CREEP-STRESS RELAXATION COUPLING FAILURE IN CONCRETE AND ITS CRITICAL POWER-LAW BEHAVIOR

Creep-stess relaxation coupling experiments were carried out and the induced catastrophic failure in concrete materials was investigated in the paper. An initial displacement was imposed to the cross-head of testing machine and then it was kept constant, a stress relaxation was observed associated with the increase of deformation. The growth of concrete's deformation leads to a continuous increase of the stored energy in the concrete samples. But, the total energy of the system decreases monotonically. This indicates that the tested concrete undergoes a damage propagation process even though the stress is relaxing. The energy-time curves can be typically divided into three temporal stages: the primary stage with rapid evolution, followed by a steady stage with a constant slope, and finally the accelerating tertiary stage which eventually leads to a macroscopic failure. Ahead of macroscopic failure, the energy release rates of all samples present a power law behavior with the same critical exponent -2/3, although these experiments exhibit a large variability in time-to-failure and failure strain or stress. This observation suggests a way to predict the timing of failure by monitoring the critical accelerating behaviors of the quantities such as energy, strain or stress.