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针对岩石类材料,试图在关联Drucker-Prager条件下建立更一般化的等效塑性应变定义方法,并研究等效塑性应变系数在塑性变形过程中的变化。首先列举了国内外常用的等效塑性应变定义方法,并分析了它们的不合理性。然后从等效应力和等效塑性应变的定义出发,推导出关联Drucker-Prager条件下等效塑性应变系数。结合室内致密砂岩三轴压缩试验,以塑性体应变为内变量,研究了致密砂岩峰后内摩擦角和粘聚力随内变量的变化,进而研究了等效塑性应变系数随塑性变形的变化。研究发现:等效塑性应变系数依赖于屈服准则的选取,等效塑性应变系数为(2/3)~(1/2)是Mises屈服准则下的特例;关联Drucker-Prager条件下等效塑性应变系数C<(2/3)~(1/2),并且随着塑性变形的发展而减小最终趋于稳定值;对于岩石类材料,很多有限元软件中不区分具体情况而直接选用C=(2/3)~(1/2)计算等效塑性应变存在较大的误差。
Aiming at the rock-like materials, a more general method of defining equivalent plastic strain is proposed under the condition of Drucker-Prager, and the change of equivalent plastic strain coefficient during plastic deformation is studied. First of all, the common definitions of equivalent plastic strain at home and abroad are listed, and their irrationality is analyzed. Then from the definition of equivalent stress and equivalent plastic strain, the equivalent plastic strain coefficient under Drucker-Prager condition is deduced. Combined with the triaxial compression tests of the tight sandstone in the laboratory, the variation of internal friction angle and cohesion with the internal variables of the tight sandstone was studied by taking the plastic strain as the internal variable. Then the variation of the equivalent plastic strain coefficient with the plastic deformation was studied. The results show that the equivalent plastic strain coefficient depends on the selection of yield criterion, and the equivalent plastic strain coefficient (2/3) ~ (1/2) is a special case under the Mises yield criterion. The equivalent plastic strain The coefficient C <(2/3) ~ (1/2), and decreases with the development of plastic deformation finally tends to a stable value; for rock-like materials, many finite element software does not distinguish between the specific circumstances and direct selection C = (2/3) ~ (1/2) There is a big error in calculating the equivalent plastic strain.