岩石在动载作用下破坏模式与强度特性研究

岩石在高应变率下的破坏类型及动态强度理论是工程爆破中的一个重要的基本问题。以往研究岩石的破坏类型只停留在静载作用下,而其强度理论也多采用静态强度理论。作者利用ＳＨＰＢ装置对常见的四种岩石进行了大量冲击试验。结果表明,岩石在冲击载荷作用了下破坏分为四种类型：压剪破坏,拉应力破坏,拉应变破坏和卸载破坏,而且其破坏强度随冲击速度的提高而提高。最后对强度理论作了讨论。     

多向聚能爆破爆破漏斗实验研究

多向聚能爆破是一种新型爆破技术。为研究多向聚能爆破在爆破漏斗上能量分配特点,在阐明多向聚能爆破基本原理和影响因素基础上,设计了多向聚能爆破药包,进行常规爆破与多向聚能爆破的爆破漏斗体积对比实验。结果表明,多向聚能爆破能够增加爆破漏斗体积并提高了爆炸能量在岩石破裂破碎方面的分配比例,提高了炸药利用率。     

多向聚能爆破爆破漏斗实验研究

多向聚能爆破是一种新型爆破技术。为研究多向聚能爆破在爆破漏斗上能量分配特点,在阐明多向聚能爆破基本原理和影响因素基础上,设计了多向聚能爆破药包,进行常规爆破与多向聚能爆破的爆破漏斗体积对比实验。结果表明,多向聚能爆破能够增加爆破漏斗体积并提高了爆炸能量在岩石破裂破碎方面的分配比例,提高了炸药利用率。     

Behaviour of cellular materials under impact loading

The paper describes experimental and computational testing of regular open‐cell cellular structures behaviour under impact loading. Open‐cell cellular specimens made of aluminium alloy and polymer were experimentally tested under quasi‐static and dynamic compressive loading in order to evaluate the failure conditions and the strain rate sensitivity. Additionally, specimens with viscous fillers have been tested to determine the increase of the energy absorption due to filler effects. The tests have shown that brittle behaviour of the cellular structure due to sudden rupture of intercellular walls observed in quasi‐static and dynamic tests is reduced by introduction of viscous filler, while at the same time the energy absorption is increased. The influence of fluid filler on open‐cell cellular material behaviour under impact loading was further investigated with parametric computational simulations, where fully coupled interaction between the base material and the pore filler was considered. The explicit nonlinear finite element code LS‐DYNA was used for this purpose. Different failure criteria were evaluated to simulate the collapsing of intercellular walls and the failure mechanism of cellular structures in general. The new computational models and presented procedures enable determination of the optimal geometric and material parameters of cellular materials with viscous fillers for individual application demands. For example, the cellular structure stiffness and impact energy absorption through controlled deformation can be easily adapted to improve the efficiency of crash absorbers.     

基于三维离散-连续耦合方法的NPR锚索-围岩相互作用机理研究

恒阻大变形(NPR)锚索作为一种高效的吸能锚索已广泛应用于边坡和采矿工程的加固和监测预警中。NPR锚索工作时的径向膨胀特性将影响整个锚固系统的性能。因此,基于离散元法(DEM)-有限差分法(FDM)耦合方法对静力拉伸作用下NPR锚索-围岩的相互作用机理进行分析。NPR锚索考虑为连续单元体,围岩和锚固材料由离散球体单元表征,将整个NPR锚固系统实现了离散元法与有限元法耦合模拟。围岩的离散元细观参数得到校准,NPR锚索的有限差分宏观参数由相应的静力拉伸室内试验进行验证。通过分析数值结果,对NPR锚索与NPR锚固系统的恒阻力进行了比较;描述了锚索-围岩界面的正应力与切应力的分布特征;此外,对锚固剂与围岩的破坏模式进行了细观研究。研究结果描述了NPR锚索与围岩的相互作用并揭示了NPR锚索的特殊锚固机理,可用于预测和提高NPR锚索锚固系统的性能。     

爆破漏斗形成过程的数值模拟研究

爆破漏斗是爆破破坏的基本形式.利用Ls-dyna软件,模拟了条形药包和集中药包起爆时爆破漏斗的形成过程和形态,对模拟结果进行了分析,计算结果表明:靠近炸药部位的岩石是由于压缩破坏,岩体表面属于拉伸破坏,压缩破坏区和拉伸破坏区存在较明显的分界线.     

A New Static and Fatigue Compression Test Method for Composites

Abstract: A new test method to determine the compressive properties of composite materials under both static and fatigue loading was developed. The novel fixture is based on the concept of transmitting the load by a fixed ratio of end‐to‐shear loading. The end‐to‐shear load ratio is kept fixed during the test through a mechanical mechanism, which automatically maintains the gripping pressure. The combined loading method has proven very efficient in static loading and is used in the new fixture which is specially designed for fatigue testing. Optimum gripping (shear loading) and alignment of the test coupon are achieved throughout the fatigue life. The fatigue strength obtained is more reliable because bending of the specimen due to poor gripping and alignment is minimised. The application of the new fixture to static and fatigue compression is demonstrated by using unidirectional carbon/epoxy and glass/polyester composite systems. Repeatable results and acceptable failure modes are obtained under both static and fatigue loading.     

Correlation of stepwise fatigue and creep slow crack growth in high density polyethylene

The kinetics and mechanism of slow crack growth in fatigue and creep of high density polyethylene were studied. The relationship between fatigue and creep was examined by varying the R-ratio (the minimum/maximum loads in the fatigue loading cycle) in the tensile mode such that loading ranged from mainly dynamic (R = 0.1) to static (R = 1.0, creep test). The stepwise crack propagation mechanism characteristic of long-term failures in polyethylene was observed for all loading conditions studied. Fatigue fracture kinetics allowed for extrapolation to the case of creep failure, which suggested that short-term fatigue testing can be used to predict long-term creep fracture properties. The size of the craze damage zone ahead of the arrested crack tip was controlled only by the mean stress, however the lifetime of the zone was determined by both the maximum stress and the mean stress. Crack growth rate was related to the maximum stress and the mean stress by a power law relationship, which described crack growth over the entire range of loading conditions studied.     

Study on Fracture Behaviour of a Polymer‐Bonded Explosive Simulant Subjected to Uniaxial Compression Using Digital Image Correlation Method

Abstract: Quasi‐static uniaxial compression experiments were conducted on a polymer‐bonded explosive (PBX) simulant. At macro‐scale, the deformation and fracture process of samples were recorded using a charge‐coupled‐device camera. Microscopic examination was conducted to in situ observe the deformation and fracture processes of samples using SEM equipped with a loading stage. Microscopic damage modes, including interfacial debonding and particle fracture, were observed. The digital image correlation (DIC) technique was used to calculate the recorded images, and the macro‐ and micro‐scale displacement and strain fields were determined. Crack initiation, crack propagation, fracture behaviour and failure mechanism of samples were studied. The effects of aspect ratios on fracture behaviour and failure mechanism of PBX simulant were analysed.     

Experimental investigation of fracture damage of notched granite beams under cyclic loading using DIC and AE techniques

Fracture experiments of three‐point bending notched granite beams were performed under cyclic loading using digital image correlation (DIC) and acoustic emission (AE) techniques. The damage evolution process of the specimen under cyclic loading was analysed on the basis of AE ring count and b value. The strain and displacement fields and the fracture process zone (FPZ) ahead of the crack tip were revealed by DIC. The results showed that the AE characteristics of rock fracture indicated a noticeable Kaiser effect in the stage of cyclic loading and unloading. Moreover, when the loading force reached 70% of its peak value, the AE characteristics showed the Felicity effect. The damage produced during the loading‐unloading process contributed to the development of the cracks leading to the catastrophic fracture. Besides, a relatively high loading rate was found to help to suppress the development of the FPZ at the crack tip.     

Bonded particle modeling of grain size effect on tensile and compressive strengths of rock under static and dynamic loading

The effect of grain (particle) size on the strength is an interesting subject in the rock engineering. Some investigations about the impact of particle size on static strength of rock have been conducted and reported in the literature. However, this issue has not received enough attention when high loading rates are involved. In this work, by utilizing the CA3 bonded particle - finite element computer program, the combined influence of loading rate and particle size on the compressive and tensile strengths of rock is examined. The bonded particle model is used to simulate the crack initiation and failure of the rock specimen and the finite element is utilized to model the elastic bars in the Split Hopkinson Pressure Bar (SHPB) apparatus employed for the dynamic testing. Specimens with four different particle sizes were prepared. The results suggest that the particle size does not affect the rock strength under static and dynamic loading. However, the particle size modifies the nominal tensile strength of the notched Brazilian specimens. For the intact Brazilian specimens under high stress rates, the particle size contributes to the tensile strength and this contribution can be justified based on the principles of fracture mechanics. The theoretical reason for these observations is derived for a 3D bonded particle system and discussed.     

强冲击荷载下岩石破坏三维数值模拟

采用基于有限差分的拉格朗日、欧拉相结合的方法,对强荷载冲击下岩石材料破坏进行了数值模拟。在欧拉步中引入模糊方法处理界面,考虑了岩石材料、金属材料、空气的多物质场,给出了模拟结果和几个关键点的压力曲线。对强冲击荷载下岩石破坏研究具有重要的意义。     

基于TBM双滚刀破岩仿真的实验研究

为了提高滚刀破岩效率,探究滚刀间距及加载方式对全断面硬岩掘进机(Full Face Rock Tunnel Boring Machine,简称TBM)滚刀破岩效果的影响.以滚刀破岩机理、岩石破碎理论为基础,选择某类花岗岩,通过有限元分析软件ABAQUS建立一系列滚刀破岩模型,对TBM刀盘结构设计进行研究,模拟不同刀间距、不同加载方式的双滚刀对破岩效果影响.通过模拟分析得出:在一定地质条件下,滚刀顺次加载和同时加载时的最优刀间距均是80mm,但是顺次加载的破岩效果要优于同时加载.通过实验数据分析得出破岩比能在刀间距为80~90mm时最小,从而验证了仿真模拟的正确性与合理性.研究成果对于探究双滚刀破岩机理、加快国内TBM设计理论与工程应用研究有一定帮助.     

Dynamic tensile behaviour of fibre reinforced concrete with spiral fibres

This paper performs drop-weight splitting tests to study the dynamic tensile properties of fibre reinforced concrete (FRC) materials with different steel fibres. A renovated splitting tensile testing method was developed to ensure a more qualified experimental process. The splitting tensile impact tests were conducted with an instrumented drop-weight impact system consisting of a hard steel drop weight, a fast-response load cell, a high-speed video camera and a high-frequency data acquisition system. The quasi-static compressive and splitting tests were also conducted to obtain the static properties of the FRC materials. The commonly used hooked-end steel fibre and a new spiral shaped steel fibre were tested in this study. The high-speed video camera was used to capture the detailed failure process, deformation and cracking process of the tested specimens. Average strain rates and the cracking extension displacement and velocity under impact loading were estimated by analysing the recorded high-speed images. The strains were also measured by the strain gages on the specimen surface. The dynamic stress–strain and stress–COD (cracking opening displacement) relations, the rate sensitivity of tensile strength and the corresponding energy absorption capacity of plain concrete and FRC with different fibres were obtained, compared and discussed. The advantage and effectiveness of the new spiral fibre in increasing the performance of FRC under dynamic tensile loading were examined. The results show that FRC with spiral fibres outperforms that with hooked-end fibres, and is a promising construction material in resisting dynamic loadings.     

中低应变率加载下弱胶结软岩动力学特性

我国西部侏罗系煤层上覆巨厚白垩系富水软岩,为了解此类软岩在冲击荷载作用下的力学本构关系及损伤演化规律,利用Hopkinson压杆装置对干燥、饱和红砂软岩进行中低应变率下的冲击试验,结果表明:红砂软岩峰值应力、峰值应变均表现出明显的应变率效应,其中峰值应力与应变率呈指数关系;相同应变率下,干燥红砂软岩的强度大于饱和状态,对冲击荷载表现出更强的抵抗能力,但饱和红砂软岩的宏观破坏强度大于干燥状态;低应变率加载下,干燥红砂软岩出现负损伤;结合微观机理分析,低应变率下,水对红砂软岩的弱化作用占据主导地位,随着应变率的增大,在惯性效应和水的Stefan效应共同作用下,饱和红砂软岩的动态强度得到强化;基于Z-W-T模型和应变等效原理,建立了服从Weibull分布的损伤本构方程,经验证能很好的反映红砂软岩的动态本构关系,具有一定的工程实际意义。     

Impact rupture of structural adhesive joints under different stress combinations

The paper reports the results of an experimental study on bonded joints, carried out by means of an instrumented impact pendulum, equipped to load overlap specimens in shear. Such testing configuration is the most adequate and natural to study the possible modifications of the behavior of the joint, changing from static to dynamic loading condition, keeping the same specimen type. The specimens were steel strips bonded by an epoxy adhesive (Hysol 3425). Several values of lap length, adhesive and adherends thickness were adopted, to achieve rupture under different peel and shear stress combinations. The stress state at rupture has been calculated by means of a structural solution. The results show that the failure points, in a chart having as axes the maximum values of peel and shear structural stress, lie outside the rectangular limit zone previously obtained under static conditions. Therefore, in spite of the concerns associated with the impact condition, the strength of the tested adhesive does not decrease with respect to the case of static loading. In alternative, also the evaluation of the stress intensity factor proves to be effective to predict failure in the considered cases.     

The effect of approach direction on damage in MgO due to spherical particle impact

The damage produced by spherical particle impact against {1 0 0} surfaces of MgO has been investigated over a range of impact angles for a fixed particle velocity and over a range of particle velocities for a fixed impact angle. The mass of material removed by each impact was determined gravimetrically, and the crater and surrounding damage were studied by means of surface profilometry and scanning electron microscopy. A numerical computer model of the crater formation process was developed which was able to predict crater geometries in close agreement with those observed experimentally. This same model also provided estimates of the dynamic hardness, the contact time and the energy transmitted to the surface during the impact. The mean dynamic hardness was ~ 25% less than that measured in previous normal impact studies [1] on MgO of similar static hardness. The contact time and energy calculations give some insight into the reasons why the energy balance model, which successfully describes the velocity dependence of mass loss under normal impact conditions, breaks down for oblique impact.     

考虑岩石应变率效应的DDA程序

针对原经典DDA程序在研究岩石动力学问题时不考虑岩石的应变率效应,在DDA程序中引入与岩石应变率相关的动态强度表达式,将块体间接触弹簧破坏准则发展为动态破坏准则,进而完善DDA程序对岩石动力学破坏问题的处理能力。用原DDA程序和改进DDA程序对动载作用下岩石单轴拉、压破坏实验进行模拟,两者的模拟结果对比分析表明:在不同的加载速率作用下,原DDA程序得到的失效应力和破坏形式基本没有变化,这与实验结果不相符。但是,在不同的加载速率作用下,改进的DDA程序得到破坏形式能与实验结果相符,且能体现动载作用下岩石动态强度随加载速率的提高而增大的强度特性。     

岩石可释放应变能及耗散能的实验研究

地下岩石结构的变形破坏是能量耗散与能量释放的综合结果.岩石结构内部储藏的可释放应变能和己耗散能的计算,涉及到在当时工况下岩石的卸荷弹性模量和泊松比,并与加载速度与载荷水平有关.该文在不同加载速度及不同载荷水平下,对岩石试件进行了单压加卸载实验,得到了卸荷弹性模量与泊松比、可释放应变能与耗散能的变化规律;进行了SHPB动...     

Fractographic analysis of austempered ductile iron

This investigation involves a systematic study of the fracture surfaces of two grades of austempered ductile iron (ADI) broken under quasi‐static, dynamic and cyclic loading conditions. The study used electron microscopy, optical microscopy and image post‐processing. The results show that the predominating fracture mechanism in ADI upon impact loading changes from quasi‐cleavage to ductile (with little areas of cleavage facets) as the testing temperature increases. Noticeably, even at the lower temperatures tested, the fracture surface of ADI shows clear signs of ductile fracture mechanisms. In particular, graphite nodule cavities suffer marked plastic deformation. Fracture after bending tests at room temperature was characterized by a mix of quasi‐cleavage facets, deformation of the contour of nodular cavities and microvoid coalescence. In the case of fatigue fracture at room temperature, the fracture surfaces show a flat appearance which has notorious differences with those reported for other loading conditions, but the typical fatigue striations were not found. The particular features identified on the fatigue fracture surfaces can be used to identify fatigue failures. It was also shown that the determination of the direction of main crack propagation by using the experimental methodology proposed earlier by the authors is applicable to ADI fractured by impact and quasi‐static loads. The results provide information potentially useful to fractographic analyses of ADI, particularly in samples that fail in service under unknown conditions.