The effect of successive uniaxial and biaxial cyclic loading on the fracture resistance of limestone samples
Description
The results of experiments with two samples of limestone of the Kasimovskoye deposit (Russia) are discussed. The purpose was to compare their resistance to fracture under cyclic quasi-static loadings under compression in one or two directions. Acoustic emission (AE) was recorded during cycles. Between the series, the velocities of longitudinal and transverse elastic waves, and acoustic quality factor Q were measured. The destructive effect was evaluated using the damage parameter ω. The studies showed that deformation of the sample in two directions leads to greater damage, but reduces the strength of the limestone to a lesser extent than the cyclic load in one direction. Cracks formed in the biaxial action of one direction impede the development of cracks in another direction. This mechanism explains the indicated phenomenon. The study was supported by the Russian Foundation for Basic Research, grant No. 17-05-00570.
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The purpose of the tests: a comparative assessment of the damage and resistance of limestone to the destructive effect under uniaxial and biaxial cyclic mechanical loads. Test data for two 50x50x25 mm limestone samples under uniaxial and biaxial sequential cyclic compressive loading are presented. The maximum stress in the cycle is 10 MPa. Sample LM1 was tested in series of 20 cycles in one direction. Each series of 20 cycles for the LM2 sample consisted of two subseries of 10 cycles. The first subseries was carried out in the direction of the strain gage. The second subseries was carried out in the direction perpendicular to the direction of the first subseries. Test loadings were carried out before the destruction of the samples. Data are presented in two folders designated according to samples and test modes LM1 and LM2 respectively. Each of these folders contains subfolders directly with the corresponding data. Each subfolder contains three data files in which the registration results are recorded: - a file with the letters AE with data on the number of pulses of acoustic emission; - a file with the letter P with data on the load on the sample; - a file with the letter T with data on the strain gauge deformations oriented along the direction of the first loading in the series. For visualization and data processing, each folder contains programs written in the Mathcad software, the name of which contains the word Test. The sample data LM1 contains the results of loading only in the direction of sensitivity of the strain gauge in series of 20 cycles. They are presented as follows. Folder LM1_8 contains test data at a stress of 8 MPa and a number of cycles of 20 (estimated loads). Folder LM1_10_20 contains test data at a stress of 10 MPa with cycle numbers from 1 to 20. Folder LM1_10_40 contains test data at a stress of 10 MPa with cycle numbers from 21 to 40; further similarly to the folder LM1_100_122, when the destruction of the sample occurred. The LM2 sample data are presented for those series when loading was carried out by a subseries of 10 cycles along the orientation direction of the strain gauge glued to the sample. Loading data across the direction of orientation of the strain gage are not shown. Folder LM2_10_10 contains the test data at a stress of 10 MPa with load numbers from 1 to 10. Folder LM2_10_30 contains the test data at a stress of 10 MPa with load numbers from 21 to 30, etc. to the folder LM2_100_110. Last folder contains data on the subseries of loading when the destruction of the sample occurred. As a result, we obtained graphs of changes in the loads and deformations of the sample over time, as well as graphs of changes in the number of AE pulses up to failure.