被动围压条件下岩石材料冲击压缩试验研究

为研究煤矿岩石材料被动围压条件下动态力学性能和变形破坏规律,利用Ø50mm变截面分离式Hopkinson压杆(SHPB)试验装置,对45#钢质套筒环向约束状态下煤矿岩石试件进行了不同加载速率冲击压缩试验。试验结果表明：被动围压条件下SHPB试验中,岩石试件的材料延性和抗破坏能力均得到增强,试件轴向应力是采用同种加载条件无围压SHPB试验时的1.2倍,破坏应变比无围压SHPB试验提高2～3倍,且径向应力随轴向应变增大总体呈上升趋势,试件破坏为压剪破坏模式,与无围压SHPB试验有所不同。     

Further investigation on the dynamic compressive strength enhancement of concrete-like materials based on split Hopkinson pressure bar tests. Part I: Experiments

Effects of the inertia-induced radial confinement on the dynamic increase factor (DIF) of a mortar specimen are investigated in split Hopkinson pressure bar (SHPB) tests. It is shown that axial strain acceleration is unavoidable in SHPB tests on brittle samples at high strain-rates although it can be reduced by the application of a wave shaper. By introducing proper measures of the strain-rate and axial strain acceleration, their correlations are established. In order to demonstrate the influence of inertia-induced confinement on the dynamic compressive strength of concrete-like materials, tubular mortar specimens are used to reduce the inertia-induced radial confinement in SHPB tests. It is shown that the DIF measured by SHPB tests on tubular specimens is lower than the DIF measured by SHPB tests on solid specimens. This paper offers experimental support for a previous publication [Li QM, Meng H. About the dynamic strength enhancement of concrete-like materials in a split Hopkinson pressure bar test. Int J Solids Struct 2003; 40:343–360.], which claimed that inertia-induced radial confinement makes a large contribution to the dynamic compressive strength enhancement of concrete-like materials when the strain-rate is greater than a critical transition strain-rate between 10¹ and 10² s⁻¹. It is concluded that DIF formulae for concrete-like materials measured by split Hopkinson pressure bar tests need to be corrected if they are going to be used as the unconfined uniaxial compressive strength in the design and numerical modelling of structures made from concrete-like materials to resist impact and blast loads.     

Further investigation on the dynamic compressive strength enhancement of concrete-like materials based on split Hopkinson pressure bar tests. Part II: Numerical simulations

Split Hopkinson pressure bar (SHPB) tests have been used widely to measure the dynamic compressive strength of concrete-like materials at high strain-rates between 10¹ and 10³ s⁻¹. It has been shown in companion paper (Zhang M, Wu HJ, Li QM, Huang FL. Further investigation on the dynamic compressive strength enhancement of concrete-like materials based on split Hopkinson pressure bar tests Part I: Experiments. Int J Impact Eng 2009;36(12):1327–1334) that the axial strain acceleration is normally unavoidable in an SHPB test on brittle materials. Axial strain acceleration introduces radial confinement in the SHPB specimens and consequently enhances the compressive strength of concrete-like specimens. This paper employs numerical simulation to further demonstrate that the unexpected radial confinement in an SHPB test is responsible for the increase of the dynamic compressive strength of concrete-like materials at strain-rates from 10¹ to 10³ s⁻¹. It confirms the observations in Zhang et al. (Zhang M, Wu HJ, Li QM, Huang FL. Further investigation on the dynamic compressive strength enhancement of concrete-like materials based on split Hopkinson pressure bar tests Part I: Experiments. Int J Impact Eng 2009;36(12):1327–1334) that the dynamic increase factor (DIF) measured in SHPB tests can be reduced either by using tubular SHPB specimens or by reducing the diameter of the SHPB specimen. A kinetic friction model is proposed based on kinetic friction tests and is implemented in the numerical model. It shows that it is necessary to use a kinetic friction model, rather than a constant friction model, for more accurate numerical simulation of SHPB tests.     

Correlation between the accuracy of a SHPB test and the stress uniformity based on numerical experiments

Split Hopkinson pressure bar (SHPB) has become a frequently used technique to measure the uniaxial compressive stress–strain relation of various engineering materials at high strain rate. Using the strain records on incident and transmitter bars, the average stress, strain and strain rate histories within the specimen can be calculated by SHPB formulae based on one-dimensional wave propagation theory. The accuracy of a SHPB test is based on the assumption of stress and strain uniformity within the specimen, which, however, is not always satisfied in an actual SHPB test due to the existence of some unavoidable negative factors, e.g., friction and specimen size effects. Two coefficients are introduced in the present paper to measure the stress uniformity in axial and radial directions of the specimen in a numerical SHPB test. It is shown that the accuracy of a SHPB test can be correlated to these two stress uniformity coefficients. An assessment and correction procedure for SHPB test results is illustrated through a numerical example.     

端面不平行对岩石SHPB测试结果的影响分析

为探讨岩石试件加工端面不平行对岩石材料动力学特性测试结果的影响,采用有限元分析软件LS-DYNA对13种端面不平行度的岩石试件开展SHPB数值模拟,并分析了端面不平行对加载过程应力均匀性的影响。结果表明:随端面不平行度γ的增加,岩石试件动态应力-应变曲线逐渐向右和向下移动,且峰前加载段逐渐延长。当γ1.60%时,动态应力-应变曲线在加载初期出现一个微小的加载-卸载过程,且在升时为120μs的半正弦入射波加载阶段岩石试件达不到应力均匀状态。基于数值模拟结果,建立了端面不平行度与量纲一化的动态单轴抗压强度、平均应变率和峰值应变的定量表达式。     

一维动静组合加载下深部石英片岩破坏研究

为研究锡铁山铅锌矿深部石英片岩的力学特性,利用分离式霍普金森杆(SHPB)对埋深863¹ 264m的试样进行25、30、35MPa轴压下的一维动静加载实验,和采用LS-DYNA软件模拟了25、30、35、40、45、50 MPa轴压情况下的冲击实验。研究结果表明:在冲击作用下,试样的一维动态抗压强度和破坏所需的入射能随着埋深的增加而增加,并呈现出常见的压剪破坏模式;当轴压40MPa左右,埋深1 428m的岩石动态抗压值达到最大;当轴压低于40 MPa时,轴压的增大能加强试样的抗压能力;当轴压大于40MPa时,轴压的增加反而减弱了试样的抗压能力。     

Dynamic tests of cemented paste backfill: effects of strain rate,curing time,and cement content on compressive strength

This article investigates the compressive strength of cemented paste backfill (CPB) under dynamic loading. To accommodate the low impedance CPB, a modified split Hopkinson pressure bar (SHPB) system is adopted. In contrast to traditional solid steel transmitted bar, a hollow aluminum transmitted bar is introduced to reduce the impedance. With this system, the dynamic stress equilibrium is achieved, which guarantees the valid dynamic material testing condition. The dynamic tests are conducted for CPB with different cement contents and curing time. It is observed that: (1) for CPB with the same curing time and cement content, the dynamic strength increases with the strain rate, (2) for CPB with the same cement content, the dynamic strength increases with the curing time, and (3) for CPB with the same curing time and tested under similar strain rate, the dynamic strength increases with the percentage of cement. This observation can be understood by considering the hydration process of cements.     

Inertia-induced radial confinement in an elastic tubular specimen subjected to axial strain acceleration

This paper extends the study in [10] on the stress state in an elastic solid specimen subjected to axial strain acceleration to a tubular cylindrical specimen. A perturbation solution is presented, based on which, it is found that the radial confinement stress induced by the compressive axial strain acceleration decreases with the increase of the inner radius of the tubular specimen. It is shown that the radial stress distribution predicted by perturbation solution can be used to estimate the distribution of the maximum radial stress in tubular specimen. The solutions presented in this paper can be used to estimate the radial confinement stress and additional axial stress due to the existence of axial strain acceleration in split Hopkinson pressure bar tests of brittle materials using tubular specimens.     

两种致密度2D-C/SiC层向动态压缩性能试验研究

对两种致密度的2D-C/SiC复合材料进行了层向动态压缩性能试验研究, 两种致密度材料通过控制CVI(Chemical vapor infiltration)工艺参数得到。试验在SHPB装置上进行, 使用改变波形整形器几何尺寸的方法基本实现恒应变率加载。试验结果表明: 动态压缩应力-应变曲线呈明显的非线性, 与静态试验相比两种致密度试样均有一定的应变率强化效果, 即随着应变率的增加, 抗压强度提高, 失效应变减小, 剪切损伤角增大。致密度提高后抗压强度明显增加但失效应变减小, 且表现出脆性特征, 剪切损伤角也明显增大。动态试验数据有较大的分散性, 低、 高致密度试样动态破坏强度的Weibull分布系数分别为8.36和5.27。SEM观察发现, 低致密度试样纤维束断口不平整, 高致密度试样断口相对平整; 纤维束多发生整束剪断, 动态条件下纤维破碎多于静态。      

脆性材料水泥砂浆多轴应力下的动态响应分析

在实际的结构应用中,混凝土类材料一般处于复杂工作应力状态,且可能承受动态荷载的作用。据此,本文采用Instron3421液压伺服试验机和具有主动围压加压装置的SHPB研究了混凝土材料-砂浆宽应变率范围多轴应力下的动态力学行为;基于Johnson-Cook强度模型框架,确定了等效强度模型的率相关参数及其他材料常数;提出了适用于描述主动围压下砂浆受冲击荷载的损伤演化规律,并确定了损伤演化常数,实验数据与理论值吻合较好     

三维四向编织复合材料动态压缩性能实验研究

利用分离式霍普金森压杆(SHPB)研究了三维四向编织碳纤维环氧树脂复合材料在动态压缩载荷作用下的力学性能。在横向对复合材料进行了动态压缩实验,得到了应变率从900/s―1500/s下的应力-应变曲线,并且与准静态压缩下的结果进行了对比。分析比较了应变率对三维编织复合材料横向压缩强度和模量的影响。实验中根据SHPB理论假设,采用波形整形技术,使得试件在加载过程中处于应力平衡和均匀变形状态。实验结果表明:压缩强度和模量具有一定的应变率强化效应;与准静态结果相比,在高应变率下的复合材料的强度和模量有明显的增大,并表现出明显的脆性。还分析了应变率对复合材料破坏模式的影响。     

平纹机织玻璃纤维增强复合材料面内压缩力学行为及破坏机制

为了研究平纹机织玻璃纤维复合材料SW200/LWR-2 的面内压缩力学性能并建立其本构模型, 对其进行了应变率为0. 001 s-1 、0. 1 s-1 、500 s-1 , 温度从- 55 ℃到100 ℃范围内的面内压缩实验研究。动态压缩实验在SHPB 装置上进行, 通过波形整形器实现了恒定应变率加载, 且经过验证试样两端应力平衡。实验结果表明, SW200/ LWR-2 复合材料性能具有明显的应变率敏感性及温度敏感性, 其强度随着应变率的升高而增大, 随着温度的升高而减小。对破坏后试样进行宏观及微观观察发现, 准静态加载时试样为剪切破坏, 伴随大量纤维束内脱粘和纤维拔出; 动态加载时试样为剪切破坏与分层破坏并存, 并出现大量碎屑, 纤维束为整束剪断, 束内脱粘受到抑制。根据损伤力学理论, 建立了SW200/ LWR-2 复合材料应变率及温度相关面内压缩损伤统计本构模型, 本构模型结果与实验结果吻合较好。      

钢管钢纤维高强混凝土抗冲击压缩性能的试验研究与数值模拟

遮弹层的建成及优化对防护工程的发展尤为重要。钢管钢纤维高强混凝土蜂窝遮弹层是一种具有高强抗力的新型遮弹层,文章对其组成构件钢管钢纤维高强混凝土进行霍普金森压杆(SHPB)动态力学性能试验,并借助动力有限元分析软件LSDYNA进行数值模拟。冲击压缩试验中,试件的钢纤维掺量分别为0%、0.5%、1.0%、1.5%,钢管壁厚分别为2mm、3mm。结果表明钢管钢纤维高强混凝土具有应变率强化效应,应变率越高,试件的动态抗压强度越大。当气压为1.0 MPa时,壁厚3mm、钢纤维掺量1.5%的试件强度达258.3 MPa。与钢纤维高强混凝土相比,钢管钢纤维高强混凝土的抗冲击压缩性能更好,动态抗压强度最大增幅达35.4%,且具备承受多次冲击压缩作用的能力。数值模拟与试验结果吻合度高,表明数值模拟方法具有可行性。     

Study on energy properties and failure behaviors of heat-treated granite under static and dynamic compression

Abstract

The material testing machine and the split Hopkinson pressure bar (SHPB) were adopted, respectively, to conduct the static and dynamic compression tests on granite specimens heat treated by different temperatures. The effects of strain rate and heat-treatment temperature on the mechanism of energy evolution of the specimen during deformation and failure process were studied. The results show a significant strain rate effect on the granite, with the energy dissipation density increasing with increasing impact velocity (or strain rate), regardless of the treatment temperature. The specimens heat treated at 300?°C and 700?°C have the minimum and maximum energy dissipation densities, respectively. The specimen in the SHPB tests easily broke into pieces or even powder; while under static compression, only macroscopic fracture surfaces and spalling phenomenon on the specimen were detected. The energy dissipation density is inversely proportional to the compressive strength of the specimen. The rate of energy dissipation change is defined, which can be used to identify the stages in the deformation process of rock and to determine the position of the failure point in the stress-strain curve. For both the dynamic and static compression tests, the value of energy utilization ratio is relatively low, with a maximum value of about 35%.     

2D-C/SiC复合材料低温动态Z向压缩性能

采用Hopkinson压杆试验装置,对2D-C/SiC复合材料进行了低温条件下的Z向动态压缩性能试验研究,低温条件通过控制酒精和液氮的配比系数得到,通过改变波形整形器几何尺寸的方法来实现恒应变率加载,以得到准确、可信的试验结果。试验结果表明: 由于复合材料内部含有大量初始微缺陷,2D-C/SiC复合材料在低温动态加载条件下呈现伪塑性行为,其破坏时并未表现出典型的脆性破坏,而是在应力达到压缩强度时出现了显著的应变软化现象,在经历了较大的变形后才最终破坏。随着温度的降低,复合材料的动态Z向压缩强度增加,但失效应变减小。2D-C/SiC复合材料在低温环境下,其内部纤维和基体之间界面结合力增强,同时强的界面结合力可以导致高的压缩强度。     

高温后钢管RPC抗冲击压缩特性与极限强度计算

采用φ74 mm分离式霍普金森压杆（Split Hopkinson Pressure Bar,简称SHPB）试验装置对30块高温后的钢管活性粉末混凝土（Reactive Powder Concrete-Filled Steel Tube,简称钢管RPC）进行了不同应变率的冲击压缩试验,得到了高温后钢管RPC的动态应力-应变关系和破坏形态,提出了高温后钢管RPC动态峰值应力和峰值应变预估方法。结果表明,高温后钢管RPC具有明显的应变率效应,经历高温作用后的钢管RPC仍保持较高的强度,较好的延性和整体性。含钢率对钢管RPC动力性能有显著影响,初始弹性刚度和峰值应力随含钢率提高而明显增大。理论计算结果与试验结果吻合良好,能够较好预测高温后钢管RPC的动态峰值应力和峰值应变。     

分离式霍普金森压杆试验中工程材料端面摩擦模型的确定

分离式霍普金森压杆(SHPB)是一种最常用于工程材料高应变率下动态压缩力学性能的技术。在SHPB试样与压杆的接触界面间不可避免地存在端面摩擦效应,这将导致SHPB试样内的应力状态可能偏离一维应力状态,而SHPB试样内的一维应力状态是决定SHPB试验结果准确性的基本假设之一。基于动摩擦试验结果,建立了端面动摩擦模型以描述端面动摩擦系数随SHPB试样与钢压杆接触界面间最大径向相对滑动速度的关系。结果发现本文提出的端面动摩擦模型可很好地拟合     

Mechanical properties of ceramic fiber-reinforced concrete under quasi-static and dynamic compression

The research herein is made on the quasi-static and dynamic mechanical properties of ceramic fiber reinforced concrete (CRFRC for short) through the adoption of a hydraulically-driven testing system as well as a 100-mm-diameter split Hopkinson pressure bar (SHPB) system. As test results have turned out, such quasi-static properties as compressive strength, splitting tensile strength and flexural strength of CRFRC increase with the rise in the volume fraction of fiber. Within the strain range of 20–120 s⁻¹, the effect of the axial strain acceleration on the dynamic strength of CRFRC could be ignored. Therefore, the dynamic increase ratio (DIF) derived from SHPB tests can truly reflect the dynamic enhancement of CRFRC. The dynamic strength, critical strain and specific energy absorption (SEA) of CRFRC are sensitive to the strain rate. The addition of ceramic fiber to plain concrete can significantly improve its properties—dynamic strength, critical strain and energy absorption. And also, an analysis is conducted of the mechanism for strengthening and toughening the concrete.     

Experimental study on impact behaviour of concrete-filled steel tubes at elevated temperatures up to 800 °C

The dynamic behaviour of normal strength concrete-filled steel tubes (CFT) at elevated temperatures up to 800 °C under axial impact loading was experimentally studied by using a newly developed spilt Hopkinson pressure bar (SHPB) together with an electrical furnace. The effects of high temperature, impact velocity, steel ratio and slenderness ratio on the impact behaviour of CFT at elevated temperatures were experimentally studied. The stress and strain time history curves of the tested specimens were recorded to analyze the impact behaviour of CFT at elevated temperatures. The failure modes and the effects of the experimental parameters on the impact resistance of CFT are discussed. The test results showed that normal strength concrete-filled steel tube at elevated temperatures had a more excellent impact resistance in the paper than that described in Huo et al. (2009). A simplified calculation method was updated by introducing the reasonable dynamic increase factor model of hot concrete to reasonably assess the impact resistance of CFT at elevated temperatures.     

Compressive strength of ice at impact strain rates

The compressive strength of ice was measured at high strain rates of 10³ s⁻¹ order of magnitude. Since ice compressive strength is known to be strongly dependent on strain rate, properties corresponding to high strain rates are needed for engineering predictions of the behavior of ice under dynamic crushing scenarios. The split Hopkinson pressure bar (SHPB) apparatus was used to successfully measure compressive strength over a strain rate range of 400–2,600 s⁻¹. Strain rate variation was achieved by adjusting the specimen length and the velocity of the SHPB striker bar; increased velocity and reduced specimen length produced higher strain rates. Since the compressive strength was found to be nearly uniform over the measured strain rate range, an average value of 19.7 MPa is reported. However, when comparing the present results with data in the existing literature spanning several orders of magnitude in strain rate, a trend of continuously increasing strength for strain rates beyond 10¹ s⁻¹ can be observed.