Dynamic rock tests using split Hopkinson (Kolsky) bar system e A review

Dynamic properties of rocks are important in a variety of rock mechanics and rock engineering problems. Due to the transient nature of the loading, dynamic tests of rock materials are very different fr...     

Experimental and numerical investigation on the mechanical responses and cracking mechanism of 3D confined single-flawed rocks under dynamic loading

Accurately characterizing the mechanical responses and cracking mechanism of three-dimensional confined fractured rocks under coupled static-dynamic loading is ...     

A waveform modification method for testing dynamic properties of rock under high temperature

In this study,a waveform modification method was proposed using a self-designed heating device combined with the split Hopkinson pressure bar(SHPB) technique for determination of dynamic behaviors of rock at high temperature.Firstly,the temperature gradient distribution on the incident bar was measured according to the variation of elastic modulus of the bar with temperature,and the relationship between the longitudinal wave velocity and temperature of the bar was obtained based on onedimensional stress wave theory.The incident bar with a temperature gradient was divided into a series of microelements,and then the transmission coefficient of the whole incident bar was obtained.Finally,the stress wave was modified by the transmission coefficient from 25℃ to 600℃.This method was used to study the dynamic properties of rock at high temperature,which not only preserves a classical SHPB device,but also effectively ensures the accuracy of the experimental results.A dynamic Brazilian disc experiment was carried out to explore the influences of loading rate and temperature on dynamic tensile strength of sandstone at high temperature using the proposed waveform modification method.     

Dynamic fragmentation of microwave irradiated rock

The microwave-assisted rock fragmentation has been proven to be a promising approach in reducing cutting tools wear and improving efficiency in rock crushing and excavation.Thus,understanding the influence of damage induced by microwave irradiation on rock fragmentation is necessary.In this context,cylindrical Fangshan granite(FG)specimens were exposed to microwave irradiation at a power of 6 kW for different durations up to 4.5 min.The damages of the specimens induced by irradiation were quantified by using both X-ray micro-CT scanning and ultrasonic wave measurement.The CT value and Pwave velocity decreased with increase of irradiation duration.The irradiated specimens were then tested using a split Hopkinson pressure bar(SHPB)system to simulate rock fragmentation.A momentum-trap technique was utilized to ensure single-pulse loading on the specimen in SHPB tests,enabling valid fragment size distribution(FSD)analysis.The dependence of dynamic uniaxial compressive strength(UCS)on the irradiation duration and loading rate was revealed.The dynamic UCS increased with increase of loading rate while decreased with increase of irradiation duration.Using the sieve analysis,three fragmentation types were proposed based on FSD,which were dictated by both loading rate and irradiation duration.In addition,an average fragment size was proposed to quantify FSD.The results showed that the average fragment size decreased with increase of loading rate.A loading rate range was identified,where a dramatic reduction of the average fragment size occurred.The dependence of fragmentation on the irradiation duration and loading rate was also discussed.     

单轴循环冲击下岩石的动力学特性及其损伤模型研究

利用改进的大直径SHPB试验装置,对花岗岩试件进行单轴循环冲击压缩试验,分析花岗岩在循环冲击载荷下的力学特性及能量吸收规律。通过基于Weibull分布的动态统计损伤模型计算岩石的累积损伤,结合试验曲线分析岩石累积损伤的演化规律。研究结果表明：随着冲击载荷循环作用次数的增加,变形模量变小,试件的屈服应变增大,峰值应力呈降低趋势。岩石的累积比能量吸收值随着冲击次数的增加而增大,且试件破坏前其值增加缓慢,试件破坏时其值急剧增大。基于Weibull分布的动态损伤本构模型的计算曲线与试验曲线具有较好的一致性,该模型能反映岩石的强度与应变、应变率的关系。累积损伤随着循环冲击次数的增加而增大,其增加速率由小变大,试件破坏前累积损伤的增加较为平缓,其主要增量由最后一次冲击破坏产生。     

冲击荷载作用下岩石动态力学特性及破裂特征研究

采用分离式霍布金森压杆(split Hopkinson pressure bar,SHPB)试验系统对灰岩,白云岩和砂岩3类岩石进行动态冲击试验,得到岩石的动强度因子,耗散能密度及破碎尺寸与应变率的变化关系。在此基础上结合晶体离散元方法,采用高分辨率扫描和图像处理技术建立了晶体尺度试样模型,研究岩石材料高应变率力学特性和损伤特征。通过与室内SHPB试验对比,验证数值模拟的准确性。结果表明:岩石材料的动态屈服强度具有明显的率相关性,但弹性模量没有随应变率的增加而显著增加;在高应变率下,材料的动强度因子与应变率更符合Ханукаев公式;随着应变率的增加,岩石的破坏形态出现完整型→劈裂破坏→粉碎性破坏转化,这是由细观裂纹的激活数目以及裂纹间的相互作用关系所决定的。裂纹密度的变化和扩展路径的选择是材料动断裂机制,其宏观表现为材料的率效应和破碎成形。     

Dynamic notched semi-circle bend(NSCB) method for measuring fracture properties of rocks:Fundamentals and applications

Rocks are increasingly used in extreme environments characterised by high loading rates and high confining pressures.Thus the fracture properties of rocks under dynamic loading and confinements are critical in various rock mechanics and rock engineering problems.Due to the transient nature of dynamic loading,the dynamic fracture tests of rocks are much more challenging than their static counterparts.Understanding the dynamic fracture behaviour of geomaterials relies significantly on suitable and reliable dynamic fracture testing methods.One of such methods is the notched semi-circle bend(NSCB) test combined with the advanced split Hopkinson pressure bar(SHPB) system,which has been recommended by the International Society for Rock Mechanics and Rock Engineering(ISRM) as the standard method for the determination of dynamic fracture toughness.The dynamic NSCB-SHPB method can provide detailed insights into dynamic fracture properties including initiation fracture toughness,fracture energy,propagation fracture toughness and fracture velocity.This review aims to fully describe the detailed principles and state-of-the-art applications of dynamic NSCB-SHPB techniques.The history and principles of dynamic NSCB-SHPB tests for rocks are outlined,and then the applications of dynanic NSCB-SHPB method(including the measurements of initiation and propagation fracture toughnesses and the limiting fracture velocity,the size effect and the digital image correlation(DIC) experiments) are discussed.Further,other applications of dynamic NSCB-SHPB techniques(i.e.the thermal,moisture and anisotropy effects on the dynamic fracture properties of geomaterials,and dynamic fracture toughness of geomaterials under pre-loading and hydrostatic pressures) are presented.     

基于能量耗散原理的盐岩动力特性及破坏特征分析

 为研究盐岩的动力特性和破坏特征,利用带围压的分离式Hopkinson压杆(SHPB)试验装置,对盐岩进行不同围压(5,15和25 MPa)下的冲击试验,并基于能量耗散原理来研究盐岩动态力学性能以及破坏特征,分析整个试验过程中的能量传递与转化,探究围压和输入能量对试件吸能及破坏的影响。研究结果表明：在同一围压下,随着入射能的增加,盐岩硬化效应越明显,表现为能量反射率增高而透射能和吸收能降低;在相同或相近的入射能下,随着围压的升高盐岩的流塑性变得越明显,但在动力荷载下盐岩由流塑性向脆性转变,最后发生脆性破坏;随着吸收能的增加,盐岩的峰值应力因围压不同而表现出不同的变化趋势,低围压时,吸收能越大,峰值应力越高,而高围压时,吸收能越大,峰值应力却越小;在有围压状态下,盐岩的冲击破坏形态与其他的脆性岩石相似,但在破坏机制上存在很大差异。     

层状盐岩及泥岩夹层动态力学特性对比试验研究

为对比研究盐岩和泥岩夹层的动态力学特性,以应城盐矿的盐岩及泥岩夹层为研究对象,利用带围压的分离式Hopkinson(SHPB)试验装置,进行不同围压(5,15,25 MPa)下的动载冲击试验研究,分析盐岩和泥岩夹层动力特性的围压效应与应变率效应,基于联合的热活化与黏性机制相互竞争的材料强度–应变率依赖的简化模型拟合出盐岩及泥岩夹层的动力强度公式。研究结果表明:(1)盐岩和泥岩夹层均属于率敏感性材料,其峰值应力和延性随应变率的增大而增加,但低围压(如5 MPa)作用下应变率强化效应较高围压(如25 MPa)作用下更加显著;(2)盐岩和泥岩夹层在动力荷载条件下的力学行为的围压效应没有静力荷载条件下明显,动力放大系数(DIF)随着围压增加而减小,泥岩夹层的围压效应要小于盐岩的围压效应;(3)动力强度计算公式拟合效果较好,盐岩平均相对误差为2.51%,泥岩夹层平均相对误差为6.58%。     

Strength and deformation characteristics of irregular columnar jointed rock mass: A combined experimental and theoretical study

The irregularity of jointed network poses a challenge to the determination of field mechanical parameters of columnar jointed rock mass (CJRM), and a reasonable prediction of deformation and strength characteristics of CJRM is important for engineering construction. The Voronoi diagram and three-dimensional printing technology were used to make an irregular columnar jointed mold, and the irregular CJRM (ICJRM) specimens with different dip directions and dip angles were prepared. Uniaxial compression tests were performed, and the anisotropic strength and deformation characteristics of ICJRM were described. The failure modes and mechanisms were revealed in accordance with the final appearances of the ICJRM specimens. Based on the model test results, the empirical correlations for determining the field deformation and strength parameters of CJRM were derived using the dip angle and modified joint factor. The proposed empirical equations were used in the Baihetan Project, and the calculated mechanical parameters were compared with the field test results and those obtained from the tunneling quality index method. Results showed that the deformation parameters determined by the two proposed methods are all consistent with the field test results, and these two methods can also estimate the strength parameters effectively.     

砂岩动静态拉伸力学性能试验与对比分析

通过对皖北矿区3个煤矿砂岩岩样加工成厚径比为0.5的圆盘试件,利用变截面分离式Hopkinson压杆(SHPB)试验装置,采用不同加载冲击气压驱动撞击杆高速运动,对圆盘试件实施不同加载速率下的动态劈裂拉伸试验,得到了3种砂岩试件的动态拉伸应力和应变率等力学参数,并与静态劈裂拉伸试验结果进行对比,分析了砂岩圆盘试件动静态劈裂破坏形态、动态拉伸应力与加载速率相关性规律;得到了试验冲击气压范围内砂岩动态拉伸应力强度与平均应变率之间近似为乘幂函数关系,比其静态拉伸应力强度提高2～3倍。对砂岩动静态拉伸力学性能研究做了一些有益的探索。     

低温热力耦合下岩体椭圆孔(裂)隙中冻胀力与冻胀开裂特征研究

寒区岩体工程含水孔(裂)隙中低温水冰相变会产生冻胀力与温度应力,岩体冻融损伤与断裂是由温度应力和孔(裂)隙中的冻胀力共同作用的结果。考虑温度应力对椭圆孔(裂)隙形变的影响,推导了椭圆孔(裂)隙中的冻胀力解析方程;基于最大拉应力准则,得到了低温热力耦合下椭圆孔(裂)隙周围最大拉应力与冻胀开裂角,建立了椭圆孔可简化为椭圆裂隙进行冻胀计算的临界条件;最后采用改进的等效热膨胀系数方法对隧道单裂隙围岩冻胀力与裂隙尖端应力场进行了数值分析。研究结果表明:(1)椭圆孔中的最大冻胀力与岩石的热膨胀性、裂隙倾角和裂隙长短轴比χ等因素有关;(2)长短轴比χ≥10的扁平椭圆孔可简化为裂隙进行计算分析,此时冻胀基本发生在裂隙尖端且尖端拉应力集中明显;(3)改进的等效热膨胀系数方法可以很好的模拟裂隙中的冻胀力与裂尖应力场。