Effect of cyclic heating on subcritical crack growth of rock beams under four-point bending test

This study considers the effects of cyclic differential heating on the velocity of the subcritical crack growth (SCG) from a central notch in rock beams under four-point bending test. Beams of both Carrara marble and Fujian granite are subjected to non-uniform heating, with heating from the top surface containing the notch (at about 60 degrees Celsius) and with cooling to the bottom side with no notch (at about 25 degrees Celsius). Beams are heated for 7-188 days before they are subject to constant load creeping test under four-point bending configuration, and the compliance method is used to interpret crack growth from the crack mouth opening displacement (CMOD). The compliance method is verified by using acoustic emissions from cracking events together with simultaneous microscopic observations. It was discovered that a microcrack processing zone (PZ) was observed in the form of white patches ahead of the notch tip during the creeping test, followed by sudden jumps of macrocrack growth. Linear elastic fracture mechanics (LEFM) is used to calculate the local stress intensity factor, which is then further related to crack growth velocity, through the commonly adopted power law. After the application of non-uniform cyclic heating, the P-wave velocity of Fujian granite increases (due to microcrack closure) whilst that of Carrara marble decreases (due to parallel crack formation). The SCG parameters in the power law (power index n and threshold velocity nu(0)) are obtained. There is no clear trend in the variation of the SCG parameters with the number of heating cycles. However, these parameters are used to simulate subcritical crack growth velocity for both heated and unheated specimens. In the light of fracture mechanics analysis, we conclude that Fujian granite is clearly preferable to Carrara marble in making rock panels on cladding of buildings.

Automated summary

The study investigates the effect of cyclic differential heating on subcritical crack growth (SCG) velocity in rock beams. Different responses were observed in Carrara marble and Fujian granite due to non-uniform heating, with the former experiencing a decrease in P-wave velocity and the latter showing an increase. Microcrack processing zone (PZ) was identified in front of the notch tip during creeping test.