Method for determining rock crack stress threshold value based on full-field strain measurement

Abstract

The invention discloses a method for determining a rock crack stress threshold value based on full-field strain measurement. The method comprises the following steps: manufacturing a rock sample; performing speckle treatment on the surface of the rock sample; carrying out test loading and collecting an image of a speckle surface of the rock sample in the test loading process; calculating the full-field displacement of the speckle surface of the rock sample; calculating the full-field strain of the speckle surface of the rock sample; calculating a volume strain, an elastic volume strain and a crack volume strain of the rock sample; acquiring a rock sample volume strain-axial strain curve, a crack volume strain-axial strain curve and an axial stress-axial strain curve, and drawing the curvesin the same subgraph; and determining changing rules of the volume strain of the rock sample and the crack volume strain and determining threshold values of the four crack stresses including the crack closing stress, the crack initiation stress, the crack damage stress and the peak stress of the rock sample. The method has the advantages of low requirement on test environment, more convenience inapplication, high result reliability, and higher representativeness and universality.

Description

technical field [0001] The present invention relates to the field of rock mechanical property testing, in particular to a method for judging rock crack stress thresholds based on full-field strain measurement. Background technique [0002] Under the action of external force, the rock material can obtain four different crack stress thresholds according to its stress-strain curve relationship, namely: crack closure stress σ cc , Crack initiation stress σ ci , crack damage stress σ cd and peak stress σ p . Most scholars believe that the crack initiation stress of rock is the lower limit of long-term rock strength, while the crack damage stress is the upper limit of long-term rock strength. In actual engineering, the long-term strength of rock can be used to measure the stability of engineering, so the determination and research of the above four different crack stress thresholds have high reference value for actual engineering design. [0003] At present, there are several...

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Problems solved by technology

[0004] Among them, the strain calculation method is to record and measure the axial strain and hoop strain generated during the sample test by attaching strain gauges on the surface of the sample or installing hoop strain gauges, and then obtain the Crack stress threshold value, the disadvantage of this method is that the number of strain gauges attached to the sample is limited, and the measurement is the local strain change data of the sample, so the obtained results may not be representative;

[0005] Among them, the acoustic emission method first installs acoustic emission probes at different positions on the surface of the sample to record the acoustic emission events during the test, and then determines the threshold value of the crack stress by analyzing the variation law of the acoustic emission events. The disadvantages of this method Yes: It is greatly affected by the noise around the test, and the heterogeneity of the microstructure of rock materials often leads to unsatisfactory test results in rock mechanics tests

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