应力偏量加载条件下混凝土力学行为试验研究

为了分离平均应力、广义剪应力和罗德角对混凝土变形的影响，采用解耦应力路径，在液压伺服真三轴试验机上对边长为100mm的立方体混凝土试块进行准静态加载。对每个试块先施加平均应力到设计值，并与罗德角一同保持不变，单调地施加应力偏量。平均应力有5档，罗德角有3档（分别对应于拉、压、剪加载），两者组合成15组应力路径。给出了15组路径对应的偏应力~偏应变曲线、广义剪应力~广义剪应变曲线，分析了平均应力、罗德角对峰值应力、峰值应变、软化特性等力学特征的影响。首先，发现在平均应力、罗德角恒定的加载过程中，广义剪应力~广义剪应变曲线在下降段的变化幅值远远小于单轴和三轴比例加载时的变化幅值；并解释为，对于后者，加载中应力球量的变化放大了强化、软化作用。其次，发现如果用等向强化的屈服面描述混凝土的力学行为，则随着加载的进行在同一偏平面上屈服面的截面图除了大小发生变化之外，形状也发生变化；在不同的偏平面上，截面图之间形状并不相似。第三，证明了由应力的第一不变量和偏应力的第二不变量组成的塑性势函数只能描述拉伸和压缩这类假三轴加载，而不适用于剪切等真三轴加载。

Experimental research on concrete mechanical behavior upon loading on deviatoric plane

In order to separate the influences of mean stress, generalized shear stress as well as Lode angle to the deformation of concrete, quasi-static loading was performed, using decoupling stress path, on concrete cubic specimens of 100×100×100mm in a hydraulic servo true triaxial testing machine. On each specimen was initially applied mean stress up to design value, which maintained constant together with Lode angle, then deviatoric stress was exerted. With 5 classes of mean stress and 3 classes of Lode angle(corresponding to tensile, compressive and shear loading respectively) combined, 15 groups of stress paths were obtained. Deviatoric stress-strain curves and generalized shear stress-strain curves have been developed, the influences of mean stress and Lode angle to these mechanical properties, peak stress, peak strain and softening behavior included, have been analyzed. It was observed that in this generalized stress-strain curve, amplitude variation of the descending part is far less than that under unaxial and triaxial proportional loading condition, for the reason that spherical tensor of stress changed under the latter loading condition and it magnified the hardening and softening effects. Besides, plastic potential function consisting of the first invariant of the stress and the second invariant of the stress deviator is only suitable for stress state with two equaled principal stresses during loading, such as the state in loading process of tension or compression rather than in real triaxial ones such as that in shearing duration.