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对砂岩进行高围压高水压条件下的三轴压缩蠕变试验。试验表明,在整个加载过程中,孔隙水压力主要起到增强轴向变形和横向变形的作用;但在加载的初始阶段,孔隙水压力在一定程度上抑制了轴向变形。当应力水平高于屈服应力时,横向蠕变速率明显大于轴向蠕变速率,且横向蠕变率先进入加速蠕变阶段。本文提出一个新的非线性黏性元件,并引入一个能判断是否进入加速蠕变阶段的计时器元件,组建一个非线性黏塑性加速蠕变启动模型,将该黏塑性模型与Burgers模型串联,构建一个新的非线性黏弹塑性蠕变模型,推导了该模型在常规三轴应力状态下的本构方程。基于试验结果,通过对非线性优化算法(BFGS)的Matlab编程,实现对本文提出蠕变模型的参数识别,识别效果比较理想。对比试验曲线与拟合曲线,二者相当吻合,验证了新提出的非线性黏弹塑性蠕变模型的正确性。
Triaxial compression creep test of sandstone under high confining pressure and high hydraulic pressure. The experimental results show that the pore water pressure plays an important role in enhancing the axial deformation and lateral deformation during the whole loading process. However, the pore water pressure suppresses the axial deformation to a certain extent during the initial stage of loading. When the stress level is higher than the yield stress, the transverse creep rate is obviously greater than the axial creep rate, and the lateral creep rate first enters the accelerated creep stage. In this paper, we propose a new nonlinear viscous element and introduce a timer element that can determine whether to enter the accelerated creep phase. A nonlinear visco-plastic accelerated creep start model is established. The visco-plastic model is connected in series with the Burgers model A new nonlinear viscoelasto-plastic creep model is derived and the constitutive equation of the model is derived under normal triaxial stress conditions. Based on the experimental results, through the Matlab programming of nonlinear optimization algorithm (BFGS), the recognition of creep model proposed in this paper is realized, and the recognition effect is quite satisfactory. The comparison between the experimental curve and the fitted curve is in good agreement with each other, which verifies the correctness of the new proposed nonlinear viscoelastic plastic creep model.