轴压下金属圆管耗能特性的改善

为提高金属圆管的抗冲击性能,分别通过两种设计方法进行试验研究。第一种方法将刚性钢环压入铝质圆管端部。轴压下,首先,刚性环扩大圆管端部;接着,沿管长方向形成塑性褶层。第二种方法在厚壁钢管外表面开槽。这个方法实际是将厚壁管分解成几个同轴相连的薄壁短管。受压时,每个钢槽内将出现塑性变形,结构的倒塌取决于厚壁部分。采用两种方法进行了不同尺寸试件的受压试验,并与同尺寸的普通管轴压下的耗能试验对比。结果表明,本设计方法和提出的圆管轴压倒塌模型均很有效。     

Analysis and optimization of externally stiffened crush tubes

Nonlinear finite element analysis is used to investigate the quasi-static axial collapse response of cylindrical tubes which are externally stiffened by multiple identical rings. The rings divide the long tube into a series of short thin-walled tubes. It is assumed that the size and shape of integral stiffeners are controlled through a machining process. The effects of various geometric parameters such as wall thickness, ring spacing, ring thickness and width on the collapse response, crush force and energy absorption of monolithic, integrally stiffened steel tubes are studied and used as a general framework for a design optimization study. Through design and analysis of computer experiments, global metamodels are developed for the mean crush force and energy absorption, using the radial basis function approximation technique. Using both single- and multi-objective design optimization formulations, optimum designs for different response characteristics are found. The crush mode in the form of progressive collapse or buckling is found to heavily depend on the ratio of stiffener spacing to stiffener height as well as the ratio of wall thickness to stiffener thickness. The optimization results show the viability of externally stiffened tubes as efficient energy absorbers.     

Energy absorbtion and mean crushing load of thin-walled grooved tubes under axial compression

In the present study, crashworthiness characteristics of thin-walled steel tubes containing annular grooves are studied. For this purpose, the grooves are introduced in the tube to force the plastic deformation to occur at predetermined intervals along the tube. The aims are controlling the buckling mode and predicting energy absorption capacity of the tubes. To do so, circumferential grooves are cut alternately inside and outside of the tubes at predetermined intervals. Quasi-static axial crushing tests are performed and the load-displacement curves are studied. Theoretical formulations are presented for predicting the energy absorption and mean crushing load. It is found a good agreement between the theoretical results and experimental findings. The results indicate that the load-displacement curve and energy absorbed by the axial crushing of tubes could be controlled by the introduction of grooves with different distances. Also, grooves can stabilize the deformation behavior and thus, the proposed method could be a good candidate as a controllable energy absorption element.     

外部加劲热轧钢管的分析和优化

利用非线性有限元法,分析了采用多种规格外部圆环加劲的圆柱形钢管的拟静力轴向破坏反应。加劲圆环将钢管沿竖向分为一系列的薄壁短柱结构。假定加劲肋的尺寸和形状由机械加工控制。研究了各种不同几何参数,如:钢管壁厚、环间距、环厚度和破坏时环的宽度,极限承载力和整体加劲钢管能量吸收的影响。将研究结果作为优化设计的基本原理。基于计算机模拟试验的分析,利用辐射函数,提出了关于平均承载力和能量消耗的后处理模型。运用单个对象和多个对象优化设计方程,得出不同反应特性的优化设计。根据渐进破坏屈曲得出的破坏模式依赖于加劲肋间距、加劲肋高度比、钢管壁厚以及加劲肋厚度比。优化结果显示,外加劲肋作为高效耗能构件是可靠的。     

Computer simulation and energy absorption of tapered thin-walled rectangular tubes

Tapered thin-walled tubes have been considered desirable energy absorbers under axial loading due to their relatively stable crush load and deformation response compared with straight tubes. This paper compares the energy absorption response of straight and tapered thin-walled rectangular tubes under quasi-static axial loading, for variations in their wall thickness, taper angle and number of tapered sides. Overall the study highlights the advantages of using tapered tubes as energy absorbers. In particular, the peak load required to crush the tubes decreases with the introduction of a taper, and as the taper angle increases. This is desirable for minimising the impact loads transmitted to the protected structure. The practical outcome of the study is design information for the use of tapered thin-walled rectangular tubes as energy absorbers in impact loading applications. Analysis has been undertaken using a finite element model, validated using existing theoretical and numerical models.     

Quasi-static axial and lateral crushing of radial corrugated composite tubes

This paper presents the effect of corrugation geometry on the crushing behavior, energy absorption, failure mechanism, and failure mode of woven roving glass fibre/epoxy laminated composite tube. Experimental investigations were carried out on three geometrical different types of composite tubes subjected to axial and lateral compressive loadings. On the addition to a radial corrugated composite tube, cylindrical composite tube, and corrugated surrounded by cylindrical tube were fabricated and tested under the same condition in order to know the effect of corrugation geometry. The results showed that the loading carrying capability is significantly influenced by corrugation geometry in axial crushing. However, no affect of corrugation geometry was observed for lateral crushing. Load–displacement curve was plotted for all conducted tests, thus clear comparison between different specimen's geometry was achieved. It is also found that radial corrugation could significantly applicable as a stable and effective energy absorber.     

Energy absorption of axially compressed thin-walled square tubes with patterns

The paper suggests the introduction of patterns to the surface of conventional thin-walled square tubes to improve the energy absorption capacity under axial compressive loads. A quasi-static axial crushing analysis has been conducted numerically by the nonlinear explicit finite element code LS-DYNA. Two types of patterns constructed using the basic pyramid elements were introduced. Type A pattern was aimed at triggering the extensional mode for relatively thin square tubes whereas type B pattern was intended to develop new collapse mode capable of absorbing more energy during collapse. A total of 30 tubes with a length of 120 mm, thickness 1.2 mm and widths of 40 or 60 mm were simulated. Numerical results showed that all tubes with type A patterns developed the extensional collapse mode instead of the symmetric collapse mode and absorbed about 15–32.5% more energy than conventional thin-walled square tubes with a mass increase less than 5%. Meanwhile, a new collapse mode named octagonal collapse mode was observed for tubes with type B pattern and the energy absorption of tubes developing this mode increased by 54–93% compared with the conventional tube. The influence of various configurations of the patterns on the deformation and energy absorption of the tubes was also discussed. The paper opens up a new avenue in design of high energy absorption components.     

Quasi-static axial compression of concentric expanded metal tubes

Previous studies have demonstrated that the failure mechanism and energy absorption capacity of expanded metal tubes strongly depends on the orientation of the cells. This paper presents an experimental investigation on the collapse of concentric expanded metal tubes subjected to quasi-static axial compression. Square tubes with two different cell orientations are tested to failure, and the energy absorption characteristics are calculated. The results show that the combination of cell geometries lead to a complex buckling mode interaction, which enhances the energy absorption capacity of expanded metal tubes.     

Experimental and numerical crashworthiness investigation of empty and foam-filled end-capped conical tubes

Foam-filled thin-wall structures exhibit significant advantages in light weight and high energy absorption. They have been widely applied in automotive, aerospace, transportation and defense industries. Quasi-static tests were done to investigate the crash behavior of the empty and polyurethane foam-filled end-capped conical tubes. Non-linear dynamic finite element analyses were carried out to simulate the quasi-static tests. The predicted numerical crushing force and fold pattern were found to be in good agreement with the experimental results. The energy absorption capacities of the filled tubes were compared with the empty end-capped conical tubes. The results showed that the energy absorption capability of foam-filled tube is somewhat higher than that of the combined effect of the empty tube and the foam alone. Finally, the crash performance of the empty and foam filled conical and cylindrical tubes were compared. Results from this study can assist aerospace industry to design sounding rocket carrier payload based on foam-filled conical tubes.     

Energy absorption of aluminium alloy circular and square tubes under an axial explosive load

The energy absorption of circular and square aluminium alloy tubes subjected to an axial explosive load, which is transmitted to a tube by a small attached mass, is discussed. Particular attention is paid to the interaction between the inertia of the attached mass and a tube when the importance of the initial compression phase is revealed. The effect of this phase on the mean load, which is characteristic of the energy absorption capacity of structural elements, is demonstrated. The influence of the material models on the prediction of the response of aluminium alloy circular and square tubes is also discussed in relation with the temperature effects caused by the high strain rates. The analysis shows that the material properties play an important role for the formation of the buckling pattern due to the finite duration of the initial compression phase when plastic stress waves at different speeds propagate along a shell.     

Axial crushing of flattened expanded metal tubes

This paper presents an investigation on the structural behavior of flattened expanded metal tubes subjected to axial crushing. At first, the study is carried out experimentally to investigate the effect of the angle formed between the expanded metal cell and the applied load. Secondly, the results are compared with experimental results for standard expanded metal sheets. Thereafter, numerical analyses are conducted by means of nonlinear finite element models, to investigate the enhancement in the energy absorption characteristics due to flattening of the expanded metal. Both results, experimental and numerical show a significant increase in energy absorbing capacity and mean force for the flattened tubes.     

Axial crushing analysis of end-capped circular tubes

The paper investigates collapse mechanisms and energy absorption capacity during the axial compression of the end-capped thin-walled circular aluminum tubes which are hollow or filled with polyurethane foam. An experimental technique is used to evaluate the crushing behavior of the circular tubes under compressive quasi-static strain rate. A numerical model is presented based on finite element analysis to simulate the crushing of circular tubes considering nonlinear response due to material behavior, contact boundary conditions and large deformation. The validated model using existing experimental results is used to evaluate the dynamic response in order to determine the dynamic amplification factor relating the quasi-static results to dynamic response. The experimental and numerical results are used to determine energy absorption capacity due to the plastic deformation of thin-wall tube and crushable foam. The performance of end-capped tubes is compared with non-capped tubes and it is found that maximum initial peak load can be controlled and convenient crash protection systems can be obtained using end-capped circular tubes.     

Plastic buckling of dented steel circular tubes under axial compression: An experimental study

This paper examines the effect of large local imperfections, known as dents, on the plastic buckling capacity of short steel tubes under axial compression. A total of 11 tests on such short columns were carried out. The specimens were indented through a separate process and the ultimate axial capacity was subsequently obtained through compression tests. Dent imperfections with various depths were introduced to different locations on the body of the specimens. Plastic buckling modes as well as the ultimate capacity of the specimens were thoroughly investigated. The adverse effect of such a local damage on the load carrying capacity was quantified for different values and types of imperfections.     

Experimental and numerical investigation of static and dynamic axial crushing of circular aluminum tubes

A comprehensive experimental and numerical study of the crash behavior of circular aluminum tubes undergoing axial compressive loading is performed. Non-linear finite element analyses are carried out to simulate quasi-static and dynamic test conditions. The numerical predicted crushing force and fold formation are found to be in good agreement with the experimental results. A summary of available analytical solutions is presented in order to estimate the mean crushing load and establish a comparison between these analytical loads and the experimental one. Some observations are made on the influence of geometrical imperfections and material strain rate effect.     

Relative merits of single-cell, multi-cell and foam-filled thin-walled structures in energy absorption

The axial crushing of hollow multi-cell columns were studied analytically and numerically. A theoretical solution for the mean crushing force of multi-cell sections were derived, and the solution was shown to compare very well with the numerical predictions. Numerical studies were also carried out on foam-filled double-cell and triple-cell columns. Based upon the numerical results, closed-form solutions were derived to calculate the mean crushing strength of these sections. It was found that the interaction effects between the foam core and the column wall contribute to the total crushing resistance by the amounts equal to 140% and 180% of the direct foam resistance for double cell and triple cell respectively. Finally, the relative merits of single-cell, multi-cell and foam-filled sections were discussed.     

Mathematical modeling of axial crushing of cylindrical tubes

Different aspects of mathematical modeling for the axial crushing of cylindrical tubes with straight fold have been discussed. The variation of circumferential strain during the formation of a fold has been taken into account. The present paper tries to answer questions such as (a) how great is the inside and outside folding, and (b) how the crushing load varies. In the present paper, the influence of the consideration of the conservation of mass on the mathematical formulation has been studied. The results of average and varying circumferential strain have also been compared.     

空心和泡沫填充且端部封闭锥形筒的耐撞性试验和数值分析

泡沫填充的薄壁结构的优点是质量轻和高吸能性能,广泛地应用于汽车、航空、运输和防护等行业。采用拟静力试验,分析空心和泡沫填充的端部封闭的锥形筒的耐撞性能,采用非线性动力有限元模拟拟静力试验,数值分析的抗冲撞力与试验数据很吻合。对未填充的锥形筒和填充的锥形筒的耗能能力进行对比,结果显示,泡沫填充的锥形筒的耗能能力比较好。最后,比较了空心、泡沫填充端部封闭的锥形筒和圆筒的耐撞性。     

配有双圆钢管的钢骨混凝土柱轴心受压承载力研究

针对配有双圆钢管的钢骨混凝土柱的轴心受压承载力分析方法进行了研究,基于核心区混凝土、外围混凝土和钢管、钢筋的材料本构关系,建立了钢骨混凝土柱的有限元分析模型,分析了轴心受压承载力的计算方法及原理,对已有的承载力计算公式进行了改进,并通过工程实例的计算结果与有限元分析结果的对比进行了验证。