Efficient energy absorption of functionally-graded metallic foam-filled tubes under impact loading

The deformation behavior and crashworthiness of functionally-graded foam-filled tubes(FGFTs)under drop-weight impact loading were investigated.Closed cell aluminum,A356 alloy and zinc foams fabricated by the liquid state processing were used as axial grading fillers for the manufacture of single-layer and multilayer structures with different configurations.The results indicate that the deformation of multilayer foam filled tubes initiates from the low-strength components,and then propagates in the high-strength components through the gradual increment of stress.The use of more A356 alloy and aluminum foam layers provides greater specific energy absorption(SEA)for the graded structures,whereas the high-strength zinc foam has no positive effect on the crash performance.The progressive collapse of graded structures consisting of the aluminum and A356 alloy foams occurs in a symmetric mode under quasi-static and drop-weight impact conditions.However,the zinc foam causes a combination of symmetric and extension modes as well as greater localized deformation under dynamic loading and greater local rupture in quasi-static loading condition.The Al−A356 foam-filled tubes with a combination of the highest SEA(10 J/g)and the lowest initial peak stress(σmax of 10.2 MPa)are considered as the best lightweight crashworthy structures.

A new hybrid energy absorption mechanism subjected to axial loading

This study aims to introduce a novel hybrid design with a combination of two more common mechanisms for improving the capacity of systems in absorbing the kinetic energy of moving vehicles or devices. This new model consists of two individual mechanisms, i.e., expansion of a circular tube accompanied by crushing of an inner tube, which dissipate the energy through friction, plastic deformations and failures of inner tube. This study comprises 24 case studies surveyed under two different design controls, constant mass and constant volume, for comparing purposes. Finite element simulations are utilized so as to investigate models’ deformations and to extract some crashworthiness parameters in aid of representing the efficiency of the mechanism as well as conducting a parametric study between three different profiles of inner tube. This study shows that models with inner circular and hexagonal tube profile absorb higher amount of energy due to experiencing three different modes of energy dissipation systems, including folding, shear and ductile damages.

THE RELATIONSHIP BETWEEN THE EM ENERGY ABSORPTION OF HUMAN BODY AND THE INCIDENT DIRECTION AND POLARIZATION OF PLANE WAVE

The problems of EM energy absorption of human body irradiated by plane wave arediscussed by the Finite-Difference Time-Domain(FD-TD)method.The local Specific AbsorptionRates(SARs),the whole-body average SARs and the layer average SARs for the inhomogeneousblock model of human body with different incident direction and different polarization of theincident waves are calculated.The results show that the appearance of maximum EM energyabsorption is not always at the situation of the front incidence and the local SARs are moreimportant for the interaction of the EM fields with human body.All results provide more infor-mation about the electromagnetic dosimetry for human body.

Optimization Design of an Embedded Multi-Cell Thin-Walled Energy Absorption Structures with Local Surface Nanocrystallization

Bymeans of the local surface nanocrystallization that enables to change the material on local positions,an innovative embedded multi-cell(EMC)thin-walled energy absorption structures with local surface nanocrystallization is proposed in this paper.The local surface nanacrystallization stripes are regarded as the moving morphable components in the domain for optimal design.Results reveal that after optimizing the local surface nanocrystallization layout,the specific energy absorption(SEA)is increased by 50.78%compared with the untreated counterpart.Besides,in contrast with the optimized 4-cell structure,the SEA of the nanocrystallized embedded 9-cell structure is further enhanced by 27.68%,in contrast with the 9-cell structure,the SEA of the nanocrystallized embedded clapboard type 9-cell structure is enhanced by 3.61%.Thismethod provides a guidance for the design of newenergy absorption devices.

Energy Absorption and Strength Evaluation for Compressed Glass Fibre Reinforced Polyester (GRP) for Automobile Components Design in Crash Prevention Scheme

This paper utilized the compressive tests results to establish some critical mechanical properties and crashworthiness parameters that may be required to design GRP composites of polyester matrix in automobile structures. Third order polynomial function was used with numerical methods to establish the elastic properties whish could not be established due to sensitivity of the Monsanto tensometer used to obtain the compression results. This study showed that the finite difference method captured the general trend of experimental solution giving optimum value of compressive stress as 23.78MPa at strain of 0.018 and elastic limit of 12.01MPa at 0.01 strain through finite difference analysis while the solution with third order polynomial interpolation gave optimum compressive stress as 36.57MPa at 0.018 strain and elastic limit of 12.143MPa. Also established with compression data is the compressive or buckling moduli of 1.2GPa. Gauss-Legendre two point rule was used to evaluate the area under the stress-strain curve which measured the amount of energy absorbed per unit volume of sample from where the energy absorbed at ultimate strength of 0.025J/M3- 0.22 J/M3 , energy at fracture of 0.62 J/M3- 1.62 J/M3 and the absorbed specific work 0.001J/Kg are established.

Energy Absorption in Functionally Graded Concrete Bioinspired by Sea Urchin Spines

Functionally Graded Concrete （FGC） is fabricated at the Institute for Lightweight Structures and Conceptual Design （ILEK） by using a layer-by-layer technique with two different technological procedures： casting and dry spraying. Functional gradations are developed from two reference mixtures with diametrically opposed characteristics in terms of density, porosity, compression strength and elasticity modulus. In this study the first mixture consists of Normal Density Concrete （NDC）, with density about 2160 kg·m^-3 while the second mixture helps to obtain a very lightweight concrete, with density about 830 kg·m^-3. The FGC specimens have layers with different alternating porosities and provide superior deformability capacity under bulk compression compared to NDC specimens. In addition, the FGC specimens experienced a graceful failure behaviour, absorbing high amounts of energy during extended compression paths. The porosity variation inside the layout of tested specimens is inspired by the internal structure of sea urchin spines of heterocentrotus mammillatus, a promising role model for energy absorption in biomimetic engineering.

偕老同穴海绵启发的仿生结构吸能特性研究

目的为得到质量更轻、吸能效果更好的结构,以自然界中偕老同穴海绵复杂硅质骨针结构为仿生原型,提出一种偕老同穴海绵仿生吸能结构。方法通过有限元仿真对偕老同穴仿生结构和4种对比结构进行准静态压缩仿真,并在此基础上分析不同构型参数对海绵仿生结构吸能性能的影响。结果结果表明,偕老同穴海绵仿生结构在压缩过程中呈现二次受力平台效应,使得其吸能效果优于传统结构,同时当斜肋板位置系数Rkl为0.3时仿生结构的吸能效果最佳。随着斜肋板厚度的增大,结构的比吸能线性增加。从压溃力效率来看,当斜肋板厚度是纵横筋板厚度的1.6倍时,结构的压溃力峰值基本等于平均压溃力,结构压溃力效率达到最优,结构的整体吸能性能效果达到最优。结论本文所提出偕老同穴海绵仿生结构为高刚轻质吸能结构设计提供了参考,在吸能防护领域具有一定的应用前景。

墨鱼骨结构的力学行为及其应变率效应

墨鱼骨是一种墨鱼内部产生的生物矿化壳,通过调节壳内的气液比从而实现墨鱼的深浅浮动,同时满足轻质和高刚度的力学特性,使墨鱼能够很好地适应深海环境,所以墨鱼骨是一种典型的高比刚度的多孔材料。为探究墨鱼骨结构的力学性能,通过Instron材料试验机和分离式Hopkinson压杆实验装置,对墨鱼骨在不同加载应变率下的力学行为进行研究。研究结果表明,墨鱼骨在准静态加载下,其应力-应变曲线呈现典型的三阶段变化模式,即弹性段、平台段和压实段,具有很好地吸能缓冲作用;随着加载应变率的提高,墨鱼骨的初始压溃应力和平台应力也随之增加,表明墨鱼骨材料对加载应变率存在很强的敏感性。进一步分析不同生长方向的墨鱼骨在准静态压缩下的力学行为,结果表明随着生长方向的增加,墨鱼骨结构的刚度和吸能性能都得到了弱化,从而揭示了墨鱼骨材料压缩行为的各项异性。

循环冲击荷载下机制砂喷射混凝土动力特性研究

新建隧道钻爆施工过程中,邻近既有隧道机制砂喷射混凝土支护结构往往会承受循环冲击荷载。为研究轴压对循环冲击荷载下机制砂喷射混凝土动力特性的影响,采用改进的大直径分离式霍普金森压杆试验装置,开展4个轴压水平下的机制砂喷射混凝土循环冲击试验,分析循环冲击荷载下机制砂喷射混凝土的动力特性。研究结果表明:轴压和冲击速度对机制砂喷射混凝土的破坏形态、峰值应力、峰值应变和应变率均有较大影响,轴压的增加能够有效抑制试样的变形;轴压相同时,冲击速度越大试样破坏所需的冲击次数越少,冲击速度相同时,试样破坏所需要的冲击次数随轴压增大而不断增加;冲击速度和轴压均相同时,随着冲击次数的增加,试样峰值应力和动弹性模量不断降低,峰值应变和应变率不断增加,轴压对试样动弹性模量的影响不显著;随着冲击次数增加,试样的累计比能量吸收值呈线性增加趋势,冲击速度相同时,轴压越大,试样破坏时所需累计比能量吸收值越大,亦即轴压的增加可以显著提高试样的耗能能力,从而减缓试样力学性能的劣化进程。

三维增强型双箭头负泊松比结构抗冲击性能研究

为提高二维双箭头负泊松比结构的初始刚度和强度,通过在二维结构中增加支撑连杆设计一种三维增强型双箭头负泊松比结构。利用力法正则方程和摩尔积分推导结构的宏观泊松比解析公式,采用理论分析结合数值模拟的方法研究角度设置对结构宏观泊松比的影响;在此基础上,系统研究了三维增强型双箭头负泊松比结构在动态冲击下的力学特性,阐明不同角度设计和冲击速度等参数对结构变形机理、失效模式、平台应力和比能量吸收的影响规律。结果表明,三维增强型双箭头负泊松比结构表现出显著的负泊松效应,且结构的刚度、强度明显提高;在不同的冲击速度作用下,三维增强型双箭头负泊松比结构的平台应力和比能量吸收均随角度减小而显著增强。研究结果对航空航天和船舶工程等领域的结构抗冲击性能研究具有借鉴意义。

机械比能模型在潜山储集层评价中的改进与应用

渤海油田潜山储层岩性多样、地质条件复杂、非均质性强,传统机械比能模型对潜山储层储集性能响应的敏感性较差,难以高效指导勘探作业决策。为此,基于微钻头钻进实验和滑动窗口理论,分析了机械比能对工程参数的响应规律,构建了机械比能标准化模型和改进型机械比能模型,形成了潜山储层储集性能解释标准。结果表明:渤海油田潜山储层钻压系数为0.309~0.605;改进型机械比能小于0.80时为Ⅰ、Ⅱ类储层,改进型机械比能为0.80~1.15时为Ⅲ类储层,改进型机械比能大于1.15时为致密储层。研究成果在渤海油田36口潜山探井作业中进行了应用,储层储集性能解释符合率平均值为80.2%。该研究可为中途测试、完钻等勘探作业决策提供技术支持,具有很好的借鉴意义。

通孔球壳胞元结构压缩力学性能

球壳胞元结构作为一种新型轻质功能材料,在航空航天、交通运输等领域有着广阔的应用前景。本工作通过实验和数值模拟的方法对简单堆积的通孔球壳胞元结构受压缩时的力学性能进行了研究,得出其名义应力-应变曲线,分析了结构的有效弹性模量、屈服极限、平台应力、比吸能等性能随球壳壁厚和球心距变化的规律。结果表明,部分球壳胞元结构在压缩过程中出现屈曲现象,并翻转形成塑性铰,从而增强结构的承载能力。球壳胞元结构的有效弹性模量、屈服极限随着球心距增大呈先增加后减小的规律,其平台应力和比吸能随着球心距增大而增加。综合各项数据可得,球壳胞元结构的球心距大于等于18.0 mm是更理想的结构形式。

基于多目标优化方法的FGT管吸能特性研究

为提升舰船反应堆弹性支承结构的抗冲击性,保护反应堆乃至整个舰船的结构安全,对支承方案的吸能结构进行结构优化,通过提升支承结构的综合吸能特性从而实现其抗冲击性优化的目的。利用JLY-6500型号实验机对试件进行冲击试验,基于ANSYS/LS-DYNA软件建立圆柱壳吸能结构试验模型,得到的数值模拟结果与试验吻合。采用目标规划法和功效系数法对多目标优化问题进行求解,对一种新型的具有功能梯度厚度(functional gradient thickness,FGT)的金属管结构进行吸能特性研究。研究结果表明,FGT管在[20 kJ,27.5 kJ]轴向冲击能量范围内各项吸能评价指标(比吸能、冲程效率、平均载荷)都有一定程度的改善,优化效果明显;FGT管在(10°、20°、30°)的斜向冲击下更难进入全局弯曲变形模式,这意味着FGT管有着更大的临界加载角度。优化后的FGT管在大多数冲击情况下,综合抗碰撞性能都优于UT(uniform thickness)管。本文分析结果可为实际支承结构的设计和维护提供参考。

干湿循环作用下花岗岩动态力学性质研究

为研究干湿循环对花岗岩动力特性的影响,对经历不同干湿循环次数的花岗岩进行SHPB试验。比较了不同干湿循环次数下花岗岩的应力-应变曲线、应力时程曲线形态,分析了不同干湿循环次数条件下弹性模量、峰值强度、应力增长速度的变化规律。结果表明:(1)花岗岩的动态单轴抗压强度、动态弹性模量和比能量吸收(SEA)均与干湿循环次数有关,且呈指数变化。(2)在干湿循环过程中,花岗岩的动态单轴抗压强度最大幅度降低了44%,动态弹性模量最高降低45%,比吸收能量最高降低46%。(3)花岗岩的应力增长率随干湿循环次数的增加而降低,与未干湿循环相比,干湿循环的应力增长率最高降低了56%。(4)随着干湿循环次数的增加,能耗比逐渐降低,干湿循环较未进行干湿循环耗能比下降18.7%。(5)随着干湿循环次数的增加,反射能量基本保持不变。(6)透射能量随干湿循环次数的增加而缓慢增加,与未干湿循环相比,干湿循环中的透射能量增加幅度最大达70.1%。

Ballistic Penetration Damage of Hybrid Thermoplastic Composites Reinforced with Kevlar and UHMWPE Fabrics

Polymer matrix types of fiber hybrid composites are key factors to improve ballistic impact damage tolerances.Here we report ballistic penetration damages of Kevlar/ultra-high molecular weight polyethylene(UHMWPE)hybrid composites with thermoplastic polyurethane(PU)matrix.The hybrid composites were penetrated by fragment-simulating projectiles(FSPs)using an air gun impact system.The effects of stacking sequences on the ballistic performance of hybrid composites were analyzed.Two types of specific energy absorption(the energy absorption per unit area density and the energy absorption per unit thickness)were investigated.It was found that the main damage modes of PU hybrid composites were fiber breakage,matrix damage,fiber pullout and interlayer delamination.The instantaneous deformation could not be used as a reference index for evaluating the ballistic performance of the target plate.The energy absorption process of the PU hybrid composites showed a nonlinear pattern.The hybrid structure affected the specific energy absorption of the materials.

An Optimal Design of the Two-Staged Square Sectional Combined Energy Absorption Structure with Local Surface Nanocrystallization

In this paper,a local surface nanocrystallization technology is used for thin-walled structures with square cross sections,and an energy absorption device of two-staged combined energy absorption structure is proposed.In virtue of the surface nanocrystallization that enables to change the material on local positions,the structural deformation is induced and controlled to maximize the energy absorption capacity.A numerical model of the two-staged combined energy absorption structure is established,and the local surface nanocrystallization layout is optimized.The results show that the specific energy absorption of two-staged combined structure with local surface nanocrystallization can be increased by 34.36%compared with the untreated counterpart of the same material and structural shape.The ratio between the first and second peak crushing forces and the energy absorption allocation ratio between the two stages can be adjusted in the ranges of 0.26–0.55 and 0.31–0.45,respectively,which can be controlled by the local surface nanocrystallization designs.The numerical simulation and experimental results are in good agreement,which shows that the design for energy absorption device with local surface nanocrystallization is feasible and effective.

Design and 3D Printing of Graded Bionic Metamaterial Inspired by Pomelo Peel for High Energy Absorption

Light-weight,high-strength metamaterials with excellent specific energy absorption(SEA)capabilities are sig-nificant for aerospace and automobile.The SEA of metamaterials largely depends on the material and structural design.Herein,inspired by the superior impact resistance of pomelo peel for protecting the pulp and the elevated SEA ability of a functionally graded structure,a graded bionic polyhedron metamaterial(GBPM)was designed and realized by 3D printing using a soft material(photosensitive resin)and a hard material(Ti-6Al-4V).Guided by compression tests and numerical simulations,the elevated SEA ability was independent of the materials.The fluctuation region appeared in hard-material-fabricated bionic polyhedron metamaterial(BPMs)and was absent in soft-material-fabricated BPMs in the stress-strain curves,resulting in the growth rate of the SEA value of the soft-material-fabricated GBPM being enhanced by 5.9 times compared with that of the hard-material-fabricated GBPM.The SEA values of soft-and hard-material-fabricated GBPM were 1.89 and 44.16 J/g,which exceed those of most soft-and hard-material-fabricated metamaterials reported in previous studies.These findings can guide the design of metamaterials with high energy absorption to resist external impacts.

爆炸载荷下仿贝壳Voronoi砖泥结构的动态响应

基于贝壳多尺度、多层级的砖泥结构,构建仿贝壳Voronoi砖泥结构。通过将3D打印、爆炸实验和数值模拟相结合,探索仿贝壳Voronoi砖泥结构在爆炸载荷下的动力学响应,研究Voronoi单元尺寸和层内软材料厚度对结构变形破坏模式和能量吸收的影响。实验结果表明:在40 g球形乳化炸药作用下,仿贝壳Voronoi砖泥结构的前面板中心处出现了向四周蔓延的径向裂纹,后面板出现小块材料脱落。在此基础上,建立了有限元模型,并验证了其有效性。随着药量的增加,仿贝壳Voronoi砖泥结构主要分为塑性变形、前后面板裂纹、小块材料脱落、结构整体贯穿破坏伴随夹持端剪切破坏4种破坏模式。研究发现:仿贝壳Voronoi砖泥结构中硬材料的水平正应力远大于垂直正应力,层间软材料的剪应变大于层内软材料的剪应变。层间软材料的比吸能远大于硬材料的比吸能,约为硬材料的1.8~2.3倍;随着Voronoi单元尺寸的增大,层内软材料的比吸能增大了45.6%;随着层内软材料厚度增加,层内软材料的比吸能增大了31.1%,允许结构进一步的塑性变形。研究结果为仿生结构设计提供了一定的技术依据。

铝合金蜂窝吸能结构参数优化设计

基于铝合金蜂窝结构轴向平压试验和数值模拟,对不同结构参数的铝合金蜂窝结构吸能特性展开评估,通过对参数质量比吸能增率的引入,表明吸能增率与质量增率为一次线性关系。归纳得出铝合金蜂窝吸能结构参数优化设计的经验公式,经验证明,计算精度超过90%,可实现铝蜂窝吸能结构参数快速优化设计,为轻量化吸能结构的设计提供理论依据。

热处理对TiNi51/Ta记忆合金复合丝超弹性和比吸能的影响

通过差示扫描量热法和拉伸测试等方法,研究热处理制度对TiNi51/Ta复合丝超弹性和比吸能的影响。结果表明,TiNi51/Ta SMA复合丝超弹性上下平台应力差明显大于TiNi51合金,因此比吸能明显优于TiNi51合金丝。随着热处理温度升高,复合丝超弹性上下平台应力逐渐下降,下平台应力下降更显著,复合丝比吸能提高,500℃/12 s在线热处理复合丝比吸能3.18 J/g。热处理温度不变时间延长至15 min,复合丝超弹性和比吸能与在线热处理的规律相同,但热处理时间延长,比吸能略有降低,500℃/15 min热处理比吸能3.04 J/g。