Torsional crushing of foam-filled thin-walled square columns

Torsional crushing behavior of foam-filled thin-walled square columns were investigated analytically, numerically and experimentally. The lower and upper bounds on the torsional resistance of foam-filled columns were established analytically. Numerical simulations were carried out and showed that the presence of the filler changes the torsional collapse mechanism and gives rise to higher order sectional collapse modes, which results in a higher torsional resistance. Torsional experiments were performed and results were compared to the analytical and numerical solutions with reasonably good agreement. It was found that bonding of the foam to the walls changes the deformation mode by spreading deformation over the whole length. The corresponding torsional resistance is also larger for the first 40° of rotation. It is concluded that fitting prismatic members with the aluminum foam of a density ranging from 0.14 to 0.28 g/cm³ can double the energy absorption of a given member.     

Deformation and energy absorption of aluminum foam-filled tubes subjected to oblique loading

Research to quantify the energy absorption of empty and foam-filled tubes under oblique loading with different loading angles and geometry parameters was carried out. Tests on circular tubes made of aluminum alloy AA6063 under quasi-static axial or oblique loading were performed. The collapse behavior of empty, foam-filled single and double tubes was investigated at loading angles of 0°, 5°, 10° and 15° with respect to the longitudinal direction of the tube. The tubes were fixed at both ends and oblique load was realized by applying a load at the upper end of a pair of specimens. When the foam-filled tubular structures subjected to oblique quasi-static loading, some new deformation modes, such as spiral folding mode, irregular extensional folding mode and irregular axi-symmetric or diamond deformation mode, were identified and ascribed to the bending of tubes and shearing of foam filler, as well as the interaction between the tubes and the foam. The energy absorption characteristics of empty and foam-filled single and double tube structures with respect to the load angle and wall thickness are determined. It is found that the energy-absorbing effectiveness factors of the circular tube structures with aluminum foam core are significant higher than those of the empty tubes and the energy absorption capacity of the foam-filled double tubes is better than that of the empty and foam-filled single tubes.     

铝蜂窝夹芯板低速动态冲击响应研究

为研究不同结构参数对质量相同、强度不同的两种铝蜂窝夹芯板低速动态冲击响应的影响，建立了铝蜂窝夹芯板受半球型落锤低速冲击的数值模型，并将有限元计算结果与试验结果进行对比，检验了模型的可靠性。在此基础上，对比研究了不同上下铝板厚度和不同蜂窝芯壁厚对两种铝蜂窝夹芯板在低速冲击下吸能效果的影响。结果表明：在质量相同的情况下，强度小、高度大的夹芯板在低速冲击下力-位移曲线更易出现双峰模式，增加蜂窝芯壁厚或是上下铝板厚度都会使第一次的峰值力增加，第二次峰值力降低；强度小、高度大的夹芯板蜂窝芯在低速冲击中吸能占比更多，强度大、高度小的则是上层铝板吸收的能量更多，前者的质量、体积比吸能更高；铝蜂窝夹芯板质量比吸能和体积比吸能与壁厚边长比、板厚芯高比均呈幂次关系。     

泡沫铝夹芯柱体材料在汽车保险杠中的应用

通过把新型的泡沫铝夹芯柱体材料汽车保险杠和传统的钢管材料汽车保险杠在碰撞时的吸能性能进行对比,发现两种材料保险杠碰撞时的吸能性能方面,前者远远优于后者,从而为汽车保险杠材料的改进提供了依据。     

Optimum design for energy absorption of square aluminium columns with aluminium foam filler

The performance in axial compression of square aluminium columns with aluminium foam filler has been assessed based upon existing design formulas for average crush force, maximum force and effective crushing distance. Using an optimisation algorithm, the combination of (1) foam density, (2) column wall thickness, (3) column width, (4) column material strength and (5) total component length giving the component of minimum mass was determined for specific cases. It was found that optimum foam filled columns compared to the traditionally designed non-filled columns showed smaller cross section dimensions in addition to less weight. As a consequence, mass-, length- and volume reductions are possible by utilising foam filler.     

The collapse response of sandwich beams with a Y-frame core subjected to distributed and local loading

Sandwich beams comprising a Y-frame core have been manufactured by assembling and brazing together pre-folded sheets made from AISI type 304 stainless steel. The collapse responses of the Y-frame core have been measured in out-of-plane compression, longitudinal shear and transverse shear; and the measurements have been compared with finite element predictions. Experiments and calculations both indicate that the compressive response is governed by bending of the constituent struts of the Y-frame and is sensitive to the choice of lateral boundary conditions: the energy absorption for a no-sliding boundary condition exceeds that for free-sliding. Under longitudinal shear, the leg of the Y-frame undergoes uniform shear prior to the onset of plastic buckling. Consequently, the longitudinal shear strength of the Y-frame much exceeds its compressive strength and transverse shear strength. Sandwich beams were also indented by a flat bottomed punch, and a relatively high indentation strength was observed. It is argued that this is due to the high longitudinal shear strength of the Y-frame. While finite element calculations capture the measurements to reasonable accuracy, a simple analytical model over-predicts the indentation strength. Finally, the finite element method was used to investigate the energy absorption capacity of the sandwich beams under indentation loading. The calculations reveal that for a given tensile failure strain of the face-sheet material, a sandwich beam with Y-frame core has a comparable performance to that of a sandwich beam with a metal foam core. The relative performance is, however, sensitive to the choice of design parameter: when the indentation depth is taken as the design constraint, the sandwich beam with a Y-frame core outperforms the sandwich beam with the metal foam core.     

碳化硅增强泡沫铝层合圆管的制备及力学性能研究

用熔体发泡法制备了碳化硅颗粒增强泡沫铝样品，分析了碳化硅增强泡沫铝在准静态压缩条件下的变形行为。用不锈钢圆管为面板，碳化硅颗粒增强泡沫铝为夹芯制备层合圆管，研究了层合圆管在准静态压缩条件下的变形行为和能量吸收性能。研究表明：碳化硅颗粒增强泡沫铝的屈服强度在5～12MPa之间，对泡沫铝材料的力学性能有明显的增强作用；层合圆管在保持泡沫铝轻质、高吸能效率的同时，大幅度提高了吸能能力；碳化硅增强泡沫铝层合圆管的压缩屈服应力达到45MPa，平台应力达到40MPa，具有优良的吸能性能。     

Plastic collapse and energy absorption of empty circular aluminum tube under transverse quasi-static loading

This paper presents an experimental investigation on plastic collapse and energy absorption of empty circular aluminum tubes under quasi-static transverse loading. Tubular structures being a critical demand as material saving, high energy absorption and good strength characteristics were of major concerns due to its wall thinness, and so, its various diameter-to-thickness (D/t) ratios and span lengths. Studies found that empty circular Al-tube structure subjected to transverse standard three-point bending loading undergone three plastic deformation phases, starting with crumpling phase, crumpling and buckling phase, and lastly the structural collapse. The results found that energy absorption of empty aluminum tubes for a constant D/t ratio decreases as span length. On the contrary, the energy absorption of empty aluminum tubes for a given constant span length increases with the increase in D/t ratio.     

Energy absorption of aluminum foam filled braided stainless steel tubes under quasi-static tensile loading conditions

A theoretical model to predict the energy absorption capabilities of aluminum foam filled braided stainless steel tubes under tensile loading conditions has been developed and is presented. Experimental testing was completed on braided tubes, with a nominal diameter of 64.5 mm and woven from 304 stainless steel wires with a diameter of 0.51 mm, filled with rectangular prisms of closed cell aluminum foam with densities ranging from 248 to 373 kg/m³. Based upon observations from experimental testing and applying a unit cell concept to the braided tube, a theoretical model which incorporates two stages of deformation was developed. Within the first stage of deformation, which occurs prior to tow lockup of the braided tube, energy absorption is primarily due to compression of the aluminum foam core. After tow lockup has occurred the energy absorption behavior of the assembly is a sole result of the deformation of the braided tube. Comparisons between the energy absorption predictions of the analytical model and experimental observations were found to be in good agreement for assembly lengths of approximately 400 mm. For the tensile loading conditions and geometry of aluminum foam filled braided tubes considered in this research energy absorption ranged from approximately 5.2 to 7.9 kJ with corresponding tube elongations of 400 mm.     

Crashworthiness analysis on alternative square honeycomb structure under axial loading

Hexagonal metal honeycomb is widely used in energy absorption field for its special construction. However, many other metal honeycomb structures also show good energy absorption characteristics. Currently, most of the researches focus on hexagonal honeycomb, while few are performed into different honeycomb structures. Therefore, a new alternative square honeycomb is developed to expand the non-hexagonal metal honeycomb applications in the energy absorption fields with the aim of designing low mass and low volume energy absorbers. The finite element model of alternative square honeycomb is built to analyze its specific energy absorption property. As the diversity of honeycomb structure, the parameterized metal honeycomb finite element analysis program is conducted based on PCL language. That program can automatically create finite element model. Numerical results show that with the same foil thickness and cell length of metal honeycomb, the alternative square has better specific energy absorption than hexagonal honeycomb. Using response surface method, the mathematical formulas of honeycomb crashworthiness properties are obtained and optimization is done to get the maximum specific energy absorption property honeycomb. Optimal results demonstrate that to absorb same energy, alternative square honeycomb can save 10% volume of buffer structure than hexagonal honeycomb can do. This research is significant in providing technical support in the extended application of different honeycomb used as crashworthiness structures, and is absolutely essential in low volume and low mass energy absorber design.     

Collapse mechanisms of sandwich beams with composite faces and a foam core, loaded in three-point bending. Part I: analytical models and minimum weight design

Analytical predictions are made for the three-point bending collapse strength of sandwich beams with composite faces and polymer foam cores. Failure is by the competing modes of face sheet microbuckling, plastic shear of the core, and face sheet indentation beneath the loading rollers. Particular attention is paid to the development of an indentation model for elastic faces and an elastic–plastic core. Failure mechanism maps have been constructed to reveal the operative collapse mode as a function of geometry of sandwich beam, and minimum weight designs have been obtained as a function of an appropriate structural load index. It is shown that the optimal designs for composite–polymer foam sandwich beams are of comparable weight to sandwich beams with metallic faces and a metallic foam core.     

Evaluation of material properties and internal damage within CFRP and CFRP/Al sandwich panels due to impact loading

In the present paper, damage development within Carbon fiber reinforced plastic (CFRP) laminates and CFRP/Aluminum (Al) honeycomb core sandwich panels by impact loading was evaluated, and change in material properties due to the damage development was investigated. Falling weight impact tests, 3-point bending tests and cross-sectional observation were carried out. As results, it is found that falling rate of bending elastic modulus due to internal damage in the laminate only is lower than that in the upper face-sheet of the sandwich panel, and that difference in the falling rate between them becomes maximum at the impact energy of 5.1 J. As a result of investigating the relationship between reduction in bending elastic modulus and internal damage development, the reduction is caused by delamination within CFRP laminates mainly. Since total length of cracks in CFRP/Al honeycomb core sandwich panels is smaller than that in the laminates only, the sandwich panels have high impact tolerance because of absorption of impact energy by damaging Al honeycomb core.     

泡沫铝填充帽型结构轴向压缩吸能特性的试验研究

通过试验方法研究了泡沫铝填充帽型结构准静态压溃时的吸能特性。首先,进行了泡沫铝空心帽型结构以及泡沫铝填充帽型结构的轴向压缩试验;然后,根据试验结果,对泡沫铝填充帽型结构的轴向吸能特性进行了分析,并与空心帽型结构进行了比较。结果表明,填充泡沫铝之后,帽型结构的轴向压缩稳定性和吸能特性有了很大的提高。在吸收的能量一定时,泡沫铝填充能够减少吸能结构所需要的质量。     

High-velocity impact experiment of aluminum foam sample using powder gun

Porous materials such as aluminum foam have been investigated for possible use as impact shock absorbers in transportation aeronautic applications. However, the response of aluminum foam during impacts at high velocities of more than 100 m/s is not yet fully understood. A high-velocity impact experiment was therefore carried out to clarify impact shock absorption properties of aluminum foam. A one-stage powder gun was used to accelerate an aluminum foam sample to impact a rigid wall. Velocity and deformation of the aluminum foam sample during impact was studied using a digital high-speed video camera, while the pressure wave in the aluminum foam sample was measured using a PVDF gauge. The experimental observations revealed uneven collapse of the aluminum foam sample structure during high speed impact with a general stress plateau effect, typical for cellular material structures when subjected to quasi-static loading.     

含有泡沫铝芯的复合板弯曲断裂行为的原位研究

对由泡沫金属铝芯和金属面板组成的三层和多层复合板四点弯曲条件下的变形和断裂行为进行原位观察。研究结果表明：在弯曲条件下,复合板有两种基本的破坏方式,一种是复合板表面凹陷(Indentation, ID),它是表面局部集中塑性变形的结果;另一种是泡沫铝内芯切断 (Core shear, CS),它是内芯在最大切应力作用下的破坏。对一个给定的三层复合板,当凹陷破坏的载荷极限FID大于内芯切断的载荷极限FCS时发生内芯切断式破坏,反之发生表面凹陷式破坏。对于多层复合板,破坏方式受金属面板制约,不能直接应用三层板的破坏判据。若三层板发生凹陷型破坏,具有与三层板相同金属面板厚度的多层复合板发生凹陷加内芯切断的混合型破坏。当三层板只发生内芯切断型破坏时,具有与三层板相同金属面板厚度的多层复合板完全发生内芯切断型破坏。     

Collapse mechanisms of sandwich beams with composite faces and a foam core, loaded in three-point bending. Part II: experimental investigation and numerical modelling

This study focuses on the competing collapse mechanisms for simply supported sandwich beams with composite faces and a PVC foam core subjected to three point bending. The faces comprise Hexcel Fibredux 7781-914G woven glass fibre-epoxy prepreg, while the core comprises closed cell Divinycell PVC foam of relative density 6.6% and 13.3%. The mechanical properties of the face sheets and core are measured independently. Depending upon the geometry of the beam and the relative properties of the constituents, collapse is by core shear, face sheet microbuckling or by indentation beneath the middle loading roller. A systematic series of experiments and finite element simulations have been performed in order to assess the accuracy of simple analytic expressions for the strength. In general, the analytic expressions for peak load are adequate; however, simple beam theory becomes inappropriate and the analytic models are inaccurate for stubby beams with thick faces relative to the core thickness. A failure mechanism map is constructed to reveal the dependence of the dominant collapse mechanism upon the geometry of the beam.     

泡沫填充薄壁结构的抗弯性分析及多目标优化设计*

泡沫铝填充薄壁结构具有轻质、较大承载能力以及高效吸能特性,越来越多地应用于各种工程结构。提出一种新颖的轴向梯度泡沫填充薄壁结构,采用试验与数值分析的方法,系统地分析空管、均匀泡沫填充及梯度泡沫填充薄壁圆管在弯曲工况下的力学响应及能量吸收特性。研究发现,泡沫填充薄壁结构比空管具有更好的抗弯性能。与均匀泡沫填充结构相比,梯度泡沫不仅使得填充薄壁结构的变形模式从单褶皱模式变为多褶皱模式,截面扁化量和抗弯刚度损失显著减小,而且有效地提高了填充结构的承载力及吸能特性。为了进一步探索填充结构的最优耐撞性,结合Kriging近似技术与粒子群数值优化方法,对均匀泡沫和功能梯度填充泡沫薄壁结构进行多目标优化设计,得到了泡沫填充薄壁结构耐撞性的最佳参数匹配设计,并有效提高了结构的抗弯性能,为泡沫填充薄壁结构抗弯性设计提供了参考依据。     

多孔结构材料在汽车碰撞安全中的应用研究

讨论了汽车碰撞中的主要吸能元件的吸能步骤和压溃模式，从理论上阐述了填充了多孔结构材料的吸能元件在吸能上的优势。对蜂窝式和蛋盒式两种多孔结构材料的结构组成、成形技术和吸能能力进行了分析，并进一步研究了多孔结构材料在汽车保险杠、车门以及纵梁等主要安全构件中的应用，说明把多孔材料应用到汽车吸能防撞装置中是可行的，可以极大地提高整车的耐撞性。     

粉煤灰漂珠/聚氨酯复合泡沫铝材料压缩性能与本构关系研究

采用压力渗透法制备出了铝基复合泡沫材料,填充材料是以粉煤灰漂珠为主要组分、硬质聚氨酯泡沫为粘结剂的复合泡沫材料.通过准静态实验和分离式霍普金森压杆(Split Hopkinson pressure bar,SHPB)动态压缩的方法研究了复合泡沫铝的压缩力学响应,然后建立了动态本构关系.研究表明,复合泡沫铝的压缩应力-应变曲线与其它泡沫材料的应力-应变曲线类似,文中的两种铝基复合泡沫具有应变率效应,复合泡沫铝较密度相近未填充前的泡沫铝基具有更高的压缩强度与能量吸收能力.但由于漂珠尺寸的不同,导致两种复合泡沫铝的动态压缩结果不尽相同,且小颗粒复合泡沫铝在动态冲击下吸能效果最好.在本研究实验的应变率和密度范围内,本文建立的本构模型曲线与实验曲线吻合较好.     

粉煤灰漂珠/聚氨酯复合泡沫铝材料压缩性能与本构关系研究

采用压力渗透法制备出了铝基复合泡沫材料,填充材料是以粉煤灰漂珠为主要组分、硬质聚氨酯泡沫为粘结剂的复合泡沫材料.通过准静态实验和分离式霍普金森压杆(Split Hopkinson pressure bar,SHPB)动态压缩的方法研究了复合泡沫铝的压缩力学响应,然后建立了动态本构关系.研究表明,复合泡沫铝的压缩应力-应变曲线与其它泡沫材料的应力-应变曲线类似,文中的两种铝基复合泡沫具有应变率效应,复合泡沫铝较密度相近未填充前的泡沫铝基具有更高的压缩强度与能量吸收能力.但由于漂珠尺寸的不同,导致两种复合泡沫铝的动态压缩结果不尽相同,且小颗粒复合泡沫铝在动态冲击下吸能效果最好.在本研究实验的应变率和密度范围内,本文建立的本构模型曲线与实验曲线吻合较好.