岩石动态断裂韧度温度相关性的实验研究

利用CCCD—SHPB（CentralCrackedCircularDisk—SplitHopkinsonPressureBar）试验系统对花岗岩试件实施同一加载速率、不同温度下的纯I加载试验,进而研究环境温度对岩石类材料动态断裂性能的影响。实验过程中控制加载脉冲,使得测试试件的加载速率基本一致,测得不同温度下试件两端平均栽荷P随时间的变化关系,将最大P-max心裂纹圆盘应力强度因子墨公式,获得不同温度下中心裂纹巴西圆盘岩石试件的动态断裂韧度蜀。。测试结果表明,温度处于10—100℃时,花岗岩动态断裂韧度K-Id温度的升高逐步下降,近似呈线性关系。     

岩石Ⅰ型断裂韧度测试技术和理论研究综述

岩石断裂韧度是用来表示岩石抵抗裂纹起裂和扩展能力的参数,它的测试比一般的强度测试存在更大的困难.介绍了Ⅰ型静态断裂韧度测试技术以及研究现状与进展,并提出一些关于测试方法的建议.指出圆盘试件在进行岩石断裂韧度的测试时,具有体积较小,加载方便,以及可以进一步实现Ⅰ型和Ⅱ型复合型加载的优点,不断发展和完善采用圆盘试件进行岩石断裂韧度的测试技术不仅是一项有意义而且十分迫切的工作.     

岩石动态断裂性能的Ⅱ型能量型尺寸效应与应变率效应研究

目前对Ⅱ型能量型尺寸效应与应变率效应的物理本质还没有解释清楚.利用霍普金森压杆系统(SHPB)对一种带预制裂纹的半巴西圆盘岩石试件进行加载,对比不同试件尺寸和不同应变率情况下试件的起裂韧度,探究岩石材料动态Ⅱ型尺寸效应和应变率效应的规律.结果表明:岩石起始断裂韧度随着加载速度的增大,近似呈线性增大,表现出明显的应变率效应;在相同的加载速度情况下,岩石的起始断裂韧度随着试件的尺寸增大而增加,且岩石断裂韧度的尺寸效应会随着应变率的增加而增强,即更高的加载速度会使得Ⅱ型能量型尺寸效应更明显.     

利用实验和数值结合的方法测量镁合金AZ91动态断裂韧性

利用Hopkinson压杆实现镁合金AZ91三点弯曲断裂试件的动态加载,基于傅里叶变换和VC++面向对象的程序设计方法修正了加载应力波在传播过程中的弥散效应,同时扣除了附加加载杆楔形头惯性效应对加载波的影响。利用ANSYS/LS-DYNA有限元软件对三点弯曲试样在冲击载荷下的动态响应进行了分析,采用虚拟裂纹闭合技术求得动态应力强度因子时程曲线,依据监裂应变计测试信号,换算起裂时间,确定对应于动态应力强度因子时程曲线的值,即为镁合金AZ91的动态断裂韧性。本文提供的实验和有限元数值计算相结合获得镁合金断裂韧性的方法为镁合金构件抗冲击设计和动态载荷作用下结构的安全评定提供依据,也拓宽了Hopkinson压杆实验技术在测试材料动态断裂韧性方面的应用范围。     

复合型加载条件下扁平巴西圆盘应力强度因子计算方法

复合型裂纹的研究具有重要的工程实用价值。使用解析分析与有限元数值分析相结合的方法,对复合型加载条件下扁平巴西圆盘试件的应力强度因子进行了系统的分析。计算结果表明:在一定载荷分布角范围内,可使用分布载荷作用下巴西圆盘应力强度因子的公式去计算扁平巴西圆盘试件的应力强度因子;在断裂力学中圣维南原理依然成立。根据计算结果,推荐在扁平巴西圆盘断裂实验中使用载荷分布角为7.25°的扁平巴西圆盘试件。     

基于ABAQUS二次开发的巴西圆盘断裂机理

针对含中心裂纹的巴西圆盘开裂模型利用ABAQUS进行了参数化二次开发,基于扩展有限元法和最大周向应力准则对试件裂纹扩展进行数值模拟并验证,研究了围压对裂纹扩展以及裂纹尖端应力强度因子和T应力的影响.研究结果表明,试件在预制裂纹尖端发生起裂并沿最大周向应力方向扩展.随着裂纹倾角增大,Ⅰ型应力强度因子逐渐减小,Ⅱ型应力强度因子呈现先增大后减小的趋势,T应力逐渐增大.随着围压数值的升高,试件的断裂韧度增大,T应力增大,而Ⅰ型和Ⅱ型应力强度因子几乎不受影响.     

岩石材料动态断裂韧性的实验研究

为了研究岩石类材料的动态力学性能及动态破坏机理,防止出现岩石爆裂造成灾难性破坏,根据中心裂纹圆盘试件断裂韧性测试方法和分离式霍普金森压杆的基本原理,在SHPB装置上测试了花岗岩的动态断裂韧性。对测试结果按照SHPB基本原理进行处理,以试件两端平均载荷带入准静态公式得到动态断裂韧性。处理结果表明,用试件两端平均载荷获得岩石动态断裂韧性的实验方法有效的;花岗岩的动态断裂韧性具有加载速率相关性,随着加载速率的增加断裂韧性增大。     

PMMA断裂韧度尺寸相关性的实验研究

为了研究断裂韧度的尺寸相关性,采用中心裂纹圆盘试件,在岛津材料试验机上对有机玻璃(PMMA)纯Ⅰ型、纯Ⅱ型准静态加载条件下的断裂行为进行了实验研究。结果表明,PMMA的断裂韧度与试件的裂纹相对长度α相关,且在试验尺寸范围内I型断裂韧度KIc和Ⅱ型断裂韧度KⅡc均随α增加而降低;KIc受α的影响相对较大,而KⅡc受α的影响相对较小。PMMA的Ⅱ型断裂韧度KⅡc小于I型断裂韧度KIc。     

试件几何尺寸和杆材对CCCD-SHPB试验系统 测试结果影响的数值分析

为了分析CCCD-SHPB动态断裂试验系统试验结果的有效性,采用3维动态有限元方法分析了试件几何尺寸和入射杆、透射杆材料对实验结果的影响。分析结果表明,试件直径对CCCDSHPB动态断裂试验系统的试验结果有较大影响,而入射杆和透射杆的波阻抗与试件的波阻抗是否匹配会影响试验结果的精度,但在一定尺寸范围内,试件厚度对试验结果影响较小。进一步计算结果表明,在动态加载的初期阶段,由于试件两边载荷不平衡,导致CCCD-SHPB动态断裂试验系统中存在与试件尺寸相关的特征时间ΔT,且ΔT近似等于应力波在试件中来回往返两次的时间;动态断裂试验时,试件从加载至断裂的时间应大于特征时间ΔT,否则试验结果不可靠。     

基于NSCB石灰岩试样的加载速率和尺寸效应对其断裂韧度的影响研究

为研究试样不同尺寸和加载速率对岩石Ⅰ型断裂韧度试验值的影响,采用石灰岩制作圆盘直径30,50,75,100,150 mm 5种几何相似的中心直裂纹半圆盘试样(notched semi-circular bend,NSCB),在RMT-150B岩石力学试验系统上对NSCB试样进行5种加载速率(0.002,0.02,0.2...     

用Hopkinson压杆技术测试材料动态断裂韧性的方法研究

对传统的Ｈｏｐｋｉｎｓｏｎ压杆测试系统进行了改进,建立了应力波载荷作用下材料动态断裂韧性的测试方法,该方法采用３点弯曲试样进行动态断裂试验,应用试验－－数值法确定动态应力强度因子的响应曲线,进而测试材料的动态断裂韧性。４０Ｃｒ材料的试验结果表明,本文设计的测试装置是有效的,建立的测试方法是可行的。     

冲击载荷下材料动态断裂参数的有限元计算

材料在冲击载荷下的行为不同于静态载荷作用下的行为。然而,由于动态断裂问题的复杂性,即使象三点弯曲试样,也还没有获得裂纹尖端动态应力强度因子的解析表达式。为了满足理论分析和实验工作的需要,采用LS-DYNA有限元软件,对三点弯曲试样在冲击载荷作用下(包括正弦、线性和不规则载荷历程)的动态过程进行了有限元分析,获得了裂纹尖端的动态应力应变场和裂纹尖端区域节点力和位移与时间的关系曲线。基于虚拟裂纹闭合技术(VCCT),提出了在冲击载荷作用下裂纹结构能量释放率和动态应力强度因子的计算方法,得到了不同冲击载荷下三点弯曲试样的能量释放率GI和动态应力强度因子KId与时间的关系曲线。结果表明:该方法得到的有限元计算结果与实验吻合较好,且具有较高精度,文中提出的方法可用于动态断裂参数的计算。     

Mode II fracture analysis of double edge cracked circular disk subjected to different diametral compression

A detailed analysis of modeⅡstress intensity factors(SIFs) for the double edge cracked Brazilian disk subjected to different diametral compression is presented using a weight function method. The mode Ⅱ SIFs at crack tips can be obtained by simply calculating an integral of the product of mode Ⅱ weight function and the shear stress on the prospective crack faces of uncracked disk loaded by a diametral compression. A semi-analytical formula for the calculation of normalized mode Ⅱ SIF, fⅡ , is derived for different crack lengths (from 0.1 to 0.7) and inclination angles (from 10^。 to 75^。) with respect to loading direction. Comparison between the obtained results and finite element method solutions shows that the weight function method is of high precision. Combined with the authors‘ previous work on modeⅠfracture analysis, the new specimen geometry can be used to study fracture through any combination of mode Ⅰ and mode Ⅱ loading by a simple alignment of the crack relative to the diameter of compression loading, and to obtain pure mode Ⅱ crack extension. Another advantage of this specimen geometry is that it is available directly from rock core and is also easy to fabricate.     

Tests and simulation analysis on fracture performance of concrete

To obtain the fracture parameters of concrete, fracture tests were conducted with three-point bending beam method aiming at 30 concrete beams with different sizes and different intensity. The concrete specimen with prefabricated crack to determine the fracture parameters of concrete were conducted and the fracture performance of the specimen was analyzed. The test results show that, initial fracture toughness is unrelated to the size of specimens; while unstable fracture toughness is related to the size of specimens. As for specimens of bastard size, when concrete intensity is relatively low, unstable fracture toughness increases along with the increase of intensity; when concrete intensity is relatively high, unstable fracture toughness will decrease; when concrete intensity increases continuously, unstable fracture toughness will further increase somewhat. As for specimens of standard size, unstable fracture toughness will increase along with the increase of intensity. Aiming at concrete beam specimens, we conducted two-dimensional non-linear finite element analysis, obtained the stress intensity factor, and carried out contrastive analysis with the experimental results.     

Dynamic Mode Ⅱ fracture behavior of rocks under hydrostatic pressure using the short core in compression(SCC) method

The shear failure of rocks under both a static triaxial stress and a dynamic disturbance is common in deep underground engineering and it is therefore essential for the design of underground engineering to quantitively estimate the dynamic Mode Ⅱ fracture toughness K_(ⅡC)of rocks under a triaxial stress state.However, the method for determining the dynamic K_(ⅡC)of rocks under a triaxial stress has not been developed yet. With an optimal sample preparation, the short core in compression(SCC) method was designed and verified in this study to measure the dynamic K_(ⅡC)of Fangshan marble(FM) subjected to different hydrostatic pressures through a triaxial dynamic testing system. The formula for calculating the dynamic K_(ⅡC)of the rock SCC specimen under hydrostatic pressures was obtained by using the finite element method in combination with secondary cracks. The experimental results indicate that the failure mode of the rock SCC specimen under a hydrostatic pressure is the shear fracture and the K_(ⅡC)of FM increases as the loading rate. In addition, at a given loading rate the dynamic rock K_(ⅡC)is barely affected by hydrostatic pressures. Another important observation is that the dynamic fracture energy of FM enhances with loading rates and hydrostatic pressures.     

梯度非均匀有限板中裂纹动态响应的有限元分析

为了研究梯度非均匀有限板中裂纹动态响应问题,用波动有限元的方法研究了梯度非均匀板中裂纹在冲击载荷作用下的动态响应.通过对裂缝宽度与到裂端距离插值的方法求裂尖端处的动态应力强度因子(DSIFs),对指数衰减脉冲作用下弹性模量按单向线性变化的梯度非均匀有限裂纹板进行了数值计算.结果显示:无论板材料梯度参数及裂纹长度如何变化,裂尖处动态应力强度因子时程均呈起始快速上升转而缓慢下降;无论在什么时刻,裂尖处动态应力强度因子随裂纹的长度减小而减小,随板材料的功能梯度参数增大而减小.     

Dynamic fracture behavior of rock under impact load using the caustics method

We studied the dynamic fracture mechanical behavior of rock under different impact rates. The fracture experiment was a three-point bending beam subjected to different impact loads monitored using the reflected caustics method. The mechanical parameters for fracture of the three-point bending beam specimen under impact load are analyzed. The mechanism of crack propagation is discussed. Experimental results show that the dynamic stress intensity factor increases before crack initiation. When the dynamic stress intensity factor reaches its maximum value the crack starts to develop. After crack initiation the dynamic stress intensity factor decreases rapidly and oscillates. As the impact rate increases the cracks initiate earlier, the maximum value of crack growth velocity becomes smaller and the values of dynamic stress intensity factor also vary less during crack propagation. The results provide a theoretical basis for the study of rock dynamic fracture.