Evolution law of strain field and precursor identification of flawed sandstone based on Digital Image Correlation method
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摘要:
目前数字图像相关方法在岩石力学领域的应用主要集中于获取变形场云图，缺乏结合一些指标对变形数据进行定量分析。采用数字图像相关方法对裂隙砂岩试件压缩加载过程进行非接触式、实时变形测量，结合方差量化描述应变场分异特征；而后对应变场方差变化曲线进行有限差分求导，量化描述应变场分异速率，分析应变场演化规律及前兆特征。研究结果表明：裂隙砂岩试件的变形破裂过程可划分为压密、弹性变形、裂纹稳定扩展、裂纹快速扩展及破坏等4个阶段。加载过程中裂隙砂岩试件的裂纹萌生和扩展行为，在应变场上表现为应变局部化带的产生与发展，进而导致应变场方差和分异速率发生变化。应变场方差-轴向应变曲线表现出阶段性特征，可划分为稳定分异、加速分异以及加加速分异等3个阶段。应变场分异速率-轴向应变曲线在张拉裂纹起裂时均出现第一个尖峰，可作为裂隙岩体失稳破坏前的前兆信号，对应的前兆应力与峰值应力之比为0.80～0.96。研究成果对工程岩体失稳预测具有较好的理论参考价值。
Abstract:Previous studies on the application of Digital Image Correlation(DIC) method in rock mechanics have mainly focused on obtaining the contours of deformation fields, whereas little attention has been paid to perform quantitative analysis on these deformation data by combining some indicators. The digital image correlation method was applied for real-time and non-contact monitoring deformation of flawed sandstone specimens during the compressive loading process. The differentiation characteristic of strain field was quantitatively described by using the variance. The differentiation rate of strain field was quantitatively described by using the finite difference derivative of the variance variation curve. The evolution laws of strain field and precursor characteristics were analyzed. The results show that the deformation and fracturing process in flawed sandstone specimens can be divided into four stages, namely, compaction, elastic deformation, steady crack propagation, rapid crack propagation and failure. The crack initiation and propagation behavior during the loading process is associated with the generation and development of strain localization zones in the strain field, resulting in the variations of variance and differentiation rate of strain field. The evolution process of variance of strain field shows an obvious periodic characteristic. The variance of strain field-axial strain curve can be divided into three stages, namely, steady differentiation, accelerated differentiation and accelerated acceleration differentiation. When the tensile crack appears, the first peak occurs in the differential rate of the strain field-axial strain curve, which could be regarded as a precursor before the failure of fractured rock mass. The ratio of precursor stress to peak stress is in the ranges of 0.80～0.96. The research results have theoretical significance for the failure prediction of engineering rock mass.
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Key words:
- sandstone /
- flaw /
- Digital Image Correlation method /
- strain field /
- fracturing /
- precursor
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