Digital image correlation analysis of vertical strain for corrugated fiberboard box panel in compression

This work was aimed at examining the overall contributions to displacement of panels of compressed boxes, such as panel compression strain and flap and crease displacements. 3D digital image correlation (DIC) was used to analyse motion of side panels of corrugated fiberboard regular slotted containers. The vertical displacement and the vertical component of strain of the panel face during box compression test were examined. Measuring displacements of the whole compressed box with DIC enables measurement of the in‐plane compression of a panel in isolation from the horizontal fold or crease zone displacement, without having to test tube sections of the box to infer or extract the in‐plane panel compression behaviour. Detailed study of two box designs in three representative test cases was presented, which in future could be extended to other box designs. At peak load, the in‐plane compression of the panels, calculated from the average vertical component of the strain along the right edge of the long panel of the box, was 3% to 6% of total crosshead displacement for the test cases. At peak load, the portion of the box compression associated with bottom box flaps or crease zone crushing was 48% to 59% of total crosshead displacement for the different cases. The analysis showed that the majority of the vertical displacement of the box occurred in the top and bottom creased folds and that these folds are responsible for the low apparent in‐plane stiffness of a box.     

Experimental investigation of interaction effects in foam-filled thin-walled aluminum tubes

The interaction coefficients of polystyrene foam filling of thin-walled aluminum cylindrical tubes were investigated experimentally through compression testing of partially foam-filled tubes with and without adhesive. The experimental load-displacement curves and observation of the crushed sections of filled tubes have shown that partial foam filling reduced the fold length and hence increased the average crushing loads of tubes, proving the interaction effect between tube wall and filler. The interaction coefficients for the partial foam filling were further calculated to be in the level and/or higher than that of the foam plateau load of transverse direction.     

Experimental and numerical analyses of bending of foam-filled sections

Summary Numerical simulations and experiments are conducted to study the bending crush behavior of thin-walled columns filled with closed-cell aluminum foam. A nonlinear dynamic finite element code was used to simulate quasi-static three point bending experiments. The aluminum foam filler provides a higher bending resistance by retarding inward fold formation at the compression flange Moreover, the presence of the foam filler changes the crushing mode from a single stationary fold to a multiple propagating fold. The progressive crush prevents the drop in load carrying capacity due to sectional collapse. Henceforth, the aluminum foam filling is very attractive to avoid global failure for a component which undergoes combined bending and axial crushing. This phenomenon is captured from both experiment and numerical simulation. It was found that partially foam-filled beams also still offer, high bending resistance, and the concept of the effective foam length is developed. Potential applications of foam-filled sections for crashworthy structures are suggested.     

方形薄壁钢管混凝土轴压短柱约束模型的建立

为了对薄壁钢管混凝土轴压短柱在外部钢管屈曲后仍能达到较高极限承载力的试验现象与有限元分析结果进行理论解释,通过薄板的大小挠度理论,推导出计算四边夹支和两边夹支两边简支钢板屈曲后受力性能的公式;得到管壁屈曲后对内部混凝土产生的主动约束力,进而利用约束混凝土模型求得钢管中受约束混凝土极限压应力值;从理论上解析了薄壁钢管混凝土柱在外部钢管屈曲后仍能达到较高极限承载力的机理,给进一步的薄壁钢管混凝土柱理论分析研究提供了依据.     

5A03铝合金管轴向压缩失稳形式及影响因素分析

目的研究管材在承受轴向压缩时的力学行为、失稳形式及其影响因素。方法在航空航天用5A03铝合金管准静态轴向拉伸和压缩实验的基础上,进行了管压缩过程的有限元分析。结果5A03圆管拉伸与压缩力学性能有较大差异,具有拉、压双模量倾向,拉伸屈服强度略低于压缩屈服强度,抗拉强度略低于抗压强度,且拉伸与压缩均呈现锯齿波屈服特性;高径比影响管压缩失稳形式,小于1时管试样形成单鼓,大于1时将出现双鼓,且鼓凸在管材端面摩擦较大一端优先出现。结论管材失稳鼓凸后表现为一种具有一定规律性的非轴对称屈曲压溃。     

Comparison of the crushing performance of hollow and foam-filled small-scale composite tubes with different geometrical shapes for use in sacrificial cladding structures

This paper presents the quasi-static crushing performance of nine different geometrical shapes of small-scale glass/polyester composite tubes filled with polyurethane closed-cell foam for use in sacrificial cladding structures. The effect of polyurethane foam on the crushing characteristics and the corresponding energy absorption is addressed for each geometrical shape of the composite tube. Composite tubes with two different thicknesses (1 mm and 2 mm) have been considered to study the influence of polyurethane foam on the crushing performance. From the present study, it was found that the presence of polyurethane foam inside the composite tubes suppressed the circumferential delamination process and fibre fracturing; consequently, it reduced the specific energy absorption of composite tubes. Furthermore, the polyurethane foam attributed to a higher peak crush load for each composite tube. However, the presence of polyurethane foam inside the composite tubes significantly increased the stability of the crushing phenomena especially for the square and hexagonal cross-sectional composite tubes with 1 mm wall thickness. The results from this study are compared with our previous results for composite tubes without polyurethane foam [1].     

The effects of foam filling on compressive response of hexagonal cell aluminum honeycombs under axial loading-experimental study

In this paper the effects of foam filling of honeycomb panels on their plastic behavior and mechanical properties are studied experimentally. Five types of Al 5052-H39 honeycombs in bare and foam filled conditions are subjected to quasi-static axial compressive loading. The panels are selected so that the effects of parameters such as the cell size, the cell walls thickness and the panel thickness on the mean crushing strength, energy absorption capacity and the wavelength of the folds could be investigated. Tests show that foam filling of panels increases their mean crushing strength and energy absorption capacity up to 300% and the less the honeycomb density the greater the effect of foam filling. Furthermore, mean crushing strength of foam filled panels is larger than the sum of the mean crushing strengths of bare honeycomb and foam alone. The wavelength of folds and densification strain in foam filled panels are smaller than those of bare honeycombs. These tests also showed that unlike the theoretic formula the panel thickness influences the mean crushing strength of honeycomb.     

Performance measurements of a 7 mm-diameter hydrogen heat pipe

A gravity assisted heat pipe with 7-mm diameter has been developed and tested to cool a liquid hydrogen target for extracted beam experiments at COSY. The liquid flowing down from the condenser surface is separated from the vapor flowing up by a thin wall 3 mm diameter plastic tube located concentrically inside the heat pipe. The heat pipe was tested at different inclination angles with respect to the horizontal plane. The heat pipe showed good operating characteristics because of the low radiation heat load from the surroundings, low heat capacity due to the small mass, higher sensitivity to heat loads (to overcome the heat load before the complete vaporization of the liquid in the target cell) due to the higher vapor speed inside the heat pipe which transfers the heat load to the condenser.     

铺层顺序对复合材料薄壁圆管轴向压溃吸能特性的影响研究

采用仿真和试验相结合的方法探讨复合材料薄壁圆管在准静态轴向压缩载荷下的失效吸能特性和吸能机理。首先,建立复合材料薄壁圆管"层合壳"有限元模型,通过显式动力学方法求解其在准静态轴向载荷下的压溃失效力学行为。仿真与试验结果在圆管轴向压溃变形过程、初始峰值载荷、平均压溃载荷及比吸能等主要吸能参数上具有很好的一致性,验证了"层合壳"复合材料圆管有限元模型和建模方法的有效性。其次,采用解析模型与仿真分析方法分别对[0/90]_3s、[0/90/0₂/90₂]_s、[0₃/90₃]_s三种不同铺层顺序的复合材料圆管的屈曲载荷与吸能特性进行了对比,进一步分析了铺层顺序对圆管失效吸能特性的影响。研究表明,0°与90°铺层交替程度对复合材料圆管的吸能特性影响较大,保证纤维失效方式在结构宏观失效中占主导地位能够提高材料失效吸收能量。     

负泊松比点阵结构填充薄壁管轴向压缩行为及吸能特性

薄壁填充结构具有轻量化、高比吸能的优点,被广泛应用于航空航天、汽车、轨道交通等工程领域。负泊松比结构在受到冲击时力学性能会逐渐增强,因此本文基于双箭头型负泊松比点阵提出一种新型薄壁填充管吸能结构,通过准静态压缩实验和有限元数值模拟方法研究了新型填充管在压缩载荷作用下的变形失效模式与力学响应。建立了平均碰撞力的理论预测模型,并通过有限元分析验证了模型可靠性,在此基础上研究了负泊松比点阵结构的细观设计参数对填充管抗压缩性能的影响规律。结果表明,填充管在压缩载荷作用下的失效模式为局部屈曲失效,相比于单一薄壁管与点阵结构,填充管具有更好的抗压缩性能;通过参数分析明确了通过增加胞元杆件壁厚和下支撑杆夹角,能显著提高填充管抗压缩性能,这将为后续负泊松比点阵填充结构的抗冲击优化设计提供重要参考。     

Analytical Model for Energy Absorption and Plastic Collapse of Thin-Walled Grooved Frusta Tubes

In the present study, an analytical model for axisymmetric axial crushing of thin-walled frusta tubes containing annular grooves is presented. In this innovative geometrical design model, to encourage axisymmetric collapsing mode, circumferential grooves are cut from the outer and inner surfaces of frusta at determined intervals. Theoretical formulations are presented for predicting the energy absorption and mean crushing load. In order to verify these analytical results, quasi-static compression tests are performed. The results of this research indicate good agreement between the theory and experimental findings. The proposed method could be a good candidate as a controllable shock absorber in impact applications.     

Effect of aluminum closed-cell foam filling on the quasi-static axial crush performance of glass fiber reinforced polyester composite and aluminum/composite hybrid tubes

The effect of Al closed-cell foam filling on the quasi-static crushing behavior of an E-glass woven fabric polyester composite tube and thin-walled Al/polyester composite hybrid tube was experimentally investigated. For comparison, empty Al, empty composite and empty hybrid tubes were also tested. Empty composite and empty hybrid tubes crushed predominantly in progressive crushing mode, without applying any triggering mechanism. Foam filling was found to be ineffective in increasing the crushing loads of the composite tubes over the sum of the crushing loads of empty composite tube and foam. However, foam filling stabilized the composite progressive crushing mode. In empty hybrid tubes, the deformation mode of the inner Al tube was found to be a more complex form of the diamond mode of deformation of empty Al tube, leading to higher crushing load values than the sum of the crushing load values of empty composite tube and empty metal tube. The foam filling of hybrid tubes however resulted in axial splitting of the outer composite tube due to the resistance imposed by the foam filler to Al tube inward folding and hence it was ineffective in increasing crushing load and SAE values over those of empty hybrid tubes.     

Response of pultruded composite tubes subjected to dynamic and impulsive axial loading

The energy absorption of circular pultruded composite tubes subjected to axial crush load, transmitted by a small attached mass accelerated by means of an explosive load is presented in this paper. Different masses of explosive are used to provide a range of transmitted impulse and crushed distance of the pultruded composite tubes. The influence of the mass of the explosive on the tube response is investigated with regard to crushed distance, the average crushing force and the specific energy absorption (SEA). The crushing distance increases with increasing transmitted impulse. The results and failure mode are also compared with compression tests carried out on a servo-hydraulic machine (type: MTS-309).     

基于横纹管氨水溶液垂直管外降膜吸收性能的变化规律

针对三根不同尺寸规格的横纹管,通过实验研究提高其吸收效率,选择吸收性能最优的管型。实验结果表明,随着压差和管内冷却水流速的增大,溶液吸收氨气的量增加,管外溶液传质系数增大。当管外氨水溶液喷淋密度从小变大时,光滑管和横纹管的传质系数均先增加后减小,过程中出现了最大值。该系列实验的结果表明横纹管比相同工况的光滑管有更高的强化传热和传质能力,当溶液喷淋密度为479.6kg/(m?h)时,横纹管比光滑管的传质系数增大了97.8%。三组实验中均发现一个共同的规律,横纹管的传质系数随凹槽尺寸变化而改变,2号横纹管表现出更强的吸收氨气能力。该管凹槽宽度与横纹管外径的比值为0.0814。通过对凹槽内溶液流动模型分析,比较了溶液通过凹槽时掺混和涡流的流动形态,得出了不同尺寸规格横纹管吸收性能差异的一个原因。     

圆弧刻槽薄壁圆管轴向压溃吸能特性数值研究

目的为了提高能量吸收效率,设置出一种合理的诱导结构,对吸能构件产生积极影响。方法薄壁圆管设计一种环向圆弧刻槽诱导结构,在不同长径比、径厚比和刻槽深度的条件下研究薄壁结构吸能特性。结果吸能量与圆管长径比和径厚比成反比,初始压溃载荷随刻槽深度增加而减小。结论在不同的条件下,刻槽结构能够有效降低初始载荷,并获得较为平稳的压溃载荷平台。     

Numerical Study on Hybrid Tubes Subjected to Static and Dynamic Loading

The commercial finite element program LS-DYNA was employed to evaluate the response and energy absorbing capacity of cylindrical metal tubes that are externally wrapped with composite. The numerical simulation elucidated the crushing behaviors of these tubes under both quasi-static compression and axial dynamic impact loading. The effects of composite wall thickness, loading conditions and fiber ply orientation were examined. The stress–strain curves under different strain rates were used to determine the dynamic impact of strain rate effects on the metal. The results were compared with those of a simplified analytical model and the mean crushing force thus predicted agreed closely with the numerical simulations. The numerical results demonstrate that a wrapped composite can be utilized effectively to enhance the crushing characteristics and energy absorbing capacity of the tubes. Increasing the thickness of the composite increases the mean force and the specific energy absorption under both static and dynamic crushing. The ply pattern affects the energy absorption capacity and the failure mode of the metal tube and the composite material property is also significant in determining energy absorption efficiency.     

R404A在水平强化管外的冷凝实验及数据处理方法

针对一种双侧强化换热管,实验测试和分析了制冷工质R404A在管外凝结与水在管内对流的传热规律,采用"Wilson图解法"和"Gnielinski法"两种不同的方法对实验数据进行了处理。经理论分析和实验研究表明,Wilson图解法对于双侧强化换热管管内、管外表面传热系数实验容易产生较大误差,"Gnielinski法"是更合适的方法。实验得出了管内对流传热和管外凝结传热的计算关联式及传热的强化倍率。对于制冷剂R404A,在强化管外凝结的表面传热系数随着壁面过冷度的增加而增大,呈现出与纯工质光滑管外冷凝时不同的变化趋势。     

Adaptive neuro-fuzzy inference system approach to predict the mass flow rate of R-134a/LPG refrigerant for straight and helical coiled adiabatic capillary tubes in the vapor compression refrigeration system

This study deals with predicting the mass flow rate of R-134a/LPG as refrigerant inside a straight and helical coiled adiabatic capillary tube of vapor compression refrigeration system by combining dimensionless analysis and Adaptive Neuro-Fuzzy Inference System techniques. For this purpose the experimental system was designed and tested under steady state conditions, by changing the length of the capillary tube, the inner diameter of the capillary tube, the coil diameter and the degree of subcooling of the refrigerant at the capillary tube inlet. Dimensional analysis was utilized to provide generalized dimensionless parameters and to reduce the number of input parameters, while Adaptive Neuro-Fuzzy Inference System was applied as a generalized approximator of the nonlinear multi-input and single-output function. The comparison of the absolute fraction of variance (R²) (0.998 and 0.961), the root mean square error (RMSE) (0.105 kg/h and 0.489 kg/h) and the mean absolute percentage error (MAPE) (0.954% and 4.75%) demonstrated the result for combination of dimensional analysis and Adaptive Neuro-Fuzzy Inference System and dimensionless correlation model predictions respectively. The results indicated that the combination of dimensional analysis and Adaptive Neuro-Fuzzy Inference System gave the best statistical prediction efficiency.     

复合材料波纹夹层圆柱壳设计及轴压性能

结构轻量化是航空航天发展的永恒主题, 波纹夹层圆柱壳作为常见的轻质结构形式, 在航空航天领域具有很大的发展空间。采用模具热压法, 制备出纵向和环向碳纤维复合材料波纹夹层圆柱壳, 其中芯子整体成型, 面板分瓣制备。采用经典板壳屈曲理论, 分析纵向和环向波纹夹层圆柱壳的轴压力学性能, 得到了欧拉屈曲、整体屈曲、局部屈曲和面板压溃4种失效模式下的极限载荷理论公式。绘制出结构的失效机制图, 直观显示出了失效模式与试件尺寸之间的关系。通过对纵向和环向波纹夹层圆柱壳的轴向压缩试验, 获得了结构的载荷-位移曲线及局部屈曲和面板压溃2种失效模式。结果表明:纵向波纹夹层圆柱壳的轴向承载能力及载荷/质量效率优于环向波纹夹层圆柱壳, 在一定范围内增加圆柱壳面板的厚度、减小圆柱壳的高度可提高结构的载荷/质量效率。      

On the Collapse of Cotton/Epoxy Tubes under Axial Static Loading

Experimental quasi-static crushing tests and finite element analysis have been carried out for unidirectional filament wound laminated cotton/epoxy tubes. The work focuses on three main factors, which considerably affect the axial collapse load of unidirectional natural composite tubes. These factors are structural geometry, fibre diameter and fibre orientation. Cotton/epoxy tubes with different diameters (50, 70, 90, 110 and 130 mm) were examined and tested. The fibre orientation angles were 80 and 90°. The initial geometric imperfections are measured using the computerised Mistral coordinate measuring machine. The numerical prediction was obtained using commercially available finite element software. A limited agreement between the experimental and computational results was obtained. For all structures considered classical axial collapse eigenvalues were computed. The initial failure crush load computed from the finite element simulation model has been compared with the experiments.