Failure of rock under dynamic compressive loading

Split Hopkinson Pressure Bar(SHPB) test was simulated to investigate the distribution of the first principal stress and damage zone of specimen subjected to dynamic compressive load. Numerical models of plate-type specimen containing cracks with inclined angles of 0°,45° and 90° were also established to investigate the crack propagation and damage evolution under dynamic loading. The results show that the simulation results are in accordance with the failure patterns of specimens in experimental test. The interactions between stress wave and crack with different inclined angles are different; damage usually appears around the crack tips firstly; and then more damage zones develop away from the foregoing damage zone after a period of energy accumulation; eventually,the damage zones run through the specimen in the direction of applied loading and split the specimen into pieces.

The Application of Dynamic Shock Mechanics Test in Engineering Blasting

With the continuous advancement of China’s infrastructure construction to the west,according to the geographic situation in the southwest region,such as mountainous areas and complex terrain,the road construction process is inevitably accompanied by earth and rock blasting.To improve the quality and safety of the project,this paper addresses the problems of land and rock blasting faced in the construction of mountain road projects,taking the research of rock dynamic mechanics test as the starting point,and using a combination of theoretical analysis and experimental research methods.The specific research content includes the following parts:dynamic impact compression test(SHPB),dynamic splitting tensile test,and stress-strain curve analysis of the test results,which provides the theoretical basis and numerical parameters for the numerical simulation of future engineering blasting.

Application of signal sparse decomposition in dynamic test

In dynamic test,sampling rate is high and noise is strong,so a signal sparse decomposition method based on Gabor dictionary is put forward.This method iteratively decomposes the signal with the matching pursuit(MP)algorithm and takes the coherence ratio of the threshold as a condition of iteration termination.Standard MP algorithm is time-consuming,thus an adaptive genetic algorithm is introduced to MP method,which makes computation speed accelerate effectively.Experimental results indicate that this method not only can effectively remove high-frequency noise but also can compress the signal greatly.

Dynamic recrystallization of Ti-6Al-2Zr-1Mo-1V in β forging process

The dynamic recrystallization（DRX） behavior of Ti-6Al-2Zr-1Mo-1V alloy was investigated at deformation temperature of 1000-1100 °C and strain rate of 10-3-1.0 s-1 by using compression test.The results show that discontinuous dynamic recrystallization（DDRX） is the predominant recrystallization mechanism at temperature higher than 1050 °C and strain rate lower than 0.01 s-1.Meanwhile,continuous dynamic recrystallization is the main mechanism observed at temperature below 1050 °C and strain rate above 0.01 s-1,mixed with a few DDRX grains.In addition,decreasing strain rate and increasing deformation temperature are found to facilitate the progress of DRX and refinement of grains in the Ti alloy in β forging process.

Real-time modular dynamic modeling for compression system of altitude ground test facilities

Modeling of a centrifugal compressor is of great significance to surge characteristics and fluid dynamics in the Altitude Ground Test Facilities(AGTF).Real-time Modular Dynamic System Greitzer(MDSG)modeling for dynamic response and simulation of the compression system is introduced.The centrifugal compressor,pipeline network,and valve are divided into pressure output type and mass flow output type for module modeling,and the two types of components alternate when the system is established.The pressure loss and thermodynamics of the system are considered.An air supply compression system of AGTF is modeled and simulated by the MDSG model.The simulation results of mass flow,pressure,and temperature are compared with the experimental results,and the error is less than 5%,which demonstrates the reliability,practicability,and universality of the MDSG model.

Predicting the Dynamic Behavior of Asphalt Concrete Using Three-dimensional Discrete Element Method

A user-defined three-dimensional （3D） discrete element model was presented to predict the dynamic modulus and phase angle of asphalt concrete （AC）. The 3D discrete element method （DEM） model of AC was constructed employing a user-defined computer program developed using the ＂Fish＂ language in PFC3D. Important microstructural features of AC were modeled, including aggregate gradation, air voids and mastic. The irregular shape of aggregate particle was modeled using a clump of spheres. The developed model was validated through comparing with experimental measurements and then used to simulate the cyclic uniaxial compression test, based on which the dynamic modulus and phase angle were calculated from the output stress- strain relationship. The effects of air void content, aggregate stiffness and volumetric fraction on AC modulus were further investigated. The experimental results show that the 3D DEM model is able to accurately predict both dynamic modulus and phase angle of AC across a range of temperature and loading frequencies. The user- defined 3D model also demonstrated significant improvement over the general existing two-dimensional models.

Dynamic failure of dry and fully saturated limestone samples based on incubation time concept

This paper outlines the results of experimental study of the dynamic rock failure based on the comparison of dry and saturated limestone samples obtained during the dynamic compression and split tests. The tests were performed using the Kolsky method and its modifications for dynamic splitting. The mechanical data(e.g. strength, time and energy characteristics) of this material at high strain rates are obtained. It is shown that these characteristics are sensitive to the strain rate. A unified interpretation of these rate effects, based on the structuraletemporal approach, is hereby presented. It is demonstrated that the temporal dependence of the dynamic compressive and split tensile strengths of dry and saturated limestone samples can be predicted by the incubation time criterion. Previously discovered possibilities to optimize(minimize) the energy input for the failure process is discussed in connection with industrial rock failure processes. It is shown that the optimal energy input value associated with critical load, which is required to initialize failure in the rock media, strongly depends on the incubation time and the impact duration. The optimal load shapes, which minimize the momentum for a single failure impact, are demonstrated. Through this investigation, a possible approach to reduce the specific energy required for rock cutting by means of high-frequency vibrations is also discussed.

航空座椅垫集中参数模型研究

为解决航空座椅垫由于变形较大,易导致航空座椅有限元模型冲击模拟中出现负体积和计算时间过长的问题,本文提出一种由并联的非线性弹簧和线性阻尼构成的航空座椅垫集中参数模型。首先,开展了航空座椅垫材料的静动态压缩试验,分别建立了航空座椅垫有限元模型和集中参数模型;其次,根据有限元仿真结果拟合了集中参数模型的弹簧阻尼参数,并对比两种模型在14、16、19 g三角脉冲下的动力学响应。结果表明,两种模型的一致性较好,本文建立的航空座椅垫集中参数模型可为含座椅垫的复杂有限元模型简化提供支持。

新型智能孔板天然气计量装置原理与应用

为了解决天然气流量计及其计算机系统现场测量精度不足、校正流程繁琐、数据实时性差等问题,通过对现有流量测量系统进行智能式优化改造,实现对流量检测的精准执行与数据的精密搜集,可以实时监控气体流量,并完成了压缩因数与流量数值的实时运算。研究结果显示,通过融合PXI机箱与PXI板卡的相关技术以编写数据搜集与处理程序,实现了天然气动态监测与独立核算。实验数据表明,现场流量与设备测量值的相对误差远低于系统预设的0.3%标准,满足了现场测量要求,确保了天然气计量任务的顺利完成。

土-石混合填土强夯动应力的简化与修正算法

强夯法是一种加固某些土体的施工操作较为简单的方法,合理分析其夯击作用在土体中产生的动应力是工程实践中的关键环节之一。针对成都平原地区的典型土-石混合填土,通过现场夯击试验,测得了在4000 kN·m的夯击能作用下土体中不同深度处的竖向夯击动应力,鉴于既有算法与试验值的差异,从两个方面确定了适于土-石混合填土夯击动应力的简单计算方法。一方面针对较为复杂的既有理论公式问题,采用敏感性分析与回归分析法,建立了以夯锤质量、夯锤落距、夯锤半径、土体密度、土体动力剪切模量、土体泊松比、土体阻尼比、夯锤入土的速度损失率等8个参数表征夯击点冲击应力的线性回归方程;另一方面采用竖向动应力传递指数对理想弹性静力学理论公式进行修正,得到了基于拟静力法的土体中夯击动应力计算表达式,进而可分析确定强夯有效加固深度。试验结果显示,土-石混合填土的竖向动应力传递指数约为1.67357,土-石混合填土地层的强夯有效加固深度约为8.0m。

高温循环作用含孔砂岩动态力学特性试验研究

为研究高温循环作用含孔砂岩动态力学特性,利用SHPB试验装置对常温和经历200~800℃高温循环作用后含孔和完整砂岩试件开展冲击压缩试验。研究表明:随循环作用温度升高,砂岩试件由灰色逐渐变成褐色;质量损失率、体积膨胀率和密度降低率等物理参数均呈增大趋势,超过400℃时变化幅值显著增加;常温砂岩含有少量微孔隙,随循环作用温度升高试件表面微孔隙数量增多、宽度增大。高温循环作用后含孔试件动抗压强度呈二次函数关系减小趋势;动应变和动弹性模量则分别呈幂函数增大和线性函数关系减小趋势。随循环作用温度升高,试件破碎程度加剧,破碎块度减小,分形维数呈幂函数关系增大趋势;循环作用温度超过400℃时,试件动抗压强度、动应变、平均粒径和分形维数变化幅值均显著增大。研究成果对深部矿山资源开采和地热利用具有一定参考价值。

CacheCompress:一种新颖的面向IP核的动态字典测试压缩技术

提出一种称为CacheCompress的新颖的测试压缩技术。与以往基于静态字典压缩技术的最大不同在于,该技术中的字典是动态的,在整个测试过程中,伴随着写字典和读字典的操作,字典只需保留最常用的测试数据,从而大大减少了字典的容量需求,并消除了静态字典的初始化步骤。实验表明,CacheCompress将字典容量需求缩小为原来的千分之一,并提高了30%的测试压缩率。

风积沙静动力特性实验研究

针对我国沙漠公路中风积沙填料经水泥改良后在荷载作用下静动力特性不明确问题,以沙漠公路为依托,进行无侧限抗压试验、三轴剪切试验及动模量与动强度特性试验。研究结果表明,随着水泥掺量的提高,风积沙填料的无侧限抗压强度逐渐增强,而压实度对于抗压强度的影响并不明显。在水泥掺比低于6%时,改良后的风积沙表现出黏聚力和内摩擦角的快速增加,且一旦水泥掺量超过6%,这种增长趋势就开始减缓,随着围压和水泥掺量的增大,风积沙累积塑性应变逐渐减小,临界动应力增加,动模量显著提高。

基于微观机理的高温后大理岩动态力学特性分析

为研究温度对大理岩动态力学特性的影响,对常温(25℃)及高温(200℃、400℃、600℃和800℃)后的大理岩试样开展SHPB试验、XRD和SEM微观试验,探究了高温后大理岩动态力学特性与温度的关系及微观损伤机理。结果表明:高温后大理岩的动态压缩应力-应变曲线分为弹性、屈服、破坏3个阶段;大理岩的峰值应力及破坏特征均存在明显的温度效应,即随温度的升高,大理岩的峰值应力逐渐下降,破碎程度加剧;大理岩的动态力学特性与其矿物组分及晶体结构密切相关,200℃~600℃时,微缺陷增多,且白云石发生了热分解转化,在800℃时,矿物分解生成CO_(2)气体和氢氧化钙,且晶体结构发生熔融破坏,内部损伤严重,塑性增强,从而导致宏观力学特性的大幅下降。

Compressive deformation behavior of an indirect-extruded Mg-8Sn-1Al-1Zn alloy

The medium and warm deformation behaviors of an indirect-extruded Mg-8Sn-IAI-IZn alloy were investigated by compression tests at temperatures between 298 and 523 K and strain rates of 0.001-10 s-1. It was found that the twinning-slip transition temperature was strain rate dependent, and all the true stress-true strain curves could be divided into two groups： concave and convex curves. Associated microstructural investigations indicated that the dynamic recrystallization （DRX） be- havior of the alloy varied with deformation conditions. At high strain rate and low temperature, dynamically recrystallized grains preferentially nucleated and developed in the twinned regions, indicating that twinning-induced DRX was dominant. While, at low strain rate, DRX developed extensively at grain boundaries and twins, and the process of twinning contributed to both oriented nucleation and selective growth. For the studied alloy, cracks mainly initiated from the shear band and twinning lamellar over the ranges of temperature and strain rate currently applied.

Arrhenius公式和环境作用动力学对压缩橡胶的精度比较

目的 精确描述压缩橡胶永久变形率的变化规律,准确评估其使用寿命。方法 应用环境作用动力学理论,建立压缩橡胶永久变形率的变化微分方程,求解微分方程得到压缩橡胶永久变形率变化规律的微分方程通解。再以氟硅橡胶为例,通过高温加速试验获取其在100、125、150、175、200℃下的试验数据,分别采用环境作用动力学通解和阿伦尼乌兹公式建立氟硅橡胶压缩永久变形率模型。最后,与3.5 a的自然环境试验数据进行对比。结果 应用环境作用动力学理论建立的氟硅橡胶压缩永久变形率模型与3.5 a自然环境试验数据的最大误差约为3.32%,而应用阿伦尼乌兹公式建立的氟硅橡胶压缩永久变形率模型的最大误差约为14%。结论 阿伦尼乌兹公式只适用于没有环境作用或固定环境作用下的物质特征变化,而环境作用动力学方程中,有明确的环境作用项σ,适用于复杂环境作用下物质特征变化规律的描述。

压缩感知动态测试信号模型与电能表动态误差测试

文中针对智能电能表动态误差的高效测试问题,分析了长时间范围内复杂动态负荷信号幅度域的快速随机波动特性,建立了压缩感知伪随机动态负荷测试信号的模型,采用Hadamard矩阵和降采样矩阵结合的测量矩阵构建方法,确定了该测试信号的模型参数,提出了压缩感知测量信号的产生方案。采用试验方法,对比给出了压缩感知和m序列动态测试信号条件下电能表动态测试的误差数据。研究结果表明相比较于m序列伪随机测试信号,压缩感知动态测试信号的动态误差测试效率提高了4倍。

不同应变率下铅锌尾矿砂混凝土动态抗压力学性能试验研究

为了研究铅锌尾矿砂对混凝土动态抗压强度的影响,利用直径为100mm的分离式霍普金森压杆试验系统对尾矿砂掺量分别为0%、20%、40%、60%的铅锌尾矿砂混凝土试件进行动力压缩试验,对铅锌尾矿砂混凝土的动态抗压力学性能进行分析。结果表明:铅锌尾矿砂混凝土是一种典型的应变率敏感性材料,其动态抗压强度和极限应变均随着应变率的增大而增加;铅锌尾矿砂混凝土的应变率敏感性较普通混凝土的低,其碎块平均尺寸的应变率敏感性低于普通混凝土;不同尾矿砂掺量的混凝土动态抗压强度不同,随着掺量的增大呈现先上升后下降的变化趋势,掺量为20%左右时,动态抗压强度最高。通过使用离散元软件模拟掺量为20%组试件在不同应变率下的破坏情况,发现模拟出来的结果与试验结果能较好地吻合。

基于超声波测试的片岩单轴抗压强度预测模型

岩石单轴抗压强度是岩土工程中最基础、最重要的参数之一,建立其快速、方便、经济的预测方法一直是岩土界的研究热点。为了获取片岩单轴抗压强度的预测模型,基于超声波试验和单轴压缩试验数据,对福建某矿山的片岩岩样分别开展了单轴抗压强度与纵波波速、横波波速、纵波模量、横波模量、动弹性模量和静弹性模量的回归性分析,并各自建立了线性、对数、多项式、指数函数和幂函数5种回归模型。分析表明,除了动弹性模量以外,其他参量都易受空间变异性和各向异性影响,不适合用于片岩单轴抗压强度的预测。最终,通过拟合度、所包含参量、量纲平衡、测试方法以及显著性分析,确定基于动弹性模量建立的线性回归模型是最合理、可靠、方便的片岩单轴抗压强度预测模型。研究成果可为开展岩石单轴抗压强度预测的相关理论研究和工程应用提供参考和帮助。

基于压缩及油脂逃逸试验的盾尾刷性能评价研究

盾尾密封失效事故时有发生,严重时易造成了重大涌水涌砂安全事故,已经引起工程界与学术界的高度关注。基于盾尾刷动态压缩试验和盾尾密封油脂逃逸试验结果及分析,结果表明:①动态压缩试验测试结果能较好反映盾尾刷弹塑性力学性能,大幅度节约试验时间;②随着盾尾间隙不断减小,盾尾刷贴合力、弹性系数不断增大,塑性变形占比不断增大、弹性变形占比不断减小。盾尾间隙为110 mm时弹性变形占比为90%,盾尾间隙压缩至50 mm时弹性变形占比降低到60%;③建立了盾尾间隙、盾尾油脂逃逸量与盾尾刷贴合力关系图,获得了盾尾密封系统的工作安全区域,可对盾尾密封状态有效性进行评估。建立的盾尾刷密封性能评价方法,为盾尾刷性能评价及检测提供了参考。