高速颗粒流冲击下负泊松比力学超材料夹芯梁的动态响应及缓冲吸能机理

建立了颗粒流子弹发射有限元模型,利用离散元和有限元的联合模拟方法,研究了高速颗粒流冲击负泊松比内凹蜂窝夹芯梁的动态响应及缓冲吸能机理。分析了加载冲量、冲击角、芯材强度以及颗粒流子弹与面板间的摩擦力等因素对夹芯梁动态响应的影响。研究结果表明:夹芯梁在正向颗粒流子弹冲击载荷作用下表现为局部凹陷和整体弯曲的耦合变形模式,面内设计芯材因胞壁弯曲呈现局部内凹的变形模式,面外设计芯材因胞壁屈曲呈现局部褶皱的变形模式。在等面密度的条件下,采用面外设计的硬芯夹芯梁面板的跨中最大挠度比采用面内设计的软芯夹芯梁小,但初始冲击力峰值和冲击力整体水平较高,冲击力响应时间较短。夹芯梁前后面板的跨中最大挠度与冲击载荷近似呈对数线性递增关系。与正向冲击相比,斜冲击下夹芯梁的变形模式具有非对称性,局部凹陷程度减小;在颗粒流子弹不同冲击角度作用下,夹芯梁前后面板的跨中最大挠度、初始冲击力峰值以及传递到夹芯梁的动能和动量占比随冲击角度的增大而减小,而颗粒流子弹与夹芯梁面板间的摩擦因数对夹芯梁的动态响应无显著影响。     

星型负泊松比超材料防护结构抗爆抗冲击性能研究

采用数值方法对星型宏观负泊松比效应夹芯结构的抗冲击响应过程以及抗水下爆炸过程中的破坏形式进行了研究:探讨了星型负泊松比结构胞元壁厚、层数和胞元泊松比等参数对弹体侵彻及水下爆炸防护性能的影响。研究结果表明:对于高速或超高速弹体侵彻问题，单纯依靠结构性的被动防御无法应对；负泊松比效应蜂窝夹芯防护结构相较常规防护结构具有良好的水下抗爆性能；等质量条件下，泊松比的变化对抗爆性能影响明显，层数3层、泊松比为?1.63的星型夹芯结构的抗爆性能相对更优；等壁厚条件下，其水下抗爆性能随蜂窝胞元层数减小而增强。     

负泊松比蜂窝材料抗爆炸特性及优化设计研究

为了深入研究车辆底部防护组件爆炸冲击下的结构响应，提高防护型车辆的抗爆炸冲击性能，建立了某车辆底部防护组件在爆炸冲击下的有限元模型，并进行爆炸冲击台架试验验证了有限元模拟的可靠性；将内凹六边形负泊松比蜂窝材料作为防护组件的夹芯部分，分析负泊松比蜂窝材料在爆炸冲击下的变形模式，并对比了同等质量的其他3种防护组件的抗爆炸冲击性能。结果表明，含有负泊松比蜂窝夹芯的防护组件具有更优的抗爆性能。建立了以内凹六边形负泊松比蜂窝胞元尺寸参数为设计变量的多目标优化问题的数学模型，采用多目标遗传算法获得胞元几何参数的最优方案，有效降低了防护组件基板的最大挠度和最大动能。     

泡沫金属固支夹芯圆板的大挠度变形分析

论文分析了大挠度情况下固支夹芯圆板在准静态中心荷载作用下的承载能力.提出了考虑芯层强度影响的夹芯结构屈服条件,应用该条件,并基于边界条件和平板的初始变形机制假设夹芯板的速度场,推导了夹芯圆板考虑弯曲和膜力联合作用的大挠度响应,并应用数值算例验证了分析模型的合理性,在此基础上,分析和讨论了面板厚度、芯层厚度和芯层强度对夹芯圆板承载能力的影响.     

爆炸载荷下双向梯度仿生夹芯圆板的力学行为

基于王莲仿生面内梯度芯层,通过引入面外梯度,设计了一种双向梯度仿生夹芯圆板。在此基础上,运用ABAQUS有限元软件,对不同排列方式的双向梯度夹芯圆板在不同爆炸载荷作用下的响应进行了数值仿真,着重分析了不同仿生夹芯圆板的前后面板挠度、芯层压缩量、变形模式和能量吸收等特性,得到了一种抗爆性能较好的芯层排列方式。结果表明:相较于单一的面外梯度夹芯圆板,合理设计的双向梯度仿生夹芯圆板可以有效降低后面板挠度,并提高芯层的能量吸收。     

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。     

嵌锁式CFRP方形蜂窝夹芯梁低速冲击响应及失效机理

采用嵌锁组装工艺制备了碳纤维/树脂基复合材料方形蜂窝夹芯梁，实验研究了低速冲击载荷下简支和固支夹芯梁的动态响应及失效机理，获得了不同冲击速度下夹芯梁的失效模式，分析了其损伤演化过程和失效机理，探讨了冲击速度、边界条件、面板质量分布以及槽口方向等因素对夹芯梁破坏模式及承载能力的影响。研究结果表明，芯材长肋板槽口方向对夹芯梁的失效模式有较大影响，槽口向上的芯材跨中部分产生了挤压变形，而槽口向下的芯材跨中部分槽口在拉伸作用下出现了沿槽口开裂失效，继而引起面板脱粘和肋板断裂；同等质量下，较厚的上面板设计可以提高夹芯梁的抗冲击能力，冲击速度越大，夹芯梁的峰值载荷和承载能力越高；固支边界使得夹芯梁的后失效行为呈现出明显的强化效应，在夹芯梁跨中部分发生初始失效后出现了后继的固支端芯材和面板断裂失效模式。     

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.     

撞击载荷下Nomex蜂窝夹芯梁的变形模式研究

本文研究了Nomex蜂窝夹芯结构在不同冲量下的变形模式和失效模式.实验采用子弹撞击的加载方式,对Nomex蜂窝夹芯梁施加大小不同的冲量,使用激光位移传感器测量每个试件后蒙皮的变形位移.分析了同芯层厚度,不同蒙皮厚度的Nomex蜂窝夹芯梁在不同冲量作用下抵抗变形的能力,以及冲量大小与蒙皮厚度对夹芯梁抵抗撞击能力的影响,计算分析了蒙皮与芯层的吸能性.实验结果表明:增加蒙皮的厚度能够改善夹芯梁在撞击荷载下抵抗变形的能力,在撞击过程中芯层吸收了50％左右的能量,且冲量越大,芯层吸收的能量越多.     

泡沫铝夹芯梁四点弯曲性能试验研究

通过准静态四点弯曲试验对泡沫铝夹芯梁的弯曲力学性能进行了测试,研究了它的破坏过程、破坏形态和典型荷载-位移曲线,分析了芯层厚度和面层厚度等参数对其弯曲力学性能的影响。结果表明,泡沫铝夹芯梁四点弯曲破坏过程历经三个阶段,呈现三种失效模式:整体弯曲破坏、局部屈曲破坏以及整体屈曲破坏;芯层厚度和面层厚度对夹芯梁的弯曲承载力和吸能效果有明显影响;在本试验参数范围内,芯层厚度为25mm,面层厚度为0.4mm时,夹芯梁具有最优弯曲力学性能。     

Impulsive loading of clamped monolithic and sandwich beams over a central patch

An analytical model is developed for the response of clamped monolithic and sandwich beams subjected to impulse loading over a central loading patch. A number of topologies of sandwich core are investigated, including the honeycomb core, pyramidal core, prismatic diamond core and metal foam. The various cores are characterised by their dependencies of through-thickness compressive strength and longitudinal tensile strength upon relative density. Closed-form expressions are derived for the deflection of the beam when the ratio r of length of loading patch to the beam span exceeds 0.5. In contrast, an ordinary differential equation needs to be solved numerically for the choice r<0.5. Explicit finite element calculations show that most practical shock loadings can be treated as impulsive and the accuracy of the impulsive analytical predictions is confirmed. The analytical formulae are employed to determine optimal geometries of the sandwich beams that maximise the shock resistance of the beams for a given mass. The optimisation reveals that sandwich beams have a superior shock resistance relative to monolithic beams of the same mass, with the prismatic diamond core sandwich beam providing the best performance. Further, the optimal sandwich beam designs are only mildly sensitive to the length of the loading patch.     

Underwater blast loading of sandwich beams: Regimes of behaviour

Finite element (FE) calculations are used to develop a comprehensive understanding of the dynamic response of sandwich beams subjected to underwater blast loading, including the effects of fluid–structure interaction. Design maps are constructed to show the regimes of behaviour over a broad range of loading intensity, sandwich panel geometry and material strength. Over the entire range of parameters investigated, the time-scale associated with the initial fluid–structure interaction phase up to the instant of first cavitation in the fluid is much smaller than the time-scales associated with the core compression and the bending/stretching responses of the sandwich beam. Consequently, this initial fluid–structure interaction phase decouples from the subsequent phases of response. Four regimes of behaviour exist: the period of sandwich core compression either couples or decouples with the period of the beam bending, and the core either densifies partially or fully. These regimes of behaviour are charted on maps using axes of blast impulse and core strength. The simulations indicate that continued loading by the fluid during the core compression phase and the beam bending/stretching phase cannot be neglected. Consequently, analyses that neglect full fluid–structure interaction during the structural responses provide only estimates of performance metrics such as back face deflection and reaction forces at the supports. The calculations here also indicate that appropriately designed sandwich beams undergo significantly smaller back face deflections and exert smaller support forces than monolithic beams of equal mass. The optimum transverse core strength is determined for minimizing the back face deflection or support reactions at a given blast impulse. Typically, the transverse core strength that minimizes back face deflection is 40% below the value that minimizes the support reaction. Moreover, the optimal core strength depends upon the level of blast impulse, with higher strength cores required for higher intensity blasts.     

The impulsive response of sandwich beams: Analytical and numerical investigation of regimes of behaviour

An analytical model is developed to classify the impulsive response of sandwich beams based on the relative time-scales of core compression and the bending/stretching response of the sandwich beam. It is shown that an overlap in time scales leads to a coupled response and to the possibility of an enhanced shock resistance. Four regimes of behaviour are defined: decoupled responses with the sandwich core densifying partially or completely, and coupled responses with partial or full core densification. These regimes are marked on maps with axes chosen from the sandwich beam transverse core strength, the sandwich beam aspect ratio and the level of blast impulse. In addition to predicting the time-scales involved in the response of the sandwich beam, the analytical model is used to estimate the back face deflection, the degree of core compression and the magnitude of the support reactions. The predictions of the analytical model are compared with finite element (FE) simulations of impulsively loaded sandwich beams comprising an anisotropic foam core and elastic, ideally plastic face-sheets. The analytical and numerical predictions are in good agreement up to the end of core compression. However, the analytical model under-predicts the peak back face deflection and over-predicts the support reactions, especially for sandwich beams with high strength cores. The FE calculations are employed to construct design charts to select the optimum transverse core strength that either minimises the back face deflections or support reactions for a given sandwich beam aspect ratio or blast impulse. Typically, the value of the transverse core strength that minimises the back face deflection also minimises the support reactions. However, the optimal core strength depends on the level of blast impulse, with higher strength cores required for greater blasts.     

The dynamic response of composite sandwich beams to transverse impact

The dynamic response of glass fibre–vinylester composite beams is measured by impacting the beams at mid-span with metal foam projectiles. The beams exist in composite monolithic form, and in sandwich configuration with composite face-sheets and a core made from PVC foam or end-grain balsa wood. High-speed photography is used to measure the transient transverse deflection of the beams and to record the dynamic modes of deformation and failure. For both monolithic and sandwich configurations, a flexural wave travels from the impact site towards the supports. Ultimate failure of the monolithic and sandwich beams is by tensile tearing of the faces. The sandwich beams also exhibit cracking of the core, and face-sheet delamination. The dynamic strength of the beams is quantified by the maximum transient transverse deflection at mid-span of the beams as a function of projectile momentum. It is demonstrated that sandwich beams can outperform monolithic beams of equal mass. The trade-off between core strength and core thickness is such that a low density PVC foam core outperforms a higher density PVC foam core. End-grain balsa wood has a superior stiffness and strength to that of PVC foam in compression and in shear. Consequently, sandwich beams with a balsa core outperform beams with a PVC foam core for projectiles of low momentum. The order reverses at high values of projectile momentum: the sandwich beams with a balsa wood core fail prematurely in longitudinal shear by splitting along the grain.     

Performance of metallic honeycomb-core sandwich beams under shock loading

Stainless steel square honeycomb core sandwich and solid monolithic beams have been subjected to high-pressure, short-duration impulses using a shock simulation technique involving high-speed impact of Al foam projectiles. The experiments have been designed to achieve two objectives: (i) to demonstrate the benefits of sandwich construction, and (ii) to assess the fidelity of dynamic finite element calculations in simulating the structural response. The results affirm that, when subjected to impulse levels representative of those associated with nearby explosions, the sandwich beams exhibit smaller displacements than the solid beams at equivalent weight. The benefit is especially large at lower impulses where the effective dynamic strength of the honeycomb core prevents crushing. The measurements and finite element simulations having greatest relevance to the shock resistance are found to correspond closely, particularly the displacements and the core crushing strains. One implication is that the dynamic finite element model has the requisite fidelity at impulse levels of interest.     

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。     

Novel stacked folded cores for blast-resistant sandwich beams

Recent research has established the effectiveness of sandwich structures with metallic cellular cores for blast mitigation. The choice of core architecture can enhance sandwich performance, dissipating energy through plastic core compression and exploiting fluid–structure interaction effects to reduce the momentum imparted to the structure by the blast. In this paper we describe the first analysis of a novel sandwich core concept for blast mitigation: the stacked folded core. The core consists of an alternating stacked sequence of folded sheets in the Miura (double-corrugated) pattern, with the stack oriented such that the folding kinematics define the out-of plane compressive strength of the core. It offers a number of distinct characteristics compared to existing cellular cores. (i) The kinematics of collapse of the core by a distinctive folding mechanism give it unique mechanical properties, including strong anisotropy. (ii) The fold pattern and stacking arrangement is extremely versatile, offering exceptional freedom to tailor the mechanical properties of the core. This includes freedom to grade the core properties through progressive changes in the fold pattern. (iii) Continuous manufacturing processes have been established for the Miura folded sheets which make up the core. The design is therefore potentially more straightforward and economical to manufacture than other metallic cellular materials. In this first investigation of the stacked folded core, finite element analysis is used to investigate its characteristics under both quasi-static and dynamic loading. A dynamic analysis of an impulsively loaded sandwich beam with a stacked folded core reveals the versatility of the concept for blast mitigation. By altering the fold pattern alone, the durations of key phases of the dynamic sandwich response (core compression, beam bending) can be controlled. By altering both fold pattern and sheet thickness in the core, the same is achieved without altering the density of the core or the mass distribution of the sandwich beam.     

轻质金属泡沫夹芯曲板的抗爆炸冲击响应研究

夹芯结构具有高比强度、高比刚度和优异的吸能能力,已经被广泛应用于工程结构用来抵御高强度的爆炸冲击载荷。本文采用有限元数值模拟方法研究了爆炸载荷作用下四边固支夹芯曲板的动力响应。比较了同等质量下夹芯曲板、夹芯平板、实体曲板和实体平板四种结构的抗爆炸冲击性能,讨论了不同曲率和非对称因子对结构动力响应的影响,得到了使得夹芯曲板抗爆炸性能最佳的非对称因子。研究结果表明：夹芯曲板的抗爆炸冲击性能优于等质量的夹芯平板、实体曲板和实体平板结构,增大夹芯曲板的曲率能够提高结构的抗爆炸冲击性能。