Mechanical Behavior of Shale at Different Strain Rates: Fid-Bau Portal

Mechanical Behavior of Shale at Different Strain Rates

Hou, Zhenkun / Gutierrez, Marte / Ma, Shuqi / Almrabat, Abdulhadi / Yang, Chunhe

Abstract The strain rate-dependent mechanical behavior of shale is characterized using triaxial compression tests under a constant confining pressure of 50 MPa and axial strain rates $$\dot{\varepsilon }_{1}$$ ranging from 5 × $ 10^{−6} $ $ s^{−1} $ to 1 × $ 10^{−3} $ $ s^{−1} $. This study is conducted on the Longmaxi shale from Dayou in China, which is predominantly composed of brittle minerals including quartz (55%), albite (15%) and cristobalite (3%). The experimental results show that higher axial loading strain rates $$\dot{\varepsilon }_{1}$$ lead to higher elastic modulus and higher peak shear strength, both following exponential relationships with $$\dot{\varepsilon }_{1}$$. When $$\dot{\varepsilon }_{1} \le 1 \times 10^{ - 5} {\text{s}}^{ - 1}$$, failure results in a single linear fracture, whereas a more complex multiple crisscrossing fracture network is formed when $$\dot{\varepsilon }_{1} \ge 1 \times 10^{ - 4} {\text{s}}^{ - 1}$$. Failure in shale specimens can be described by a damage parameter $$D$$, which is strongly affected by the axial strain $$\varepsilon_{{1{\text{s}}}}$$. In addition, the strain rate $$\dot{\varepsilon }_{1}$$ had different effects on $$D$$, which also depends on axial strain $$\varepsilon_{{1{\text{s}}}}$$. Energy accumulation and dissipation are also closely related to $$\dot{\varepsilon }_{1}$$ with the total absorbed energy $$U_{\text{A}}$$, the recoverable elastic strain energy $$U_{\text{A}}^{\text{e}}$$ and the dissipated energy $$U_{\text{A}}^{\text{d}}$$ at the peak stress increasing with $$\dot{\varepsilon }_{1}$$. As for the total energy accumulation $$U_{\text{A}}$$, the recoverable elastic energy $$U_{\text{A}}^{\text{e}}$$ decreases while the dissipated energy $$U_{\text{A}}^{\text{d}}$$ increases with increasing strain rate.