结合混凝土试件的真三轴静载冲击实验结果,分别运用考虑应变率效应的Holmquist-Johnson-Cook (HJC)模型和考虑静水压效应的Drucker-Prager (DP)模型进行数值分析,以探讨研究混凝土试样应变率效应和惯性效应的方法.在探究混凝土的应变率效应和横向惯性效应的关系时,使用HJC模型的数值模拟结果来拟合DP准则的各个参数.结果 表明:随着应变率的升高,混凝土的强度会提高,并且这种强度的提高,也有一部分原因是第一应力不变量I1的增大所导致的.因此,混凝土试件的应变率效应和横向惯性约束具有较强的耦合作用.理论和数值分析了冲击下试样内部的横向应力分布特征与应变率、静水压和试样尺寸的关系,结果发现:试样内部横向应力的幅值随着应变率、静水压的升高而增大,但随着试样尺寸的增大而减小.为了探讨横向惯性带来的强度提升效果,提出了一个有关冲击方向最大应力σx和等效应力σe的参数ζ,且ζ=(σx-σe)/σx..此参数具有尺寸效应、应变率效应和静水压效应,但是此参数与应力三轴度的关系表现出应变率无关特性,可为应变率效应的研究提供新的思路.

By using a SHPB device combined with high-speed photography technology, low-velocity impact experiments of quartz glass beads with diameters of 7.90, 11.80 and 15.61 mm were carried out by means of respectively three kinds of transmission bars, i.e., steel bar, aluminum bar, and polymethyl methacrylate (PMMA) bar. According to the load-displacement curves in the breakage process of glass beads under different transmission bar conditions, combined with the load adjustment of glass beads under impact and the strain of glass beads during the experiment, the influence of stress adjustment on the breakage process of glass beads subjected to low-velocity impact is explored. The results show that under the same impact conditions, the adjustment of the material of the transmission bar will alter the load distribution in the glass bead during impact breakage, that is, the change of the wave impedance at the transmission end will change the reflected wave, which leads to the load adjustment in the process of multiple reflection loading. When the transmission bar is made of aluminum and PMMA, the load in the glass bead decreases obviously during the crushing process, and the stress adjustment duration of the glass bead becomes longer with more deformation of the cushion block during the loading process. When the transmission bar is made of steel, the strain in the glass bead is the largest at both ends, while the closer to the middle of the bead, the smaller the strain. For the glass beads loaded with aluminum and/or PMMA transmission bar, local unloading behavior is found at the transmission end of bead. By employing the PMMA transmission bar, the local stress and deformation both decrease, resulting in the glass bead being broken with larger deformation. It is further shown that glass bead breakage is controlled by local deformation and local deformation gradient.

本文对不同类型、不同组合的Aramid纸蜂窝结构进行了抗压实验,并与单层蜂窝的抗压实验结果进行对比,总结其力学性能和吸能特性.组合的类型包括不带隔板的2个规格相同的蜂窝组合,以及包含铝隔板的相同规格的2个蜂窝组合.结果 表明,复合纸蜂窝结构具有一定的应变率效应,并且其吸能特性远优于单层纸蜂窝,加入铝隔板的纸蜂窝吸能特性会进一步提升.为了验证实验结果,基于数值方法建立了合理的分析模型,计算结果与实验结果吻合较好.研究结果表明,含有铝隔板的组合适用于需要较大坍塌应力的防撞结构中,而无隔板组合适用于需减小初始破坏应力的阻尼吸能结构中.

冲击过程中岩石界面动摩擦特性对于地震滑移等现象的研究有重要意义.基于分离式霍普金森压杆(SHPB)杆束技术对含倾斜界面的花岗岩进行冲击实验,分别采用光学显微镜和台阶仪,观测较大视场(毫米尺度)和较小视场(亚毫米尺度)下花岗岩界面粗糙形态.结果表明:微动滑移条件下,表面仍非常粗糙,没有大的凸起,但是对于局部初始较平滑的表面,冲击后由于表面的摩擦作用变得粗糙,很难观察到大位移滑移时的光滑滑移面.采用斜条型有限子群表示,结合微界面相对滑移磨损扩散的控制方程,建立岩石界面粗糙形态动力学演化的描述方法.初步结果验证了此方法的可行性,但需要结合深入的实验观测进行完善.研究结果对界面动摩擦演化过程及其机制的认识具有良好的参考意义.

对于水泥砂浆的抗弹性能研究,目前很少考虑靶体所处的应力状态,为此基于自研的真三轴静载混凝土侵彻实验装置和水泥砂浆抗弹性能实验结果,讨论了水泥砂浆在不同应力状态下的开坑深度和开坑阻力.应用侵彻深度的经验公式和基于HJC模型的有限元数值计算方法,对比分析了水泥砂浆侵彻实验,结果表明,对于低速冲击过程,采用UMIST公式和HJC模型的数值分析对开坑深度的预测较为有效.应力状态对开坑深度有明显的影响,即随着侧限增加,水泥砂浆的三轴强度提高,弹丸的开坑深度减小.应用基于HJC模型的数值分析方法,研究了弹丸开坑过程中弹体内的加速度波形和y轴支撑杆上的波形,结果表明:弹丸开坑过程对两种波形都有影响,其中y轴支撑杆上的波形可以更好地反映开坑过程.虽然数值模拟结果与实验波形的趋势基本一致,但是应力幅值有一定的差异,说明基于HJC模型的数值分析对开坑阻力的计算能力尚待提高.

应用分离式霍普金森压杆(SHPB)加载装置,对直径为8.30、11.68、15.42、17.50 mm的石英玻璃珠开展了冲击速度为5.6～11.5 m/s的双玻璃珠系动态破碎实验.利用高速摄影技术记录双玻璃珠在动态冲击下的破碎过程,结合透射载荷-位移曲线以及破碎产物的粒度分析结果,探讨了石英玻璃双颗粒在冲击下的破坏机制.结果表明:由于双颗粒系中载荷的不均匀特性,两个玻璃珠的破碎具有时序特征,随冲击速度的增加而改变;玻璃珠的冲击破碎源于接触部位局部的Hertz裂纹扩张和裂纹系的扩散,而不是通常认为的贯穿性的斜裂纹体系;瞬态红外测温揭示了玻璃珠冲击破碎的两种主要机制和临界破碎扩散阻力的存在.研究结果对认识脆性颗粒介质的动态破坏机制具有良好的参考意义.

节理岩体摩擦普遍存在于地震孕震、板块滑动等自然现象中.目前研究的重点主要集中于大位移下滑动摩擦特性的揭示,很鲜少有人对摩擦滑移初期阶段的相关特性进行研究.本文基于改进的分离式霍普金森压杆装置(SHPB)建立了多点声发射和红外测温等实验装置,研究了5种角度节理表面在摩擦滑动初期的声发射和产热特性.结果 表明,与节理摩擦滑移相关的信息位于声发射信号的高频域中,对于所研究的花岗岩样品,其频率范围为78.1～312.5kHz,低于该频率范围的信号源于撞击界面的扰动;与节理摩擦滑移相关的产热信息位于红外测温信号的低频域中,5种节理面摩擦滑移产热对应的温升明显较低.为了揭示这些测量信号的内在规律,基于数值方法建立了合理的分析模型.计算结果表明,随着节理角度的增大,节理面越易滑移,节理表面温升幅值越大,但都低于0.1℃,与实验结果相一致.

研制了真三轴应力状态作用下混凝土侵彻实验装置.该装置采用液压伺服控制系统对立方体试件施加三向独立的静载、采用高压气体驱动子弹侵彻试件;同时,试件六个面的动态信号可由六根杆上的应变片记录.以MI0水泥砂浆试件为例,研究水泥砂浆在不同的应力状态下的侵彻性能,建立了相应的数据处理方法,对比分析了立方体试件无侧限、单向侧限、双向侧限下侵彻差异,揭示出应力状态对侵彻性能的影响.该研究对防护工程等领域有很好的参考意义.

脆性材料具有复杂的细微观结构,其宏观力学性能表现出明显的应力敏感性和应变率效应.基于改进的霍普金森压杆(split Hopkinson pressure bar,SHPB)装置的系统实验结果,总结了岩石、石英砂堆积体和K9玻璃珠3类脆性材料与应变率相关的动特性,揭示了脆性材料应变率的内在机制为局部非均匀性的演化.

In this study we developed a hydraulic servo control system for experimental study on concrete penetration under triaxial stress for independently-controlled triaxial confinement on cubic specimens, and launched bullets to penetrate concrete specimens with high pressure, using the strain gauges to record the dynamic compression signals and side friction signals on the six bars of six surfaces of the specimens. Taking the concrete specimens as an example, we investigated the cubic specimens’ penetration performance under different stress states based on the independently-controlled triaxial confinement of 0-100 MPa, and obtained their penetration differences under unilateral, unilateral and bidirectional lateral confinements, revealing the effect of the stress state on penetration performance.

Based on plate impact experiment of light gas gun,the impact property of quartz fiber cloth is investigated in this paper.Impact property comparison experiment was carried out for two kinds of specimens made of adhesive laminated material and the bolted tensioning composite material respectively,the difference of impact properties between two specimens was discussed.The former is an epoxy-cured composite,while the latter is a "structural material" with a loose.The impact response of quartz fiber cloth is essentially the response of structure to disturbance signal.Therefore,a method of wave propagation in variable-density viscoelastic materials is proposed to analyze the dynamic characteristics of quartz fiber cloth.

研制了一种真三轴静载作用下混凝土、岩石动态实验系统.该系统采用液压伺服控制系统可对试件施加三向独立的100 MPa静载、采用霍普金森杆(SHPB)冲击加载可对试件施加1 GPa以下的冲击动载;同时,立方体试件六个面的动态信号可由六根杆上的应变片记录.由此,研究了C30混凝土材料在不同的真三轴静载条件下的动态压缩性能,得到了三向独立的动态应力应变关系、动态体积应变、动态Drucker-Prager强度参数等.尼龙和花岗岩试件作为对比材料,进行了初步探讨.

Uniaxial compression experiments of K9 glass spheres with a diameter of 8 mm were conducted to obtain the fracture responses of brittle particles at five loading velocities,i.e.2 × 10 7 and 2 × 10-6 m/s for quasi-static loading and 3.4,7.1 and 10.6 m/s for impact loading using a split Hopkinson pressure bar.Based on the Weibull distribution and recovery specimen products,a novel model combing the tensile failure and the shear failure was proposed to explain the process of the breaking evolution,revealing the relationship of the loading velocity and the three breaking zones.The model was validated using numerical simulation.Our study can serve as valuable reference for the study of the dynamic failure of brittle granular materials.

In order to study the frequency dispersion characteristics of elastic wave in cement matrix composite,adopting three kinds of acoustic probe with main frequency of 50kHz,300kHz and 1MHz respectively,elastic wave measurement was carried out for steel fiber reinforced cement mortar specimens with three different steel fiber volume contents of 0.5％,1.0％ and 3％ and subjected to uniaxial compression.Results show that on the initial stage of loading,with the increase of loading,P wave velocity increases obviously.But this trend is gradually weakening and finally P wave velocity achieves a relatively stable value.With the increase of steel fiber volume content,wave velocity presents increasing trend.S wave has similar trend,but its increase amplitude is much smaller than that of P wave.All three kinds of material present certain frequency dispersion.In order to eliminate material nonlinear effect in the initial loading process,the relative velocity was adopted,and the frequency dispersion effect of relative velocity was discussed.Combining with multi component unconsolidated model and Hashin-Shtrikman upper bound model and adopting a theoretical dimensionless model,elastic wave velocity frequency dispersion was comparatively analyzed.

Research on the longitudinal impact compression of an aluminum alloy ring found that an obvious stress-drop process will appear in the macro plastic hardening stage of the specimen under certain conditions.In order to reveal the mechanism of this stress-drop process,we conducted the longitudinal impact compression experiment on LY12 aluminum alloy ring specimens whose ratio of OD,ID and height was 6 ∶ 3 ∶ 2 using the split Hopkinson pressure bar (SHPB) under the three end face roughness conditions:lubrication,fine grinding and rough grinding.The experiment results show that the stress-drop process occurs mainly in the large strain and high strain rate loading conditions.Moreover,the results of the metallurgical analysis of the aluminum alloy ring specimens show that the formation and development of the adiabatic shear band is the intrinsic mechanism of the stressdrop process,which is a dynamic plastic instability.This study can serve as a reference for the study of the heat insulation shear band in metal materials under impact.

对单轴压缩下两种密度的泡沫铝进行了三种频率(50kHz、200kHz和300kHz)的声波测试,同时运用CCD对实验进行跟踪拍摄.分析结果表明:P波波速随载荷增大而增加,当载荷达到屈服力时,波速有所下降;S波有相同趋势,但变化比P波小.应用数字图像相关方法对CCD拍摄图片进行处理,得到不同载荷阶段下泡沫铝的全场应变;采用Weibull函数对全场应变分布进行拟合,研究了Weibull分布参数随载荷变化的规律.由此,初步建立了载荷作用下材料结构变化与波速的关系.此研究对于声波探测领域有很好的指导意义.