Tunnel and Underground Space (터널과지하공간)

Korean Society for Rock Mechanics and Rock Engineering (한국암반공학회)
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A Study on Subcritical Crack Growth Parameters in Rock-like Material under Monotonic and Cyclic Loading

단조 및 반복하중 하에서의 모사 암석 시료의 임계하 균열성장 지수에 관한 연구

  • Received : 2019.04.22
  • Accepted : 2019.04.26
  • Published : 2019.04.30
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Abstract

Subcritical crack growth in rock material can occur under monotonic and cyclic loading. Subcritical crack growth plays an important role in evaluating the long-term stability of structures in rocks. This paper presents the results of studies conducted to determine subcritical crack growth parameters under monotonic and cyclic loading in rock-like material. The constant stress rate method was employed for monotonic loading. The subcritical crack growth parameter of n under cyclic loading was determined by the relation between the rate of crack growth per cycle and stress intensity factor range. The specimens contained pre-existing flaws with 45 and 60 degrees of inclination angle and flaws spacing and continuity were varied to arrange crack growth in shear or tensile manner. The results show that the parameter of n is almost constant regardless of the applied load conditions such as monotonic and cyclic or shear and tension.

암석에서의 임계하 균열성장은 단조 및 반복하중 하에서 일어날 수 있다. 임계하 균열 성장은 암반에 건설되는 지하구조물의 장기 안정성의 평가에 큰 영향을 미친다. 본 연구에서는 모사 암석 시료를 사용하여 단조 및 반복하중 하에서의 임계하 균열성장 지수를 구하였다. 단조하중 조건에서는 일정 응력 속도법이 적용되었으며, 반복하중에 의한 임계하 균열성장 지수는 반복에 의한 균열성장 속도와 응력확대계 수폭의 관계를 이용하였다. 연구에 사용된 시험편은 $45^{\circ}$와 $60^{\circ}$의 균열 경사각을 가지고 있으며, 균열의 간격 및 연속성에 변화를 주어 전단 또는 인장에 의한 균열성장이 가능하도록 하여 전단 또는 인장에 의한 임계하 균열성장 지수도 구하였다. 그 결과, 임계하 균열성장 지수 n은 작용하는 하중 조건, 즉 단조 및 반복하중, 혹은 전단 및 인장에 관계없이 거의 일정한 값을 나타내었다.

Keywords

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Fig. 1. Schematic configuration of specimen geometry

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Fig. 2. Specimen geometry

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Fig. 3. Specimen geometry after crack growth

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Fig. 4. Schematic illustration of the crack model: (a) shear crack model; (b) sliding crack model

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Fig. 5. Results of constant stress rate tests under monotonic loading

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Fig. 6. Variation of the crack growth da/dN as a function of the stress intensity factor range ΔK

Table 1. Specimen geometry used in this study

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Table 2. Experiment results

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