Dynamic progressive buckling of circular and square tubes

A series of over 120 axial crushing tests were conducted on circular and square steel tubes loaded either statically or dynamically. Approximate theoretical predictions for static and dynamic progressive buckling are developed. Fair agreement with the experimental results is achieved provided the effective crushing distance is taken into account and the infuence of material strain rate sensitivity is retained for dynamic loads.     

Energy absorption of a thin-walled cylinder with ribs subjected to axial impact

We performed experimental and theoretical analyses that show a thin-walled cylinder with stiff ribs can be used as a structural element to improve or adjust energy absorption characteristics. We conducted impact crushing tests using several different cylinders with ribs. The experimental results showed that the axisymmetric and non-axisymmetric crushing modes were dependent on not only the cross-section size but also on the distances between the ribs. A critical distance between the ribs was found to exist for generating axisymmetric and non-asxisymmetric crushing modes and it was more than double the wavelength of axisymmetric wrinkles regardless of cylinder size. The mean crushing forces of the axisymmetric modes were found to be roughly 1.3 times larger than those of the non-axisymmetric modes. The theoretical results based on plastic hinge behavior showed good agreement with the experimental results. The effects of material and cylinder size on the crushing behavior of a cylinder with ribs were expressed using approximate mathematical equations. The critical distance between ribs for generating axisymmetric or non-axisymmetric crushing mode was also expressed approximately. Stiff ribs appropriately spaced in a cylinder were found to be effective in absorbing a large amount of energy with a short crushing deformation.     

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。     

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。     

The effective crushing distance in axially compressed thin-walled metal columns

This paper examines the effective crushing distance of thin-walled box columns. In contrast to previous work on this subject where a perfectly plastic material was assumed, the hardening property of a material is now taken into account. A simplified theoretical model of a compressed rigid-linearly strain hardening metal strip is studied and a closed-form solution is derived for the crushing distance of unstiffened as well as transversly stiffened box columns. The theoretical predictions are in excellent agreement with experimental data.     

Collision energy absorption of ships' bow structures

The energy absorbed during the collapse of ship's bow structures in a collision is largely due to the plastic work done by axial crumpling of the plate elements in the structures. In this paper a method is presented for predicting crushing strength of ships' bow structures during a collision.The method of predicting the crushing strength of a variety of structural elements is described using the kinematic method of plasticity. Effects of strain-rate on the axial of crushung of structural elements are included. The crushing strenght of a ship's bow structure is obtained by summing the energy dissipated in all individual structural elements. The theoretical predictions are compared with experimental results for ships' bow models. The paper concludes with an example of the application of the theoretical method to a ship collision with a concrete pier.     

Some theoretical considerations on the dynamic response of sandwich structures under impulsive loading

A theoretical solution is obtained to predict the dynamic response of peripherally clamped square metallic sandwich panels with either honeycomb core or aluminium foam core under blast loading. In the theoretical analysis, the deformation of sandwich structures is separated into three phases, corresponding to the transfer of impulse to the front face velocity, core crushing and overall structural bending/stretching, respectively. The cellular core is assumed to have a progressive crushing deformation mode in the out-of-plane direction, with a dynamically enhanced plateau stress (for honeycombs). The in-plane strength of the cellular core is assumed unaffected by the out-of-plane compression. By adopting an energy dissipation rate balance approach developed by earlier researchers for monolithic square plates, but incorporating a newly developed yield condition for the sandwich panels in terms of bending moment and membrane force, “upper” and “lower” bounds are obtained for the maximum permanent deflections and response time. Finally, comparative studies are carried out to investigate: (1) influence of the change in the in-plane strength of the core after the out-of-plane compression; (2) performances of a square monolith panel and a square sandwich panel with the same mass per unit area; and (3) analytical models of sandwich beams and circular and square sandwich plates.     

Approximate elastic-plastic analysis of the static and impact behaviour of polymer composite sandwich beams

An elastic-plastic beam bending model has been developed to simulate the post-upper skin failure energy absorption behaviour of polymer composite sandwich beams under three-point bending. The beam skins consist of woven and chopped strand glass, while the core is a resin impregnated non-woven polyester material known as Coremat. A polyester resin was used for the construction. The theoretical model consists of a central hinge dominated by a crushing core and tensile elastic strains in the lower skin. Experimental measurements of the non-linear force-deflection characteristics for the beam are compared to the theoretical predictions from the model, and it is shown that the shear crushing of the core has an important effect on the behaviour of the beam. The model shows that the most important material properties are the lower skin tensile failure strain and the core crushing strength. Dynamic effects are included in the model in the form of a strain rate dependence of the core crushing stress and the strain rate dependence of the failure strain in the lower skin. The increase in material strength with strain rate gives rise to an improved energy absorption capacity for the beam under impact loading.     

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.     

潜孔锤破岩系统动力学特性研究

为深入研究潜孔锤破岩过程中推进力、激振频率等对潜孔锤破岩系统特性的影响,基于弹簧、阻尼、滑动器等元件建立了考虑潜孔锤与岩石局部接触、完全接触状态的动力学模型。分别建立不同状态下系统的动力学方程,并基于阶跃函数建立破岩系统的连续无量纲微分方程组,采用龙格-库塔法求解获得不同状态下的潜孔锤钻头位移图、速度图、相空间图以及庞加莱截面图。结果表明:破岩系统的运动状态随推进力改变而改变,当系统处于周期-1状态时,系统相对较稳定且破岩效率最佳;随着激振力频率增大,系统稳定的区间范围随之增加,但破岩效率反而降低。破岩系统动力学特性研究结果为潜孔锤在实际工作中的参数确定提供理论依据。     

A theoretical and experimental study on metal hexagonal honeycomb crushing under quasi-static and low velocity impact loading

In the study of honeycomb crushing under quasi-static loading, two parameters are important; the mean crushing stress and the wavelength of the folding mode. On the other hand, the kinetic energy absorbed by the honeycomb is investigated in the impact loading. In this paper, through fully considering the cylindrical curvature effects and implementing the energy method, a new theoretical model for the estimation of the mean crushing stress and the wavelength of the folding mode of the metal hexagonal honeycomb is presented. Afterwards, developing this static model to the dynamic state, a theoretical model for study of the behavior of these energy absorbers, in the low velocity impact loading, is proposed and the required initial velocity of the impactor, for creation of the desired folding length in these structures, is determined, analytically. The presented theoretical models have been compared with experimental results obtained from experiments on three kinds of honeycomb with the various minor diameters and thicknesses of the cell walls under quasi-static and low velocity impact loading in the axial direction. Excellent correlation has been observed between the theoretical and experimental results.     

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.     

泡沫变形模式对泡沫填充圆管压溃行为的影响

将泡沫填充圆管的平均压溃载荷视为圆管、泡沫及圆管与泡沫相互作用三部分之和, 基于作者提出的直链塑性铰改进模型, 研究了两种泡沫变形模式对泡沫填充圆管准静态压溃行为的影响, 得到了新的最优屈曲半波长和平均压溃载荷的理论计算公式, 并研究了两种泡沫变形模式下, 偏心率和塑性角参数对最优屈曲半波长和平均压溃载荷的影响。结果表明, 泡沫变形模式 Ⅰ 下的平均压溃载荷略高于泡沫变形模式 Ⅱ 下的相应值, 泡沫变形模式对最优屈曲半波长影响较大; 与文献[14]相比, 所得平均压溃载荷理论预测值与试验结果吻合得更好。      

Analysis of the influence of crushing on the behavior of granular materials under shear

The behavior of granular materials mainly depends on the mechanical and engineering properties of particles in its structural matrix. Crushing or breakage of granular materials under compression or shear occurs when the energy available is sufficient to overcome the resistance of the material. Relatively little systematic research has been conducted regarding how to evaluate or quantify particle crushing and how it effects the engineering properties of the granular materials. The aim of this study is to investigate the effect of crushing on the bulk behavior of granular materials by using manufactured granular materials (MGM) rather than using a naturally occurring cohesionless granular material. MGM allow changing only one particle parameter, namely the “crushing strength”. Four different categories of MGM (with different crushing strength) are used to study the effect on the bulk shear strength, stiffness modulus, friction and dilatancy angle “engineering properties”. A substantial influence on the stress–strain behavior and engineering properties of granular materials is observed. Higher confining stress causes some non-uniformity (strong variations/jumps) in volumetric strain and a constant volumetric strain is not always observed under large shear deformations due to crushing, i.e. there is no critical state with flow regime (with constant volumetric strain).     

大破碎比颚式破碎机及对破碎工艺流程的变革

介绍了新型破碎设备--外动颚大破碎比颚式破碎机及该系列产品的技术参数、性能特点;可用一段大破碎比破碎机取代传统流程中的两段或三段破碎,新型破碎设备的研制成功带来了破碎工艺的变革。     

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.     

煤块冲击破碎粒度的分形特征

煤块冲击破碎后的粒度分布具有分形特征,根据分形理论建立了煤块冲击破碎粒度的分形模型,对不同矿区的煤块进行冲击破碎试验。在不同试验条件下对冲击破碎后煤块的筛下质量累积概率进行函数拟合,拟合结果表明分形模型能够很好地描述煤块冲击破碎后的粒度分布特征,粒度分形维数是评价煤块冲击破碎效果的重要参数。采用Matlab软件建立了粒度分形维数与试验参数之间的二次方模型,该模型的预测结果与试验结果的平均误差为2.51%,满足预测误差要求,为控制煤块冲击破碎后的产品粒度分布提供了理论依据。     

Ice crushing tests with variable structural flexibility

To learn more on ice crushing phenomena against a compliant stiffened plate structure, near full-scale ice crushing tests were conducted in Aker Arctic test basin with a 1:3 scaled model. The dimensions of the to be crushed ice sheet and the stiffened plate were chosen to present a full size ship or offshore structure steel plating which are designed to withstand the crushing loads of 60 cm thick level ice. A major difference to the crushing tests published earlier in literature was that the compliance of one stiffener could be adjusted. The instrumentation in the plate included both strain gauges for load paths from the plate to the stiffeners and a large tactile sensor for detailed direct crushing pressure distribution measurement. In order to have repeatable and homogeneous model ice properties the ice blocks were manufactured by snow ice technique with low salinity water impregnation under vacuum in the mould. Altogether 22 ice blocks were crushed with different ice velocities and plate compliancy. The well-known line like contact prevailed in continuous crushing. The test data indicates that the crushing load distribution is independent from the underlying plate stiffness distribution and no higher crushing pressure at the location of stiffeners was found.     

地铁盾构孤石预爆破破碎范围计算方法

在沿海地铁盾构掘进孤石爆破预处理施工中,为能更好的描述符合现场实际情况的破碎效果,对影响孤石爆破破碎的炮孔内不耦合介质进行了初步探讨。利用MISES强度准则,根据爆炸动力学理论,结合施工过程中炮孔柱形装药地下水以及上部空气垫层的影响,给出了爆破破碎范围的理论计算公式。依据厦门地铁盾构隧道施工现场的爆破参数进行了计算,计算结果与相关文献资料、现场实验结果进行比较分析,验证了现场爆破参数设计的合理性,证明了理论公式的可行性。可为地铁盾构施工孤石预爆破及类似岩石爆破问题的参数设计提供理论参考。     

地铁盾构孤石预爆破破碎范围计算方法

在沿海地铁盾构掘进孤石爆破预处理施工中,为能更好的描述符合现场实际情况的破碎效果,对影响孤石爆破破碎的炮孔内不耦合介质进行了初步探讨。利用MISES强度准则,根据爆炸动力学理论,结合施工过程中炮孔柱形装药地下水以及上部空气垫层的影响,给出了爆破破碎范围的理论计算公式。依据厦门地铁盾构隧道施工现场的爆破参数进行了计算,计算结果与相关文献资料、现场实验结果进行比较分析,验证了现场爆破参数设计的合理性,证明了理论公式的可行性。可为地铁盾构施工孤石预爆破及类似岩石爆破问题的参数设计提供理论参考。