HR: 1340h
AN: S43A-1066    [Abstracts]
TI: Finite Element Simulations of Dynamic Shear Rupture Experiments and Path Selection Along Branched Faults
AU: * Templeton, E L
EM: templet@fas.harvard.edu
AF: Harvard University, Division of Engineering and Applied Sciences, 29 Oxford St., Cambridge, MA 02138 United States
AU: Baudet, A
EM: abaudet@esag.deas.harvard.edu
AF: Institut de Sciences et de l'Ingenieur de Lyon, Department de Mecanique, Lyon, FRA 969622 United States
AU: Bhat, H S
EM: hbhat@fas.harvard.edu
AF: Harvard University, Division of Engineering and Applied Sciences, 29 Oxford St., Cambridge, MA 02138 United States
AU: Dmowska, R
EM: dmowska@esag.harvard.edu
AF: Harvard University, Division of Engineering and Applied Sciences, 29 Oxford St., Cambridge, MA 02138 United States
AU: Dmowska, R
EM: dmowska@esag.harvard.edu
AF: Harvard University, Department of Earth and Planetary Sciences, 29 Oxford St, Cambridge, MA 02139 United States
AU: Rice, J R
EM: rice@esag.harvard.edu
AF: Harvard University, Division of Engineering and Applied Sciences, 29 Oxford St., Cambridge, MA 02138 United States
AU: Rice, J R
EM: rice@esag.harvard.edu
AF: Harvard University, Department of Earth and Planetary Sciences, 29 Oxford St, Cambridge, MA 02139 United States
AU: Rosakis, A J
EM: rosakis@aero.caltech.edu
AF: California Institute of Tehcnology, 1200 E. California Blvd. Mail Code 105-50, Pasadena, CA 91125 United States
AU: Rousseau, C E
EM: rousseau@egr.uri.edu
AF: University of Rhode Island, 222-B Wales Hall, Kingston, RI 02881 United States
AB: The study of dynamically propagating shear cracks along geometrically complex paths is important to understanding the mechanics of earthquakes. Recent laboratory fracture studies of Rousseau and Rosakis examined a branched configuration, analogous to their study of rupture along a bent fault path [Rousseau and Rosakis, JGR, 2003], to enhance understanding of the behavior of a shear rupture approaching the intersection of two paths. Whereas crack motion along a simple bent path is readily explained by means of the energy available to sustain the propagating crack, or through a crack tip stress field criterion, the behavior of multiple paths displays more intricate variations featuring the inability of the crack to extend along secondary paths situated at shallow angles with respect to the initial direction of propagation. Secondary paths located at larger angles, on the extensional side, generally promote simultaneous extension along both paths beyond the junction, in contrast to preferred motion along the straight path, which is favored when secondary paths are situated on the compressional side. The experiments involve impact loading of thin plates of Homalite-100, a photoelastic polymer, which are cut along branched paths and weakly glued back together everywhere except along a starter notch near the impact site. High-speed photography of isochromatic fringe patterns (lines of constant difference between in-plane principal stresses) characterized the transient deformation field associated with the impact and rupture propagation. We adapted the ABAQUS/Explicit dynamic finite element program to analyze the propagation of shear cracks along such branched weakened paths. Two configurations for weakened paths, branches at 35° to the compressional side and the extensional side, were analyzed. We implemented a linear slip-weakening failure model as a user-defined constitutive relation within the ABAQUS program, where weakening could be included in either or both of (1) a cohesive part, c = c(Δ u) (where Δ u = slip) of the shear strength that is insensitive to compressive normal stress σ, and (2) a frictional part f σ, with friction coefficient f = f(Δ u). The analyses of impact loading, and rupture nucleation and propagation were carried out in a 2D plane stress framework. A set of studies of slip weakening parameters and impact velocity were done to investigate the relationship between the strength of the interface and the speed of rupture propagation. For a branch on the extensional side of the main fault, increasing f(0) decreases the propagation speed on the continuation of the straight main fault while increasing speed on the branch. Whether the rupture is propagating at an intersonic or sub-Rayleigh speed when it reaches the branching junction has a large effect on the nature of rupture propagation along the inclined path. While not achieving perfect agreement with the experimental measurements, principal features observed in dynamic isochromatic line patterns were reproduced.
DE: 7200 SEISMOLOGY
DE: 7209 Earthquake dynamics (1242)
SC: Seismology [S]
MN: Fall Meeting 2005