Theoretical prediction and numerical simulation of honeycomb structures with various cell specifications under axial loading

The axial crushing of honeycomb structures with various cell specifications is studied analytically and numerically. Based on the Super Folding Element theory, a new method for predicting the mean crushing stress of honeycomb structures with various cell specifications under axial loading is developed. In this new theoretical method, two types of simplified folding modes named SFM1 and SFM2 are proposed. The mean crushing stress and the folding wavelength for honeycomb structures with various cell specifications are then determined by a minimum principle. The effective crushing distance and the loading rate effect are both considered. In order to illustrate the effectiveness of the proposed approach, numerical simulations are carried out by employing the explicit finite element code LS-DYNA. The bond of the honeycomb panels is simulated by using a tie-break contact. It can be seen that the analytical solutions are in agreement with the numerical results as well as the Wizerbicki’s solutions.     

Crushing analysis of metal honeycombs

A method for determining the crushing strength of hexagonal cell structures subjected to axial loading is given. The method is based on energy considerations in conjunction with a minimum principle in plasticity. The problem is shown to be equivalent to the analysis of a system of collapsing angle elements undergoing bending and extensional deformations. The theory is first developed for an arbitrary angle between panels and then is specified for the 120° angle, appropriate for the hexagonal cell structures. Simple formulas are derived relating the crushing force and the wavelength of the local folding wave to the wall thickness and diameter of the cell. The theoretical solution has been compared with experimental results published in the literature and an excellent correlation has been obtained for the wide range of geometrical parameters involved. This solution replaces the less accurate earlier analysis of the same problem due to McFarland. The purpose of this study was to provide a simple and rational means by which hexagonal cell structures can be designed for use as energy absorbers in impact or impulsive loading situations.     

Bending Crush Resistance of Partially Foam‐Filled Sections

Potential applications of foam‐filled sections are for the automotive structures. A foam‐filled section can be used for the front rail and firewall structures to absorb impact energy during frontal or side collision. In the case of biaxial loading where bending and axial compression are involved in the crushing mechanics, the foam filler will be significant in maintaining progressive crushing of the thin‐walled structures so that more impact energy can be absorbed. In the case of side collision, the foam‐filled section can be used to strengthen the B‐pillar structure to avoid severe intrusion in the passenger compartment.     

Dynamic energy absorption characteristics of hollow microlattice structures

Hollow microlattice structures are promising candidates for advanced energy absorption and their characteristics under dynamic crushing are explored. The energy absorption can be significantly enhanced by inertial stabilization, shock wave effect and strain rate hardening effect. In this paper we combine theoretical analysis and comprehensive finite element method simulation to decouple the three effects, and then obtain a simple model to predict the overall dynamic effects of hollow microlattice structures. Inertial stabilization originates from the suppression of sudden crushing of the microlattice and its contribution scales with the crushing speed, v. Shock wave effect comes from the discontinuity across the plastic shock wave front during dynamic loading and its contribution scales with v². The strain rate effect increases the effective yield strength upon dynamic deformation and increases the energy absorption density. A mechanism map is established that illustrates the dominance of these three dynamic effects at a range of crushing speeds. Compared with quasi-static loading, the energy absorption capacity at dynamic loading of 250 m/s can be enhanced by an order of magnitude. The study may shed useful insight on designing and optimizing the energy absorption performance of hollow microlattice structures under various dynamic loads.     

转向机动条件下的拖线阵WP模型适用性研究

阵形估计是拖曳阵声呐在拖船转向机动情况下不能回避的问题。已知的Water-Pulley(WP)模型所需信息易于获取,运算复杂度小并且可以预判阵形,在工程实际中有一定应用价值。但WP模型稳健性有限,阵形估计效果受拖船机动情况影响较大。为探究WP模型适用性以指导拖船机动避免模型失效,首先通过计算机仿真证明拖船转弯半径是最主要的影响因素;然后提出一种以最大测向误差和最大增益损失为模型适用准则,结合某船旋回特性以指导拖船机动的方法;最后分析了存在水流扰动时应注意的拖船机动情况。     

Analysis of cushion systems for impact protection design of bridges against overheight vehicle collision

Based on several theoretical models of elastic and elastic–plastic impact as well as energy method, a systematic methodology for design analysis of cushion structures for impact protection of bridges against overheight vehicle collision is presented with consideration of the shear-off effect of projectiles and the nonlinear crushing behavior of sandwich cores. Three design criteria based on contact force, deflection, and energy are proposed, and the theoretical models for elastic, elastic–plastic, and after-densification impact including the shear-off effect of projectile are developed to improve the analysis and design of cushion structures against overheight vehicle impact. Realistic analysis of cushion structures is resulted from the above models, and it can be applied to design of cushion structures for the sake of bridge protection from overheight vehicle collision.     

Static and dynamic axial crushing of spot-welded thin-walled composite steel–CFRP square tubes

Thin-walled metallic tubular components have long been adopted in the transportation industries, where the stable energy absorbing crushing process provides protection to occupants and cargo in the event of a collision. Fibre–epoxy tubes provide superior strength to weight ratios, however brittle failure modes may limit their energy absorbing capacity under large axial deformation. Composite steel–CFRP (carbon fibre-reinforced polymer) tubes are a recent advent, and combine the benefits of the stable, ductile plastic collapse mechanism of the steel and the high strength to weight ratio of the fibre/resin composite, to form a composite tube with high energy absorption capability. In this paper the applicability of steel–CFRP tubes to structures typical to the automotive industry is investigated. Thin-walled square tubes with width to thickness ratios up to 120 are cold-formed and spot-welded from high strength, low ductility steel, and subjected to static and dynamic axial compression. Four different steel tube geometries and two different carbon fibre matrix layouts are investigated, and comparisons are made between static and dynamic crushing, steel and composite steel–CFRP tubes, and regular and low ductility steels. It is shown that the crashworthiness properties of the steel–CFRP tubes exceed those of the steel tubes, however some issues particular to low ductility steels and such steels under impact conditions prove detrimental to the crashworthiness characteristics. Theoretical procedures are developed to design the crashworthiness characteristics of the composite tubes, and are shown to compare well with the experimental results.     

两类船-桥碰撞力差异及桥梁结构响应分析

 船桥碰撞是跨航道桥梁需考虑的重要问题。本文以美国AAHSTO规范推荐两类船舶为例,研究了驳船和散装货轮撞击桥梁后碰撞力、船艏刚度和碰撞能量的变化过程,讨论了导致两类船舶碰撞力、船艏刚度和碰撞能量变化差异的原因,分析了两类船桥碰撞桥梁结构的主要响应,并将本文动力模型计算响应与已有规范计算得到响应进行了对比。结果表明,两类船舶不同的船艏外形及内部构造会对碰撞力造成较大影响;同等吨位和碰撞速度下,驳船碰撞峰值荷载比散装货轮大,驳船碰撞的墩顶位移比散装货轮小,基底剪力和弯矩比散装货轮大,驳船与散装货轮作用下桥梁结构响应的动力反应系数存在较大差异;不同规范对于碰撞荷载规定差异较大,欧洲规范计算得到响应总体较大,中国公路规范荷载对于内河船舶撞击计算得到的响应最小,中国铁路规范计算得到的响应与其他规范海轮撞击响应进行对比最小。     

凹槽结构对 PET 瓶轴向承载性能的影响

以一典型PET瓶为研究对象,建立了其结构模型,利用ANSYS加载垂直载荷时,基于屈曲分析得到了PET瓶的理论轴向压溃载荷和临界点的变形。试验测定了该PET瓶的轴向压溃载荷,进行了理论与试验比较。结果表明,理论值与试验结果误差小,验证了理论分析的有效性。利用ANSYS分析进一步研究了不同环状结构、不同尺寸和不同分布等对瓶轴向承载能力的影响,并分析了其变形特点。     

半潜式平台结构抗撞性能研究

在分析显示非线性有限元基本理论和碰撞仿真关键技术的基础上,研究了半潜式平台在遭遇船舶正向撞击时的抗撞特性及其影响因素。模拟了整船与半潜式平台的碰撞,船首结构及半潜式平台立柱结构模拟为弹塑性材料,并考虑船舶与半潜式平台运动惯性的影响,定义了三种不同的碰撞场景,撞击船分别沿纵向、横向和斜向撞击平台立柱,获取了碰撞力——撞深曲线、各构件能量吸收和结构损伤变形等。重点讨论了半潜式平台立柱在不同撞击位置条件下的撞击特性,分析了影响结构碰撞性能的因素,包括结构特性和撞击位置,提出了改善半潜式平台抗撞性能的一些建议     

薄壁开孔圆管在轴向荷载作用下的理论研究

研究薄壁开孔圆管的轴向耐撞性有助于其在缓冲、吸能领域的广泛应用。通过分别考虑开孔区域和未开孔区域的能量吸收特征并引入材料的应变强化效应,根据塑性铰理论建立了轴向荷载下开孔圆管轴对称压溃模式的理论模型,得到了弯曲应变能、拉伸应变能、平均压溃力、比吸能的解析表达式。分析结果表明:该理论模型的预测结果与数值和实验结果相吻合;正则化平均压溃力会随半皱褶长细比的降低而显著增加;单层孔数对正则化平均压溃力的影响会随管壁厚度的增加或孔半径的减小而降低;比吸能可通过减少单层孔数或减小孔半径提高。     

A proposed method of predicting ship collision damage

In the past, research on ship collision strength has centered on nuclear ship structures, but now emphasis is shifting to low-energy collisions of ordinary ships carrying hazardous cargoes including crude oil.A ship collision is too complex to study using theoretical methods alone, yet tests with small-scale models of thin steel plate fail to duplicate actual ship collision damage for the following reasons:

1. (1) The fracture of actual ship shell plate and model shell plate defies the law of similarity;

2. (2) Some structural members are usually omitted for ease of fabrication in relatively small models.

Accordingly, the authors propose a method for predicting ship collision damage that resorts to three combined experiments:

1. (1) A fundamental test determining the initiation of plate fracture;

2. (2) A local structure model test evaluating the effects of structural details;

3. (3) A structural model test investigating the deformation of a ship hull.

This paper reviews, by way of example, some results of the experimental studies which the authors have performed.The laws of similarity proved very important in the study of plate fracture.The authors believe that the proposed method will prove useful especially in dealing with low-energy ship collisions.     

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.     

Effect of natural stitched composites on the crashworthiness of box structures

In the present paper the effects of stitching on the energy absorption and crashworthy behaviour of composite box structures will be studied. The combination of unidirectional carbon fibre-reinforced polymer (CFRP) and glass fibre-reinforced polymer (GFRP) composite materials are used to laminate the composite boxes. Delamination study in Mode-I with the same lay-up was carried out to investigate the effect of stitching on delamination crack growth on energy absorption of stitched and non-stitched composite box structures. The double cantilever beam (DCB) standard test method was chosen for delamination studies. For non-stitched and stitched composite boxes the lamina bending and brittle fracture crushing modes were observed. It was found that the stitched composite boxes which show higher fracture toughness in Mode-I delamination tests, are not necessarily able to absorb more crushing energy in comparison with non-stitched composite boxes. It was also observed that the position of stitched area can affect the crushing mode and consequently energy absorption capability of composite box structures. The main reason can be related to other mechanisms such as bending, friction and bundle fracture which significantly contribute to energy absorption. The analytical model based on energy balance approach is proposed to estimate the mean crushing force, F_m, in axial crushing of square composite box.     

Analysis of Crushing Response of Composite Crashworthy Structures

The paper describes quasi-static and dynamic tests to characterise the energy absorption properties of polymer composite crash energy absorbing segment elements under axial loads. Detailed computer tomography scans of failed specimens are used to identify local compression crush failure mechanisms at the crush front. The varied crushing morphology between the compression strain rates identified in this paper is observed to be due to the differences in the response modes and mechanical properties of the strain dependent epoxy matrix. The importance of understanding the role of strain rate effects in composite crash energy absorbing structures is highlighted in this paper.     

Crushing analysis of polygonal columns and angle elements

Energy absorption characteristics of regular polygonal columns and angle elements under dynamic axial compression are investigated by using non-linear explicit finite element code LS-DYNA. The influence of central angle on deformation mode and mean crushing force of angle elements is studied. Based on two types of deformation mechanisms known by experiments, two types of initial indentation triggers are introduced. By assuming appropriate boundary condition on the edges, a simplified finite element model is adopted in the analysis of angle elements and validated by comparing with full polygonal column model. Numerical investigations are also carried out to study the influence of angle on angle elements with three and four panels by using the simplified model. Several useful conclusions are drawn about the axial crushing of polygonal columns and angle elements and can be used to guide the design of crashworthiness structures. In addition, a comparison is conducted between the numerical results and theoretical predictions of the mean forces of some special angle elements. Good agreement is obtained.     

Mechanical behaviors of carbon fiber composite sandwich columns with three dimensional honeycomb cores under in-plane compression

Mechanical properties and failure modes of carbon fiber composite egg and pyramidal honeycombs cores under in plane compression were studied in the present paper. An interlocking method was developed for both kinds of three-dimensional honeycombs. Euler or core shear macro-buckling, face wrinkling, face inter-cell buckling, core member crushing and face sheet crushing were considered and theoretical relationships for predicting the failure load associated with each mode were presented. Failure mechanism maps were constructed to predict the failure of these composite sandwich panels subjected to in-plane compression. The response of the sandwich panels under axial compression was measured up to failure. The measured peak loads obtained in the experiments showed a good agreement with the analytical predictions. The finite element method was used to investigate the Euler buckling of sandwich beams made with two different honeycomb cores and the comparisons between two kinds of honeycomb cores were conducted.     

Investigating the quasi-static axial crushing behavior of polymeric foam-filled composite pultrusion square tubes

The capability of structures to absorb large amounts of energy is a crucial factor, particularly for structural components of vehicles, in reducing injury in case of collision. In this study, an experimental investigation was conducted to study the crashworthiness of polymeric foam-filled structures to the pultruded square cross-section E-Glass fiber-reinforced polyester composite tube profiles. Quasi-static compression was applied axially to composite tubes to determine the response of the quasi-static load displacement curve during progressive damage. Three pultruded composite tube wall thicknesses at different sizes were examined, and the effects of crushing behavior and failure modes were analyzed and discussed. Experimental results indicated that the foam-filled profile is superior to the non-filled foam composite tube profile in terms of the capacity to absorb specific energy.     

基于整船整桥模型的船桥碰撞数值仿真

桥梁在船舶碰撞时受到的动力载荷和响应是复杂的动力非线性问题。近代非线性有限元技术为该问题的求解提供了有效的工具。简述了该技术的基本原理,并基于整船整桥模型对一艘4万吨实船与桥梁的碰撞过程进行了计算。仿真结果显示了船艏结构损坏、碰撞力演变、能量传递和桥墩内部应力变化的详细情景,讨论了船-桥碰撞的力学特征。演示的方法比传统的经验公式和简化解析法提供更为精确的结果。所提供的桥墩应力状态对桥梁的设计与碰撞后的损伤评估有重要参数价值。     

Low velocity axial impact crushing performance of empty recyclable metal beverage cans

This paper focuses on the axial impact crushing behaviour of recyclable empty metal beverage cans available in the market. The idea is to make a macro foam (sacrificial cladding structure) out of these cans to protect the main load bearing members of civil engineering structures from the air blast load. Axial drop weight tests have been conducted to understand the crushing characteristics and the corresponding energy absorption of a single empty beverage can in detail. To conduct such tests a small-scale drop weight test set-up has been designed and manufactured. The deformation mechanisms and the corresponding energy absorption of the beverage cans were studied in detail for different initial impact velocities (1.4 m/s, 2.2 m/s, 3.1 m/s, 3.8 m/s, 4.4 m/s and 4.9 m/s). Furthermore, an analytical model is proposed to calculate the crushing parameters of empty metal beverage cans. The results from the analytical model are compared and validated with the experimental results.