循环载荷作用下岩石损伤演化规律研究

1、循环载荷作用下岩石损伤演化规律研究【中文摘要】岩石作为一种非均质脆性材料在循环载荷作用下损伤破坏题目涉及到诸多工程领域。本文利用先进的MTS815岩石力学测试系统和12CHs SAMOS? System声发射测试系统对岩石在循环载荷作用下的损伤演化特性进行了较深进的研究。本文通过实验研究与理论分析相结合的方法,探讨了不同上限应力水平、不同下限应力水平、不同加载速率、不同含水量等不同实验条件下循环载荷作用时岩石的声发射特征,并利用岩石的声发射特征作为岩石损伤的宏观表现,分析了岩石在循环载荷作用下的损伤演化规律,建立了以声发射参数为损伤变量的岩石损伤演化方程,同时,在运用分形理论计算了循环载荷作用

2、下岩石声发射关联维数的基础上分析了岩石关联维数的变化规律。所取得的主要研究成果如下:(1)在深进分析单轴压缩作用时不同载荷条件下岩石声发射特征的基础上改进了基于岩石声发射参数的损伤演化方程;同时利用岩石声发射Kaiser及Felicity效应探讨了循环门槛值题目,并发现Kaiser效应上限应力值为相应峰值强度的70%左右;(2)在等幅循环作用下上限应力对声发射的影响起主导作用,决定着声发射变化的趋势;下限应力的影响主要在循环末期,每循环中进步了声发射产生的时间,即Felicity比值减小;加载速率对声发射的影响主要在声发射率上,速率加大使循环过程中的主裂纹形成、扩展速率增快,增大了声发射率,从

3、而加快了岩石破坏的速率;不同饱和度下的声发射结果表明,含水量越多,声发射率越低,声发射数少,破坏时开释的能量少;(3)不同加载速率和不同应力变化幅度条件下的等幅循环载荷实验结果表明,岩石的声发射规律也体现出了相应的不同发展模式。不同的模式预示着岩石不同的破坏速率,稳定型表明岩石在循环载荷过程中破坏进程缓慢,需要更长的时间;而突变型表明循环过程中破坏进程快速,岩石变形破坏的速率加快;建立了基于声发射参数的循环损伤演化模型;通过声发射定位技术分析了循环条件下声发射的时空演化特征,从时间和空间上研究了岩石的损伤演化规律;同时探讨了影响声发射定位的几个相关因素;(4)等幅循环载荷条件下声发射关联维数随

4、着循环比呈降低趋势,即是一个降维的过程,但受不同实验条件的影响,其降维方式有所差异。声发射维数的变化和表示累积损伤的声发射数有良好对应关系,维数的变化是由于累积损伤变化的结果,与损伤有很好的相关关系。声发射分形维数变化和裂纹发展状态具有一致性,维数明显变化则表明裂纹发展快速,维数变化稳定表明裂纹变化不大。);【Abstract】 As a kind of non-homogeneity & brittle materials, the damage failure of rock is a very important problem relating to many engineering

5、fields under cyclic load. In the *, studies on damage evolvement characteristics of rock have been presented with advanced rock mechanics test equipment named on MTS815 and 12CHs SAMOS(TM) system acoustic emission (AE) instrument under cyclic load.In this *, the acoustic emission rules have been stu

6、died using the methods of experiment research and theory analysis with different upper limited stress level, different lower limited stress level, different load rates and different saturation under cyclic load. Based on the theory that AE is the macroscopical behavior of damage, and is consistent w

7、ith the damage, the damage evolvement rules have been analyzed; At the same time, the damage evolvement equations have been established; At last, the AE correlation dimension have been calculated using fractal theory, and analyzed the changing rules of correlation dimension. The results could be sum

8、marized as follows:(1)AE characteristics of rock have been studied under different load conditions under uniaxial stress state, and the damage evolvement equation based on AE parameter has been improved; The cyclic stress threshold has been studied through the AE Kaiser effect & Felicity effect expe

9、riment, and the upper stress of Kaiser effect is the 70% of peak stress.(2) The upper stress is the most important factor to AE under cyclic load, which determined the changing tendency of AE; The lower stress advanced the time of AE in every cycle at the end of cyclic load, that is to say, the Feli

10、city ratio becomes smaller; Load rate affects the AE rate mostly, especially in the phase of main crack expanding, which improves the rate of main crack forming and expanding during the cyclic load, and reduces the time of failure; The AE results of different saturation experiment shows that the big

11、ger saturation, the lower AE rate, and the total counts become few, at the same time the lower energy releases at the failure.(3) There are different load rates and stress ranges in cyclic load, there are different AE changing modes; Different mode predicts the different failure rate of rock, that i

12、s to say, the type of stabilization needs more time of failure, and the type of mutationist needs little time of failure; The cyclic damage evolvement mode based on AE parameter has been established; The space-time evolvement characteristics have been analyzed through AE location, and damage evolvem

13、ent rule has been studied from time and space; At the same time several factors influencing the precision of AE location have been studied.(4) The correlation dimension shows the downward tendency with the cyclic ratio increasing under cyclic load, but there are some discrepancies under different ex

14、periment condition; The AE correlation dimension is according with the AE total counts which show the cumulate damage, and the correlation dimension which has the correlativity with the damage will change because of the cumulate damage under cyclic load. The downward tendency of correlation dimension shows that the crack of forming and expanding have the tendency from chaos to regularity; The AE