冲击载荷下岩石材料动态断裂韧性测试研究进展

岩石动态断裂韧性是岩石动力学的基本力学参数之一,也是评价岩石抵抗裂纹动态起裂和扩展性能的重要参数之一。随着采矿工程、岩土工程的不断发展,冲击动态载荷下岩石动态断裂韧性的研究也愈来愈为国内外岩土工程界所关注。综述了冲击载荷下岩石材料动态断裂韧性测试研究进展,主要介绍了冲击载荷下岩石动态断裂韧性测试技术研究成就及其优缺点,并就冲击载荷下岩石动态断裂韧性测试研究发展趋势给予展望。     

层板复合材料动态断裂韧性测试的SHPB技术研究

为测试层板复合材料的断裂韧性，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。该方法采用三点弯曲试样进行动态断裂试验，应用动态断裂韧性测试系统ANSYSED5．4确定动态应力强度因子的响应曲线，进而测试材料动态断裂韧性。对层板复合材料试验结果的分析表明，设计的测试装置有效，建立的测试方法是对层板复合材料断裂韧性测试的有益尝试，有较大的参考价值。     

冲击载荷作用下岩石材料模型实验验证

利用ANSYS/LS-DYNA有限元程序建立计算模型,模拟了岩石靶板在冲击载荷作用下的动态响应过程,给出了岩石靶板在不同冲击速度下其内部不同Lagrangian位置处的应力-时间响应曲线,数值模拟结果与实验结果吻合较好.通过对模拟结果和实验结果的对比分析可知,冲击载荷作用下纵向冲击压缩波和横向稀疏卸载波的双重作用是导致岩石靶板破坏的主要原因,这对进一步开展岩石材料动态力学性能研究提供了重要的指导.     

冲击载荷作用下岩石Ⅰ型裂纹动态断裂试验研究

以可调速落锤冲击试验机作为试验加载装置,采用数字散斑相关方法作为试验的观测手段,通过搭建高速数据采集系统,对岩石Ⅰ型裂纹在冲击载荷作用下的动态断裂进行试验研究。试验研究了冲击载荷作用下岩石Ⅰ型裂纹扩展过程位移场的演化特征;分析了岩石在冲击加载速度下裂纹扩展速度以及裂纹扩展距离随时间的变化规律;定量得到了岩石Ⅰ型裂纹动态断裂的裂纹张开角;同时开展了不同冲击加载速度下岩石Ⅰ型裂纹扩展速度的关系研究,研究结果表明,在试验所进行的中低速冲击加载情况下,裂纹扩展速度随着冲击速度的增加而增加,近似呈线性关系。     

压力容器钢及其焊接接头高速冲击韧性研究

在自行设计的高速冲击韧性测试系统上 ,采用预制疲劳裂纹的标准Charpy冲击试样 ,测试了常用压力容器钢I6MnR及其焊接接头的动态冲击韧性 ,研究了高加载速率条件下材料的断裂韧性特征 ,分析了加载速度、接头匹配性质和试验温度对动态冲击韧性的影响。研究结果表明 :焊缝金属对冲击加载速度最敏感 ,热影响区次之 ;焊接接头的匹配性质对冲击断裂韧性有较大的影响     

基于重整化方法的冲击载荷下岩石振动分析

旋转冲击钻井是当前钻进深井硬地层应用较多且效果显著的一种高效破岩技术。基于振动学理论,在考虑岩石重力的情况下,建立钻头冲击载荷下岩石振动响应的数学模型,采用重整化方法对其求解,利用MATLAB软件分析各参数对钻头高频冲击下岩石振动的影响,并进行了室内实验对理论分析结果进行了验证。结果显示:冲击载荷下岩石的运动为两个简谐振动的互扰振动;岩石的密度越小,刚度越小,冲击力越大,岩石的振动幅度越大,振动速度也越快;岩石存在一个固有频率,冲击载荷冲击频率越接近这个固有频率,岩石的振动越剧烈。当钻头高频振动频率和岩石固有频率相等时,岩石振动幅度和振动速度最大,即达到了共振。冲击载荷下岩石响应的分析对于揭示动载作用下岩石的破碎机理,指导冲击工具的设计具有重要意义。     

实心和空心滚子结构阻尼的动态分析

结构阻尼是结构动力分析的重要参数之一,运用有限元方法研究实心和空心滚子在冲击载荷作用下的动态响应,并用傅立叶变换处理自由衰减中不同起点的两段相同长度的数据,求得滚子的结构阻尼,分析了滚子在不同冲击载荷、结构参数和材料参数下的阻尼特性。通过对滚子本身结构阻尼特性的研究,为轴承的振动研究提供了理论基础。     

岩石爆破孔壁动态参数的理论探讨

岩石爆破工程中,孔壁近区动态参数是研究岩石与炸药能量关系的重要内容.孔壁爆炸载荷作用下的动态参数分析是爆破模拟实验方案设计和仪器选择的依据.本文通过岩石爆炸冲击波力学模型的建立与计算,分析了孔壁动态参量.     

预加载下岩石的动态力学性能研究

动态和静态载荷共同作用下的岩石力学特性是深部地下岩石工程的关键问题。设计了用于测试静态预加载下岩石动态力学性能的分离式霍普金森压杆系统,并详细介绍了具有预加载装置的分离式霍普金森压杆系统的原理、数据分析和应力波的传播过程。通过具有预加载装置的分离式霍普金森压杆系统研究了岩石在不同预拉伸应力下的拉伸强度。结果表明:动态拉伸强度和总拉伸强度随着加载率的增加而增加,同时,在相同加载率下,动态拉伸强度随着预拉伸载荷的增加而减小,而总拉伸应力与预拉伸载荷的大小无关。此外,对不同预加载条件下岩石的动态断裂韧度也进行了研究,实验结果说明岩石的动态断裂韧度和总断裂韧度随着加载率的增加而增加。在相同加载率下,动态断裂韧度随着预加载荷的增加而减小,而总断裂韧度随着加载率的增加而增加。     

预加载下岩石的动态力学性能研究

动态和静态载荷共同作用下的岩石力学特性是深部地下岩石工程的关键问题。设计了用于测试静态预加载下岩石动态力学性能的分离式霍普金森压杆系统,并详细介绍了具有预加载装置的分离式霍普金森压杆系统的原理、数据分析和应力波的传播过程。通过具有预加载装置的分离式霍普金森压杆系统研究了岩石在不同预拉伸应力下的拉伸强度。结果表明:动态拉伸强度和总拉伸强度随着加载率的增加而增加,同时,在相同加载率下,动态拉伸强度随着预拉伸载荷的增加而减小,而总拉伸应力与预拉伸载荷的大小无关。此外,对不同预加载条件下岩石的动态断裂韧度也进行了研究,实验结果说明岩石的动态断裂韧度和总断裂韧度随着加载率的增加而增加。在相同加载率下,动态断裂韧度随着预加载荷的增加而减小,而总断裂韧度随着加载率的增加而增加。     

Progress and development in the instrumented Charpy impact test

Toughness is the most important characteristics for structural component materials and has been evaluated widely by Charpy impact test. Charpy test has been presented firstly in 1901, and instrumentation to record load history during impact has been attempted since 1920's. Various methods to estimate quantitative fracture toughness values under dynamic loading condition have been presented. In the development of fracture mechanics, one of the authors has successfully developed the new dynamic fracture toughness testing and evaluation system using the instrumented Charpy impact test, which is called “CAI system”. This paper introduces history of instrumented Charpy impact test and CAI system. Moreover, instrumented impact testing method on brittle materials is also mentioned. Worldwide standard on dynamic fracture toughness evaluation by the instrumented impact testing is highly expected to be established.     

Determination of dynamic rock Mode-I fracture parameters using cracked chevron notched semi-circular bend specimen

Rock dynamic fractures are common in many geophysical processes and engineering applications. Characterization of rock dynamic fracture properties such as the initiation fracture toughness, the fracture energy, and the fracture velocity, is thus of great importance in rock mechanics. A novel method is proposed in this work to measure dynamic Mode-I rock fracture parameters using a cracked chevron notched semi-circular bend (CCNSCB) specimen loaded by a split Hopkinson pressure bar (SHPB) apparatus. A strain gauge is mounted on the sample surface near the chevron notch to detect the fracture onset, and a laser gap gauge (LGG) is used to monitor the crack surface opening distance (CSOD) during the dynamic test. With dynamic force balance achieved in the tests, the stable–unstable transition of the crack propagation crack is observed and the initiation fracture toughness is calculated from the dynamic peak load. The average dynamic fracture energy as well as the fracture propagation toughness are calculated based on the first law of thermodynamics. The measured dynamic fracture properties of Laurentian granite using CCNSCB method are consistent with those reported in the literature using other methods.     

Dynamic effects during instrumented impact testing

This paper presents a method to analyse dynamic effects in instrumented impact testing for fracture toughness determination. The notched specimen is replaced by a chain of nine lumped masses and the tup is connected to the impact point through a contact stiffness. A modal analysis of the mechanical system, i.e. specimen-loading machine, is achieved. In this study, it is attempted to understand the influence of the dynamic effects on the measured fracture load. Formally, two types of correction were pointed out through the presented model: calculation of effective fracture load and calculation of nominal stress or fracture toughness. The first correction is the most important.     

Experimental and numerical studies on dynamic crack growth in layered slate rock under wedge impact loads: part I—plane strain problem

The experimental and numerical investigations presented in this paper were carried out to determine the splitting forces and crack propagation scenarios of naturally bedded layered slate rock. Splitting loads were determined by impact splitting of regular‐sized slate blocks under plane strain test loading conditions, using a hydraulic actuator with a wedge‐shaped indenter. The mechanical properties of slate blocks required for numerical analyses were obtained from detailed experimental testing. The velocity of dynamic crack propagation in slate blocks under indenting wedge impact loading was determined using a series of strain gauge sensors. Numerical studies were carried out using ABAQUS, a general purpose, finite element analysis (FEA) program. Mode I dynamic crack propagation was simulated numerically by the gradual releasing of the restrained node on the symmetric plane of the specimens. Mode I stress intensity factors were computed for different crack lengths and the results were compared with the plane strain material fracture toughness obtained from earlier experiments/FEA. Very good agreement was obtained between analysis results and the measured fracture toughness value of slate, for the applied impact splitting load. Using the equation derived from a parametric study, of results obtained from the numerical analysis of different sizes of slate blocks, the maximum theoretical impact splitting force was determined using the plane strain fracture toughness value obtained from FEA. The difference between the loads obtained from the experimental studies and the derived empirical equation, varied between + 4.96% and −32.34%.     

霍普金森杆冲击压缩单裂纹圆孔板的岩石动态断裂韧度试验方法

对压缩单裂纹圆孔板(single cleavage drilled compression--SCDC)砂岩试样,利用分离式霍普金森压杆(SHPB)冲击加载,进行了岩石张开型(I型)动态断裂实验。分别采用2种方法确定砂岩的动态断裂韧度,第1种方法是实验-数值法:由SHPB弹性杆上应变片获得作用在试件上的加载力,然后输入有限元分析程序求得试样裂尖动态应力强度因子,对应于裂尖起裂时刻的动态应力强度因子即为材料动态断裂韧度值;第2种方法是准静态法:将载荷峰值代入静态应力强度因子公式确定动态断裂韧度。2种方法的结果差异较大,对无量纲裂纹长度a/R= 0.64(A组)试样,准静态方法确定的断裂韧度值要比实验-数值法确定的断裂韧度值平均要小35%~62%;对无量纲裂纹长度a/R=1.61(B组)试样,准静态方法的计算结果比实验-数值法的计算结果平均要小72%~83%。从原理上讲,实验-数值法比准静态法能更合理地测定岩石的动态断裂韧度。     

Results from investigations with an Instrumented Impact Machine on a molybdenum base alloy,nickel base alloys,and incoloy 800

Experiments were performed on the molybdenum base alloy TZM, the nickel base alloys Nimocast 713 LC, Inconel 625, Nimonic 86, Hastelloy S, and the iron base alloy Incoloy 800 with an instrumented impact machine. The results are discussed in terms of absorbed impact energies and dynamic fracture toughness. In all cases the agreement between the energy determined by the dial reading and the energy determined by the integration of the load vs. load point displacement diagram was excellent. A procedure for the determination of the dynamic fracture toughness for load vs. load point displacement diagrams exhibiting high oscillations using an averaged curve is proposed. Using this procedure a pronounced influence of the experiments with tup and chisel (5.0 m/s and 0.1 m/s respectively) on the dynamic fracture toughness is not detectable. Using half the drop height, i.e. halving the total energy, lowers the dynamic fracture toughness values for these types of alloys. Low absorbed impact energies are often combined with high fracture toughness values. In these cases there is no or only a small reserve in deformation and/or stable crack growth.     

岩石Ⅰ型断裂韧度测试方法研究进展

岩石断裂韧度测试方法研究是准确获取岩石断裂韧度值的重要前提, 也是进行岩石断裂力学理论和应用探索的重要途径. 本文综述了国内外岩石Ⅰ型断裂韧度测试方法, 着重介绍了美国材料与测试协会 (ASTM) 和国际岩石力学协会 (ISRM) 提出的建议测试方法及其研究进展; 对比了不同测试方法获得的岩石Ⅰ型断裂韧度值之间的差异, 并分析了产生这种差异的原因; 指出了岩石断裂韧度测试方法中有待于进一步研究的问题.     

木材断裂解离分形特征与分形断裂力学模型研究

目的 以椴木为研究对象,研究冲击载荷作用下椴木试件的断裂解离形貌特征和断裂力学特性,建立适用于木材原料断裂解离的分形断裂力学模型,并对其断裂解离力学行为进行描述。方法 对椴木试件进行冲击加载试验,分析试件断口的形貌特征和断裂力学特性,构建适用于木材原料断裂解离的分形断裂力学模型。结果 椴木试件横向冲击断裂断口裂纹形状和断口形貌特征比纵向冲击复杂,横、纵向冲击断裂断口均具有分形特征;椴木试件纵向冲击断裂韧性均值是横向冲击断裂韧性均值的1.112倍,椴木试件横、纵向冲击断口的分形维数均值分别为2.063 5和2.075 1,椴木试件横、纵向冲击韧性与其断口分形维数之间存在线性正相关关系,拟合优度分别为0.778 7和0.812 2;构建的木材原料断裂解离临界解离应力和断裂韧性的分形断裂力学模型也适用于脆性材料。结论 在木材原料冲击断裂解离时,木材原料初始裂纹长度越短,断裂解离断口越粗糙复杂,木材原料断裂解离所需要的能量越大;当裂纹沿着与冲击加载力方向垂直成大约1.055rad方向扩展时所需的能量最小,木材原料最易沿该方向进行断裂解离。     

Dynamic fracture toughness measurements in composites by instrumented Charpy testing: influence of aging

The dynamic behavior of three different fiber fabric composite laminates was studied by testing notched specimens in an instrumented Charpy machine. The registered impact force and displacement at the specimen hammer contact point were used to evaluate Mode-I fracture energy and dynamic fracture toughness. The changes in fracture toughness due to impact velocity, crack size and stacking sequence of the specimen were investigated with different degrees of aging conditions. Aging was found to significantly affect the dynamic fracture toughness, but had less effect on the static fracture toughness.