低速大质量冲击下伪弹性TiNi合金固支梁响应的数值研究

摘要：本文对低速大质量冲击下伪弹性TiNi合金固支梁的响应和相变演化特性进行了数值研究,目的是了解相变与结构动态响应之间的相互影响。结果表明,落锤冲击载荷作用下,相变固支梁的响应可以分为5个阶段：弹性波动响应,局部相变失稳,驻定相变铰形成,相变铰区扩展和相变铰移动,杆机构。相变铰为弯矩和轴力共同作用下形成的广义铰,同时表现出与塑性铰不同的特征。     

Experimental and numerical study of the impact behavior of SMC plates

Steel components absorb impact energy by plastic deformation whilst composite materials absorbing it by damage mechanisms such as fiber debonding, fiber fracture, and matrix cracking. Therefore, in order to properly substitute metal components with composite ones in industrial applications, the impact property of composite materials must be well known. In this study, the impact behavior of sheet molding compounds (SMC), which is widely used in automobile industry due to its relatively low cost and high productivity, was examined both experimentally and numerically. In order to investigate the impact behavior of SMC, an experimental study was carried out by setting up a drop weight impact test system. Using this system, the dissipated impact energies of SMC flat plates were measured to investigate the influence of the mass and shape of impactor, initial velocity, and specimen thickness on the impact behavior.

For numerical predictions, a modified damage model for SMC was developed and adopted in the user defined material subroutine of the commercial simulation program LS-DYNA3D. For the sake of improving efficiency of impact simulations, the SMC material property was determined in consideration of the local differences of the fiber volume fractions. The dissipated impact energies under various conditions and the reliability of the developed impact simulation process were examined through comparisons of the predicted data with the experimental results.

From this comparison, it was found that, in the scope of current study, the specimen thickness is the most important parameter that should be considered in the design of SMC components for the aspect of impact behavior.     

Numerical simulation of reinforced concrete beams with different shear reinforcements under dynamic impact loads

The behavior of concrete/reinforced concrete structures is strongly influenced by the loading rate. Reinforced concrete structural members subjected to impact loads behave quite differently as compared to the same subjected to quasi-static loading. This difference is attributed to the strain-rate influence on strength, stiffness, and ductility as well as to the activation of inertia forces. These influences are clearly demonstrated in experiments. Moreover, for concrete structures, which exhibit damage and fracture phenomena, the failure mode and cracking pattern depend significantly on loading rate. In general, there is a tendency that with the increase of loading rate the failure mode changes from mode-I to mixed mode. Furthermore, theoretical and experimental investigations indicate that after the crack reaches critical speed of propagation there is crack branching. The present paper focuses on 3D finite-element study of reinforced concrete beams with different amount of shear reinforcement under impact. The experiments reported in literature are numerically simulated using the rate sensitive microplane model as constitutive law for concrete, while the strain-rate influence is captured by the activation energy theory. Inertia forces are implicitly accounted for through dynamic finite element analysis. However, the impact was modeled not by explicit modeling of two bodies but by incrementing the load point displacement till the maximum value and at the rate reported from the test. The results of the numerical study show that the numerical analysis using the procedure followed in this work can very well simulate the impact behavior of reinforced concrete beams. The static and dynamic reactions, crack patterns and failure modes as predicted in analysis are in close agreement with their experimentally observed counterparts. It was concluded that under impact loads, of the order as simulated in this work (blunt impact with velocity of around 1 m/s), the shear reinforcement does not get activated and therefore the dynamic reactions, unlike static reactions, are almost independent of the amount of shear reinforcement in the beams. However, the presence of shear reinforcement significantly affects the crack pattern and the cracks are well distributed in the presence of shear reinforcement, thus avoiding the formation of shear plugs.     

连续侧向冲击作用下钢筋混凝土管动力响应试验研究

为了揭示钢筋混凝土管在连续侧向冲击荷载作用下的破坏机理,完成了6个钢筋混凝土管的横向冲击测试,考虑了不同落锤高度、冲击次数以及简支、固支两种约束形式对钢筋混凝土管侧向冲击动力响应的影响。提出了冲击力和跨中变形的预测公式并采用试验数据进行了拟合,得到了不同冲击速度、冲击次数对管道冲击力峰值和跨中位移的变化规律。采用吸能系数来量化评价管道承受侧向撞击时的吸能能力。结果表明,固支约束管道变形破坏显著好于简支约束试件,承受多次侧向撞击后,吸能系数增大,抗冲击变形能力明显下降。     

非标准状况下直燃型溴化锂机组动态特性的实验研究

根据现有检测手段对非标准工况下溴化锂机组进行了现场测试,分析了非标准工况下冷媒水进出口温度、冷却水进口温度、冷媒水流量、燃气流量的变化对制冷量和COP的影响.结果表明非标准工况下COP值与标准工况下的COP值相比,减少的最大幅度达到了29%,机组的启停次数、燃烧器的控制对系统的COP都有着较大的影响.     

An experimental investigation on the impact behavior of hybrid composite plates

In this experimental study, the impact behavior of hybrid composite plates has been investigated. The increasing impact energy was performed on two types of hybrid composite plates (glass–carbon/epoxy) until complete perforation of specimens. An energy profiling method, showing the relationship between impact energy and absorbed energy, was used together with load–deflection curves to determine the penetration and perforation thresholds of hybrid composites. The failure processes of damaged specimens for different impact energies were evaluated by comparing load–deflection curves and images of damaged samples taken from impacted sides and non-impacted sides. Cross-sections of damaged specimens were also inspected visually and discussed to assess the extent of damage, such as fiber fracture in layers, expansion of delaminations between adjacent layers. The perforation threshold of hybrid composite impacted from surface with carbon fibers was found approximately 30% higher than that of surface with glass fibers.     

冲击作用下CFRP修复损伤RC叠合梁动力性能试验研究

采用落锤冲击试验机,进行了现浇梁、叠合梁以及碳纤维增强复合材料(carbon fiber reinforced polymer,CFRP)修复的损伤梁的动力性能对比试验。冲击作用下试件破坏形态以及冲击力与变形时程曲线表明,叠合面在一定程度上抑制了跨中裂缝向上开展的趋势,损伤修复后的叠合梁在冲击荷载下的破坏程度明显减轻,初始损伤减弱了梁跨中位移的滞后现象;相比完好梁,现浇与叠合修复梁抗冲击承载力有着同等程度的提高。基于有效应变计算的修复梁承载能力提升与试验结果的对比显示,CFRP能有效改善并增强构件的整体受力性能,在冲击作用下对构件的实际抗力贡献大于原有构件承载力与FRP受拉能力简单叠加时的理论抗力贡献。     

不同温度环境中沥青混凝土动态抗压性能试验研究

为研究沥青混凝土在不同温度环境中的动态力学特性,该研究在-20～30 ℃和10-5～10-2 s-1条件下对其进行了动态抗压试验研究.试验结果表明:温度和应变速率对沥青混凝土的力学性能有显著影响,降低温度或增加应变速率导致抗压强度和弹性模量增加,峰值应变减小;当温度大于20 ℃或小于-10 ℃时,应变速率由10-5 s...     

The effect of hybridization on the GFRP behavior under high velocity impact

In the present study, experimental and analytical investigations for the behavior of E-glass fiber reinforced composite hybridized with a layer of Kevlar 29 fiber, under high velocity impact, were performed. The experimental work includes the placement of the Kevlar layer at four different locations to verify the effects of the stacking sequence on the impact behavior. Three different projectile geometries, namely, flat-ended, hemispherical and conical were used. The experimental results reveal that hybridization improves the laminates performance under dynamic penetration. The results also indicate that the laminates response was found to be highly sensitive to the projectile geometry. In the case of analytical modeling, two energy models were conducted to calculate the projectile residual velocities. The results obtained from the two models were compared with those obtained experimentally and some conclusions were drawn.     

钢管混凝土梁在侧向冲击荷载作用下动力响应的试验研究和数值模拟

为研究不同轴压比对钢管混凝土柱侧向冲击性能的影响,该文对已有的冲击试验进行了验证。在验证模型基础上建立了不同轴压比的钢管混凝土柱在侧向冲击作用下的动力有限元模型,计算得到连续变化轴压比下钢管混凝土的抗冲击性能参数。结果表明：轴压比对钢管混凝土的侧向抗冲击性能有显著影响。在轴压比小于0.7时,轴力对钢管混凝土构件侧向抗冲击能力有提高作用,当轴压比大于0.7时,轴力对钢管混凝土侧向抗冲击能力有削弱作用。     

冲击荷载下单层球面网壳动力响应分析与试验研究

为分析带下部支承结构的Kiewitt-6型单层球面网壳在冲击荷载下动力响应,在ANSYS/LS-DYNA中建立钢管柱支承的单层球面网壳数值分析模型,据冲击响应特点,总结四种响应模式,研究冲击能量、冲击位置、环梁刚度对上部网壳动力响应影响。进行钢管柱支承的单层球壳模型冲击试验,测量、分析结构的动应力、动位移及加速度,研究冲击柱破坏模式。结果表明,四种响应模式以冲击柱破坏模式(轻微损伤、局部凹陷、压弯破坏、剪切破坏)为典型特征;除响应模式4,网壳动力响应随冲击能量增大而增大;柱中为最不利冲击位置;环梁刚度增大,网壳动力响应减小;有限元分析结果与实测结果吻合较好,验证数值计算方法的正确性。     

An investigation on the dynamic response of polymeric,metallic, and biomaterial foams

Mechanical characterization of foams at varying strain rates is indispensable for the selection of foam as core material for the proficient sandwich structure design at dynamic loading application. Both servo-hydraulically controlled Material Testing System (MTS) and Instron machines are generally considered for quasi-static testing at strain rates on the order of 10⁻³ s⁻¹. Split Hopkinson pressure bar (SHPB) with steel bars is typically utilized for characterizing metallic foams at high strain rates, however modified SHPB with polycarbonate or soft martial bars are used for characterizing polymeric and biomaterial foams at high strain rates on the order of 10³ s⁻¹ for impedance match between the foam specimens and bars. This paper reviews the effect of strain rate of loading, density, environmental temperature, and microstructure on compressive strength and energy absorption capacity of various closed-cell polymeric, metallic, and biomaterial foams. Compressive strength and energy absorption capacity increase with the increase in both strain rate of loading and density of foams, but decrease with the increase in surrounding temperature. Foams of same density can have different strength and can absorb unequal amount of energy at the same strain rate of loading due to the variation of microstructure.     

Experimental study of the impact behavior of repaired thin laminates with double composite patch

Abstract

The aim of this article is to present a study of the behavior of patch-repaired laminates subjected to low-velocity impacts. A broad range of impact energies was selected. Results for repaired laminates in terms of contact load, damage and absorbed energy were compared to those obtained from intact specimens. At impact energies below 10?J, energy absorption in repaired specimens was higher than the one given in intact laminates, although the measured damage area was found to be greater in the former configuration. For higher impact energies, both damage area and energy absorption in intact specimens were greater than in repaired laminates.     

地震作用下车辆-轨道系统轮轨动态响应试验研究

为研究地震作用下高速铁路地震预警阈值,进行准静态全尺寸车辆-轨道模型振动台试验研究,对车辆轨道模型施加正弦地震波,试验结果显示《铁道车辆动力学性能评定和试验鉴定规范》中所规定的轮重减载率限值和脱轨系数限值可能偏于保守,且导致列车脱轨的原因是由于地震作用使轨道结构发生大幅的水平向振动,引起车轮发生水平向晃动,致使车辆发生侧向滚摆运动所造成的;接着对车辆轨道模型施加实测地震波,试验结果表明地震波频谱特性对列车运行安全有一定的影响;对车辆轨道模型同时施加水平向和垂向地震波,发现对车辆轨道系统动力响应影响较大的为水平向地震波,垂向地震波则对其影响较小;根据振动台试验模型建立与之对应的多刚体、多自由度三维车辆-轨道数值模型,研究当考虑轨道不平顺时,地震作用下不同车速对列车轮动动力响应的影响,通过数据分析表明,在一定范围内,地震作用下的列车脱轨与列车速度关系不大,为高速铁路地震预警阈值的研究提供了一定的理论依据。     

Experimental study on the flexural behavior of stone beams strengthened with a combination of angle steels and PET belts

This paper focuses on a novel strengthening method for stone beams. An experimental study on the flexural behavior of six full scale stone beams, including three beams unstrengthened and three beams strengthened with a combination of angle steels and PET (polyethylene terephthalate plastic) belts, was performed. The failure modes, flexural capacity, deformability, and influence of different types and dimensions of stones, along with the different specifications of angle steels on the flexural behavior, were analyzed. The experimental results indicated that: unstrengthened greenish white marble beams exhibited a typical brittle failure mode, and unstrengthened white marble beams with better deformation properties exhibited a non-fully brittle failure mode; each of the strengthened stone beams exhibited a non-fully brittle failure mode. Furthermore, the flexural capacity and deformation capacity of the strengthened stone beams were improved to some extent. After the ultimate load, strengthened stone beams still had a certain flexural capacity, namely the flexural capacity margin, because of the action of angle steels. A theoretical analysis of the flexural capacity of stone beams was conducted, and a simplified calculation formula of the ultimate flexural capacity and flexural capacity margin was proposed.     

Experimental and numerical study of oblique impact on woven composite sandwich structure: Influence of the firing axis orientation

During flight, aircrafts can be submitted to complex loadings. The reliability of their structure is an essential aspect in ensuring passenger safety. In the specific case of helicopters, blades are subjected to impact loading. The following work will focus on the experimental and numerical study of an oblique impact on the skin of the blade. It is equivalent in a first approach to an impact on a sandwich panel comprising a foam core and a thin woven composite skin. This study aims to identify the mechanisms of damage to the skin for different orientations of the firing axis, and to develop a representative model of the damage kinetics adapted to the modeling of the complete structure. Thus, an F.E. semi-continuous explicit model has been developed. It relies on the development of a specific damageable element at the woven mesh scale. Numerical results obtained are accurate, allowing the identification of the damage mechanism of the woven skin for different firing orientations.     

复合材料层压板抗冲击行为及表征方法的实验研究

对14种复合材料体系约800个试样进行了冲击阻抗和含损伤层压板压缩强度试验研究,研究发现对于同一种复合材料层压板的冲击能量-凹坑深度曲线和凹坑深度-压缩破坏应变曲线均存在拐点,在出现拐点后内部的分层损伤叠加面积基本不再增加,压缩剩余强度基本不再降低,表面冲击部位开始出现纤维断裂。研究表明,采用传统CAI来表征损伤容限性能的方法可能得到与实际结构损伤容限特性相反的结论。因此,提出了利用拐点附近特性来表征复合材料层压板的抗冲击行为（包括损伤阻抗和损伤容限）的建议,即分别采用QSI方法得到的准各向同性层压板的最大接触力F_max和压缩破坏强度（应变）的门槛值CAIT来表征复合材料层压板的损伤阻抗和损伤容限行为。      

填充泡沫铝的多层铝管动态压溃吸能特性研究

采用数值模拟的方法研究和分析了无填充物的多层铝管结构的吸能特性,结果发现多层铝管相比单层铝管,不但具有较大的吸能量,而且还具有较高的比吸能率;在此基础上,设计了不同层数的多层管泡沫铝填充结构,研究发现泡沫铝不但受轴向压溃变形,同时也受到了铝管层之间的相互作用力使其在径向发生了变形;之后对多层管填充3种不同密度的泡沫铝,采用变参分析的方法研究了多层管层数和泡沫铝密度对整个结构吸能特性的影响;研究结果表明:填充泡沫铝的多层管,随着层数的增加,其比吸能率和吸能量也随之有所增加,随着泡沫铝密度的提高,比吸能率的提高量开始下降,但仍高于填充相同泡沫铝的单层管。     

不同工况下含间隙铰链接触碰撞力特性研究

为了更加准确地研究不同工况环境对含间隙铰链接触碰撞力的影响,以提高空间机构的运行及空间指向精度,基于分型理论、Lankarani-Nikravesh模型及宏微观理论,考虑摩擦与微凸体间的阻尼等因素,得到了新的含间隙旋转运动副元素间接触碰撞力模型,并通过试验验证了该模型的正确性.采用单一因素试验法,研究了转速、间隙、不同...     

双向荷载作用下空间夹心节点受力性能试验研究

节点核心区采用同梁等强的低强度混凝土浇筑的夹心节点和采用同柱等强的高强度混凝土浇筑的传统节点相比,施工简单且易保证质量,但是我国规范对其规定过于简单,没有明确的验算方法。通过三组不同混凝土强度等级差的空间夹心节点和传统节点对比试件的双向低周往复性能试验研究,对比分析了二者破坏形式、延性、耗能、变形和承载力等方面的差异,结果表明:中低剪压比夹心节点的整体抗震性能稍弱于传统节点,但相差不明显;中低轴压比、剪压比条件下,当柱与梁混凝土强度等级之比小于1.5时,节点区可直接采用与梁相同强度等级的混凝土浇筑,当柱与梁混凝土强度等级之比大于1.5时,其破坏形式可转变为节点核心区剪切破坏,需采取相应的加强措施。最后在此基础上,给出了与试验结果吻合较好的夹心节点抗剪承载力计算公式。