A micro-macro confined compressive fatigue creep failure model in brittle solids

Fatigue properties under cyclic static compressive loading and unloading (i.e., compressive fatigue/cyclic creep properties) have an important meaning for evaluation of lifetime in brittle solids containing numerous microcracks. The total deformation during cyclic static compression consists of time-independent elastic, time-dependent viscoelastic, time-dependent viscoplastic and time-independent plastic deformations. Henceforth, the viscoplastic and plastic deformations will be collectively referred to as plastic deformation in this article. Past publications have already established that the plastic deformation dominates the lifetime of brittle solids. Furthermore, the rebound of elastic and viscoelastic deformations at static unloading has been widely studied. However, the rebound of plastic deformation at static unloading under constant lateral confining pressure and the total time-dependent deformation during cyclic static compressive failure are both rarely studied in theory. Noteworthy publications have already reported that the rebound of plastic deformation has a great significance for cyclic static compressive failure, and microcrack variable influences seriously plastic mechanical properties of brittle solids. Unfortunately, the theoretical relationship between plastic deformation rebound and microcrack variable in brittle solids during a cyclic static compressive failure is rarely established.

To address this, Professor Xiaozhao Li, Professor Chengzhi Qi and Dr. Pengchong Zhang from the Beijing University of Civil Engineering and Architecture developed a new analytical model of cyclic fatigue creep failure in brittle solids. Specifically, their goal was to find an analytical solution by coupling the confined cyclic static loading and unloading path, the HookeKelvin viscoelastic model and the formulated micro-macro model, which explains the total time-dependent visco-elastic-plastic deformation caused by microcracks variable during cyclic static compressive failure. Their work is currently published in the research journal, International Journal of Fatigue.

In their work, the researchers adopted the aforementioned analytical model and used it to study the effects of the residual static axial stress after unloading and confining pressure on cyclic creep failure. In addition, the researchers probed the irreversible elastic and viscoelastic deformations caused by residual static stress after unloading. Overall, they aspired to establish the relationship between the rebound of plastic deformation and microcrack recovery.

The authors reported an interesting rebound phenomenon of plastic deformation induced by microcrack recovery. Moreover, a critical value of axial stress causing a rebound of plastic deformation was also reported. The researchers proceeded to explain the total visco-elastic-plastic deformation relating to the microcrack variable.

In summary, the study demonstrated an analytical confined fatigue creep failure model in brittle solids containing numerous microcracks. The presented technique was based on the confined cyclic static loading and unloading path, the Hooke-Kelvin viscoelastic model, and the micro-macro mechanical model as proposed in an earlier study. Remarkably, using the proposed technique, a dramatic plastic rebound phenomenon induced by microcrack recovery was demonstrated. In a statement to Advances in Engineering, Professor Xiaozhao Li pointed out that the presented results of the rebound phenomenon will provide important help for evaluating the fatigue creep lifetime of brittle solids in engineering.