撞击型触发器对帽形薄壁截面轴向挤压影响的数值分析

主要介绍了触发器的设计和性能。为了分析撞击型触发器的几何特征对于轴向冲击荷载作用下耗能构件的抗挤压性能的影响,对其进行数值分析。该耗能构件由一个平盖加一个帽形顶部剖面构成。将触发器视为一个在帽形剖面上具有半圆形横截面的突起物,采用有限元软件LS-DYNA模拟所有的挤压作用。结果显示：在挤压力峰值和轴向冲击荷载作用下的构件耗能能力上,触发器的引入非常有效。同时发现,通过改变触发器的位置和几何尺寸,可以控制构件的挤压响应。     

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.     

Multi-Objective Optimization of aluminum hollow tubes for vehicle crash energy absorption using a genetic algorithm and neural networks

A numerical study of the crushing of thin-walled circular aluminum tubes has been carried out to investigate their behaviors under axial impact loading. These kinds of tubes are usually used in automobile and train structures to absorb the impact energy. A Multi-Objective Optimization of circular aluminum tubes undergoing axial compressive loading for vehicle crash energy absorption is performed for five crushing parameters using the weighted summation method. To improve the accuracy of the optimization process, artificial neural networks are used to reproduce the behavior of the crushing parameters in crush dynamics conditions. An explicit finite element method (FEM) is used to model and analyzed the behavior. A series of aluminum cylindrical tubes are simulated under axial impact condition for the experimental validation of the numerical solutions. A finite element code, capable of evaluating parameters crush, is prepared of which the outputs are used for training and testing the developed neural networks. In order to find the optimal solution, a genetic algorithm is implemented. With the purpose of illustrating optimum dimensional ratios, numerical results are presented for thin-walled circular aluminum AA6060-T5 and AA6060-T4 tubes. Multi-Objective Optimization of circular aluminum tubes has been performed in the basis of different priorities to create the ability for designer to select the optimum dimension ratio. Also, crush parameters of two aluminum alloys has been compared.     

Axial crush simulation of braided carbon tubes using MAT58 in LS-DYNA

This paper examines a composite damage constitutive model, MAT58, in LS-DYNA and its application for use in braided composite tube axial crush simulations. The constitutive response of MAT58 was investigated using single element simulations. It was found that MAT58 reproduced the softening behavior of the braided composite under monotonic compressive loading, but failed in subsequent unloading and tensile loading cycles. A deficiency in the damage law in MAT58 was identified. Unloading and reloading a volume of material that had suffered some degree of damage was a part of the process with the progressing of crush zone during the axial crush of composite tubes. Consequently, this deficiency hinders the success of MAT58 in such applications. In tri-axial braided composite tube axial crush simulations, although the predicted initial peak forces were within 20% of the experimental values, the predictions for the specific energy absorption (SEA) values were consistently low, particularly for tubes without a plug as crush initiator. These discrepancies are attributable to the deficiency in the damage law in MAT58.     

Analytical and experimental studies on quasi-static axial crush behavior of thin-walled tailor-made aluminum tubes

In this paper, the crush behavior of segmented circular tubes, made of aluminum alloy 6061 and subjected to quasi-static axial loading, has been analytically and experimentally investigated. Crush behavior of these tubes was modeled by integrating available analytical models and superposition principle. In the certain overall length of segmented circular tubes, effects of changing the wall thickness and length of each segment on the energy absorption characteristics have been evaluated. One successful approach toward obtaining lightweight energy absorbers with high energy absorption capacity is the use of thin-walled Tailor-Made Tubes (TMTs). In these tubes, the thickness and mechanical properties of the wall vary along the length of the tube. Applying these tubes; crush force can be controlled by changing the length and thickness of each tube segment, improving the performance of energy absorbing systems. Results of this research showed that Tailor-made tubes have higher energy absorption capacity at identical crush lengths, and they can absorb more energy per unit weight compared to simple tubes with constant wall thickness and mechanical properties. Moreover, for the same specific energy absorption, the TMTs exhibit a considerable reduction in the magnitude of the mean and initial maximum crush forces. With the use of TMTs, the maximum crush force shifts to the end of the crush range, reducing the exerted deceleration on occupants and equipments. Comparing mean crush force and specific energy absorption obtained by analytical and experimental approaches, it was observed that combining current analytical models with superposition principle can prepare a set of analytical formulations to predict TMTs crush characteristics within an acceptable proximity.     

Concurrent multi-scale crush simulations with a crystal plasticity model

The crush behavior of polycrystalline metallic square tubes under quasi-static axial loading condition is investigated through a mesoscale crystal plasticity model embedded in an explicit finite element simulation code as a concurrent multiscale model. The boundary value problem is defined at the local continuum scale whereas the material behavior is modeled at the mesoscale through crystal plasticity defined in a representative volume element. The anisotropic behavior of the tubes emerges from the texture induced by the large plastic deformations created during the manufacturing process. In this work, this effect is modeled by considering the texture generated by deforming a single element model with an embedded polycrystalline aggregate of face center cubic (FCC) crystals under basic loading paths, including uniaxial tension, uniaxial compression, and simple shear. This initial texture is then used at each integration point in the explicit crush simulations of a square tube model made of an FCC aluminum alloy. As energy absorption is dominated by the plastic collapse mechanisms at the corner elements, the influence of the initial texture and its evolution during crush are found to be significant.     

单双向约束下冲击荷载对煤样渐进破坏的影响规律研究

采用自行研制开发的单双向约束摆锤式冲击动力加载试验装置,并配合超声波检测设备,分别进行单向和双向约束条件下,冲击荷载对煤样渐进破坏规律的系统试验研究,分析煤样在不同循环冲击直至形成宏观破坏的整个过程中表现出的破坏特征与能量耗散规律.结果表明:随着冲击次数的增加,煤样损伤量表现为倒"S"型累积增长模式;在单向约束条件下,...     

Design of thin wall structures for energy absorption applications: Enhancement of crashworthiness due to axial and oblique impact forces

This paper describes a computationally aided design process of a thin wall structure subject to dynamic compression in both axial and oblique directions. Several different cross sectional shapes of thin walled structures subjected to direct and oblique loads were compared initially to obtain the cross section that fulfills the performance criteria. The selection was based on multi-criteria decision making (MCDM) process. The performance parameters used are the absorbed crash energy, crush force efficiency, ease of manufacture and cost. Once the cross section was selected, the design was further enhanced for better crash performances by investigating the effect of foam filling, increasing the wall thickness and by introducing a trigger mechanism. The outcome of the design process was very encouraging as the new design was able to improve the crash performance by an average of 10%.     

岩石动静组合加载力学特性研究

 根据深部岩石力学研究的需要,在分析深部开挖中岩石受力特点的基础上,提出岩石动静组合加载问题。通过对多载荷凿岩机、INSTRON系统、SHPB装置的不断改进和尝试,研制出中高应变率段岩石动静组合加载试验系统,该系统可实现岩石轴向静压0～200 MPa、围压0～200 MPa和冲击动载0～500 MPa的同时加载。基于新研制的试验系统,对岩石在不同动静组合加载下的强度特性、破碎规律及吸能效率进行研究。结果表明：冲击动载一定,轴向静压从0增大到其单轴静压强度70%时,岩石的组合加载强度大于其纯静载强度或纯动载强度。轴向静压不变,随着冲击动载的增大,岩石的组合加载强度逐渐增大,表现出率相关性。动静组合加载下,岩石的破坏呈拉伸破裂模式,岩石的破碎块度在冲击动载或轴向静压增大时都向细粒端发展。岩石的吸能率随着动静组合加载的不同而不同,通过选择合适的动静组合加载,可使岩石的吸能率最大。     

高应力岩石围压卸载后动力扰动的临界破坏特性

 利用改造的动静组合分离式霍普金森压杆(SHPB)加载装置,系统研究砂岩历经三维加载–围压卸载–轴向冲击的临界破坏特性。试验结果表明：砂岩受外界冲击时的临界破坏特性受轴向静压影响明显,冲击强度随着轴向静压的增加出现先增加后减小的趋势;当无轴压和轴向静压为单轴抗压强度的20%时,应力–应变曲线为典型的I型曲线;随着轴向静压的增大,应力–应变曲线逐渐转变为II型曲线。试样破坏过程中能量变化逐渐由吸收扰动能量转变为释放弹性储能,该现象可以较好地反映岩爆发生过程中高静应力和动力扰动的相互作用机制,为深部岩爆机制的深入研究提供试验支持。另外,利用数字散斑相关计算方法对试样应力加载过程进行表面位移场监测;结果表明,常规冲击加载下,试样表现出为整体膨胀特性,当轴向静压为72 MPa时,则表现为入射端张剪性破坏和膨胀性破坏的共同作用,反映出轴向静载对试样动态破裂面断裂方式的影响。     

Effect of the cross-sectional shape of hat-type cross-sections on crash resistance of an “S”-frame

This paper addresses a design aspect of a front side rail structure of an automobile body from the point of view of weight efficiency and crush energy absorption. Various orientations of the cross-section and ways of reinforcing the cross-section by an internal stiffening member are investigated. The specific energy absorption (i.e. energy absorption per unit weight) is taken as a measure of the performance of a structure. Also the advantages of reinforcing the side rail by means of aluminum foam filling are assessed. It is shown through extensive numerical simulation using nonlinear finite element code PAM–CRASH, that the model with a diagonally positioned internal stiffener and suitable triggering dents can absorb up to 200% more energy than the typical double-hat/double-cell profile member. At the same time there is a 3 fold increase in the specific energy absorption. By using the concept of aluminum foam-filling with 3 MPa foam, the specific energy absorption increases by a factor of 2.84.     

一维动静组合加载下岩石冲击破坏试验研究

 利用研制的岩石动静组合加载SHPB试验装置,系统研究岩石在一维动静组合加载下的冲击破坏特性。首先按照一维应力波传播理论,对动静组合加载的试验原理进行理论论证。试验过程中预先在轴向施加不同载荷,按照静载强度的20%,30%,40%,70%,80%和90%等6个系列进行,然后沿轴向进行冲击加载,考察岩石的临界破坏承载强度。研究结果表明：在临界破坏的情况下,动态冲击的应力–应变曲线(包括常规冲击和动静组合加载)最后都会出现总应变减小的现象,这是由于冲击过程中岩石内部储存弹性能释放所致。在轴向静压较小时,岩石的组合加载应力–应变曲线跟常规的冲击试验曲线类似;轴压较大时,岩石的组合加载应力–应变曲线没有初始的近似线弹性段,直接从非线性段开始。随着轴向静压的增大,岩石的抗冲击强度呈现出先增大后减小的趋势,大约在静载强度60%时,抗冲击强度达到最大值。在入射能较小时,岩石吸收的能量会缓慢增加,在入射能较高时,岩石吸能会快速增加。常规冲击下岩石的临界破坏模式为劈裂形式,动静组合加载下呈现压剪形式。     

上海中心大厦伸臂桁架与巨柱和核心筒连接的抗震性能试验研究

在上海中心大厦伸臂钢桁架与柱和核心筒连接单调静力试验的基础上,进行了该连接的抗震性能试验。试验设计了3种不同的反复加载路径,以考察普通循序渐增加载方式和不同损伤累积后再以普通循序渐增加载方式下试件滞回特性和耗能能力的差别。结果表明：在几种不同路径反复荷载作用下,试件最终破坏均发生在伸臂桁架斜腹杆和下弦杆端部,伸臂桁架与巨柱和核心筒连接的节点板塑性应力水平较低,滞回曲线形状饱满,延性较好,满足结构抗震设计要求;伸臂桁架在不同加载路径下的累积塑性耗能引起的塑性损伤对伸臂桁架的滞回性能退化有一定影响,但并不显著;单斜腹杆作为伸臂桁架耗能的主要构件,其累积轴力耗能占伸臂桁架总耗能的70%左右。     

低速冲击下双钢板混凝土组合墙的力学性能研究

对8片双钢板混凝土组合墙进行了落锤冲击试验和数值模拟,研究了冲击能量和轴向压力对试件力学性能的影响。试验记录了冲击力、轴力、位移和应变等时程曲线,分析了试件的动力响应全过程。采用ANSYS/LS-DYNA建立了双钢板混凝土组合墙在冲击和轴力共同作用下的有限元模型,根据试验结果验证了计算模型的可靠性,并进一步探讨了轴力和冲击能量对墙体抗冲击性能的影响。研究结果表明：双钢板混凝土组合墙在低速冲击作用下的动力响应经历了五个阶段;采用本文建立的数值模型可以很好地模拟墙体的力学性能;轴压比超过一定临界值后将极大降低墙体的抗冲击性能。     

Impact energy dissipation characteristics of thin-walled cylinders

Thin-walled, closed-end cylindrical specimens of both aluminium and steel alloys were tested under axial and diametrical compression loading in static as well as in impact conditions. The load-deflection behaviour of the specimens were recorded and the modes of collapse were observed. The two loading conditions were found to give the same pattern of buckling deformation, although the energy absorbed under impact loading was higher.The main purpose of results for circular cylinders under axial compression is to give a basis of comparison for the cylinders under diametrical compression and also for cylinders filled with liquid (soft drink) or sand under either longitudinal or lateral compression. In all these cases absorption was achieved.     

撞击荷载下带吸能装置的钢筋混凝土桥墩动力响应研究

对带吸能装置的钢筋混凝土桥墩进行了落锤撞击荷载动力响应分析。根据伯努利-欧拉理论求解其振型,利用拉格朗日方程和落锤运动方程推导其弹性阶段的动力响应和吸能装置的位移时程表达式,从而求得桥墩的动内力。然后,将计算结果与承受轴力的侧向落锤撞击荷载试验结果进行对比,两者符合较好。这表明,本算法用来求解撞击荷载作用下带吸能装置的钢筋混凝土桥墩其弹性阶段的动力响应是可行的,因而具有一定工程应用价值。     

高强钢筋混凝土复合受扭构件开裂性能试验研究

以轴压比和相对偏心距为参数,对8根高强钢筋混凝土压弯剪构件在单调扭矩作用下的性能进行了试验研究,探讨了试件裂缝的产生和发展、破坏特征以及影响裂缝倾角和开裂扭矩的因素。推导出了压弯剪复合受扭构件开裂扭矩的计算公式,与试验结果进行对比,计算值与试验值吻合较好,为高强混凝土复合受扭构件开裂扭矩的计算和设计提供了参考。     

Collapse behavior of square thin-walled columns subjected to oblique loads

The crush behavior of a square column subjected to oblique loads, which is undergoing both axial and bending collapses, is analyzed. Oblique load conditions in numerical simulations are realized by means of impacting the column on a declined rigid wall with no friction. Mean crush loads corresponding to load angles are investigated with such geometrical parameters as thickness, width and length. Results show that there is a critical load angle at which a transition takes place from the axial collapse mode to the bending collapse mode. The dimensionless mean crush load is employed by normalizing the mean crush load with the analytical axial mean crush load and bending moment equations. It is expressed as a function of only one variable, the load angle. Finally, the formulation for the mean crush load is developed in terms of geometrical parameters and the critical load angle. The equation of the critical load angle is expressed as a function of the ratio of l/b. The value of the mean crush load drops to about 40% of the mean crush load in pure axial collapse after the critical load angle. Some cases of thin-walled columns are examined to verify the formulas of the mean crush load, and the results of numerical simulations are in good agreement with the predicted mean crush loads.     

Numerical simulation of the axial collapse of thin-walled polygonal section tubes

This paper deals with the post-buckling deformation characteristics of aluminum alloy extruded polygonal section tubes subjected to dynamic axial impacts. The explicit finite element code LS-DYNA is the primary analytical tool used in this investigation. The study focuses on investigating a post-buckling deformation phenomenon that is primarily manifested by an axial crumpling action that generates material folds as the impact energy is dissipated. The research is conducted in two phases. The first phase consists of validating the LS-DYNA model parameters and numerical results pertaining to thin-walled aluminum extruded square tubes with actual published experimental data. The post-buckling deformation characteristics of the specimens such as the overall final configuration and the various folding deformation modes (extensional, symmetric and asymmetric) resulting from the axial collapse of the member is also investigated in a subsequent phase. Based on the numerical simulation results, it is apparent that the increase in the number of walls (flanges) has a direct impact on the mean axial crushing force and permanent displacement parameters. In particular, the adoption of a hexagonal tube section as an axially loaded energy absorbing column yields an average increase of 11% in the mean axial crushing force and an average decrease of 10% in the permanent displacement. The greatest benefits are obtained in the specimens with the thinnest nominal wall thickness, where the upper bound results show an average increase of 27% in the mean axial crushing force and average decrease of 20% in the permanent displacement.     

L形钢管混凝土柱抗震性能非线性有限元分析

为深入了解低周反复荷载下L形钢管混凝土柱的抗震性能,以试验研究为基础,依据L形钢管混凝土柱核心混凝土在低周反复荷载作用下的应力-应变关系,采用有限元程序Opensees,对L形钢管混凝土柱的抗震性能进行非线性分析,给出其荷载-水平位移关系曲线;并分析L形钢管混凝土柱抗震性能的影响因素。结果表明:计算结果与试验结果吻合较好;截面宽厚比D/t和截面长宽比D/B对构件骨架曲线的影响相似,总体上对荷载-位移骨架曲线的形状影响很小,主要表现在对水平承载力大小的影响;轴压比是构件骨架曲线的主要影响因素,轴压比对试件弹性阶段的刚度影响不大,对构件弹塑性阶段刚度影响明显,随着轴压比的增大,试件的刚度也逐渐变小,水平极限承载力变小,并且曲线将会出现下降段,且下降段的下降幅度随轴压比的增加而增大,表明构件的位移延性也越来越差。