单轴拉伸条件下田下凝灰岩力学特性时间效应试验研究

发布时间：2018-04-26 23:24

本文选题：直接拉伸 + 时间效应　；参考：《重庆大学》2015年硕士论文

【摘要】：众所周知,由于岩石变形损伤引发的诸如岩爆、地基开裂、滑坡等工程灾害存在着明显的时效性,即岩土工程灾害并不一定在工程建设过程中或项目建成运行较短时间内发生,而往往会经历不等的时间,故探究岩石力学特性的时间效应对减少和避免相关工程灾害有着十分重要意义。由于当前岩石时间效应的研究主要集中于压缩,拉应力作用下的时间效应研究非常的匮乏,而岩石在许多工程条件下都处于拉应力状态,所以研究岩石拉应力条件下时间效应的工程指导意义尤为突出。本文选用日本的田下凝灰岩作为研究对象,在学习总结前人研究基础上,研发了适用于岩石直接拉伸试验的单轴拉伸试验系统,在传统的应力控制、应变控制基础上实现了应力应变的线性组合—应力归还法控制;进行了恒定荷载率直接拉伸试验、交替荷载速率直接拉伸试验,在应力归还法控制的基础上进行了广义应力松弛试验(应力应变同时改变,但应力应变的线性组合不变),以及蠕变试验、松弛试验;针对田下凝灰岩的直接拉伸试验和广义应力松弛的特性,选取合适的本构模型—可变模量非线性粘弹性本构模型,根据直接拉伸试验和广义应力松弛试验确定本构模型中的参数,最后进行模型计算结果的验证。取得主要结论如下:1)试验研究了直接拉伸条件下恒定荷载试验、交替荷载试验的基本力学参数荷载速率依存性,结果表明:田下凝灰岩恒定荷载速率试验的抗拉强度σt的荷载依存指数为0.0214,杨氏模量E的荷载依存指数为0.0087,破坏应变εt的荷载速率依存指数为0.0129,非弹性应变不具有荷载速率依存性,破坏时的非弹性应变约为0.4×10-3,交替荷载速率试验获得的强度值及荷载速率依存性与恒定荷载试验十分接近,交替荷载试验能较好的替代恒定荷载试验;2)试验研究了不同应力水平的拉伸蠕变试验、不同应变水平的拉伸松弛试验,同一启动点不同方向的广义应力松弛试验的流变特性,得到结果:拉伸蠕变试验的蠕变应变与时间的关系式、蠕变速率与时间的关系式,拉伸松弛试验中应力降与时间的关系式、松弛速率与时间的关系式,分析相同启动点不同方向的的广义应力松弛特性,经历相同的流变时间时,方向角越小,广义应力松弛的应变变化量、应力变化量和非弹性应变变化量均随着方向角的增加而减小,得到了广义应力松弛等时曲线,可以预测不同启动点、不同方向的广义应力松弛试验;3)选取适合田下凝灰岩直接拉伸条件下的本构模型,解析得到本构方程,确定了本构模型中的6个参数a1=1,a2=0.0001,m1=43,m2=20,n1=n2=46,并用该本构模型成功的模拟了直接拉伸作用下田下凝灰岩不同速率的全应力应变试验以及不同应力水平的蠕变试验,计算结果和试验结果一致性较好。
[Abstract]:As we all know, engineering disasters such as rock burst, foundation cracking, landslide and other engineering disasters caused by rock deformation damage have obvious timeliness, that is, geotechnical engineering disasters do not necessarily occur in the process of engineering construction or in a short period of time when the project is completed and run. Therefore, it is very important to explore the time effect of rock mechanical properties to reduce and avoid engineering disasters. Due to the fact that the study of the time effect of rock is mainly concentrated on compression, the study of time effect under tension stress is very scarce, and the rock is in the state of tensile stress under many engineering conditions. So it is very important to study the time effect under rock tensile stress. In this paper, Tanaka tuff from Japan is selected as the object of study. On the basis of studying and summarizing previous studies, a uniaxial tensile test system suitable for direct tensile test of rock is developed, which is under traditional stress control. On the basis of strain control, the linear combinatorial stress-strain control method is realized, and the constant load rate direct tensile test and alternating load rate direct tensile test are carried out. Based on the control of the stress return method, the generalized stress relaxation test is carried out (the stress and strain changes simultaneously, but the linear combination of stress and strain remains unchanged, as well as creep test and relaxation test; According to the direct tensile test of tuff and the characteristics of generalized stress relaxation, a suitable constitutive model-variable modulus nonlinear viscoelastic constitutive model is selected. The parameters of the constitutive model are determined by direct tensile test and generalized stress relaxation test. Finally, the calculation results of the model are verified. The main conclusions are as follows: (1) the dependence of load rate on the basic mechanical parameters of constant load test and alternating load test under direct tensile condition is studied. The results show that the load-dependent exponent of tensile strength 蟽 _ t is 0.0214, Young's modulus E is 0.0087, failure strain 蔚 _ t is 0.0129, and inelastic strain is not available. With load rate dependence, The inelastic strain during failure is about 0.4 脳 10 ~ (-3). The strength and load rate dependence of alternating load rate test is very close to that of constant load test. Alternating load test is a good alternative to constant load test. The rheological properties of tensile creep test with different stress levels, tensile relaxation tests with different strain levels and generalized stress relaxation tests with different directions at the same starting point are studied. The results are as follows: the relationship between creep strain and time, creep rate and time, stress drop and time, relaxation rate and time in tensile creep test. The generalized stress relaxation characteristics in different directions at the same starting point are analyzed. When the flow time is the same, the smaller the direction angle, the strain variation of the generalized stress relaxation. The variation of stress and inelastic strain decrease with the increase of direction angle. The generalized stress relaxation isochron curve can be used to predict different starting points. The constitutive model suitable for direct stretching of tuff in different directions is selected, and the constitutive equation is obtained. The six parameters of the constitutive model a _ (1) 1 ~ (1) A ~ (2 +) ~ (0.0001) / m ~ (-1) ~ (43) m ~ (2) ~ (2) ~ (20) ~ (1) ~ (1) ~ (1) ~ (1) N ~ (21) N ~ (21) ~ 4 ~ (-6) were determined. By using the constitutive model, the full stress-strain tests at different rates of tuff and creep tests at different stress levels were successfully simulated The calculated results are in good agreement with the experimental results.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU45

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