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.     

基于颗粒流离散元模型的弹丸侵彻细观混凝土数值模拟方法研究

利用颗粒离散单元法,研究弹丸侵彻细观混凝土模型中弹丸受到介质的阻应力与侵彻速度的关系。采用蒙特卡罗法随机生成并投放混凝土骨料且骨料的粒径分布满足级配曲线。通过对混凝土颗粒离散元细观力学模型进行单轴压缩实验、巴西劈裂实验和双轴压缩实验的参数反演,确定细观模型参数,能使细观混凝土模型具有和一般混凝土等效的力学性能。分析了骨料、过渡层和砂浆三相材料各细观参数对混凝土单轴压缩应力应变关系影响以及锥形弹和平头弹弹丸直径对侵彻阻应力的影响。将颗粒离散元细观力学模型方法计算的弹丸阻应力与空腔膨胀理论计算模型相比较,表明计算离散元方法具有良好的精度和实用性。     

弹丸垂直侵彻无钢筋混凝土数值模拟

本文利用所提出的无钢筋混凝土动态材料模型对半球形头部钢弹以300m/s速度垂直侵彻无钢筋混凝土目标进行了有限元计算模拟，得到的弹丸减速度时间历程曲线、最大侵彻深度与试验结果符合得较好，靶上弹坑形状和大小试验结果有差异。     

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。     

对弹体侵彻混凝土靶体阻力函数计算公式的探讨

基于动态球形空腔膨胀理论,探讨了混凝土材料的单轴抗压强度、弹性模量、泊松比、压力硬化系数对阻力函数的影响,并指出,混凝土靶体的弹性模量和单轴抗压强度对阻力函数影响较明显,而泊松比和压力硬化系数的影响可以忽略不计。在此基础上,该文忽略泊松比和压力硬化系数的影响,通过引入弹性模量与单轴抗压强度的关系式,分别建立了基于弹性-断裂-塑性和弹性-塑性两种靶体响应模型下,同时考虑单轴抗压强度和弹性模量影响的阻力函数理论公式,并建立了弹体侵彻靶体的加速度时程计算模型。通过与不同尺寸弹体侵彻实验数据对比,验证了该文提出阻力函数表达式的适用性及其在加速度时程以及较大尺寸弹体侵彻深度计算中的优 越性。     

有限柱形空腔膨胀理论及其应用

为研究有限平面尺寸金属厚靶侵彻问题,提出了有限柱形空腔膨胀理论.考虑侧面自由边界,将理想弹塑性材料的空腔膨胀过程分为弹塑性阶段和塑性阶段,得到了空腔壁径向压力的解析解.基于Tate磨蚀杆模型,应用有限柱形空腔膨胀理论计算靶的侵彻阻力,建立了长杆弹侵彻有限直径圆柱形金属厚靶工程模型.与现有文献试验比较表明,文中工程模型计算的侵彻深度与弹道试验结果吻合较好.     

基于Hoek-Brown准则的混凝土-岩石类靶侵彻模型

基于空腔膨胀理论建立工程模型是研究侵彻问题的常用方法。针对射弹侵彻岩石-混凝土类脆性材料半无限靶问题,基于靶体的弹性-裂纹-粉碎响应模式,粉碎区采用考虑围压的Hoek-Brown准则,得到了准静态球形空腔膨胀的空腔壁压力。在Forrestal两个阶段侵彻模型中,用所得空腔壁压力代替隧道侵彻阶段的侵彻阻力,得到刚性弹侵彻岩石-混凝土类脆性材料半无限靶的侵彻深度预估公式,与文献侵彻试验以及现有典型侵彻深度预估公式比较表明,预估公式适用范围更广,对于(超)高强混凝土和岩石材料靶的预测精度更高。     

单层紧密排列刚玉球砼抗弹丸冲击特性分析

本文利用ANSYS／LS－DYNA有限元软件，首先对弹丸在混凝土中的侵彻过程进行了数值模拟分析，并将计算结果与经验公式给出的结果进行了对比，两者吻合较好，表明模拟计算中材料参数的选取是合理的，计算方法是正确的。在此基础上，对弹丸在单层紧密排列刚玉球混凝土中的冲击侵彻情况进行了数值计算，结果表明，刚玉球混凝土能够有效地使弹丸偏转，减小弹丸侵彻深度，降低弹丸的冲击破坏效应，与已有的试验现象和试验结果相近。     

HJC模型模拟钢筋混凝土侵彻实验的参数研究

运用LS-DYNA程序将表征钢筋的梁单元和表征混凝土的实体单元通过节点耦合进行钢筋混凝土分离建模,数值模拟Hanchak等关于钢筋混凝土靶的穿甲实验,进一步修正HJC模型的参数,在讨论单元失效删除准则的静水压和主应变2种参数对混凝土拉伸破坏影响的基础上,重点对HJC模型关键字参数中的失效类型参数（FS）进行分析,并研究其对混凝土压实破坏的影响。通过改变弹丸侵彻钢筋混凝土靶时的着靶位置,加深了对钢筋在侵彻过程中作用的认识,同时验证该数值模拟方法可行性。所确定的建模方法及参数进一步用于某大质量卵形弹侵彻钢筋混凝土试验的研究工作。     

球形破片侵彻明胶的瞬时空腔简化模型

对破片侵彻明胶形成的瞬时空腔现象进行了研究,基于LS-DYNA软件建立了球形破片侵彻明胶的二维轴对称模型,结合相关试验结果验证了仿真结果的正确性,进而对不同破片直径和着靶速度侵彻有限厚明胶靶后的速度衰减和瞬时空腔尺寸的规律作了分析和讨论。利用遗传算法对不同工况的仿真数据进行拟合,得到了计算瞬时空腔的简化数学模型,通过与更多仿真结果的比对,验证了模型的有效性。该简化模型可用于快速计算球形破片侵彻生物靶标造成的损伤区域,对提高人员目标毁伤评估和易损性分析的效率有实际意义。     

Bond strength and effective bond length of FRP sheets/plates bonded to concrete considering the type of adhesive layer

Recent experimental results of the FRP–concrete bonded joint using flexible adhesive showed that the most popular analytical models available in the literature underestimate the bond strength and the effective bond length of these experiments. Most of these existing models need to be modified to consider the type of adhesive layer. Consequently, the bond strength model proposed by Chen and Teng (2001) has been modified to consider the type of adhesive layer. An extensive database consisting of about 100 test results of FRP–concrete joint has been assembled to examine the validity of the proposed model taking the type of adhesive layer into consideration. The modified bond strength model is accurately capable of predicting the bond strength and the effective bond length.     

MATERIAL MODELLING FOR TRANSIENT DYNAMIC ANALYSIS OF REINFORCED CONCRETE STRUCTURES

Reinforced concrete is a composite structural material which has been the subject of extensive research since it was first used. When considering the rational properties, the research has mainly centred on the behaviour of the concrete, that of the reinforcing steel and the interaction between the steel and the surrounding concrete subject to static loading. The behaviour of reinforced concrete, and, in particular, that of the concrete itself when subject to dynamic loading has been less thoroughly studied. This paper proposes a material model for the concrete which includes the effect of high strain rate upon both the stiffness of the material and upon the crushing strength. It proposes expressions for the yield and failure surfaces of the concrete which account for the effects of high strain rate and then incorporates this material model into an existing finite element program to compare with a series of test results. The paper illustrates that this improved material model can now produce a displacement/time history for reinforced concrete elements which is very close to that observed in tests on elements which are far outside the elastic range.     

Mechanics of bonds in an FRP bonded concrete beam

Fibre-reinforced plastic (FRP) materials have been recognised as new innovative materials for concrete rehabilitation and retrofit. Since concrete is poor in tension, a beam without any form of reinforcement will fail when subjected to a relatively small tensile load. Therefore, the use of the FRP to strengthen the concrete is an effective solution to increase the overall strength of the structure. The attractive benefits of using FRP in real-life civil concrete applications include its high strength to weight ratio, its resistance to corrosion, and its ease of moulding into complex shapes without increasing manufacturing costs. The speed of application minimises the time of closure of a structure compared to other strengthening methods. In this paper, a simple theoretical model to estimate shear and peel-off stresses is proposed. Axial stresses in an FRP-strengthened concrete beam are considered, including the variation in FRP plate fibre orientation. The theoretical predictions are compared with solutions from an experimentally validated finite element model. The results from the theory show that maximum shear and peel-off stresses are located in the end region of the FRP plate. The magnitude of the maximum shear stress increases with increases in the amount of fibres aligned in the beam's longitudinal axis, the modulus of an adhesive material and the number of laminate layers. However, the maximum peel-off stress decreases with increasing thickness of the adhesive layer.     

Modeling the effect of high temperature on the bond of FRP reinforcing bars to concrete

The effect of high temperature on the bond between fiber reinforced polymers (FRP) reinforcing bars (rebars) and concrete was studied. The bond strength exhibited a severe reduction of 80–90% at relatively low temperature (up to 200°C), accompanied by changes in the pullout load-slip behavior. A semi-empirical model was developed in order to describe the extent of reduction in the bond strength as the temperature rises. The model is based on the following parameters: glass transition temperature of the polymer layer at the surface of the rod; polymer's degree of crosslinking; the residual bond strength at high temperature after the polymer of the external layer of the rebar ceased to contribute to the bond. The parameters of the rods that were tested for pullout at various temperatures were introduced into the model. The output curves of bond–temperature relationships showed good agreement with the test results.     

Roller compacted concrete-tensile strength of horizontal joints

Roller Compacted Concrete is a very dry material consolidated by the use of a powerful external vibatory compaction. This material is used mainly in gravity or arch/gravity dams, and pavements. RCC dam construction methodology, by concrete layers, involves a high number and an extensive area of horizontal joints. These joints are the weakest parts of RCC in terms of strength and permeability, being one hindrance to more widespread use of RCC. This study analyses the influence of different parameters on the direct tensile strength of the joints, namely the relative humidity in the concrete surface, the setting and hardening state of concrete, and the cold joint treatment. The results obtained indicated that the decrease in the joint quality with the time of exposure is continuous being important the compaction of the upper layer before the initial setting time of the lower layer. Cold joint treatments should expose aggregate particles.     

Fracturing behaviors of FRP-strengthened concrete structures

In this paper, we focus on the study of concrete cracking behavior and interfacial debonding fracture in fiber reinforced polymer (FRP)-strengthened concrete beams. An experimental program is systematically reviewed according to the observed failure modes, in which it is found that the interfacial debonding may propagate either within the adhesive layer or through concrete layer in the vicinity of bond interface. A finite element analysis is performed to investigate the different types of debonding propagation along FRP-concrete interface and crack distribution in concrete. For the numerical fracture models, interfacial debonding that initiates and propagates in adhesive layer is modeled by fictitious interfacial crack model. And concrete cracking, including the debonding fracture through interfacial concrete, is modeled by smeared crack model. Properties of the interfacial adhesive layer and concrete are considered to significantly influence the debonding propagation types and crack distribution. The interactions between interfacial bond strength, interfacial fracture energy of bond adhesive layer and tensile strength, fracture energy of concrete are discussed in detail through a parametric study. According to the results, the effects of these properties on different types of interfacial debonding, concrete cracking behavior and structural load-carrying capacity are clearly understood.     

预应力钢箱高强混凝土组合梁受扭性能全过程分析

为研究预应力钢箱高强混凝土组合梁从加载到破坏受扭全过程的力学性能,把受扭全过程分为开裂前和开裂后两个阶段.基于变角空间桁架理论模型,通过受力平衡方程、几何条件和应力-应变关系等,推导出适用于预应力组合箱梁全过程分析的一系列方程,进而提出了预应力钢箱高强混凝土组合梁全过程分析的简化算法,并利用VB编制了预应力钢箱高强混凝...     

Simulation of hygral crack growth in concrete repair systems

In this paper, results of numerical simulations of a repaired concrete structure are presented. A repair layer of mortar was cast on top of a substrate of old concrete. The repair mortar was staturated with water, and allowed to dry at the top surface. The moisture distribution was determined using the finite element code DIANA. The moisture gradients lead to shrinkage cracking. Using the smeared crack model available in DIANA, and from the effect of decreasing the thickness of the overlay of repair mortar (from 60 to 15 mm), and by decreasing the bond strength between repair mortar and substrate from 3 to 1 MPa, it is shown that the number of hygral shrinkage cracks depends largely on the thickness of the repair layer. Moreover, in analyses with high interfacial strength, the cracks were found to propagate into the substrate. However, at lower bond strength, debonding was observed. The analyses show that hygral strains may cause severe damage in a repaired concrete system. Problems may decrease when the overlay thickness increases or when the bond between substrate and overlay is improved. In addition, applying reinforcement in the repair layer, either as discrete bars or as distributed fibres, may decrease the spacing and width of the shrinkage cracks, thereby reducing the probability of delamination. The numerical programme is shown to be a viable tool for damage analyses not only under mechanical load, but also under hygral gradients (and thermal gradients).     

钢管钢纤维高强混凝土抗冲击压缩性能的试验研究与数值模拟

遮弹层的建成及优化对防护工程的发展尤为重要。钢管钢纤维高强混凝土蜂窝遮弹层是一种具有高强抗力的新型遮弹层,文章对其组成构件钢管钢纤维高强混凝土进行霍普金森压杆(SHPB)动态力学性能试验,并借助动力有限元分析软件LSDYNA进行数值模拟。冲击压缩试验中,试件的钢纤维掺量分别为0%、0.5%、1.0%、1.5%,钢管壁厚分别为2mm、3mm。结果表明钢管钢纤维高强混凝土具有应变率强化效应,应变率越高,试件的动态抗压强度越大。当气压为1.0 MPa时,壁厚3mm、钢纤维掺量1.5%的试件强度达258.3 MPa。与钢纤维高强混凝土相比,钢管钢纤维高强混凝土的抗冲击压缩性能更好,动态抗压强度最大增幅达35.4%,且具备承受多次冲击压缩作用的能力。数值模拟与试验结果吻合度高,表明数值模拟方法具有可行性。     

纳米SiO2对钢纤维/混凝土高温后力学性能及微观结构的影响

研究了掺纳米SiO₂的钢纤维混凝土(NSFC)、 钢纤维混凝土(SFRC)和普通混凝土(NC)三种材料在不同加热温度后的抗压、 劈裂和抗折强度等力学性能, 对不同温度热处理后的微观结构进行了SEM分析, 对钢纤维与过渡区界面的相结构进行了XRD分析。结果表明: 在测试温度范围内, NSFC的抗压、 劈裂和抗折强度均高于SFRC和NC的强度, 且在400 ℃时达到最大值。在常温下, NSFC的抗压、 劈裂和抗折强度较NC分别提高27.01%、 63.28%和54.12%, 400 ℃高温热处理后比NC分别高35.09%、 84.62%和87.23%; SEM分析表明, 在钢纤维与过渡区的界面处, 致密度提高, 显微硬度提高。由于固相反应, 使界面区结构发生变化, 在钢纤维表层形成扩散渗透层(白亮层), 即化合物层, 呈锯齿状, XRD分析证明, 白亮层主要由FeSi₂和复杂的水化硅酸钙组成, 从而增强了钢纤维与基体的粘结力, 提高了混凝土的高温力学性能。