Atomistic Studies of Crack Branching at Bimaterial Interfaces: Preliminary Results
- PDF / 131,645 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 54 Downloads / 220 Views
0929-II04-20
Atomistic Studies of Crack Branching at Bimaterial Interfaces: Preliminary Results Sriram Krishnan1, and Markus J Buehler2 1 Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Mass. Ave, Cambridge, 02139 2 Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Mass. Ave, Room 1-272, Cambridge, MA, 02139 ABSTRACT In this paper we summarize recent progress in applying atomistic studies of cracking along interfaces of dissimilar materials under quasi-static crack growth conditions. We consider two linear-elastic material strips in which atoms interact with harmonic potentials, with a different spring constant in each layer leading to a soft and a stiff strip. The two strips are bound together with a tunable potential, which allows to independently control the interface and bulk fracture surface energy . An initial crack serves as initiation point for the failure. This provides a model system to investigate how elastic properties and interface strength interplay and determine the crack growth direction, leading to either interfacial cracking or branching into the film material. We observe a clear transition to interface failure when the interface fracture energy is less than 80% of the bulk fracture energy. We further find that branching in the film material is controlled by the elastic properties of the film material, suggesting interfacial cracking for extremely soft films and branching for stiffer films. Analysis of the virial stress field around the crack suggests that the circumferential hoop stress controls the branching behavior.
z X
ao Region1
lz
a
Region 3
r
Efilm
θ Weak interface
Region 2
Esubstrate
lx
Figure 1: Simulation geometry and lattice orientation for the studies of interfacial cracking. The figure shows a stiff substrate with a soft film on top, under mode I (tensile) loading applied to the film. The simulation domain is dividing into several regions. The interface between region 1 and 2 serves as a starter crack. The schematic further shows the definition of crack angle around the crack tip. The inlay shows the orientation of the atomic FCC lattice in [100][010][001] orientation.
Crack Angle (degrees)
Normalized interface energy
Figure 2. The angle at which crack grows in region 3 is shown, as a function of the ratio of interface fracture energy to bulk fracture energy. When the interface fracture energy is up to 80% of the bulk fracture energy, the crack angle is 0o and the crack grows along the interface. Beyond the 80% limit, the crack has a sharp change in behavior and grows at an angle of about 20o in the bulk.
INTRODUCTION Atomistic simulation is becoming an increasingly important tool to investigate fundamental aspects of crack initiation and propagation. Recent progress in this field include systematic atomistic-continuum studies of fracture [1,2], investigations of the role of hyperelasticity in dynamic fracture [3] and studies on the instability dynamics [4]. There have been several continuum-b
Data Loading...
