基于双谱时延估计的爆心定位研究

爆心距是影响爆破振动强度的重要因素,对爆心的准确定位可获取更接近实际情况的爆心距,从而更加准确的对爆破振动质点速度峰值进行预测.基于现场的实测爆破振动信号,利用MATLAB软件编制程序,进行双谱时延估计仿真试验,验证了此方法对于爆破振动信号时延估计的可靠性.然后利用该方法确定不同传感器接收的爆破振动信号延迟时间,采用正...     

基于LSTM和响应分解的冲击载荷识别方法研究

同一量级的冲击载荷所产生的动响应要远大于静态响应,因此准确识别冲击载荷对于航空器结构件的动强度设计、校核与结构健康监测都具有重要意义。该文章提出的方法主要针对一般线性结构的冲击载荷识别问题,从实测冲击响应应变信号出发,主要解决了冲击载荷与响应信号样本长度不一致这一突出矛盾。首先基于冲击响应信号分解方法来进行振动信号特征提取,然后基于长短期记忆神经网络对载荷和响应信号样本特征进行映射,从而实现冲击载荷识别。通过对挂架模型实测冲击载荷信号进行识别,结果表明4种工况下,该方法识别的冲击载荷的均方根相对误差小于0.6,相关系数大于0.94。结果初步表明,在理想的试验环境中,该方法具备一定的识别精度。     

核反应堆心的失压冲击响应

根据堆心的三维均匀化动力学模型，给出了分析堆心压力失稳的基本方程和定解条件。采用有限元法进行离散，以流体速度势和管梁挠度为未知量，得到了一组具有对称性的控制方程。然后，通过模态展开法，获得了系统在失压冲击下的响应。     

全钒液流电池离子交换膜合成方法综述

全钒氧化还原液流电池(VRFB)具有储能效率高、循环寿命长、安全可靠、低成本等优点,在大规模储能中具有良好的应用前景.而作为VRFB的核心部件,离子交换膜应具有钒离子透过率低、电导率高、化学稳定性好等性能.总结了近年来国内外相关的研究进展,对比了不同合成方法的优缺点,并提出了开发适用于VRFB的高性能离子交换膜的建议.     

下心盘除锈机设计

货车下心盘起着连接车体与走形部和传递牵引力的作用，是铁路货车的关键部件。以往心盘检修除锈工序采用手工电刷进行，污染严重、效率低、劳动强度大。为此作者设计了心盘除锈专用设备，大幅度提高了心盘除锈效率，减少了环境污染、降低了劳动强度。本文从设计预想、结构设计、电气原理、气动原理、运行动作等方面对心盘除锈机的设计进行了较为详细的说明。     

基于修正Anderson 模型的冲击载荷下地基振动响应预测方法

提出了一个预测潜在冲击载荷下振动效应的理论模型与现场实测相结合的综合预测方法。通过一系列具有针对性的室外重锤冲击振动试验,以及现场实测数据对Anderson模型进行了验证并修正,然后利用修正的Anderson模型预测冲击荷载的振动效应。将预测结果和现场试验结果进行对比分析,结果表明:预测结果与实测结果吻合较好。     

冲击能力验证中可疑数据的分析

阐述了冲击能力验证产生可疑数据的原因，并通过试验作了验证。试验表明，由于使用的JB30B摆锤式冲击试验机在摆锤铅垂时，冲击刀刃到垂直支撑面的距离公差过小，且砧座之间跨距公差过大，造成了金属夏比能力验证在高能量级组数据出现了可疑数据的现象。就冲击试验现行的有关国家标准对这两项指标的规定作了比较与分析，提出了建议。     

心相印抽纸被曝“欠抽”

事件Background日前,有网友发现恒安集团心相印品牌抽纸存在"缺斤少两"的现象,标注200抽的抽纸,实数只有172抽。之后,《三湘都市报》记者对纸品市场产品进行了实测,结果发现标注130抽/包的心相印抽纸实际有126抽。而根据国家标准规定,纸巾装量偏差为2%的才为合格产品。如此看来,心相印的抽纸确属于不合格产品。     

钻井取心常规技术措施的实践与认识

钻井取心是获取准确地层资料的主要手段之，有时甚至是唯一的手段。取心技术措施的合理与否不仅会影响取心收获率、密闭率、作业效率，而且会影响到岩心的质量和区域油田勘探开发方案的实施进程。文章拟结合部分现场取心作业实际施工情况．对现行的钻井取心技术措施提出一些可行性建议，旨在进一步提高取心作业的质量与效率。     

采用非连续变形分析对空气冲击湿砂造型过程的数值模拟

空气冲击湿砂造型过程有着本身的特点：快速冲击，离散的材料体系，材料非线性和几何大变形并存，是一个非常复杂的力学过程。本文首次使用非连续变形分析(DDA)的方法建立了粘弹性本构非连续块体模型模拟松散型砂体系，对松散型砂在空气冲击作用下的密实过程进行了数值模拟。通过与相应的实验数据以及有限元方法的计算结果进行比较，本文得出以下结论：非连续变形分析方法可以较好地解决湿砂造型空气冲击紧实过程的数值模拟问题，其应力时间曲线与实测曲线趋势基本相同，相对于有限元方法的计算结果来说，DDA的计算应力值与实测应力值的偏差比较小；使用非连续变形分析进行松散型砂应力场的数值模拟比有限元方法更接近真实情况。     

The effect of short cardio on inhibitory control ability of obese people

To study the effect of short cardio on obese male college students’ inhibitory control ability, we investigate difference on brain activation patterns before and after short cardio by analyzing the resting state fMRI data. The experiment results of this study show that short cardio can improve the inhibitory control ability of obese people.     

Recent advances in metals and metal oxides as catalysts for vanadium redox flow battery:Properties,structures,and perspectives

Vanadium redox flow battery(VRFB)is a kind of battery with wide application prospect.Electrode mate-rial is one of the key components of VRFB,and its stability directly affects the performance of battery.Among all kinds of electrode materials,carbon-based material has the best comprehensive properties.However,carbon-based electrodes still have disadvantages such as poor hydrophilicity and low electro-chemical activity which need to be improved.One of the effective ways to improve the performance of electrode is to modify carbon-based material with metals and metal oxides.The metal catalysts have excellent electrical conductivity and high catalytic activity.The metal oxide catalysts have the advan-tages of low cost,wide variety and strong oxidizing properties.This work introduced the application of metal and metal oxide modified electrodes in VRFB in recent years,classified the catalysts,studied their catalytic performance and mechanism.The metal catalysts were reviewed from precious metals and base metals.The metal oxide catalysts were classified and discussed according to the similar proper-ties of the same group elements.This work compared different modification methods,summarized the research progress of metal and metal oxide modification,and proposes the future development direction of electrodes and catalysts.     

A numerical investigation into the influence of fabric construction on ballistic performance

The use of high-performance fibres has made it possible to produce lightweight and strong personal body armour. Parallel to the creation and use of new fibres, fabric construction also plays an essential role for performance improvement. In this research, finite element (FE) models were built up and used to predict the response of woven fabrics with different structural parameters, including fabric structure, thread density of the fabric and yarn linear density. The research confirmed that the plain woven fabric exhibits superior energy absorption over other structures in a ballistic event by absorbing 34% more impact energy than the fabric made from 7-end satin weave. This could be explained that the maximum interlacing points in this fabric which help transmit stress to a larger fabric area, enabling more secondary yarns to be involved for energy dissipation. It was found that fabric energy absorption decreases as fabric is made denser, and this phenomenon becomes more pronounced in a multi-ply ballistic system than in a single-ply system. The research results also indicated that the level of yarn crimp in a woven fabric is an effective parameter in influencing the ballistic performance of the fabrics. A low level of yarn crimp would lead to the increase of the fabric tensile modulus and consequently influencing the propagation of the transverse wave. In addition, it was found that for fabrics with the same level of yarn crimp, low yarn linear density and high fabric tightness were desirable for ballistic performance improvement.     

尖头弹侵彻延性金属靶板弹道极限的解析模型

现有的尖头弹侵彻金属靶板的弹道极限计算模型往往需要大量的试验数据和靶板材料的动态性能参数,且没有考虑侵彻速度对侵彻效果的影响,这给工程应用带来了很大的不便和误差。基于这一问题,考虑速度效应和靶板材料参数对侵彻的影响,结合流体动力学原理与动态空穴膨胀理论,分别提出了双模式和单模式侵彻模型。双模式侵彻模型的侵彻过程可分为两个阶段：流体动力变形阶段和塑性变形阶段,当侵彻速度小于靶材产生流体动力变形的临界速度时,侵彻进入塑性变形阶段,根据功能原理,建立了计算弹道极限的解析模型;单模式侵彻模型仅考虑塑性变形阶段。解析模型计算的弹道极限与弹道试验结果吻合的较好,且模型中不涉及弹道试验数据和靶板材料的动态性能参数,易于迅速求解,便于工程应用,可用于对延性金属靶板抗尖头弹侵彻能力的评估。     

Modeling the impact behavior of AD85 ceramic under multiaxial loading

This paper presents an advanced constitutive model to describe the complex behavior of ceramic materials under impact loading conditions. The governing equations utilize a set of microphysically based constitutive relationships to model deformation and damage processes in a ceramic. The total strain is decomposed into elastic, plastic and microcracking components. The model parameters for AD85 ceramic were determined using the data from split Hopkinson bar and bar-on-bar experiments under uniaxial stress state and plate impact experiment under uniaxial strain state. To further validate the generality of the model parameters, modeling of a diagnostic ballistic experiment in which a steel projectile impacted a AD85 ceramic-front-faced thick aluminium plate, was considered. In this experiment, stress histories were measured in the target by embedded manganin and carbon stress gauges. The results from the numerical simulations of the ballistic experiment using a shock-wave propagation based finite element code, successfully matched the measured stress history.     

Numerical and experimental investigations into ballistic performance of hybrid fabric panels

Strong, low density fibres have been favoured materials for ballistic protection, but the choice of fibres is limited for making body armour that is both protective and lightweight. In addition to developments of improved fibres, alternative approaches are required for creating more protective and lighter body armour. This paper reports on a study on hybrid fabric panels for ballistic protection. The Finite Element (FE) method was used to predict the response of different layers of fabric in a twelve-layer fabric model upon impact. It was found that the front layers of fabric are more likely to be broken in shear, and the rear layers of fabric tend to fail in tension. This suggested that using shear resistant materials for the front layer and tensile resistant materials for the rear layer may improve the ballistic performance of fabric panels. Two types of structure, ultra-high-molecular-weight polyethylene (UHMWPE) woven and unidirectional (UD) materials, were analyzed for their failure mode and response upon ballistic impact by using both FE and experimental methods. It was found that woven structures exhibit better shear resistance and UD structures gives better tensile resistance and wider transverse deflection upon ballistic impact. Two types of hybrid ballistic panels were designed from the fabrics. The experimental results showed that placing woven fabrics close to the impact face and UD material as the rear layers led to better ballistic performance than the panel constructed in the reverse sequence. It has also been found that the optimum ratio of woven to UD materials in the hybrid ballistic panel was 1:3. The improvement in ballistic protection of the hybrid fabric panels allows less material to be used, leading to lighter weight body armour.     

能量平衡法在防弹性能估算中的应用研究

为了合理设置装甲板,并进行有效的性能评估,使用图解方法研究了能量平衡原理在装甲板弹道性能估算中的应用,并以不饱和聚酯树脂基玄武岩纤维增强复合材料和钢为例进行了实验验证,研究表明：估算过程中虽然没有从装甲板的毁伤机理方面研究,并简化了抗弹性能的影响参数,但保证了较高的估算精度,预测速度偏差在50m/s以下,预测相对偏差在10%以下,能够满足工程需要。     

Ballistic resistance of spaced multi-layer plate structures: Experiments on Fibre Reinforced Plastic targets and an analytical framework for calculating the ballistic limit

As the use of complex multi-layer structures in defense, marine, aerospace and automotive applications becomes increasingly common, it is vital that the response of such structures to impact loading is better understood and that engineers have adequate analysis tools to design structures optimised for resistance to ballistic penetration. This paper presents the results of a series of ballistic impact experiments carried out on a range of spaced multi-layer fibre reinforced-plastic (FRP) composite targets, with a constant total number of plies per target, but varying numbers of plies per layer and varying layer arrangements. It is shown that varying the ratio of plies between layers can have a significant effect on resistance to ballistic penetration. In light of these experimental results, the validity of applying the Lambert–Jonas equation to spaced multi-layer structures is discussed and an extended framework developed to determine the ballistic limit of a projectile impacting such a structure. The extended Lambert–Jonas framework is then validated with data from the literature. It is hoped that this framework will allow engineers to quickly determine the optimum layer arrangement to maximise the ballistic resistance of complex spaced multi-layer structures.     

三维编织复合材料弹道侵彻准细观层次有限元计算

三维编织复合材料相比于层合复合材料有较高的层间剪切强度和断裂韧性,因而具有更高的冲击损伤容限。用钢芯弹对三维编织复合材料作弹道贯穿测试,得到弹体的入射速度和剩余速度,并考察侵彻破坏模式。目前对三维编织复合材料弹道侵彻性能计算主要建立在连续介质假设上,从真实细观结构计算三维编织复合材料弹道冲击性能尚有一定难度,用三维结构复合材料的纤维倾斜模型在准细观结构层次上分解三维编织复合材料,就其中的一块倾斜单向板作弹道侵彻有限元计算,由弹体动能损失得到贯穿整个复合材料靶体后弹体的剩余速度。有限元计算及与弹道测试结果的比较证明在准细观层次上计算三维编织复合材料弹道冲击性能的有效性。      

Multi-scale finite element analysis for tension and ballistic penetration damage characterizations of 2D triaxially braided composite

The multi-scale finite element model is presented to analyze tension and ballistic penetration damage characterizations of 2D triaxially braided composite (2DTBC). At the mesoscopic level, the damage of fiber tows is initiated with 3D Hashin criteria, and the damage initiation of pure matrix is predicted by the modified von Mises. The progressive degradation scheme and energy dissipation method are adopted to capture softening behaviors of tow and matrix. The macro-scale damage model is established by maximum-stress criteria and exponential damage evolution. To simulate interface debonding and inter-ply delamination, a triangle traction–separation law is adopted in each scale. Both scale damage models are verified with available experimental results. Based on numerical predictions, the stress–strain responses and damage developments of 2DTBC under axial and transverse tension loading are studied. For ballistic penetration loading, the meso-scale damage mechanisms of 2DTBC are predicted using 1/4 model, 1/2 model, 1-layer model, 2-layer model and 3-layer model. Then, effects of different model and impactor radius on damage modes are analyzed. Additionally, the macro-scale ballistic penetration behaviors of 2DTBC are simulated and compared with experiment. The prediction results for tension and penetration correlate well with experiment results. Both tension and penetration damage characterizations for tow, matrix within tow, pure matrix, interface and inter-ply delamination are revealed. A comparison of penetration damage between meso- and macro-scale presents a similar crack mechanism between two scales.