The Effect of Dynamic Stress Cycling on the Compressive Strength of Rocks

Abstract

Quasi‐static rock strength is a nonconservative property, as fatigue during cyclic loading reduces the macroscopic strength. When strain rate under compressive loading increases above a lithology‐specific threshold, the primary failure mechanism transitions from localized failure along discrete fractures to distributed fracturing. However, the role of load path under high strain rate conditions has not been explored in any detail. We examine the effect of rapid stress cycles on the dynamic compressive strength of Westerly Granite using a modified split Hopkinson pressure bar approach and explore the implications of our results for the formation of pulverized fault zone rocks. Under cyclic loading conditions, the compressive strength can be reduced by a factor of 2, demonstrating that, like the quasi‐static strength, the dynamic rock strength is also a nonconservative property. Therefore, traditional high strain rate experimental approaches utilizing simple load paths may overestimate strength when rocks are subjected to complex load paths.

Energy Partitioning, Dynamic Fragmentation, and Off‐Fault Damage in the Earthquake Source Volume

“…Barber and Griffith (2017) have shown in weakly confined dynamic compression experiments that Arkansas Novaculite produces ∼86 times more surface area per unit mass (∼6.0 m 2 g −1 ) than Westerly Granite (∼0.07 m 2 g −1 ), highlighting the important role played by material properties and microstructure. Several experimental studies have shown that rapid dynamic stress cycling reduces dynamic strength and more easily leads to intense fragmentation (Badge & Petroš, 2005; Braunagel & Griffith, 2019; X. Li et al., 2021; Liu & Zhao, 2021). Additionally, material contrast across a fault may strongly amplify dynamic effects (e.g., Ben‐Zion & Rice, 1997; Rice & Ben‐Zion, 1996; Shi et al., 2008; Shlomai et al., 2021; Shlomai, Kammer, et al., 2020; Thomas et al., 2017), and the background stress orientation can markedly influence the spatial scale of the damage zone (Xu et al., 2012a, 2012b).…”

Rayleigh‐Love Discrepancy Highlights Temporal Changes in Near‐Surface Radial Anisotropy After the 2004 Great Sumatra Earthquake

“…As the rock tensile strength ( T O ) is low (∼1–10 MPa) for sedimentary rocks near the surface, it is conceivable that supralithostatic overpressure (i.e., P f = σ 3 + T O ) under the condition ( σ 1 − σ 3 )/ T O < 4 results in extension fractures, forming sub‐horizontal extension veins perpendicular to σ 3 (Figure 1 of Sibson, 2017). It is conceivable that, during the great earthquakes, rapid cyclic dynamic stresses from strong ground motions may compromise the rock strength (Bagde & Petros, 2005; Braunagel & Griffith, 2019; Erarslan & Williams, 2012), facilitating new horizontal extensional veins near the surface in the Sumatra forearc (Figure 8).…”

Dynamic Characteristics and Damage Constitutive Model of Mudstone under Impact Loading

“…Ping et al [ 18 ] carried out impact compression tests on coal-mine sandstone samples under different loading rates, and the analysis showed that the dynamic compressive strength, dynamic elastic modulus, and strain rate of sandstone were positively correlated with the incident energy. Braunagel et al [ 19 ] used an improved split-Hopkinson compression bar to study the effect of cyclic-impact loads on the dynamic compressive strength of westerly granite. The dynamic strength and deformation characteristics of rock under impact loading can be comprehensively described using a dynamic constitutive model.…”