Abstract
As a key dynamic feature of the rock mass, joint results in wave attenuation when a stress wave propagates across it. An experimental study has obtained the relation between the transmission coefficient and the contact area ratio of joints with different thicknesses (Chen et al. (doi:10.1007/s00603-015-0716-z)). However, the spatial geometry of the contact surface also determines the dynamic behavior of the discontinuous masses. Thus, the present study is focused on the effects of distribution and dimension of the sawn notches on the contact surface of the joint, which lead to the different spatial geometry. The joint matching coefficient (JMC) was used in this study to define the contact condition. Using a modified SHPB apparatus, all the bars and specimens were aluminum, and the artificial joint formed a rough surface of the specimen contacted to the output bar. Based on the wave separation method, the incident, reflected and transmitted waves across the joint were acquired from the records of the strain gauges on pressure bars. Then the transmission coefficient and specific stiffness of the joint were obtained. Comparisons of them were made on different JMCs, spatial geometries and thicknesses of the joint.
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Abbreviations
- \(\varepsilon_{\text{A}} (t)\), \(\varepsilon_{\text{B}} (t)\) :
-
Test records of the strain gauges A and B
- \(\varepsilon (t)\) :
-
Strain at time t
- \(\varepsilon^{p} (t)\), \(\varepsilon^{n} (t)\) :
-
Positive and negative strains
- \(\varepsilon_{A}^{p} (t)\), \(\varepsilon_{A}^{n} (t)\), \(\varepsilon_{B}^{p} (t)\), \(\varepsilon_{B}^{n} (t)\) :
-
Positive and negative strains at the positions of the strain gauges A and B
- x A , x B :
-
Distance between the end surface O and the strain gauge A and B respectively
- \(\Delta t\) :
-
Time interval for positive or negative strain wave propagation between the positions of the strain gauges A and B
- \(\sigma\) :
-
Stress of the joint
- E :
-
Young’s modulus of the aluminum bar
- \(\varepsilon_{I}\), \(\varepsilon_{T}\) :
-
Strains of the input and output bars
- \(\varepsilon_{I}^{p}\), \(\varepsilon_{I}^{n}\), \(\varepsilon_{T}^{p}\), \(\varepsilon_{T}^{n}\) :
-
Positive and negative strains of the input and output bars respectively
- v(t):
-
Particle velocity
- c :
-
P wave propagation velocity in the aluminum bar
- \(\dot{\varepsilon }\) :
-
Strain rate of the joint
- L :
-
Joint thickness
- \(\Delta L\) :
-
Normal closure of the joint
- T :
-
Transmission coefficient of the joint
- α, β, γ, φ:
-
Coefficients of the fitting curves
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Acknowledgments
This work was supported by the Chinese National Science and Technology Support Project (Nos. 2013BAB02B08, 41525009), and China Scholarship Council (CSC). The authors also would like to thank Mr. L. Goh in Monash University for his excellent assistance in test preparation.
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Chen, X., Li, J.C., Cai, M.F. et al. A Further Study on Wave Propagation Across a Single Joint with Different Roughness. Rock Mech Rock Eng 49, 2701–2709 (2016). https://doi.org/10.1007/s00603-016-0934-z
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DOI: https://doi.org/10.1007/s00603-016-0934-z