【作者】 郭刘伟；

【导师】 虞吉林；

【作者基本信息】 中国科学技术大学 ， 工程力学， 2010， 博士

【摘要】 薄壁管结构作为缓冲吸能构件在交通及航天等领域有着广泛的应用前景。泡沫铝填充薄壁管作为改进结构,提高了结构的承载力及吸能特性,且其轻质特点对减小能耗,降低大气污染方面有着重要作用。而目前的泡沫铝填充圆管结构在轴压加载下,能量吸收效率低下,不及空管结构,在弯曲作用下,填充结构均易发生断裂失效,严重影响到结构的能量吸收效率,且更为实际的弯曲、压缩同时作用下填充管结构的行为研究甚少。故本文针对目前填充管结构的缺点,优化设计泡沫铝填充管的结构构型,对新型的双管夹芯结构在纯轴压、三点弯曲及弯压共同作用下的性能进行了系统的实验及有关数值模拟研究,具体内容如下：1)对于更为轻质的泡沫铝填充铝合金双方管结构的准静态轴压性能进行了实验研究,对比空管及传统的单管夹芯结构,给出各种结构的不同变形模式。新型的双管夹芯结构可发生两种变形模式,均较单管夹芯结构稳定。详细对比了各结构间的承载力及吸能效率等特性。结果表明,新型的双管夹芯结构的能量吸收效率高于传统的泡沫铝填充单管及空管结构,且新型结构在四角撕裂模式下的能量吸收效率高于周期折叠模式。同时研究了内管壁厚对双方管夹芯结构轴压性能的影响。最后利用泡沫铝填充管结构中芯层泡沫铝的变形特点,去除了利用效率不高的部分泡沫铝,提出一种更优化的改进结构：四角填充双方管结构,并对其变形模式及相关性能进行了分析讨论。该改进结构的变形更为稳定,能量吸收效率更高。2)针对研究尚缺乏的泡沫铝夹芯铝合金双方管结构的三点弯曲性能进行了准静态实验研究。对比空管、传统的泡沫铝夹芯单管结构,研究了该新型结构在三点弯曲下的承载力、破坏抗性及能量吸收能力等特性。双管夹芯结构增强了结构的破坏抗性,大大提高了结构破坏前的能量吸收能力。探讨了双方管夹芯结构的破坏模式,内管壁厚不同,双管夹芯结构的破坏模式有所改变。且就结构跨径、内管壁厚等参数对双方管夹芯结构弯曲性能的影响开展了一定的实验研究。同时对内外管与芯层间的胶合作用进行了分析讨论。结果发现,胶合作用提高了结构的抗弯刚度,但同时降低了结构的弯曲破坏抗性,导致结构的能量吸收能力减弱。实验中对管壁的材料性质也进行了对比研究,同时开展了不锈钢夹芯管的实验,并对两种材质的夹芯管结构的弯曲性能进行了比较。3)就目前尚未研究的泡沫铝夹芯铝合金双圆管结构的纯轴压及各小角度斜压下的性能进行了详尽的实验研究。首先对泡沫铝夹芯双圆管在纯轴压加载下的内外管变形特征进行了分析讨论,双管夹芯结构中内管更易发生金刚石模式,但内外管的不同组合同时影响着内管的变形模式。对比空管、泡沫铝夹芯单管结构,给出双管夹芯结构变形的机制解释。且优化组合的双管夹芯结构的承载力及能量吸收效率远远高于传统的单管夹芯结构,接近甚至超过空管结构。探讨了内管壁厚、管径及外管壁厚等对该新型夹芯结构性能的影响。针对斜压特点,设计出一套用于准静态实验的斜压实验装置,并成功地开展了泡沫铝夹芯双圆管结构在各种小角度斜压加载下的实验研究。对比轴压性能,给出空管、传统的泡沫铝填充单管及新型的双管夹芯结构在各种小角度斜压加载下的变形模式。在小角度斜压加载下,泡沫铝填充管结构发生一种特殊的上下双半瓣对称混合模式,并易发生横向滑移变形,从而导致了泡沫铝夹芯结构在小角度斜压加载下的承载力非常平稳,承载后期接近理想承载结构,且平均承载力大小基本保持不变。实验结果表明,该新型双管夹芯结构在两端固支加载下,其比质量能量吸收效率远远高于传统的单管夹芯结构,且超过相应的空管,同时实现了提高承载力大小,增强承载稳定性及提升结构的能量吸收效率的综合目标。并就斜压加载角度对各种结构性能的影响进行了实验研究。4)对新型的泡沫铝夹芯双圆管结构在准静态三点弯曲加载下的性能进行了实验及有限元模拟研究。不同与单管填充结构的单裂纹失效,双管夹芯结构在三点弯曲下出现特殊的双裂纹破坏模式。且新型结构的破坏抗性大大高于传统的单管夹芯结构,能量吸收能力得到大幅提升。在合理的内外管组合下,双管夹芯结构的承载力相当平稳,非常适合做缓冲吸能装置。同时就跨径、内管壁厚、管径及外管壁厚对双管夹芯结构三点弯曲性能的影响进行了一定的实验研究。利用ABAQUS有限元软件建立双管夹芯结构三点弯曲下的有效模型,通过分析芯层泡沫铝的应力分布给出新型结构特有破坏模式的产生机制。且由对外管管壁下端等效塑性应变及最大拉伸应变的讨论,发现最大拉伸应变可作为外管管壁断裂失效的评判参量。探讨了双管夹芯结构较单管结构弯曲破坏抗性提升的机制,并给出一定的解释。最后综合结构的承载力特性及破坏抗性,给出综合性能较优的内外管管径比。5)对新型的泡沫铝夹芯双圆管结构在动态冲击下的三点弯曲性能进行了落锤冲击实验及有限元模拟研究。不同于准静态下的失效模式,双管夹芯结构在动态冲击下芯层泡沫铝下端出现多裂纹现象,且较均匀分布于中间区域,有利于泡沫铝吸收更多的冲击能量。且泡沫铝填充结构在低速冲击下的惯性效应并不明显,承载力大小与准静态结果相差不多。但动态冲击下结构的破坏抗性较准静态结果大幅提高,泡沫铝填充结构在动态下的能量吸收能力远远高于准静态结果。而对比传统的泡沫铝填充单管结构,该新型夹芯结构的破坏抗性及能量吸收效率更高,承载力也较稳定,更适合作为承载缓冲结构。且就跨径、外管壁厚等因素对新型结构性能的影响进行了讨论。最后在有限元模型中分别分析了低速冲击下新型结构特有破坏模式产生的机制、弯曲破坏抗性提高的机理及动态冲击下与准静态结果差别产生的原因。更多还原

【Abstract】 Thin-walled tube structures used as energy absorbers have broad potential applications in traffic tools and aero areas. As an improved structure, the load carrying capacity of the foam-filled single tube is higher than the empty tube and the light weight character of this foam-filled structure is very important for reducing the fuel dissipation and the pollution to the atmosphere. But the critical problem is that the energy absorption efficiency of the foam-filled single tube structure is lower than the empty tube under the axial crushing. And the foam-filled single tube fails much earlier under the three point bending condition which limits the energy absorption ability of this structure at some extent. In the most possible situations when the impact happens, structures are subjected to not only the axial crushing but also the bending loads. But the study of foam-filled structures under combined loads is so little by now. So a new topology structure, foam-filled double tube structure, was given by improving the traditional foam-filled single tube in this paper. And the experimental and numerical investigations about the performances of this new structure under the pure axial crushing, three point bending and the combined loading condition were carried out. The detailed contents are as follows:1) The pure axial crushing behavior of the foam-filled double square aluminum alloy tube structure was studied experimentally. Compared with the empty tube and the traditional foam-filled single tube structure, the different deformation modes of these structures including the new structure were obtained. The deformation stabilization character of this new structure is much better than the traditional foam-filled single tube. The energy absorption efficiency of this new structure under the axial crushing is much higher than the foam-filled single tube and empty tube structures. Furthermore, the energy absorption efficiency of this new structure with the deformation mode of tearing in corners is higher than that with the axisymmetric mode. The effect of the inner tube thickness to the axial crushing behavior of this new structure was also investigated. According to the axial crushing behavior of the foam-filled double tube, a new improved structure, double tube structure filled with aluminum foams in corners, was given out by cutting off parts of aluminum foams with lower efficiency in the structure. The deformation modes and the axial crushing behavior of this improved structure were studied. The results show that this new improved structure stabilizes the deformation and increases the energy absorption efficiency of the foam-filled double tube structure.2) The quasi-static three point bending behavior of the foam-filled double square tube structure was studied experimentally. The load carrying capacity, crashworthiness and the energy absorption of this new structure under the three point bending condition were investigated. Compared with empty and foam-filled single tubes, the crashworthiness of this new structure is enhanced and the energy absorption efficiency is increased. The deformation of this new structure was studied and the results show that the inner tube thickness is so important. The effect of the span and the inner tube thickness to the new structure was also investigated. The adhesion effect between aluminum foam core and the profiles to the new structure was analyzed. The results show that the adhesion effect increases the load carrying capacity but weakens the crashworthiness and the energy absorption ability of the structure before failure. The study of the profile materials was also performed. The bending behavior comparisons between different profile materials were carried out.3) The detailed quasi-static experimental studies of the foam-filled double cylindrical tube structures under the pure axial and the oblique loading condition were carried out. The deformation modes of profiles in the foam-filled double tube structure under the pure axial crushing were studied. The inner tube deforms with the diamond mode much easier. But the inner and outer tubes influence the deformation mode of profiles together. Compared with the empty and foam-filled single tube, the deformation mechanism of this new structure was given. The energy absorption efficiency of the optimized foam-filled double tube structure is much higher than the traditional foam-filled single tube structure and comes close to or even higher than the empty tube structure. The effect of profiles to the new structure was also investigated in the experiments. An instrument used for quasi-static oblique loading was designed and the experimental studies of the foam-filled double cylindrical tube under the oblique loading condition were carried out. The deformation modes of empty tube, foam-filled single tube and the foam-filled double tube structures under the oblique loading conditions differs from those under the pure axial crushing. Under the small angle oblique loading condition, a special deformation mode, mixed mode with symmetric half folding up and down, appears in foam-filled cylindrical tubes. And this special deformation mode makes the load carrying capacity of foam-filled cylindrical tubes much steadier and comes close to the ideal structure for loading. Under small angle oblique loading conditions, the load carrying capacity nearly keeps the same as the results under the pure axial crushing. The experimental results show that, the energy absorption efficiency of this new structure under different angle oblique loading conditions is much higher than the traditional foam-filled single tube and the most important point is that this new structure surpasses the empty tube on the energy absorption efficiency. So, this foam-filled double tube structure with two fixed boundary condition achieves the combined goal of increasing the load carrying capacity, enhancing the load steadiness and improving the energy absorption efficiency of structures at the same time. And the effect of the oblique loading angle to these structures was studied experimentally.4) The quasi-static three point bending behavior of foam-filled double cylindrical tube structures was studied experimentally and numerically. Differing from the single crack failure mode of the traditional foam-filled single tube, two obvious cracks appear symmetrically about the center of the foam-filled double tube. The crashworthiness and the energy absorption efficiency of this new structure are much enhanced compared with the traditional foam-filled single tube. With the proper assembling of the inner and outer tube, the load carrying capacity of this new structure is much steadier, which is much suitable for the energy absorbers. The effect of the span, the inner and outer tube to this new structure was also investigated experimentally. An effective model of this new structure under the three point bending condition was created with the finite element code in ABAQUS. The failure mechanism was analyzed by studying the stress distributing of the foam in the foam-filled double tube structure. According to the analysis of the equivalent plastic strain and the maximum tension strain, the maximum tension strain could be as the critical parameter for the failure of these structures. Some explanations have been given for the experimental results that the crashworthiness of this new structure is higher than the traditional foam-filled single tube. At last, considering the combined performances of the structure, some optimizations for this new structure have been performed and the proper assembling of the inner and outer tube diameter was given.5) The dynamic three point bending behavior of the foam-filled double cylindrical tube structure was studied experimentally and numerically. Differing from the failure mode under the quasi-static condition, there are several cracks located symmetrically about the center of the foam in the foam-filled double tube structure, which is much suitable for the much more energy absorption of the structure. Although the load carrying capacity of the foam-filled structures remains the same level of the quasi-static results, but the crashworthiness of these structures is much higher than the quasi-static ones. So, under the impact condition, foam-filled structures could absorb much more energy than the static results. Compared with the traditional foam-filled single tube, the load carrying capacity of this new structure is much higher and steadier, the crashworthiness and the energy absorption efficiency of this new structure is much higher, which shows that this new structure is much suitable as an energy absorber under the three point bending load. The effect of the span and the outer tube thickness to the new structure was also studied. The dynamic failure mechanism of this new structure was analyzed using the finite element code in ABAQUS. The difference of the crashworthiness between static and dynamic results is also investigated.更多还原