基于颗粒流的直切槽式巴西圆盘裂纹扩展分析

摘要

利用颗粒流程序(PFC)对直切槽式圆盘试样进行巴西试验模拟,分析了不同的裂隙倾角和裂隙长度对直切槽式圆盘试样裂纹扩展规律的影响.根据起裂位置的不同,主裂纹可分为从裂隙尖端萌生的Ⅰ型主裂纹和从裂隙尖端一定距离处萌生的Ⅱ型主裂纹;次生裂纹可分为从加载点附近萌生的Ⅰ型次生裂纹和从远离加载点的一侧萌生的Ⅱ型次生裂纹.当裂隙长度保持不变而增大裂隙倾角时,主裂纹从Ⅰ型过渡为Ⅱ型,次生裂纹则从Ⅰ型转变为Ⅰ型和Ⅱ型共存,最后又变为Ⅰ型.当裂隙角度保持不变而增大裂隙长度时,主裂纹保持不变,次生裂纹则由Ⅰ型逐渐过渡为Ⅰ型和Ⅱ型共存.另外,当径向应力达到峰值应力之后,试样内会有大量的微裂纹萌生、扩展,造成了圆盘试样的破坏.从力链和能量角度来看,巴西圆盘试样的破裂过程是试样内部拉应力集中产生的颗粒间黏结破裂以及应变能释放的过程.%The Brazilian tests on Cracked Straight Through Brazilian Disc(CSTBD) specimens are simulated using Particle Flow Code(PFC).Then,the effects of inclination angle and length of the pre-existing crack on the crack evolution behavior are analyzed.The results indicate that depending on the crack initiation positions,two types of main crack exist,including mode Ⅰ main crack and mode Ⅱ main crack.Mode Ⅰ main crack is initiated at the tip of the pre-existing crack.And mode Ⅱ main crack is initiated at a distance from the tip of the pre-existing crack.There also exist two types of secondary crack,including mode Ⅰ secondary crack and mode Ⅱ secondary crack.Mode Ⅰ secondary crack is initiated near the load point.And mode Ⅱ secondary crack is initiated at a distance from the load point.When the crack length keeps constant and inclination angle increases,main crack would change from mode Ⅰ to mode Ⅱ and secondary crack would change from mode Ⅰ to mixed-mode(Ⅰ + Ⅱ),and finally transform into mode Ⅰ.When the inclination angle keep constant and crack length increases,main crack keep steady and secondary crack would change from mode Ⅰ to mixed-mode (Ⅰ + Ⅱ).After the radial stress exceeds the peak stress of the specimen,a large number of micro cracks would develop and propagate,which lead to the broke of the Brazil disc.The failure process of Brazil disc is mainly resulted from the ruptures of inter-particle bonding caused by tensile stress concentration and internal strain energy release.