弹性弹体侵彻混凝土靶板的过载特性研究

研究了弹性弹体侵彻半无限混凝土靶板的冲击过载特性,利用泰勒级数将弹体两个侵彻阶段的阻力表示为一个函数并考虑应力波的影响,提出了简化的侵彻方程。对边界条件进行齐次化,介绍了求解弹体加速度历程的分离变量算法。尖形弹丸垂直侵彻混凝土靶板试验和Sandia实验室的侵彻过载试验数据与计算结果对比,显示两者一致性较好。分析了弹体内不同位置的过载波动特性,为侵彻用火工品和小型装药的过载安定性和可靠性评估提供了理论参考和分析方法。     

弹体侵彻刚玉块石混凝土的理论分析模型

根据弹体侵彻刚玉块石混凝土后破坏、变形特征,在Taylor理论的基础上,建立了变形弹体侵彻刚玉块石混凝土靶体的理论分析模型.通过Rang-Kutta法数值解,得到了弹丸侵彻刚玉块石混凝土靶体过程中弹体尾部的位移时程、速度时程和侵彻深度计算公式,计算结果与试验数据吻合良好.     

刚性弹侵彻有限直径金属厚靶的机理与模型研究

采用统一强度理论,考虑靶板中间主应力效应和靶体侧面自由边界的影响,得到线性硬化靶材在弹塑性阶段和塑性阶段的空腔壁径向应力的表达式,建立线性硬化靶材的统一侵彻模型,求出中低速(v₀≤1000 m/s)刚性弹体侵彻有限直径金属厚靶时侵彻阻力、侵彻深度计算公式,并利用Simpson算法对其进行求解,分析了包括强度准则差异在内的弹道终点效应的一系列影响因素。结果表明:该文计算方法可以更好地描述侵彻过程中弹靶的动态响应,还可以得到一系列基于不同强度准则的侵彻阻力和深度的解析解、对靶材在不同撞击速度下侵彻深度的区间范围进行有效预测;强度参数、弹体撞击速度、靶体半径和弹头形状对有限直径金属厚靶的抗侵彻性能均有较大的影响,其中强度参数值由1减小为0时,侵彻深度增加了22.45%;随着靶弹半径比的减小,侵彻深度不断增大,当靶弹半径比小于等于16时,侵彻深度增大的程度显著,此时靶体边界尺寸对侵彻性能的影响很大,不能继续按照半无限靶体进行计算。     

高速长杆弹对有限直径金属厚靶的侵彻分析EI北大核心CSCD

采用基于统一强度理论的有限柱形空腔膨胀理论,结合Tate磨蚀杆模型,考虑中间主应力、靶体侧面自由边界的影响及高速(1500 m/s~2200 m/s)侵彻弹体的变形和消蚀现象,推导线性硬化有限直径金属厚靶在长杆弹高速侵彻时的空腔壁径向应力,建立侵彻阻力和侵彻深度计算模型,并利用MATLAB软件编程求解,分析包括强度准则差异在内的弹道终点效应的一系列影响因素。结果表明:该文计算方法可以更好地描述弹靶的动态响应,还可以得到一系列基于不同强度准则的侵彻阻力和深度的解析解、对不同靶弹半径比的靶材侵彻深度的区间范围进行有效预测;强度参数、弹体撞击速度和靶体半径对有限直径金属靶体的抗侵彻性能均有较大的影响,其中强度参数值由1减小为0时,侵彻阻力可减小33.33%,侵彻深度可增加15.93%;当靶弹半径比小于等于20时,侵彻深度增大的程度显著,当靶弹半径比由19.88减小至4.9时,侵彻阻力减小了41.30%,侵彻深度增长了32.61%,此时靶体边界尺寸对侵彻性能的影响很大,不能继续按照半无限靶体进行计算。     

普通混凝土HJC本构模型参数确定

Holmquist-Johnson-Cook(HJC)本构模型广泛应用于冲击爆炸作用下混凝土类材料的动态响应分析中。基于已有普通混凝土(单轴抗压强度≤60 MPa)的准静态单轴压缩实验、三轴围压实验、一维SHPB实验和一维平面应变Hugoniot冲击压缩实验数据,确定了一组适用于不同强度普通混凝土材料HJC本构模型的强度参数、率效应参数和状态方程参数取值。基于上述确定参数值通过LS-DYNA有限元分析软件,对十五组普通混凝土(单轴抗压强度13.5~58.4MPa)靶体的刚性弹体侵彻贯穿实验进行了数值模拟。通过与实验中弹体侵彻深度,贯穿残余速度以及弹体过载和靶内径向应力时程结果对比,验证了所确定模型参数的准确性。     

刚性尖头弹侵彻圆柱形金属厚靶分析模型

考虑金属厚靶侧面自由边界的影响,研究了刚性尖头弹侵彻有限平面尺寸金属厚靶问题。基于有限柱形空腔膨胀理论和线性硬化材料模型,得到了空腔壁径向压力的解析式,建立了刚性尖头弹侵彻有限直径圆柱形金属厚靶工程模型。与试验和数值模拟比较表明,该文工程模型计算精度很好。基于所建立的工程模型,研究了靶板半径对侵彻深度和侵彻阻力的影响,结果表明:当靶板与弹丸半径比值小于20时,靶板半径对侵彻阻力和侵彻深度有显著影响,不能按无限尺寸靶板计算;当靶板与弹丸半径比值大于20时,靶板半径对侵彻阻力和侵彻深度影响较小,可近似按无限尺寸靶计算。     

刚性弹体对素混凝土厚靶侵彻响应的LDPM数值模拟研究EI北大核心CSCD

基于一种新的细观离散元模型Lattice Discrete Particle Model(LDPM),该研究建立了刚性弹侵彻素混凝土厚靶的数值仿真模型。对LDPM基本假设和细观模型构建简单介绍,结合三轴压缩响应曲线,对23 MPa强度素混凝土进行LDPM参数标定。通过对比弹体减速度和侵彻深度试验值,验证数值模型对于混凝土厚靶侵彻问题的适用性。LDPM模拟弹体恒定速度侵彻混凝土厚靶,获得侵彻行程中侵彻阻力变化曲线,结合Forrestal阻力公式得到靶体静态阻应力。仿真结果表明,尖卵形弹头不同CRH值以及侵彻速度对靶体静态阻应力基本没有影响;弹径为最大骨料直径3倍、6倍和8倍的弹体受到靶体静态阻应力分别为260 MPa、175 MPa和163 MPa。该结果对混凝土侵彻缩比实验研究具有重要的实际工程意义。     

刚性弹体对素混凝土厚靶侵彻响应的LDPM数值模拟研究

基于一种新的细观离散元模型Lattice Discrete Particle Model(LDPM),该研究建立了刚性弹侵彻素混凝土厚靶的数值仿真模型。对LDPM基本假设和细观模型构建简单介绍,结合三轴压缩响应曲线,对23 MPa强度素混凝土进行LDPM参数标定。通过对比弹体减速度和侵彻深度试验值,验证数值模型对于混凝土厚靶侵彻问题的适用性。LDPM模拟弹体恒定速度侵彻混凝土厚靶,获得侵彻行程中侵彻阻力变化曲线,结合Forrestal阻力公式得到靶体静态阻应力。仿真结果表明,尖卵形弹头不同CRH值以及侵彻速度对靶体静态阻应力基本没有影响;弹径为最大骨料直径3倍、6倍和8倍的弹体受到靶体静态阻应力分别为260 MPa、175 MPa和163 MPa。该结果对混凝土侵彻缩比实验研究具有重要的实际工程意义。     

陶瓷-活性粉末混凝土复合靶抗侵彻试验研究

为研究陶瓷材料应用到工程防护领域的抗侵彻性能。设计了3块陶瓷-活性粉末混凝土复合靶,利用直径125 mm的特制弹体对陶瓷-活性混凝土复合靶体进行DOP(Depth of Penetration)侵彻试验,得到了弹体的飞行姿态、着靶速度、破坏形态和靶体的侵彻深度、弹坑范围、破坏形态等试验参数,定性分析了陶瓷靶厚度和纤维层约束作用对复合靶体抗侵彻性能的影响;结果表明:陶瓷靶具有优良的抗侵彻性能,在低速(360～400 m/s)情况下对弹体能产生一定侵蚀作用;随着陶瓷靶厚度的增加,陶瓷靶的破坏形态由冲切贯穿型转变为变形凸起型破坏,耗能能力增加,复合靶体的整体抗侵彻能力增强;采用修正的别列赞公式对陶瓷靶的侵彻系数进行了初步分析,并计算了三种厚度陶瓷靶的质量防护系数和差分防护系数。结果表明,试验所用陶瓷靶的抗侵彻能力约为普通C40混凝土的4.9倍,从而为陶瓷材料在重要防护工程的推广使用提供参考。     

弹体对半无限厚混凝土靶侵彻的数值分析

本文采用混凝土的全过程动态计算本构模型,利用拉郎日弹性塑性有限元程序分析了刚性弹体侵彻半无限厚混凝土靶的深度与弹重、着靶速度、弹头形状、弹体长径比等之间的关系,并分析了弹体侵砌混凝土靶的过程中弹体的结构响应。     

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。     

Elasto-optics in double-coated optical fibers induced by axial strain and hydrostatic pressure

Stresses, microbending loss, and refractive-index changes induced simultaneously by axial strain and hydrostatic pressure in double-coated optical fibers are analyzed. The lateral pressure and normal stresses in the optical fiber, primary coating, and secondary coating are derived. Also presented are the microbending loss and refractive-index changes in the glass fiber. The normal stresses are affected by axial strain, hydrostatic pressure, material properties, and thickness of the primary and secondary coatings. It is found that microbending loss decreases with increasing thickness, the Young's modulus, and the Poisson's ratio of the secondary coating but increases with the increasing Young's modulus and Poisson's ratio of the primary coating. Similarly, changes in refractive index in the glass fiber decrease with the increasing Young's modulus and Poisson's ratio of the secondary coating but increase with the increasing Young's modulus and Poisson's ratio of the primary coating. Therefore, to minimize microbending loss induced simultaneously by axial strain and hydrostatic pressure in the glass fiber, the polymeric coatings should be suitably selected. An optimal design procedure is also indicated.     

Effective creep Poisson's ratio for damaged concrete

First, creep data are presented for concrete under high sustained compressive stress which is, over the long-term strength of the concrete. Creep in both axial and lateral directions is reported. Creep Poisson's ratio has remarkable change before failure, and a sharp increase of creep Poisson's ratio can be observed in the region of failure.Secondly, a damage model is developed for the analysis of creep damage in both axial and lateral directions; effective Poisson's ratio of damaged material as a model parameter plays an important role for evaluating lateral damage, which is similar to the effective Young's modulus in evaluating axial damage.     

Compressive strength of a rigid-rod polymer fibre embedded in an isotropic matrix

The results are presented of an approximate elastic stability analysis for an anisotropic polymer fibre under compressive stress, which is embedded in an isotropic elastic matrix. This case, which thus far has not been treated properly, corresponds most closely to the experiments, which yield the best quantitative measurements of the compressive strength of high-modulus polymer fibres. Within the limits of a weak matrix, i.e. the shear modulus of the matrix is small compared to the shear modulus of the fibre, a simple analytical formula has been obtained for the compressive strength of the fibre in terms of its longitudinal Young's modulus, and the Poisson's ratio and shear modulus of the matrix. On the other hand, for a strong matrix the compressive strength of the fibre is solely determined by its shear modulus. For the intermediate regime, a simple but highly accurate interpolating expression has been constructed.     

Critical reevaluation of the prediction of effective Poisson's ratio for porous materials

An equation has been derived for the prediction of the Poisson's ratio of porous materials having ribbon like pores. The equation fits the data of silica gel with ribbon like pores quite well for the whole range of porosity. For spherical pores, a relation derived by previous researchers showed an anomalous variation in Poisson's ratio with porosity. It has been shown that it was due to the mathematical form of the function chosen to describe the relation between the bulk and Young's moduli with porosity. In this analysis, a modified form of the function to describe Young's and bulk modulus with porosity has been suggested for spherical pores. The derived relation for variation of Poisson's ratio with porosity shows good agreement with the prediction by self consistent theory.     

Young Arctic frazil sea ice: Field and laboratory strength tests

Methods of conducting and analysing uniaxial compressive strength and deformation measurements in the field and in the laboratory by means of conventional and closed-loop controlled test machines, respectively, are described, plus procedures for sampling, shipping, storing specimens and microstructural studies. Reliable measurements of the rate sensitivity of strength and deformation modulus of young congealed frazil sea ice can be obtained irrespective of location. Observations of Poisson's ratio, its variation during the tests, and its dependence on rate of loading are discussed.     

Effects of Young's modulus of epoxy resin on axial compressive strength of carbon fibre

Using epoxy resins with various molecular weight between cross-linkings, attempts have been made to estimate the fibre axial compressive strength of pitch-based graphitized fibre, and the effect of Young's modulus of epoxy resins on compressive strength was investigated. The estimated compressive strength of fibre decreases with increasing temperature. This decrease in compressive strength may be accounted for by a decrease in the radial compressing force due to a decrease in the residual thermal stress. There is a linear relationship between the estimated compressive strength and radial compressive force in a temperature range from room temperature to 80 °C. The estimated compressive strength of the fibre increases with increasing Young's modulus of epoxy resins. In order to realize reinforcing fibres with a higher compressive strength, it will be necessary to use a resin matrix with a higher modulus.     

泡沫塑料杨氏模量所满足的微分方程和一些近似解的讨论

本文通过复合材料力学中的微分法和微观力学分析直接导出了泡沫塑料杨氏模量和泊松比所满足的微分方程组，并通过对方程组的讨论得到了泡沫塑料杨氏模量理论预测的近似公式。这些公式形式简单，与实验符合较好，便于工程应用。     

Studies of Size Effects on Carbon Nanotubes' Mechanical Properties by Using Different Potential Functions

We use molecular mechanics calculations to study size effects on mechanical properties of carbon nanotubes. Both single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs) are considered. The size-dependent Young's modulus decreases with the increasing tube diameter for a reactive empirical bond order (REBO) potential function. However, we observe a contrary trend if we use other potential functions such as the modified Morse potential function and the universal force field (UFF). Such confliction is only obtained for small tubes within cutoff diameters (3 nm for REBO and 1.5 nm for others). In light of these predictions, Young's moduli of large nanotubes concur with experimental results for all the potential functions. No matter which potential function is used, the Poisson's ratio decreases with the increasing tube diameter. We also study the chirality effects on mechanical properties of SWNTs. We find that the Young's moduli are insensitive to the chirality of nanotubes. The chirality effect on the Poisson's ratio is significant for the UFF but not the REBO or modified Morse potential functions.