Dynamic Mechanical Properties of Dry and Water-Saturated Siltstones Under Sub-Zero Temperatures
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ORIGINAL PAPER
Dynamic Mechanical Properties of Dry and Water‑Saturated Siltstones Under Sub‑Zero Temperatures Lei Weng1 · Zhijun Wu1 · Quansheng Liu1 Received: 6 May 2019 / Accepted: 17 December 2019 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract The effects of low temperature and strain rate on the dynamic mechanical properties of dry and saturated siltstones under sub-zero temperatures were investigated and presented in this paper. The siltstone specimens were first frozen to different sub-zero temperatures (from − 10 to − 50 °C), and then were tested at those temperatures using a split Hopkinson pressure bar (SHPB) system. The results indicated that compared to the dry specimens, the saturated specimens exhibit a much shorter compaction phase in the dynamic stress–strain curve due to the presence of the pore water or ice at sub-zero temperatures. The dynamic elastic modulus (Ed) and dynamic uniaxial compressive strength (UCSd) monotonically increase with the increase in the strain rate for both the dry and saturated specimens, and the dry specimens are more sensitive to the strain rate effect with respect to the U CSd. Furthermore, for both the dry and saturated specimens, the Ed and U CSd first increase with the decrease in the temperature from 18 to − 30 °C, and then decrease with a further drop in the temperature from − 30 to − 50 °C. Manifold reasons are responsible for this phenomenon, including the shrinkage of mineral grains, enhancement of the ice strength and interaction of the water/ice mixture with rock as the temperature drops. Using the NMR technique, the mechanisms of the mixed water/ice weakening and strengthening effects on the dynamic mechanical properties of siltstones at sub-zero temperatures were discussed. Keywords Sub-zero temperature · Strain rate · Water/ice-to-rock interaction · Siltstone · SHPB List of symbols Ab Cross-sectional area of the bar As Cross-sectional area of the specimen Cb P-wave velocity in the bar cp Specific heat of the specimen D Diameter of the specimen Eb Dynamic elastic modulus of the bar Ed Dynamic elastic modulus of the specimen Ls Length of the specimen s Radial distance t Required time to achieve an isothermal equilibrium T Ambient temperature Tc Environmental chamber temperature
Tf Desired temperature at which the specimen was tested Ti Initial temperature of the specimen 𝜀cl Crack closure strain 𝜀e Elastic strain 𝜀p Plastic strain 𝜀i (t) Incident strain 𝜀r (t) Reflected strain 𝜀t (t) Transmitted strain 𝜀̇ Strain rate 𝜂 Dynamic stress equilibrium factor 𝜅 Temperature gradient ratio 𝜆 Thermal conductivity of the specimen 𝜌 Density of the specimen 𝜎i (t) Incident stress 𝜎r (t) Reflected stress 𝜎t (t) Transmitted strain
Special Issue on CouFrac2018.
Abbreviations BTS Brazilian tensile strength COD Coefficient of determination ISRM International Society for Rock Mechanics LN2 Liquid nitrogen
* Zhijun Wu [email protected] 1
School of Civil Engineering, Wuhan University, No. 8 Donghu South
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