On one condition for the development of an isolated defect
In the case of a plane stress-strain state, a thermodynamically complete energy condition for the development of an isolated defect is obtained, generalizing the classical condition of A. Griffiths, for the case when destructive loads are applied both to the external contour of the body and to the contour of the isolated defect. This problem arises when modeling hydraulic fracturing of an oil reservoir under the influence of lateral pressure. Taking into account the entropy component of the released internal energy in the proposed brittle fracture condition determines the dependence of critical loads on the characteristic dimensions of the isolated defect, which takes into account the temperature and the linear coefficient of thermal expansion of the material. The A. Griffiths condition does not explicitly take into account the temperature and the linear coefficient of thermal expansion of the material and follows from the proposed condition if the entropy component of the internal energy is neglected.