加气混凝土填充薄壁圆柱形壳轴压下的屈曲分析

研究了部分填充加气混凝土对薄壁圆柱形壳屈曲性能的影响。以往的研究大多局限于100%填充或简单地选定填充混凝土的厚度。这种做法对结构设计并不适宜。为了进一步研究此问题,用瑞利-里兹逼近算法进行理论分析,并提出了能计算从0%填充到100%填充的壳的临界屈曲应力的公式。使用此公式的计算结果与文献的试验结果能良好地吻合。研究表明在薄壁圆柱形壳内填充加气混凝土能提高构件的屈曲强度。同时,提出了一个适用于工程设计的简化公式。研究表明,当加气混凝土厚度超过10%的外壁半径时,增加混凝土用量的经济性较差。     

推板上的弯销侧抽芯薄壁深腔壳体压铸模设计

由于铸件对成型铸件内腔的型芯包紧力大,将成型铸件内腔的纵向型芯设在定模,以便利用压铸机的开模力抽拔纵向型芯.动模设有异形弯销-滑块机构辅助控制铸件脱模顺序.中心浇口进浇,铸件质量好,生产效率高;模具两次分型,定模上的可动模板拉断浇口,固定于推板的弯销侧抽芯.模具结构紧凑,工作可靠,操作方便.     

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。     

倾斜荷载作用下屈曲诱因对薄壁方管力学性能的影响

倾斜荷载作用下薄壁结构常按照欧拉屈曲模式破坏。这种类型的破坏结构其能量耗散能力和耗能效率较低,可利用破坏诱因提高这些能力。采用试验和数值模拟方法,研究了破坏诱因对倾斜准静态荷载作用下方钢管的能量耗散性能的影响,对钢管的转角进行削切形成诱因。结果显示,大多数试样的破坏诱因改变了各类屈曲(由一般屈曲至渐进屈曲)的变形模式,使峰值荷载大幅减小,从而提高了耗能效率。此外,研究了诱因位置和数量的影响。其数值分析结果与试验数据相吻合。     

膨胀金属管轴向破坏的试验研究

膨胀金属薄膜广泛应用于世界各地的人行道设计和装饰用途。在文献中,很少有关于膨胀金属结构单元特性的信息。本文旨在研究压应力作用下方形和圆管状的膨胀金属薄膜的轴向破坏。当金属开始膨胀时,在金属片中可得到一种类似于钻石的单元,然后这些单元的特点是有两个几何轴线。一系列的试验测试可以印证膨胀金属的主轴和压力载荷之间角度的影响。从结果来看,根据轴线的方向有三种类型的破环模式:1)模式1的特点是塑性破坏机制;2)模式2会在个别元件处产生局部屈曲;3)模式3为管壁的整体屈曲。     

不同开启角度双层圆柱拱壳体系抗震性能的数值分析及试验研究

通过薄壁钢管模型对不同开启角度双层圆柱拱壳体系的抗震性能进行数值分析及试验研究。圆柱拱壳分析模型包含了6种开放角度和4种基本频率。利用MIDAS软件建立了24种双层圆柱拱壳结构模型,施加阻尼比为5%的3种不同的地震作用。研究了水平和垂直地震作用下分析模型在X、Y、Z三个方向上的动力响应特性。此外,对缩尺薄壁钢管模型进行了振动台试验。将试验结果和数值分析结果进行对比,二者加速度反应分布情况相似。水平地震作用下,数值分析和试验均在1/4和3/4节点处出现最大值,在中心节点处出现较小值。研究结果显示,圆柱拱壳模型最佳开启角度为90°。     

覆板加强的方钢管T形节点轴向滞回性能试验研究

为研究采用覆板加强的冷弯方钢管T形节点的轴向滞回性能,对2组支管与主管的截面宽度比β分别为0.4和0.8的方钢管直接焊接节点和采用覆板加强的方钢管T形节点进行了轴向往复加载试验。详细介绍了试验节点的设计、试验过程及破坏形态,并对节点试件的滞回曲线、骨架曲线、耗能和延性等性能进行了分析。试验中,试验节点经历了主管屈服、初始开裂、裂纹闭合、裂缝扩展、裂缝贯通五个主要阶段,但各试件的开裂位置并不相同。加强覆板阻止了裂缝向主管管壁发展,有效避免了主管管壁的撕裂破坏,使开裂后支管的受压荷载继续上升,因而节点开裂后受拉能力较未加强节点的好。支管与主管截面宽度比越小,试件的耗能能力和延性越好。但覆板加强处理降低了试件的耗能能力,且支管与主管宽度比越小其耗能能力的降低越明显。受拉裂缝会降低试件的延性,故轴拉循环的延性较对应的轴压循环的差。在β=0.8时,覆板加强对试件的抗震延性有所改善,但β=0.4时加强节点试件的位移延性系数低于未加强节点。覆板加强节点在支管轴向往复荷载作用下的拉压不均衡问题应引起重视。     

An analytical model for axial crushing of a thin-walled cylindrical shell with a hollow foam core

A thin-walled tube filled with light-weighted foam has wide engineering applications because of its excellent energy absorption capacity. When the structure is axially crushed, the interaction between the tube and foam core plays an important role in its energy absorption performance. Previous theoretical studies so far have largely been concerned with fully in-filled tubes. In this paper, a theoretical model is proposed to predict the axi-symmetric crushing behaviour of such structures but with a partial infill. Using a modified model for shell and considering the volume reduction for the foam core, the mean crushing force is predicted by the energy balance. The proposed formula agrees well with previous results reported in literature. A parametric study is carried out to examine the contribution of foam core plateau stress (σ_f), amount of filling and shell's radius-to-thickness ratio (R/h) on the axial crushing behaviour of the structure. This study can give valuable design guidelines in using thin-walled structures as an energy absorber.     

Buckling of a thin-walled cylindrical shell with foam core under axial compression

This paper investigates the effect of partially filled foam core on the behavior of buckling in a thin-walled cylindrical shell. Previous studies have focused on 100% infill or simply used a fixed thickness of foam core. However, this may not be the optimum arrangement in terms of design. To further investigate this, a theoretical analysis is carried out using the Rayleigh–Ritz approximation, and a new formula is proposed to predict the critical buckling stress of an infill ranging from 0% up to 100% rigid. The proposed formula agrees well with works reported in the literature. It also shows that filling a foam core in a thin-walled cylindrical shell can enhance its resistance to buckling failure. Meanwhile, a simplified formula is provided to the practicing engineer. The paper concludes that an excessive increase in foam core thickness beyond 10% of outer radius is inefficient due to extra cost and weight.     

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.     

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.     

轴压下薄壁管断裂的可能性分析

在车辆的防撞设计中薄壁管作为耗能构件被广泛采用,轴压力是防撞部位承受的最典型荷载之一。为了减轻重量,薄壁管采用轻质材料诸如高强度钢材、铝和镁制成。然而,这些轻质材料中的大多数与传统的钢材相比更脆且易断裂。由于材料的应力、应变状态通常被作为判断其构造断裂点的依据,故对薄壁管的三轴应力分布和时程及其等效应变进行了有限元模拟。分析结果显示,三轴应力和等效应变沿着管长波动,方形薄壁管的断裂更可能发生在边缘而非其他位置。对于相同的轴压冲击,当初始冲击速度在6～24m/s变化时,方形薄壁管内部的应力、应变变化不大。对影响应力、应变状态的参数,包括横截面角的形状、壁厚和横截面形状分别进行研究。所得结果可为薄壁管的设计及轻质材料力学性能的试验特性研究提供参考。     

Axial crushing and optimal design of square tubes with graded thickness

Introducing thickness gradient in cross-section is a quite promising approach to increase the energy absorption efficiency and crashworthiness performance of thin-walled structures. This paper addresses the deformation mode and energy absorption of square tubes with graded thickness during axial loading. Experimental study is firstly carried out for square tubes with two types of thickness distributions and numerical analyses are then conducted to simulate the experiment. Both experimental and numerical results show that the introduction of graded thickness in cross-section can lead to up to 30–35% increase in energy absorption efficiency (specific energy absorption) without the increase of the initial peak force. In addition, structural optimization of the cross-section of a square tube with graded thickness is solved by response surface method and the optimization results validate that increasing the material in the corner regions can indeed increase the energy absorption efficiency of a square tube.     

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.     

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.     

Theoretical prediction and numerical simulation of multi-cell square thin-walled structures

The axial crushing of square multi-cell columns were studied analytically and numerically. Based on the Super Folding Element theory, a theoretical solution for the mean crushing force of multi-cell sections were derived by dividing the profile into 3 parts: corner, crisscross, and T-shape. Numerical simulations of square multi-cell sections subjected to dynamic axial crushing were conducted and an enhancement coefficient was introduced to account for the inertia effects for aluminum alloy AA6060 T4. The analytical solutions show an excellent agreement with the numerical results. It was found that the crisscross part was the most efficient component for energy absorption and the energy absorption efficiency of a single-cell column can be increased by 50% when the section was divided into 3×3 cells. Finally, the proposed method was extended to analyze the plateau stress of square cell honeycomb subjected to out-plane axial crushing and to some extent validate the mechanical insensitivity of honeycomb to cell size.