固体介质三轴实验中样品半延性-延性变形对应力曲线影响的修正

CORRECTION OF STRESS-STRAIN RELATIONSHIP IN TRIAXIAL COMPRESSION TESTS WITH SOLID CONFINING PRESSURE MEDIUM

在岩石高温高压三轴变形实验中达到岩石的极限强度之后 ,岩样的宏观几何变形显著增加 ,几何变形成为表观应力与真实应力之间出现较大偏差的主要原因。针对此问题 ,假定岩样从圆柱体变形成为桶形体 ,在一些理想假设前提下 ,给出了高温高压条件下三轴实验中 ,当试样出现半延性 -延性行为时 ,应力曲线的一种修正方法。

In triaxial compression experiments with solid confining pressure medium, especially under high temperature and high confining pressure condition, after reaching the peak strength the macroscopic geometrical deformation of the sample increases obviously with increasing of differential stress. This will lead to a large difference between the observed stress-strain curve and the actual stress-strain relationship. This false appearance will give rise to the unreasonably high residual stress in the sample. To solve this problem, during the semi-ductile and ductile deformation stage of rock sample under the HT-HP condition, a correction of stress-strain curve has been carried out based on the following three assumptions:1) With increasing of differential stress, the originally columnar rock sample deforms into a barrel-shape body;2) The volume of rock sample remains constant;3) During the deformation process, the upside and downside surfaces of the sample keep their original size and shape. That is, the diameter of the upside and downside surfaces of the barrel-shape body should be equal to that of the original sample. The observation after the experiments shows that the rock sample was shortened and bulged in the middle part. This qualitatively indicates that the above assumptions are reasonable to some extent. The examination by using actual experiment data indicates that the correction method proposed here is of practical significance. This method is also applicable to the correction of the stress-strain curve during the semi-ductile or ductile deformation process under axial compression condition.