正弦波下砂岩ms级损伤预测模型

为获得毫秒(ms)级正弦波损伤变量预测模型,对岩样在不破坏情况下进行了不同波形不同频率的轴向力加卸载试验。提出了不同步时间段的定义,进而获得不同峰值荷载下不考虑不同步时间条件下的动态泊松比分别与即时荷载、即时横向长度、即时轴向高度之间的线性关系,从而得到线性关系中系数与峰值荷载间的拟合公式,即可联立不同已知条件,通过少量几个加载力峰值下的试验数据,对任意峰值荷载下动态泊松比与相关参数间的线性关系进行预测。以此为基础研究得到,在误差允许的范围内,采用动态泊松比与即时横向长度的线性关系,推导出体积应变、损伤变量的计算公式和方法,可以很好地对加卸载过程中岩样的体积应变、损伤的变化做出ms级的精确预测,也为在已知少量循环试验下获得岩石动态参数,即可对ms级的损伤进行精确预测的模型提供了方法。     

基于应变率损伤本构模型的围岩分区破裂化现象数值模拟

为了探究深部巷道围岩的分区破裂化现象,利用ANSYS/LS-DYNA软件数值模拟,使用Cowper-Symonds本构模型结合GISSMO模型,将巷道的开挖视为动力过程。从岩石的细观角度出发,考虑岩石的应变率效应以及损伤对岩石的力学性质的影响,构建应变率损伤本构模型。同时结合应力三轴度,以更全面地描述岩石在各种应力条件下的力学特性,并基于最大应变和最大拉应力准则建立单元破坏准则。对岩石进行单轴压缩数值、掘进开挖法模拟及实际观测的结果表明:岩石单轴压缩全应力-应变曲线拟合效果较好;掘进开挖速率对分区破裂化现象有影响;掘进开挖法的分区破裂化模拟结果与实际观测数据具有一定的一致性。提出的模型对于围岩分区破裂化现场的模拟及预测有一定的参考意义。     

Rockburst mechanism in soft coal seam within deep coal mines

A number of rockburst accidents occurring in soft coal seams have shown that the rockburst mechanism involved in soft coal seams is significantly different from that involved in hard coal seams. Therefore, the method used to evaluate rockburst in hard coal seams is not applicable to soft coal seams. This paper established an energy integral model for the rockburst-inducing area and a friction work calculation model for the plastic area. If the remaining energy after the coal seam is broken in the rockburstinducing area is greater than the friction work required for the coal to burst out, then a rockburst accident will occur. Mechanisms of ‘‘quaking without bursting" and ‘‘quaking and bursting" are clarified for soft coal seams and corresponding control measures are proposed as the optimization of roadway layouts and use of ‘‘three strong systems"(strong de-stressing, strong supporting, and strong monitoring).     

混杂PVA-ECC配合比优化设计及力学性能试验研究

为了降低工程用水泥基复合材料(ECC, Engineered Cementitious Composites)制造成本,使ECC能够在实际工程中大规模应用,将中国产PVA纤维和日本产PVA纤维以一定的比例混合,配制混杂PVA-ECC。基于ECC的材料设计理论,兼顾抗压强度和受拉能力,对掺有硅粉的混杂PVA-ECC中的纤维体积含量进行了优化设计。通过四点弯曲试验和轴心抗压试验,研究了混杂PVA-ECC在不同龄期下的弯曲性能和抗压性能。试验结果表明,混杂PVA-ECC试件均表现出明显的应变硬化和多缝开裂的特征,此外,其抗压强度后期增长明显。基于UM法,提出一种改进的反分析方法,可利用四点弯曲试验结果推导ECC的极限拉伸应变,并与试验结果进行了比较,结果表明,通过建议的反分析方法得到的预测值与试验值吻合较好。     

小湾拱坝应力监测资料分析

小湾水电站以发电为主,兼顾防洪、灌溉和库区水运等.坝址处河谷基本对称,河谷深切呈"V"字型.为深入研究小湾拱坝坝体的动、静工作性态,对小湾拱坝坝体进行应力监测;根据应力监测资料进行徐变应力计算,得到实际应力,然后利用作图、特征值统计等定性时空分析方法推断出大坝应力无明显异常;通过分析统计结果以及压应力变量分离模型得到了应力的统计模型.     

易碎弹复合材料动态特性数值研究

利用Split Hopkinson Pressure Bar （SHPB）实验装置获取复合材料易碎弹试件的动态力学特性,并应用LS-DYNA软件对SHPB实验过程进行数值模拟.结合SHPB应力波理论,研究不同撞击速度对试件破坏程度、压杆轴向应变波形以及试件动态力学特性的影响.仿真结果表明：试件仿真结果与实验结果基本吻合,说明SHPB实验仿真是可行的;试件的破坏程度随着撞击速度的增大而显著,但压杆轴向应变波形以及试件动态力学特性随着撞击速度的增大变化不明显.     

基于虚拟仪器技术的轮荷测量仪电测系统开发

依据电阻应变测量原理,应用机电一体化技术,开发测量汽车轮荷的测量仪电测系统.该系统由数采硬件电路和上位机车辆轮荷测量系统软件组成.应变传感器测得的电压信号,先后经过调理电路、A/D转换电路和光电隔离电路,传输给MCU.通过串口通信协议,MCU与上位机轮荷测量系统间进行指令和数据的传输,数据经过存储和运算处理后,通过上位机系统面板把轮荷值传达给用户,并将结果储存到PC机中.采用砝码加载,在可倾斜卡具上对测量仪进行了实验标定.根据实验数据算得测量仪的非线性误差为±0.72%,重复性误差为±1.37%,迟滞性误差为±1.47%,灵敏度误差为±1.67%,最终得到综合误差为±2.71%,满足轮荷测量仪预期设计的测量精度和功能要求.     

Crack growth angle prediction of an internal crack under mixed mode load for unfilled elastomer using the strain energy density factor

This article investigates the prediction of the crack growth angle of an existing internal crack under mixed mode loading at the crack tip for an unfilled ethylene propylene diene terpolymer rubber (EPDM). For the realization of mixed mode loading, the cracks of the uniaxial loaded specimens were oriented with different angles to the loading direction. The energy density factor was used as a potential criterion for determining the crack growth angle. The determination of the strain energy density factor was carried out simulatively in Abaqus. The second-order Ogden model was used to describe the rubber-like material behavior. The relative local minimum of the strain energy density factor provides the possible growth angle. The experimental investigations show that the initial cracks grow orthogonally to the loading direction for the different crack orientation angles. For the crack orientation angle parallel to the load direction, the crack growth was observed because the strong stretching of the specimen caused strong necking in the crack region. The crack growth for the remaining crack orientation angles were induced due to shear loading at the crack tip. The predictive angle of different crack orientation angles shows very good accordance to the measured crack growth angles.     

新颖的绕线拉紧装置

本文介绍一种新型适用的线圈绕制中的线材拉紧装置，并将其与传统的拉紧装置进行比较，得出各自的优缺点。     

Dynamic hardness of detonation sprayed WC-Co coatings

The objective of the present work was to determine the dynamic hardness of WC-Co coatings from the dynamic hardness of the coating substrate system. It was also the purpose of this work to evaluate the influence of coating composition, coating thickness, and substrate materials on the dynamic hardness of the coating. To achieve the above-mentioned objectives, WC-12%Co and WC-17%Co coatings were deposited by detonation spraying on three different substrate materials: mild steel, commercially pure (CP) aluminum, and CP titanium. The dynamic hardness of the coating/substrate composite was evaluated by a drop weight system. The dynamic hardness of the coating independent of the substrate was determined from the dynamic hardness of the coating/substrate composite.