Full-field Ultrahigh-speed Quantification of Dynamic Shear Ruptures Using Digital Image Correlation

Abstract

Producing dynamic ruptures in the laboratory allows us to study fundamental characteristics of interface dynamics. Our laboratory earthquake experimental setup has been successfully used to reproduce a number of dynamic rupture phenomena, including supershear transition, bimaterial effect, and pulse-like rupture propagation. However, previous diagnostics, based on photoelasticity and laser velocimeters, were not able to quantify the full-field behavior of dynamic ruptures and, as a consequence, many key rupture features remained obscure. Here we report on our dynamic full-field measurements of displacement, velocities, strains and strain rates associated with the spontaneous propagation of shear ruptures in the laboratory earthquake setup. These measurements are obtained by combining ultrahigh-speed photography with the digital image correlation (DIC) method, enhanced to capture displacement discontinuities. Images of dynamic shear ruptures are taken at 1-2 million frames/s over several sizes of the field of view and analyzed with DIC to produce a sequence of evolving full-field maps. The imaging area size is selected to either capture the rupture features in the far field or to focus on near-field structures, at an enhanced spatial resolution. Simultaneous velocimeter measurements on selected experiments verify the accuracy of the DIC measurements. Owing to the increased ability of our measurements to resolve the characteristic field structures of shear ruptures, we have recently been able to observe rupture dynamics at an unprecedented level of detail, including the formation of pressure and shear shock fronts in viscoelastic materials and the evolution of dynamic friction.

Enhanced Digital Image Correlation Analysis of Ruptures with Enforced Traction Continuity Conditions Across Interfaces

“…This section briefly summarizes the experimental setup, diagnostics, image analysis, and numerical methods that are used to obtain the displacement, strain, and stress fields before using the algorithm. This setup is the evolution of the Caltech " Laboratory Earthquake Setup " developed by Rosakis and his co-workers over a span of 15 years [1][2][3][24][25][26][27][28][29]. A more detailed description of the current form of the setup is given in [3].…”

“…Generally, local DIC approaches that provide the solution up to half a subset from the interface may also be sufficient when tracking the quasi-static propagation and opening of tensile crack faces and the associated strain field, using a large field of views and high-resolution cameras. However, these correlation approaches are not possible when the subset size is large compared to the field of view (i.e., when using low-resolution cameras), such as our ultra-high-speed camera (which has a resolution of 250 × 400 pixels 2 ) or high-resolution cameras, but with comparatively large subset sizes, situations typically arising in the study of dynamic problems [3]. To resolve the displacement discontinuities on the interface associated with the propagation of dynamic shear ruptures, the studies in [1][2][3] used the commercial DIC software Vic-2D (Correlated Solutions, Inc.) to separately correlate the domains above and below the interface.…”

“…However, these correlation approaches are not possible when the subset size is large compared to the field of view (i.e., when using low-resolution cameras), such as our ultra-high-speed camera (which has a resolution of 250 × 400 pixels 2 ) or high-resolution cameras, but with comparatively large subset sizes, situations typically arising in the study of dynamic problems [3]. To resolve the displacement discontinuities on the interface associated with the propagation of dynamic shear ruptures, the studies in [1][2][3] used the commercial DIC software Vic-2D (Correlated Solutions, Inc.) to separately correlate the domains above and below the interface. While standard local DIC methods calculate displacements up to half a subset away from the interface, the "fill boundary" algorithm of Vic-2D employed in [1][2][3] uses affine transformation functions to extrapolate the displacements from the center of the subset up to the interface.…”

“…To resolve the displacement discontinuities on the interface associated with the propagation of dynamic shear ruptures, the studies in [1][2][3] used the commercial DIC software Vic-2D (Correlated Solutions, Inc.) to separately correlate the domains above and below the interface. While standard local DIC methods calculate displacements up to half a subset away from the interface, the "fill boundary" algorithm of Vic-2D employed in [1][2][3] uses affine transformation functions to extrapolate the displacements from the center of the subset up to the interface. This enables the use of large subsets in each side of the interface, which are essential to overcoming the noise associated with ultra-high-speed photography and the analyzed rapid ruptures.…”

“…Understanding the dynamics of shear rupture of interfaces is important for fields ranging from failure of composites and bimaterial structures, to earthquakes, car brakes, and even to pistons of internal combustion engines. Recent advances in high-speed camera technologies have enabled the development of an experimental setup that combines ultra-high-speed photography with digital image correlation (DIC) to quantify the behavior of propagating dynamic ruptures in the laboratory [1][2][3], including full-field measurements of displacements, velocities, strains, and stresses ( Figure 1). Figure 1.…”