土和冻土的动态力学性能及本构模型研究

发布时间：2019-02-16 20:17

【摘要】：以粘性土以及冻土材料为研究对象，进行了粘性土和冻土在冲击荷载作用下的动态本构关系的研究，开展的研究工作和取得的成果如下： 首先，进行了粘性土在准静态加载条件下的无侧限抗压试验，获得了粘性土的静态力学参数，以便与动态加载条件下粘性土的试验进行对比。为了获得粘性土在冲击荷载作用下的动态力学性能参数，利用SHPB装置在500~1200s1的应变率范围内，对粘性土进行了动态冲击压缩试验。研究表明：粘性土表现出显著的应变率敏感性。 然后，针对粘性土在冲击荷载作用下的本构模型进行研究。从材料弹塑性理论着手，建立了一个粘性土的准静态弹塑性本构方程来描述其力学性能，并运用损伤力学中的微孔洞损伤，对其有效弹性模量进行计算。通过在原有准静态屈服函数中加入应变率效应的影响来得到一个适用于粘性土的动态本构方程。并对其中的微孔洞损伤进行描述并给出损伤演化方程，建立了一个损伤与塑性相耦合的本构方程。最后运用土体的有效应力原理，加入粘性土中的孔隙水压力和孔隙气压力。 其次，为了获得冻土材料在冲击荷载作用下的动态力学性能参数，利用SHPB装置在-3℃、-8℃、-13℃、-17℃、-23℃、-28℃六个负温下，在300~1200的应变率范围内，，对冻土材料进行了动态冲击压缩试验，得到了冻土材料的应力-应变曲线。研究表明：冻土材料表现出显著的温度敏感性和应变率敏感性。 再次，针对冲击荷载作用下冻土的动态力学性能及本构模型展开研究。采用复合材料细观力学中的混合律思想，将冻土材料看做是由土颗粒基体和冰颗粒夹杂组成的两相复合材料，并假设土颗粒和冰颗粒为各向同性且均匀的，对轴向加载情况下的冻土的等效弹性模量和等效泊松比进行了计算。基于材料的弹塑性理论，以修正的Drucker-Prager函数作为屈服函数，构造了一个考虑应变率效应的各向同性强化本构模型用于描述冻土材料的冲击特性。接下来运用损伤力学中的损伤变量来描述冻土材料中微裂纹和微孔洞对冻土动态力学性能的弱化作用，并给出了损伤演化方程。 最后，为了验证第三章和第五章建立的粘性土、冻土在冲击荷载作用下的动态本构模型的有效性，基于第二章、第五章中的粘性土、冻土的SHPB试验，对其本构方程的参数进行确定，并将模型数值计算结果与试验进行对比。
[Abstract]:The dynamic constitutive relations of cohesive soil and frozen soil under impact load are studied. The results are as follows: firstly, The unconfined compressive tests of clayey soil under quasi-static loading were carried out, and the static mechanical parameters of clayey soil were obtained for comparison with those under dynamic loading. In order to obtain the dynamic mechanical properties of cohesive soil under impact loading, the dynamic impact compression test of cohesive soil was carried out in the range of 500~1200s1 strain rate using SHPB device. The results show that clayey soil exhibits remarkable strain rate sensitivity. Then, the constitutive model of cohesive soil under impact load is studied. A quasi-static elastoplastic constitutive equation of cohesive soil is established to describe its mechanical properties based on the elastic-plastic theory of materials. The effective elastic modulus of cohesive soil is calculated by using the micro-void damage in damage mechanics. By adding the effect of strain rate effect into the original quasi static yield function, a dynamic constitutive equation for cohesive soil is obtained. The damage of microvoids is described and the damage evolution equation is given. A constitutive equation of the coupling of damage and plasticity is established. Finally, the pore water pressure and pore gas pressure in cohesive soil are added by the effective stress principle of soil. Secondly, in order to obtain the dynamic mechanical properties of permafrost materials under impact load, the strain rate of 300,1200 was obtained at six negative temperatures of -3 鈩

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