Abstract
We report the strength and deformation behavior of Solnhofen limestone across its brittle (localized) to ductile (distributed) transition. We conducted conventional triaxial compression tests on water‐saturated and nominally dry cores of Solnhofen at temperatures up to 200°C and effective confining pressures up to 350 MPa to evaluate the roles of pore water and temperature on the deformation mechanisms of low‐porosity limestone at conditions of the upper crust. The combined effects of water and temperature on deformation and strength of the limestone are complex and reflect the concurrent operation of microfracturing, which is enhanced by both pore water and temperature, crystal plasticity, which is enhanced by temperature but not pore water, and likely also dissolution which is enhanced by water but inhibited by temperature. At ambient temperature, water causes a small reduction in the yield strength and the strength in the ductile field, but has no measurable effect of the brittle peak strength or the effective pressure of the brittle to ductile transition. At elevated temperatures, water‐saturated Solnhofen exhibits weakening in both the brittle and ductile fields up to 200 MPa effective pressure. In addition, the combined effects of pore water and temperature reduce the pressure of the brittle to ductile transition dramatically. We propose that under dry conditions temperature reduces the pressure of the brittle to ductile transition by enhancing crystal plasticity and under water‐saturated conditions enhanced microcracking is responsible. At effective pressures greater than 200 MPa, ductile deformation becomes temperature strengthening indicating the onset of dissolution mediated deformation.
Key Points
At room temperature, water has negligible effect on peak strength and the pressure of the brittle‐ductile transition in Solnhofen limestone
Water and elevated temperature together promote compaction and strain hardening and decrease the pressure of the brittle‐ductile transition
Water and thermal weakening are explained by water‐enhanced fracturing and thermally enhanced glide and twinning