混凝土蠕变与应力松弛耦合破坏及临界幂律行为
CREEP-STRESS RELAXATION COUPLING FAILURE IN CONCRETE AND ITS CRITICAL POWER-LAW BEHAVIOR
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摘要: 该文设计和开展了单轴加载下混凝土的蠕变与应力松弛耦合试验,分析了混凝土蠕变与应力松弛耦合诱发宏观破坏的演化过程。试验表明,在给试验机作动器施加一个初始位移并保持其恒定的过程中,混凝土试样发生变形单调增长时伴随着应力松弛过程,表现出两者的耦合行为。在该过程中,虽然混凝土试样的变形在增加,但是系统的总能量在单调减小。这种能量损失表明了混凝土材料的内部损伤在不断发展。在蠕变与应力松弛耦合过程中,能量演化经历了三个典型阶段,即初始快速演化阶段(但速度在减小)、稳定演化阶段和最后的加速演化阶段,直至试样发生宏观破坏。虽然试样的破坏时间呈现出较大分散性,但是在宏观破坏前,系统能量释放率呈现出相同的临界幂律行为,且具有相同的临界幂指数-2/3。该结果为基于响应量临界行为的监测,探索破坏预测提供了线索和依据。Abstract: 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.