泡沫铝填充金属薄壁圆管侧向压缩的实验和理论

利用实验研究与理论分析相结合方法研究了泡沫铝填充金属薄壁圆管在准静态侧向压缩下的力学响应。基于能量法,建立了泡沫铝填充圆管和金属薄壁圆管在侧向均匀压缩时的瞬时侧向力、平均侧向力和总吸能的理论公式。对泡沫铝填充管与金属薄壁圆管进行了准静态侧向压缩实验,并且将实验结果与理论公式进行了对比,结果表明理论预测值与实验结果吻合较好。基于建立的理论分析模型,研究了管的几何尺寸以及泡沫铝材料的密度对结构的瞬时侧向力、平均侧向力、总吸能和比吸能的影响。结果表明,在准静态侧向压缩下,泡沫铝填充管的总吸能大于对应的金属薄壁圆管;泡沫铝填充管的侧向压缩力和总吸能随管长度、壁厚和直径的增加而增大;当填充材料泡沫铝密度增大时,填充管的总吸能与侧向压缩力均增加。     

泡沫铝填充金属薄壁圆管的实验和理论研究

利用实验研究与理论分析相结合的方法研究了泡沫铝填充金属薄壁圆管在准静态侧向压缩下的力学响应.基于能量法,建立了泡沫铝填充圆管和金属薄壁圆管在侧向均匀压缩时的瞬时侧向力、平均侧向力和总吸能的理论公式.对泡沫铝填充管与金属薄壁圆管进行了准静态侧向压缩实验,并且将实验结果与理论公式进行了对比,结果表明理论预测值与实验结果吻合较好.基于建立的理论分析模型,研究了管的几何尺寸以及泡沫铝材料的密度对结构的瞬时侧向力、平均侧向力、总吸能和比吸能的影响.结果表明,在准静态侧向压缩下,泡沫铝填充管的总吸能大于对应的金属薄壁圆管;泡沫铝填充管的侧向压缩力和总吸能随管长度、壁厚和直径的增加而增大;当填充材料泡沫铝密度增大时,填充管的总吸能与侧向压缩力均增加.     

薄壁管及其泡沫金属填充结构耐撞性的实验研究

对两种AA 6063T6铝合金薄壁空管(方/圆管)结构以及填充泡沫铝的5种不同几何截面的薄壁夹芯管(单方/圆管填充,双方/圆管填充,双方管四角填充结构)分别进行了准静态轴向压缩实验,研究了各种薄壁结构的变形模式和吸能性能,比较了反映不同结构耐撞性的各种参数,如比能量吸收和能量吸收效率因子等。同时,研究了各种填充结构的几何参数对结构耐撞性能的影响,发现填充结构内管的尺寸对结构的耐撞性影响显著。研究结果显示,圆管类型的结构平均压垮载荷、比质量能量吸收、单位行程能量吸收以及能量吸收效率因子都较方管类型结构高。泡沫填充单/双圆管结构由于其较高的压垮力效率和能量吸收效率,能够较平稳高效地吸能,作为耐撞性结构元件具有很大的优势。     

金属泡沫填充薄壁圆管的轴压载荷-位移关系

将泡沫填充圆管的能量吸收视为泡沫与圆管两者之和, 基于包含偏心率效应的直链塑性铰模型和Reddy等对Alexander模型的改进结果, 对圆管的变形模式进行了更改, 以此来反映管壁与金属泡沫之间的相互作用效应, 导出了金属泡沫填充圆管的静、动态轴向平均压溃力的表达式. 通过理论预测与实验的对比, 发现理论预测偏低, 但与实验曲线的趋势保持一致, 比空管与金属泡沫的平均载荷之和略高一些. 此外, 泡沫填充圆管的平均压溃力随填充泡沫平台应力的增大而呈线性增加, 与已有研究结果及实际情况一致, 由此表明了模型的合理性.      

泡沫铝填充薄壁圆管的三点弯曲实验的数值模拟

泡沫金属填充薄壁结构的应用日趋广泛,建立合理的数值计算模型对结构设计和工程应用非常重要.该文通过对泡沫铝填充薄壁铝合金圆管的三点弯曲实验的数值模拟,研究了它的力学行为.采用ABAQUS软件,建立了空管和泡沫铝全填充管的有限元模型,并对这两种结构在三点弯曲下的力学行为进行了数值模拟,所得结果与实验结果符合得较好.通过数值模拟分析了结构的承载机理和不同压头直径对结构承载能力的影响.此外,还研究了泡沫铝部分填充圆管的三点弯曲行为,分析了不同填充长度对结构承载能力的影响.     

泡沫铝合金填充圆管三点弯曲实验研究

用实验方法研究了三种不同管壁厚度、两种跨径的泡沫铝合金填充圆管的三点弯曲力学性能,得到了泡沫铝合金填充管结构承载过程中的三种变形模式,即压入、压入弯曲和管壁下缘拉裂破坏。给出了空管和泡沫铝合金填充管的载荷位移曲线,并进行了比较。实验发现泡沫铝合金填充管结构的承载能力随泡沫铝合金密度的增大而增大,但破坏应变则随之减小。结构承载力的相对提高量随着管壁厚度的减小和跨径的增大而增大。此外,分析了泡沫铝合金提高填充管结构承载能力的机理。泡沫铝合金填充使管壁压入量和管截面抗弯刚度的损失显著减小,从而提高了结构的抗弯能力。     

泡沫铝填充薄壁方形铝管的静态弯曲崩毁行为

研究了泡沫铝填充的方形铝管的准静态三点弯曲行为，实验表明：泡沫铝填充有效地改变了铝管的局部崩毁变形模式；界面粘接提高了填充结构的抗弯刚度，但使结构易在较小转角下发生破坏，最后，基于实验提出了一个分析填充结构弯曲崩塌行为的理论方法，在小转角下给出了与实验相当吻合的结果。     

高压水射流冲击HTPB推进剂的安全性分析

以高压水射流冲击HTPB推进剂的动态加载过程和准静态加载过程在作用压力和持续时间上的巨大差异为基础, 在水锤压力和滞止压力计算的基础上分别进行了点火模式预判, 然后以模型类比和实验方法分析了动态和准静态加载过程的安全性。结果表明, 使用出口压力在300 MPa以内的高压水射流冲击HTPB推进剂装药在动态加载过程中不会有点火起爆危险性, 但使用100M Pa以上的高压水射流冲击HTPB推进剂装药在准静态加载过程中其内部可能会发生温度突跃情况, 这可能会引起热点火、甚至热起爆。     

泡沫金属在冲击载荷下的动态压缩行为

基于微CT扫描影像信息,建立泡沫金属材料二维细观有限元模型,考虑不规则胞孔的不均匀分布,根据实验结果拟合孔壁材料的弹塑性本构参数。研究了泡沫金属在不同加载速度下的压缩变形机理,重点讨论泡沫金属中弹塑性波的传播、惯性效应和从冲击端传递到静止端的应力变化特征。对于相对密度为0.3的泡沫铝,弹性波速约为5 km/s,与孔壁材料的弹性波速相当,塑性波速表现为随着加载速度的增大而增大。在加载速度为50~100 m/s间变形模式从准静态模式转变为动态模式,未发现明显的临界速度,动态锁死应变随着加载速度的增大而增大。由于塑性波发生反射,试件会发生二次压缩过程,相应地,静止端产生二次应力平台。受惯性作用的影响,二次应力平台也随着加载速度的增大而提高。     

正多边形基多胞薄壁管的吸能特性

多胞薄壁结构具有轻量化、高比吸能的特点，在汽车、轮船、航空航天等领域得到了广泛的应用。已有研究表明结构的耐撞性与结构的拓扑方式及胞元数量密切相关。为了研究结构形状和拓扑优化对其吸能效果的影响，基于正多边形结构，通过内嵌多边形和外接圆管的方式设计了两类新型多胞薄壁结构，并对这两类多胞薄壁结构进行准静态和落锤冲击实验，利用高速相机记录结构的变形模式，并定量分析了结构的吸能特性。实验结果表明:除正三角形二级内嵌四边形所得结构在准静态加载实验后期出现了局部失稳现象外，其余结构在准静态和落锤冲击实验过程中均保持垂直受压，结构变形模式与吸能效果较好。通过比较两类结构的实验结果得出:不论是在准静态加载还是在落锤冲击的情况下，内嵌多边形结构的各项吸能指标都明显优于外接圆管的结构；同等质量的情况下，内嵌四边形结构的吸能效果明显优于内嵌三角形的结构。     

粘接多胞管三点弯曲实验与数值研究

基于实验和数值模拟方法,本文研究了一种易制备粘接多胞薄壁结构的弯曲性能,分析了粘接多胞管在横向三点弯曲加载下的变形和能量吸收性能。三点弯曲准静态实验表明：由于粘接的作用,通常情况下粘接多胞管的能量吸收性能高于其基本构成单胞管能量吸收的总和,但在某些情况下粘接可以带来70%的性能提升。借助于LSDYNA,我们计算模拟了三点弯曲实验,计算得到的粘接多胞管变形模式和力-位移曲线与实验结果吻合良好。此外,采用计算模拟方法,我还对三种不同接触条件下的结构响应进行了对比分析,结果表明：如果未出现明显的粘接脱开,则粘接多胞管的吸能特性与完整的多胞结构相当,否则其能量吸收性能会被严重削弱。     

BENDING BEHAVIOR OF EMPTY AND FOAM-FILLED ALUMINUM TUBES WITH DIFFERENT CROSS-SECTIONS

In this paper, the energy absorption mechanism of empty and foam-filled aluminum tubes with different cross-sections (circular, square and elliptic) under bending load is investigated numerically. The load-displacement curves of the present simulations are in very good agreement with those of published experimental data. Here, the existing analytical formulations are reviewed and compared with experimental results. In addition, the effects of different cross-sections and wall thicknesses on the energy absorption capacity and specific energy absorption of these tubes are fully investigated. The results indicate that the energy absorption of an elliptic foam-filled tube with 1.5 mm and 2 mm thicknesses increases about 45% and 73% in comparison with a square one, respectively.     

Ductile–brittle transitions in the fracture of plastically deforming,adhesively bonded structures. Part II: Numerical studies

To enable the effective and reliable use of structural adhesive bonding in automotive applications, the cohesive properties of a joint need to be determined over a wide range of loading rates. In this paper, a strategy for determining these properties has been described and used to analyze a set of experimental results presented in a companion paper. In the particular system studied, a crack growing in a toughened quasi-static mode could make a catastrophic transition to a brittle mode of fracture. The cohesive parameters for both the toughened and brittle modes of crack growth were determined by comparing numerical predictions from cohesive-zone simulations to the results of experimental tests performed using double-cantilever beam specimens and tensile tests. The cohesive parameters were found to be essentially rate-independent for the toughened mode, but the toughness dropped by a factor of four upon a transition to the brittle mode. The results of wedge tests were used as an independent verification of the cohesive parameters, and to verify that the quasi-static properties remained rate-independent to very high crack velocities corresponding to conditions of low-velocity impact. The effects of friction, and the use of the wedge test to determine cohesive parameters, were also explored.     

Performance of Rubberized and Hybrid Rubberized Concrete Structures under Static and Impact Load Conditions

In this study, rubberized concrete samples were prepared by partial substitution (5 %, 10 % and 20 % replacements by volume) of sand by waste crumb rubber, and tested under impact three-point bending load, as well as static load. Three types of specimens (size 50?×?100?×?500 mm) namely, plain concrete, rubberized concrete, and double layer concrete (with rubberized concrete top and plain concrete bottom) were loaded to failure in a drop-weight impact machine by subjecting to 20 N weight from a height of 300 mm, and another three similar specimens were used for the static load test. In both the tests, the load–displacement and fracture energy of each specimen were investigated. Finite-element simulations were also performed to study the dynamic behaviors of the samples, by using LUSAS V.14 software. It was noticed that, the impact tup, and inertial and bending loads increased with the increase in the percentage of sand replacement by crumb rubber. It was interesting to observe that these effects were more significant in the double layer specimen compared to the plain and rubberized concrete samples. The static peak bending load always decreased with increase of rubber in the mix. In general, the strength and energy absorbing capability of rubberized concrete was better under impact loading than under static loading. The simulated load against displacement behaviors of all the samples were validated by the experimental results.     

Interface Forces in Laterally Impacted Steel Tubes

In engineering mechanisms, solid bodies frequently come to a contact with a variety of geometric and kinematic situations. There has been a trend to express the interaction of the contacted bodies in the form of equivalent interface forces. The interface force represents the level of load transferred from one body to another. In a static or quasi-static contact problem, the interface forces could be sensibly evaluated by integrating the normal and the shear stresses over the common interfaces. In a dynamic contact, the interface stresses and subsequently the interface forces happen to be more complicated. They are, furthermore, affected by other parameters such as inertia forces, stress waves propagation, the material strain rate dependency and damping. This paper reports interface forces recorded in a series of experimental impact tests on axially pre-compressed steel tubes along with those from the numerical simulations of the tests. To monitor the so called impact loads, two small steel rings as load cells have been built in the striker. Based on the experimental and numerical results, the concept of equivalent interface forces in the impacted tubes has been verified. It has been highlighted that the interface forces (or the impact loads) may vary on the striker or the specimen themselves, depending on the measuring locations. Effects of axial compressions on the interface forces picked up by the striker load cells, impact loads imparted to the specimen supports and on the impact duration have been discussed. It has been reported that the initial compression applied to the tubes does not remain constant during and after the impact event. The amount of variations also depends on the initial level of the tube compression.     

Experimentally Observed Strain Distributions Near Circular Discontinuities of AA6061-T6 Extrusions During Axial Crush

An experimental investigation to determine the strain distribution and collapse behaviour for AA6061-T6 square cross-sectional extrusions with and without circular discontinuities under quasi-static axial compressive loading was completed. Three-dimensional digital image correlation (DIC) was utilized for strain assessment. In order to validate the results of the optical strain measurement system, tensile tests were first conducted employing both the DIC technique and a traditional extensometer. Strain observations from both methods were found to be very consistent prior to strain localization in the test specimen. Quasi-static axial crushing tests were then conducted. Extrusions considered for the present research had a nominal side width, wall thickness and length of 38.1 mm, 3.15 mm, and 200 mm, respectively. A centrally-located circular hole with diameter of either 14.29 mm, 10.72 mm or 7.14 mm was incorporated into the extrusion. Square tubes without any discontinuities were also considered in the experimental testing program. Testing results showed that the collapse mode of the extrusion altered from global bending to a cutting and splitting deformation mode with the presence of the circular discontinuity. Strain localization occurred near the vicinity of the holes for all specimens. For discontinuities sized 14.29 mm and 10.72 mm the location of strain localization and the initiation of material fracture was at the edge of the discontinuity while the location for extrusions with a 7.14 mm hole was found to occur at the intersection of the extrusion side walls. Maximum values of the effective strain were found to vary from approximately 60% to 100%. The region of strain localization was consistent with the location where material fracture initiated.     

应变率对SiC颗粒增强铝基复合材料拉伸性能的影响

本文利用岛津试验机和自行研制的冲击拉伸试验装置,对体积含量为10%的SiC颗粒增强铝基复合材料进行了准静态的拉伸试验、冲击拉伸试验和冲击拉伸加卸载试验,获得了复合材料在应变率为0.002s^-1-1000s^-1范围内从弹塑性变形直至断裂的完整应力应变曲线。试验结果表明,随着应变速率的提高,复合屈服应力,拉伸强度以及破坏应变均相应提高,具有明显的应变率强化效应和高速韧性现象;同时,由于冲击拉伸试验过程中热力耦合效应的影响,准静态加载下复合材料的应力指数与冲击拉伸加载下复合材料的应力指数相比降低了17.8%;在用冲击拉伸复元试验解耦出热力耦合效应的影响后,材料的静、动态等温应力应变曲线具有相同的应变硬化规律。最后,根据复合材料在不同应变率下的试验结果和Eshelby‘s等效夹杂理论,本文建立了一个计及应变率强化效应的弹塑性自洽模型,模型拟合结果与试验结果吻合得很好。     

Kevlar层合板动静态侵彻贯穿特性的实验研究

本文以Kevlar/环氧树脂层合材料为对象,通过动静态侵彻实验,研究层合板的抗贯穿特性。利用MTS810材料试验机进行准静态侵彻实验,根据测得的加载载荷-位移曲线及靶板的破坏模式,分析了靶板的准静态侵彻行为。实验指出,准静态侵彻时层合板的整体弯曲变形是其主要吸能模式,织物铺层板的吸能量要高于无编织铺层板,表现出更好的抗侵彻性。采用7.62mm口径滑膛枪开展了初速为200～700m/s的弹道冲击实验,讨论了不同弹形弹丸侵彻靶板的效果以及不同铺设方式靶板的抗弹性能和破坏模式。通过与准静态侵彻实验结果的对比,发现靶板的抗侵彻性能和破坏模式与侵彻速度有明显关系。动态侵彻时层合板的破坏局域化,破坏模式多样化。弹形对侵彻效果的影响主要体现于接近弹道极限的低速段。     

基于红外热成像的编织复合材料低速冲击和冲击后压缩试验研究

针对二维三轴编织复合材料（two-dimensional triaxially braided composite, 2DTBC）在低速冲击和冲击后压缩（compression after impact, CAI）载荷下的损伤失效机理,开展了2DTBC试样的不同能量低速冲击试验以及相应的CAI试验,并采用红外热像仪监测在低速冲击和CAI试验过程中的温升现象。通过C扫描表征了不同能量低速冲击后试样的分层损伤情况,讨论了试样背面温度场分布特性及其随冲击能量的演化规律;对比分析了2DTBC冲击后剩余压缩强度与冲击能量的对应关系,基于数字图像相关（digital image correlation, DIC）技术监测了CAI试验中的全局应变场,结合热成像、变形场和光学图像数据,阐明了不同能量冲击后2DTBC的压缩失效特性,讨论了基于红外热成像技术表征编织复合材料损伤失效行为的有效性。试验结果显示:编织复合材料低速冲击和CAI试验中的温度场分布图与编织几何构型有明显关联度;低速冲击试验的温升幅值随冲击能量的增加而快速上升,CAI试验的温升现象随着冲击能量的增加而减弱;分层面积随冲击能量的增大而增大,冲击后剩余压缩强度随冲击能量的增大而降低。研究结果表明:红外热成像技术能够很好地捕捉试样破坏瞬间释放断裂能所产生的温升现象,温度场图像相较于全局应变场能更好地捕捉破坏的起始位置和失效特征。