostic indicators of loading conditions during brittle failure. In addition, we use numerical impact simulations to assess the significance of dynamic strength increase and compressive fragmentation during impact cratering at a variety of scales.

Methods: Mechanical data and samples were obtained using a hydraulic loading frame and a Split-Hopkinson Pressure Bar (SHPB). The hydraulic loading frame achieves strain rates from 10-6 s-1 to 10-4 s-1, while the SHPB achieves strain rates from 101 s-1 to 103 s-1. As sample materials, we chose a variety of igneous, metamorphic, and sedimentary rocks in order to investigate differences between target types and material properties. From the mechanical experiments, the strain-rate dependency of strength was calculated and samples were generated for microstructural analysis. We focussed our microanalysis on the distributions of fragment size and fragment shape as functions of strain rate. Numerical impact simulations in this study were conducted using the iSALE shock physics code [4 and refs. therein].

Results: We find that the characteristic strain rates of rocks, where the dynamic strength is twice the quasi-static strength, ranges between ~150 and ~350 s-1 depending on lithology (Figure 1). Fragment size analysis demonstrates an inverse power-law relationship between fragment size and strain rate for dynamic failure under uniaxial compression. Unlike fragment size, we find that fragment shape is independent of strain rate under dynamic uniaxial loading (Figure 3)

Object Details

• Location: Deutsche Nationalbibliothek Frankfurt am Main
• Extent: Online-Ressource
• Language: Englisch
• Notes: Europlanet Science Congress 2022

Contributors, Places and Time

• Event: Veröffentlichung
• (where): Freiburg
• (who): Universität
• (when): 2023
• Creator: Rae, Auriol S. P. ; Kenkmann, Thomas ; Collins, Gareth S. ; Poelchau, Michael H. ; Padmanabha, Vivek ; Schäfer, Frank
• Contributor: Albert-Ludwigs-Universität Freiburg. Institut für Geo- und Umweltnaturwissenschaften

Further information

• DOI: 10.5194/epsc2022-265
• URN: urn:nbn:de:bsz:25-freidok-2364838
• Rights: Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Last update: 14.08.2025, 11:02 AM CEST