环氧树脂/泡沫铝一体型复合夹层板压缩及弯曲试验研究

提出了一种环氧树脂/泡沫铝一体型复合夹层板,通过准静态试验以及与纯泡沫铝、传统蒙皮夹层板的对比研究了其破坏过程、破坏形貌、破坏机理及压缩和弯曲力学性能。分别通过压缩应力-应变曲线和弯曲荷载-挠度曲线分析了复合层厚度对压缩及弯曲力学性能的影响,并与传统夹层板的力学性能进行了比较。结果表明,随着夹层板中环氧树脂/泡沫铝复合层厚度增加,其压缩弹性模量和抗压强度增加,弯曲承载力提高。相比传统蒙皮夹层板,由于表层和芯层之间没有明显界面,大大提高了夹芯板的整体性,在受力过程中不会出现表层剥离等现象。     

撞击载荷下泡沫铝夹芯梁的塑性动力响应

应用泡沫金属子弹撞击加载的方式研究了固支泡沫铝夹芯梁和等质量实体梁的塑性动力响应。 采用激光测速装置和位移传感器测量了泡沫子弹的撞击速度和后面板中心点的位移-时间曲线,研究了加载 冲量、面板厚度和芯层厚度对夹芯梁抗冲击性能的影响。给出了泡沫铝夹芯梁的变形与失效模式,实验结果 表明结构响应对夹芯结构配置比较敏感,后面板中心点的残余变形与加载冲量、面板厚度呈线性关系。与等 质量实体梁的比较表明,泡沫铝夹芯梁具有更好的抗冲击能力。实验结果对多孔金属夹芯结构的优化设计具 有一定的参考价值。     

高速冲击载荷下梯度金属泡沫夹芯梁的动态响应与失效

采用泡沫弹冲击加载实验对梯度金属泡沫夹芯梁结构开展了不同冲击强度下的动态响应和失效研究,分析了由三种不同密度泡沫铝组成的等面密度的五种不同梯度的夹芯结构在夹支边界条件下的抗高速冲击性能,结合三点弯曲实验,研究梯度效应对夹芯结构抗冲击性能的影响。研究表明：密度梯度对结构的失效过程和失效模式有着明显的影响,且夹芯梁结构的初始失效模式对结构整体响应和主要的能量吸收机制起着主导作用;当冲击条件不足以使得均质芯材发生压缩时,均质及负梯度夹芯结构初始失效模式为整体弯曲变形,低强度芯层位于前两层的梯度结构随着冲击强度的变化出现不同程度的局部芯层压缩;当冲击强度较低时,梯度结构通过丰富的局部失效表现出明显优于均质结构的抗冲击变形能力;当冲击强度大于临界值时,均质结构具有更好的抗冲击变形能力。通过合理地设计密度梯度实现逐层压缩吸能,能够有效的提升防护结构的抗冲击性能。     

“V型”约束下泡沫铝夹芯圆管的准静态横向压缩性能研究

论文对受“V型”约束泡沫铝夹芯管的准静态横压性能进行了实验研究,观察到三种失效模式包括整体屈服、芯材剪切和局部凹陷.分析了泡沫铝夹芯管的几何参数和横向约束夹角的角度对其失效模式和承载与吸能能力的影响.结果表明,泡沫铝芯材的厚度对三种模式的竞争具有重要影响;在准静态横向压缩下,泡沫铝夹芯管的承载与吸能能力大于对应的空管;泡沫铝夹芯管的承载与吸能能力随着外管直径的增加而增加,随着内管直径的增加而减小;“V型”约束夹角的角度越大,泡沫铝夹芯管的承载与吸能能力也越高.     

水中爆炸载荷下夹芯圆柱壳的结构优化

采用ANSYS/LS-DYNA有限元软件,研究了由三种不同相对密度的泡沫铝组合成的密度非均匀芯层泡沫金属夹芯圆柱壳的水下抗爆性能及均匀型泡沫金属夹芯结构的结构优化.结果表明:泡沫铝芯层相对密度配置顺序对夹芯圆柱壳的抗爆性能影响明显,可以通过调整芯层配置获得最佳吸能性能泡沫金属夹芯圆柱壳;采用Kriging多目标优化分析方法,获得了以夹芯壳单位面积重量最小、中心位移最小和能量吸收最大为目标,上、下面板的厚度的最优解.     

横向冲击载荷下不同约束泡沫铝夹芯圆管的动态响应

以泡沫铝夹芯圆管为研究对象,采用数值模拟研究了横向冲击载荷作用下4种不同约束夹芯圆管的动态响应。研究了夹芯圆管的几何参数、冲击速度和芯层泡沫铝相对密度对夹芯圆管力学行为的影响,对比分析了不同约束条件对泡沫铝夹芯圆管变形模式和吸能性能的影响。结果表明:随着内管直径的减小、冲击速度的增大和芯层泡沫铝相对密度的增大,泡沫铝夹芯圆管的比吸能增大;内管壁厚的增加使无约束和倾斜约束下夹芯圆管的比吸能增大,对侧壁约束和组合约束下夹芯圆管的吸能影响不明显;采用一定的外部约束条件是提高泡沫铝夹芯圆管吸能性能的一种可行的方法。     

泡沫金属夹芯梁在重复冲击下的动态响应

为了研究重复冲击载荷作用下泡沫金属夹芯梁的动态响应,采用Abaqus数值仿真软件,基于可压碎泡沫模型（crushable foam）,建立了泡沫金属夹芯梁遭受楔形质量块冲击的有限元模型。通过将仿真获得的夹芯梁上下面板最终挠度与重复冲击实验结果进行对比,验证仿真方法的准确性。在此基础之上,分析了泡沫金属夹芯梁在楔形质量块重复冲击作用下的变形模式、加卸载过程以及能量耗散特性。结果表明,在重复冲击载荷作用下,夹芯梁的变形不断累积,上面板主要出现局部凹陷和整体弯曲,而芯层则是局部压缩,下面板表现为整体弯曲。在重复加卸载过程中,加卸载刚度随着冲击次数的增加而增大。随着冲击次数的增加,上面板和芯层的能量吸收增量不断减小,而下面板的能量吸收增量不断增加,且最终均趋于稳定。泡沫金属夹芯梁的塑性变形能增量不断减小,而回弹系数随着冲击次数逐渐增加,最后趋于稳定值。     

铝面板PMI泡沫芯夹层梁弹性弯曲的二维模型

将面板PMI泡沫芯夹层梁的弯曲问题按平面应力问题研究,采用弹性理论建立了铝面板PMI泡沫芯夹层梁弯曲变形的微分方程,利用奇异函数把作用在梁上的外载荷表示为分布载荷,推导出了铝面板PMI泡沫芯夹层梁弯曲变形时的挠曲线表达式．采用该方法对面板PMI泡沫芯夹层梁弯曲挠度进行计算,将求得的计算结果与有限元法结果及实验数据进行对比,发现该方法求得的梁中点挠度更接近实验值,这说明该方法可靠的．该方法给出了铝面板PMI泡沫芯夹层梁弯曲时的挠度计算通式,而且梁中点挠度计算公式的表达形式也较为简便,可方便工程设计人员在工程实际中推广应用．     

内爆炸载荷下梯度泡沫铝夹芯管的动态响应

基于3D-Voronoi技术构建了泡沫铝芯层的三维细观有限元模型,对梯度泡沫铝夹芯管在内爆炸载荷下的动态响应进行了数值模拟。分析讨论了夹芯管结构内外管的壁厚、泡沫芯层的相对密度、芯层梯度分布等参数对夹芯管结构的抗爆性能与吸能性能的影响,并与无芯层的双层圆管进行了对比。结果表明:泡沫材料的相对密度可通过改变泡沫胞元大小和胞元壁厚进行调控,利用两种方式构建的夹芯管计算结果一致;保持内、外圆管总质量不变,增大内管壁厚可以有效减小外管的塑性变形,但会影响泡沫芯层的能量耗散;泡沫芯层的填充可以有效降低内管的塑性变形,正梯度泡沫铝夹芯管的抗爆性能优于均匀泡沫及负梯度泡沫夹芯管。     

空心及PMI泡沫填充铝波纹板夹芯梁冲击性能的数值研究

已有文献在空心及PMI泡沫填充铝波纹夹芯梁受泡沫铝块冲击作用的实验中观察到:泡沫填充夹芯梁在相同的载荷下,比相同重量的空心夹芯梁产生更大的后面板中点塑性永久位移。为了分析实验中观察到的现象并揭示其中的力学机理,本文基于商用有限元软件Abaqus/Explicit对空心及泡沫填充铝波纹夹芯梁在冲击下的动态响应进行了数值模拟研究;通过考察芯体与面板间理想连接和脱粘两种情况,研究了界面粘结性能对夹芯梁抗冲击性能的影响。结果表明,实验结果介于这两种情况的模拟结果之间。通过分析空心及泡沫填充夹芯梁不同子结构的塑性吸能差异,发现填充泡沫后夹芯梁的前面板吸能相对于空心夹芯梁有所减小,而后面板的吸能则相对增加。对两种夹芯梁前后面板中点速度的研究表明,由于填充泡沫的波纹芯体对前后面板的支撑作用增大,减缓了前面板的变形并加剧了后面板的变形,因此通过填充泡沫可以减小夹芯梁前面板的变形和撕裂,然而会增大后面板的塑性永久位移。     

铝面板厚度对Nomex蜂窝夹层结构冲击后弯曲性能影响的试验研究

通过低速冲击试验和四点弯曲试验,研究了铝面板厚度对Nomex蜂窝夹层结构抗冲击能力和剩余强度的影响。结果表明:在冲击荷载作用下,面板发生变形的区域大小随面板厚度增加而变大,当面板厚度大于0.5mm时,变形区域直径趋于稳定;无论试件是否受到过冲击,在弯曲载荷作用下,0.2mm厚面板发生芯格内屈曲失稳,而其他厚度面板均发生格间失稳;对无冲击损伤的结构,0.2mm厚面板弯曲强度显著低于其他厚度面板;对含冲击损伤的结构,0.2mm厚面板的剩余强度百分比最高。     

Test method for measuring strength of a curved sandwich beam

A fixture for testing curved sandwich beams in flexure was designed and evaluated. The test specimen is a continuous sandwich beam consisting of a central circular 90° region connected by two straight legs. The fixture was designed according to the four-point flexure principle to produce a pure bending moment in the curved region. The validity of the test fixture in producing the desired loading was examined by fitting a curved aluminum bar of similar bending stiffness as the sandwich beams considered. Strain gage readings were successfully compared to predictions from curved homogeneous beam theory. In addition, the deflection of the beam at the loading points was analyzed using straight and curved beam theory for the various sections of the beam, and predictions were compared to measured load-displacement response. Good agreement was achieved between experimental and analytical results lending confidence to the test principle. Curved sandwich beams consisting of glass/polyester face sheets over a PVC foam core were tested to failure and the loading response of the beams and their failure behavior are discussed. It was found that the beams failed at the upper face/core interface due to radial tension stress.     

Analytical modeling and finite element simulation of the plastic collapse of sandwich beams with pin-reinforced foam cores

Analytical predictions are presented for the plastic collapse strength of lightweight sandwich beams having pin-reinforced foam cores that are loaded in 3-point bending. Both polymer and aluminum foam cores are considered, whilst the facesheet and the pins are made of either composite or metal. Four different failure modes are account for: metal facesheet yield or composite facesheet microbuckling, facesheet wrinkling, plastic shear of the core, and facesheet indentation beneath the loading rollers. A micromechanics-based model is developed and combined with the homogenization approach to calculate the effective properties of pin-reinforced foam cores. To calculate the elastic buckling strength of pin reinforcements, the pin-reinforced foam core is treated as assemblies of simply supported columns resting upon an elastic foundation. Minimum mass design of the sandwich is then obtained as a function of the prescribed structural load index, subjected to the constraint that none of the above failure modes occurs. Collapse mechanism maps are constructed and compared with the failure maps of foam-cored sandwich beams without pin reinforcements. Finite element simulations are carried out to verify the analytical model and to study the performance and failure mechanisms of the sandwich subject to loading types other than 3-point bending. The results demonstrate that the weaker the foam is, the more optimal the pin-reinforced foam core becomes, and that sandwich beams with pin-reinforced polymer foam cores are structurally more efficient than foam- or truss-cored sandwich beams.     

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。     

轻质金属点阵夹层板热屈曲临界温度分析

本文针对均匀温度场下四边简支和四边固支金属点阵夹层板的临界热屈曲温度进行了求解和参数影响分析。将点阵夹芯等效为均匀连续体,并且将夹层板的剪切刚度近似为点阵夹芯的抗剪切刚度,忽略夹芯的抗弯刚度且认为夹层板主要由面板来提供抗弯刚度。对于无法获得解析解的四边固支条件,通过对未知变量进行双傅里叶展开的方法求解了Ressiner夹层板模型的临界屈曲温度,理论分析结果与有限元计算结果吻合良好。进一步分析了不同边界条件、点阵胞元构型、点阵材料相对密度、面板厚度等对临界屈曲温度的影响规律。     

多孔金属夹层板在冲击载荷作用下的动态响应

借助两种有限元软件ABAQUS和LS_DYNA, 模拟和分析了两种厚度不同的泡沫铝合金夹层板(三明治板)、方孔蜂窝形夹层板和波纹形夹层板在冲击载荷下的动态响应. 4种夹层板的单位面积密度相同,冲击载荷分别用泡沫铝子弹与不锈钢子弹模拟. 讨论了泡沫金属夹层板和格构式夹层板在不同冲击载荷作用下的变形机制,重点在于对夹层板的吸能特性及板内各部分吸能变化规律的探讨.研究结果表明: 在泡沫子弹冲击下,夹层板主要是通过自身变形来消耗子弹动能,并转化为自身内能. 厚度为22\,mm的泡沫金属夹层板吸收能量最多,底面变形最小,是结构性能最优的夹层板;在刚性子弹高速冲击穿透过程中,格构式夹层板的吸能性能比单位面积密度相同的泡沫金属夹层板的吸能性能更好. 波纹形夹层板的能量吸收能力在4种板中最高.      

Three-point bending of honeycomb sandwich beams with facesheet perforations

A novel square honeycomb-cored sandwich beam with perforated bottom facesheet is investigated under threepoint bending,both analytically and numerically.Perforated square holes in the bottom facesheet are characterized by the area ratio of the hole to intact facesheet(perforation ratio).While for large-scale engineering applications like the decks of cargo vehicles and transportation ships,the perforations are needed to facilitate the fabrication process(e.g.,laser welding)as well as service maintenance,it is demonstrated that these perforations,when properly designed,can also enhance the resistance of the sandwich to bending.For illustration,fair comparisons among competing sandwich designs having different perforation ratios but equal mass is achieved by systematically thickening the core webs.Further,the perforated sandwich beam is designed with a relatively thick facesheet to avoid local indention failure so that it mainly fails in two competing modes:(1)bending failure,i.e.,yielding of beam cross-section and buckling of top facesheet caused by bending moment;(2)shear failure,i.e.,yielding and buckling of core webs due to shear forcing.The sensitivity of the failure loads to the ratio of core height to beam span is also discussed for varying perforation ratios.As the perfo-ration ratio is increased,the load of shear failure increases due to thickening core webs,while that of bending failure decreases due to the weakening bottom facesheet.Design of a sandwich beam with optimal perforation ratio is realized when the two failure loads are equal,leading to significantly enhanced failure load(up to 60%increase)relative to that of a non-perforated sandwich beam with equal mass.