Concrete and Geologic Materials

SRI International is developing a physically-based constitutive model that describes the nucleation and growth of tensile and shear cracks in concrete. The constitutive relations are incorporated into a multiplane plasticity model that has been implemented in the finite element code DYNA2D. Microcracks nucleate and grow on several preselected planes in each element. Local variations of stresses are introduced to account for local stress variations caused by the aggregates. Time-dependence arises naturally from the finite propagation velocities of the microcracks, and helps ensure well-posedness and stability of the numerical solution. The results of numerical simulations show promising results.

Figure 1(a) shows the simulated response of specimens tested in tension at different rates. At the slowest rates the specimen develops a limited number of horizontal tension cracks and exhibits brittle post-peak response. As the loading rate is increased the strength and ductility of the concrete increases and the damage is distributed more uniformly over the specimen. The rate dependence of the response is a natural consequence of the finite speed at which cracks propagate. At high rates, the model shows increase in strength and ductility.

Figure 1(b) shows the simulated response of cylindrical specimens tested in confined compression. Unconfined specimens fail in a brittle manner as a result of vertical tensile cracks. As the confinement is increased the strength and ductility increase as the response transitions from brittle tensile to ductile shear cracking. The brittle/ductile transition is an output of the model.

Figure 2 shows results of calculations simulating an experiment in which a small explosive charge is detonated in a marble specimen. The calculated cracking patterns show the same character as the patterns observed in the experiment; a region of radial cracks around the explosive charge and circumferential cracks around the specimen edges.

Figure 1 SRI Concrete Model Model Predictions for Various Concrete Specimen Loading Conditions

Figure 2 SRI Concrete Model Prediction of Crack Patterns in Blast Loaded Marble.

References

• J. W. Simons, T. H. Antoun, L. Seaman, and D. R. Curran," A Mesomechanical Model for Softening and Localization in Concrete," Presented at the DNA Workshop on Scaling Aspects of Hardened Structures, held at BDM, Albuquerque, NM, 24-26 January 1995.
   
• J. W. Simons, D. R. Curran and T. H. Antoun, "A Computer Model for Explosively Induced Rock Fragmentation During Mining Operations," presented at 56th University of Minnesota Mining Symposium, University of Minnesota, Duluth Campus, January 25-26, 1995.
   
• J. W. Simons, T. H. Antoun, and D. R. Curran, "A Finite Element Model for Analyzing the Dynamic Cracking Response of Concrete," Presented at 8th International Symposium on Interaction of the Effects of Munitions with Structures, McClean, Virginia, April 22-25, 1997

Contact Us
Don Shockey
Director, Center for Fracture Physics
Phone: 650-859-2587
Email: donald.shockey@sri.com