加卸载后含铜矽卡岩在轴压及频繁扰动共同作用下的动力学特征

为了研究加卸载后含铜矽卡岩在轴压及频繁扰动共同作用下的动力学特征,以冬瓜山铜矿井下900 m深处出矿进路附近的含铜矽卡岩为研究对象,利用改进的SHPB加载试验装置开展加卸载后含铜矽卡岩在轴压及频繁扰动共同作用下的动态力学试验,研究含铜矽卡岩的动态变形特征、能量耗散特征和破坏模式等。结果表明：不同冲击气压产生的动荷载对含铜矽卡岩的变形特征无明显影响,表现为试样的动态应力-应变曲线呈近似抛物线形状;随频繁扰动次数增加,含铜矽卡岩的峰值应力减小,峰值应变增大;随冲击气压增大,入射能、反射能、透射能和吸收能均增大,单位体积吸收能随入射能增大而增大,表现为吸收能量的过程;频繁扰动次数不断增加导致试样内部损伤程度加剧,微裂纹增多且扩展速度加快,最终导致试样发生宏观破坏,影响岩石破坏块度大小,同时也增大了“岩爆”的发生概率。     

一种深部细砂岩的力学特性试验研究

采用通用试验机(TMT)方法和数字散斑相关(DIC)方法,得到了一种深部细砂岩的应力-应变曲线,分析了深部岩石在不同含水状态下的应变率效应及饱和水效应。利用数字散斑相关方法,研究了该种细砂岩试件不同部位的应变在试验过程中随时间变化,发现试样的应变在破坏过程中是严重不均匀的;基于TMT与DIC结果的比较,讨论了TMT方法得到的应力-应变曲线的有效范围。采用扫描电镜对回收试件的断裂表面进行微观观测,研究加载速率及饱和度对岩石破坏模式的影响。     

中等应变速率对砂岩破坏形态和力学性质的影响

以砂岩为研究对象,根据砂岩的颗粒分析试验、抗压强度、抗拉强度和强度试验结果,在颗粒流程序下,通过fish语言编程,虚拟实现了砂岩数值试件和单轴压缩试验,设计10-3、5×10-3、10-2、2×10-2、5×10-2、10-1、2×10-1s-1这7个应变率下的单轴压缩试验.分析应变率对砂岩破裂形态、裂纹数量和扩展、应力-应变曲线和能量转换的影响.结果发现:应变率的增加破坏了优势剪切带的发展,使得剪切带等速发展,材料由剪切破坏向锥形破坏发展;材料的力学性能表现出极大的伪增强,应力-应变曲线上扬、斜率提高、峰值提高,峰后曲线震荡剧烈;裂缝数量增多,其中拉裂缝减少,剪切裂缝增多;边界输入能量增加,造成加载过程中材料的摩擦能、动能和应变能单调增大,摩擦能增大说明剪切裂缝增多,动能增大说明破坏剧烈,应变能增大说明更容易产生岩爆现象.     

多次冲击下砂岩粘弹性损伤本构关系

为研究砂岩的粘弹性损伤特性,开展了多次冲击压缩下的霍普金森杆试验.通过砂岩动应力应变曲线分析了中应变率范围内两种动变形模量的定义方法,表明采用等效动变形模量能反映砂岩在动态冲击压缩作用下的损伤变化特性.从微观角度出发,砂岩的统计损伤变量可由破坏的微元体数量占全部微元体数量的比例定义;从宏观角度出发,这种统计损伤变量也可...     

混凝土压缩试验的改善及动态损伤

为了探求混凝土动态压缩试验入射波形的改善方法,从而进一步研究冲击荷载作用下混凝土动态损伤及力学性能,采用常规的大直径分离式霍普金森压杆(split Hopkinson pressure bar, SHPB)进行混凝土的动态压缩试验。然而入射脉冲的弥散效应和严重的高频震荡现象会对试验结果会产生较大的误差,所以试件在破坏前应力均匀分布要求且保持恒应变率加载是保证试验有效性及试验结果可靠性的关键。通过黄铜整形器改善入射波形以减小试验误差,然后利用理论公式与试验相结合的方式,通过控制变量,进一步研究气压、冲击次数等对混凝土动态损伤的影响。研究结果表明:较薄的小直径实心铜片整形器可以提高试验准确度;随着重复冲击次数的增加,混凝土损伤度逐渐提高,动态弹性模量减小,抵抗冲击的能力减弱。     

大掺量粉煤灰超高性能钢纤维混凝土的静动态力学行为

研究了4种不同钢纤维掺量(体积掺量分别为0%,1.0%,1.5%,2.0%)的大掺量粉煤灰超高性能混凝土的单轴压缩强度、弹性模量、单轴抗拉强度、弯曲韧性、断裂韧性、断裂能等静态力学行为,以及高速冲击、压缩作用下的应力波传播规律、应力–应变曲线和破坏特征等动态力学行为.结果表明:掺加钢纤维的大掺量粉煤灰超高性能混凝土的轴心抗压强度、弹性模量和抗拉强度略有增大,韧性指数、残余强度、断裂韧度和断裂能成倍提高;未能增加冲击、压缩作用下的应变率效应程度,但却增大动态应力–应变曲线下的面积,提高试件破坏的应变率阈值,使混凝土存在裂而不散的破坏现象.     

冲击荷载下混凝土破坏过程的数值模拟

目的 探究冲击荷载作用下混凝土内部真实的破坏机理以及在不同应变率下混凝土强度随应变率的变化规律.方法 基于离散单元法,采用细观二维梁-颗粒模型BPM(Beam-Particle Mode in Two Dimensions)模拟了三种不同应变率下混凝土材料的动态响应.结果 从混凝土破坏图形可以看出.冲击荷载下混凝土的破坏过程实际上是混凝土内部的原生裂纹的激发、扩展、贯通直至整体结构的破坏.从混凝土应力-应变曲线可以看出.混凝土是率敏感性材料,其峰值应力和应变均随应变率的提高而增大.结论 模拟结果和试验结果在达到峰值应力前的曲线基本吻合,说明梁-颗粒模型可以用来模拟混凝土在冲击荷载下的动态破坏,其结果是可靠和准确的.     

水泥砂浆高温SHPB实验及动态力学特性研究

采用一种新的混凝土类材料快速加温装置,在Ф50的SHPB系统上,对水泥砂浆试件进行了不同温度(20~600℃)下的冲击压缩实验,分析了水泥砂浆试件在不同温度和冲击速度下的破坏形态,并且获得了不同温度下水泥砂浆试件3个冲击速度下的应力应变曲线以及峰值应力、峰值应变的变化规律。研究表明,水泥砂浆材料具有明显的应变率效应,随着应变率的增加,水泥砂浆的峰值应力不断地提高。同时,水泥砂浆材料具有明显的温度损伤效应,在相同的冲击速度下,其峰值应力随温度的增加不断地减小,而其峰值应变则不断地增加。     

水-温循环作用下千枚岩的动态拉伸特性

为研究水-温耦合作用下0°层理倾角千枚岩的动态拉伸特性变化规律,分别对3组试样进行0、1、3、5、7、8、11次温度循环自然降温、温度循环冷水降温、干湿循环后,采用霍普金森杆试验装置对0°层理倾角千枚岩试样开展动态巴西劈裂试验,从动态拉伸应变曲线、动态峰值抗拉强度、动态弹性模量、能量分析与宏观破坏5个角度研究水、温劣化条件下千枚岩的动态拉伸特性。结果表明：千枚岩应力应变曲线包括极速弹性变形阶段、屈服变形阶段、破坏变形阶段;随着水-温循环次数的增加,千枚岩应力-应变曲线极速弹性变形阶段逐渐缩短,屈服变形阶段的应变增长率不断增大;千枚岩动态峰值抗拉强度呈负指数函数关系变化,耗散能比不断减小;水-温耦合条件下,千枚岩峰值抗拉强度、耗散能比普遍小于温度循环自然降温时;动态冲击下,千枚岩发生贯穿层理的张拉破坏,主要破碎为2块;随着水-温循环次数的增加,千枚岩主碎块发生沿层理面的张拉与穿层理面的剪切复合破坏,千枚岩碎块的平均尺寸不断减小;温度循环冷水降温条件下,千枚岩碎块的平均尺寸更小,且降幅最为显著。     

冻融循环层理砂岩破坏模式试验研究

在西部高寒地区,冻融循环作用对岩石路基稳定性具有不可忽视的影响,易引发一系列的工程地质问题.为研究冻融循环环境下各向异性层理砂岩的损伤特性,选取路基中典型垂直、平行层理砂岩试样开展冻融循环试验研究,基于电液伺服压力试验机进行单轴压缩试验,以应力-应变曲线、力学参数和压缩破坏形态为依据,探究了冻融循环损伤后层理砂岩强度、变形特征的演化规律及破坏模式.研究结果表明:随着冻融次数的增加,垂直、平行层理试样呈现出向右拉伸,向下压缩的应力-应变曲线;垂直层理砂岩试样峰值点下降路径平缓,而平行层理砂岩试样则沿阶梯状路径下降;冻融损伤累积减弱了破坏模式的各向异性特征,随冻融次数的增加,垂直层理砂岩试样裂缝与加载方向趋于平行,平行层理砂岩试样则始终表现为沿层理的劈裂破坏.     

Energy consumption in rock fragmentation at intermediate strain rate

In order to determine the relationship among energy consumption of rock and its fragmentation, dynamic strength and strain rate, granite, sandstone and limestone specimens were chosen and tested on large-diameter split Hopkinson pressure bar (SHPB) equipment with half-sine waveform loading at the strain rates ranging from 40 to 150 s⁻¹. With recorded signals, the energy consumption, strain rate and dynamic strength were analyzed. And the fragmentation behaviors of specimens were investigated. The experimental results show that the energy consumption density of rock increases linearly with the total incident energy. The energy consumption density is of an exponent relationship with the average size of rock fragments. The higher the energy consumption density, the more serious the fragmentation, and the better the gradation of fragments. The energy consumption density takes a good logarithm relationship with the dynamic strength of rock. The dynamic strength of rock increases with the increase of strain rate, indicating higher strain rate sensitivity. Foundation item: Projects(50674107, 10472134, 50490274) supported by the National Natural Science Foundation of China     

Dynamic tensile behaviour and crack propagation of coal under coupled static-dynamic loading

The fracture behaviour and crack propagation features of coal under coupled static-dynamic loading conditions are important when evaluating the dynamic failure of coal. In this study, coupled static-dynamic loading tests are conducted on Brazilian disc(BD) coal specimens using a modified split Hopkinson pressure bar(SHPB). The effects of the static axial pre-stress and loading rate on the dynamic tensile strength and crack propagation characteristics of BD coal specimens are studied. The average dynamic indirect tensile strength of coal specimens increases first and then decreases with the static axial pre-stress increasing. When no static axial pre-stress is applied, or the static axial pre-stress is 30% of the static tensile strength, the dynamic indirect tensile strength of coal specimens shows an increase trend as the loading rate increases. When the static axial pre-stress is 60% of the static tensile strength, the dynamic indirect tensile strength shows a fluctuant trend as the loading rate increases. According to the crack propagation process of coal specimens recorded by high-speed camera, the impact velocity influences the mode of crack propagation, while the static axial pre-stress influences the direction of crack propagation. The failure of coal specimens is a coupled tensile-shear failure under high impact velocity.When there is no static axial pre-stress, tensile cracks occur in the vertical loading direction. When the static axial pre-stress is applied, the number of cracks perpendicular to the loading direction decreases,and more cracks occur in the parallel loading direction.     

Effect of strain rate and water-to-cement ratio on compressive mechanical behavior of cement mortar

Effects of strain rate and water-to-cement ratio on the dynamic compressive mechanical behavior of cement mortar are investigated by split Hopkinson pressure bar(SHPB) tests. 124 specimens are subjected to dynamic uniaxial compressive loadings.Strain rate sensitivity of the materials is measured in terms of failure modes, stress-strain curves, compressive strength, dynamic increase factor(DIF) and critical strain at peak stress. A significant change in the stress-strain response of the materials with each order of magnitude increase in strain rate is clearly seen from test results. The slope of the stress-strain curve after peak value for low water-to-cement ratio is steeper than that of high water-to-cement ratio mortar. The compressive strength increases with increasing strain rate. With increase in strain rate, the dynamic increase factor(DIF) increases. However, this increase in DIF with increase in strain rate does not appear to be a function of the water-to-cement ratio. The critical compressive strain increases with the strain rate.     

高温高应变率下AM60B镁合金力学性能及失效行为

为了研究镁合金在高温、高应变速率下的变形行为及失效机制,采用分离式Hopkinson压杆在应变速率为1 600~4 500 s^-1、温度为27~150 ℃范围内,对真空压铸AM60B镁合金进行了动态压缩实验,并采用金相显微镜和扫描电子显微镜对压缩后的组织进行了观察.结果表明:在所测试的应变范围内,随着应变率的提高,应力-应变曲线均呈现上升趋势,且最大应变也随之增加,表现出正应变率强化效应.在150 ℃时真空压铸AM60B镁合金变形能力最好; 50 ℃时断裂强度最高.真空压铸AM60B镁合金在高温及高应变率下的断裂方式为以解理断裂为主并伴有韧性断裂的混合断裂方式.当变形温度低于150 ℃时,真空压铸AM60B镁合金在高应变率压缩下的变形机制主要是滑移.     

Mechanical and damage evolution properties of sandstone under triaxial compression

To study the mechanical and damage evolution properties of sandstone under triaxial compression,we analyzed the stress strain curve characteristics,deformation and strength properties,and failure process and characteristics of sandstone samples under different stress states.The experimental results reveal that peak strength,residual strength,elasticity modulus and deformation modulus increase linearly with confining pressure,and failure models transform from fragile failure under low confining pressure to ductility failure under high confining pressure.Macroscopic failure forms of samples under uniaxial compression were split failure parallel to the axis of samples,while macroscopic failure forms under uniaxial compression were shear failure,the shear failure angle of which decreased linearly with confining pressure.There were significant volume dilatation properties in the loading process of sandstone under different confining pressures,and we analyzed the damage evolution properties of samples based on acoustic emission damage and volumetric dilatation damage,and established damage constitutive model,realizing the real-time quantitative evaluation of samples damage state in loading process.     

采用CFRP增强的GFRP管混凝土短柱轴压性能试验研究

通过碳纤维增强复合材料(CFRP)布对玻璃纤维增强复合材料(GFRP)管约束混凝土短柱进行不同方式的加强,制作了12个两两相同的G FRP管约束混凝土短柱试件,研究不同增强模式下GFRP管约束混凝土短柱在单调轴压及重复轴压下的力学性能.分析了试件的破坏模式、承载能力、变形能力、增强效果、应力应变曲线、塑性残余应变与卸载...     

三维连通网状SiC陶瓷/Zr基非晶复合材料单轴压缩性能研究

利用分离式霍普金森压杆(SHPB)装置对三维连通网状SiC陶瓷/Zr基非晶复合材料进行不同应变率下的动态压缩实验,并与准静态压缩实验结果比较.利用X射线衍射仪和扫描电子显微镜研究了复合材料的相组成和断口形貌.结果表明:在压缩条件下三维连通网状SiC陶瓷/Zr基非晶复合材料的断裂发生在弹性变形阶段,断裂前几乎观察不到塑性变形;复合材料的准静态压缩强度达到了1 270 MPa,高于在动态压缩中的断裂强度1 100 MPa.试样发生纵向劈裂和剪切断裂,准静态下试样形成的破片数量较多,动态加载条件下试样破碎成数量较少的较大块体.三维连通网状SiC陶瓷断口形貌为层片状、台阶式的解理断裂,非晶合金发生粘性流动,在变形过程中形成脉状花样,在高应变率加载条件下,非晶热软化严重,断口形貌复杂多样.     

初始应力状态对侧限条件黏土动态压缩过程和力学性能的影响

黏土的初始应力状态对其动力学性质有显著的影响。本文采用长时、分级、高压固结方式模拟了黏土的原始应力赋存环境,采用SHPB实验装置对侧限条件下的高压固结黏土进行应变率范围为200~800 s_^-1的冲击压缩实验,分析了黏土应力记忆效应、应变率效应和动态压缩过程。实验结果表明,黏土的应力历史影响了其动态压缩过程,试样依次经历压实段—线弹性加载段—线性卸载段,在动载下黏土压实段与线弹性加载段应力拐点的均值为3.8 MPa,与先期固结应力4.2 MPa具有相关性,并且压实段应变均值约为试样破坏应变的33%;采用200 mm和300 mm的短子弹进行冲击加载时,黏土试样未发生稳定的塑性变形,分析应力-应变率曲线发现,黏土的压实过程吸收了一部分动载能量,使其无法持续进行动态压缩行为,但进入动态压缩阶段后黏土受子弹长度影响较小;黏土试样动态加卸载段模量随应变率同步增加,但加卸载模量的比值稳定在0.45左右,表明更高的冲击速度没有造成试样进一步的损伤,这与冲击后的宏观破坏现象及塑性变形分析相互印证。实验结果也说明,针对软弱、松散颗粒体材料,高压固结方式为研究其动力学性质提供了一种思路。     

Experimental investigation of rigid confinement effects of radial strain on dynamic mechanical properties and failure modes of concrete

In this study, to confirm the effect of confining pressure on dynamic mechanical behavior and failure modes of concrete, a split Hopkinson pressure bar dynamic loading device was utilized to perform dynamic compressive experiments under confined and unconfined conditions. The confining pressure was achieved by applying a lateral metal sleeve on the testing specimen which was loaded in the axial direction. The experimental results prove that dynamic peak axial stress, dynamic peak lateral stress,and peak axial strain of concrete are strongly sensitive to the strain rate under confined conditions.Moreover, the failure patterns are significantly affected by the stress-loading rate and confining pressure.Concrete shows stronger strain rate effects under an unconfined condition than that under a confined condition. More cracks are created in concrete subjected to uniaxial dynamic compression at a higher strain rate, which can be explained by a thermal-activated mechanism. By contrast, crack generation is prevented by confinement. Fitting formulas of the dynamic peak stress and dynamic peak axial strain are established by considering strain rate effects(50–250 s~(-1)) as well as the dynamic confining increase factor(DIFc).