Multiaxial softening hinge model for tubular vehicle roll-over protective structures

The purpose of the work described in this paper is to provide a computational tool for the design of roll-over protective structures (ROPS) comprised of thin-walled rectangular tubes. This tool simulates the multi-stage, regulatory quasi-static loading test (SAE Standard, SAE J1040 APR88) that new designs must pass. These tests are claimed to be indications of the performance of a ROPS under real (dynamic) roll-over conditions. The collapse of the framework involves large, three-dimensional deformation, which results mainly from large rotations in each member due to bending and torsion. To establish constitutive relationships for a framework model, biaxial bending collapse behaviour of thin-walled rectangular tubes was investigated using a kinematic approach to generate the bending interaction curves. The interaction between bending and torsion was examined separately using extensive finite element analyses of cantilevers modelled by the commercial finite element code ABAQUS. Approximate constitutive relationships were then formulated for a ‘hinge super-element’ to be implemented via the user-defined element subroutine UEL in ABAQUS. The hinge element consists of two nodes separated by a small distance. Each node has six degrees of freedom and the components of stiffness at each node are initially set to sufficiently large values to provide rigid response in the pre-collapse stage. When the collapse criterion is satisfied for the first time, the hinge element is switched to ‘softening’ hinge response and thereafter follows the local softening behaviour of a closed-section tube by modifying the stiffness of the three rotational components according to the constitutive relationships. To test the validity of the hinge model, the response of a simple, scaled ROPS to a simulated prescribed regulatory test load history (SAE Standard) was compared with the results from the analysis of an equivalent shell element model. Good agreement is demonstrated between the two models.     

An investigation of the collapse of thin-walled rectangular beams in biaxial bending

Two different thin-walled closed sections, one square and one rectangular were tested in biaxial bending using displacement controlled cantilever bending tests.Two different constraint conditions were used, the first kept the deflection axis fixed and left the direction of the load axis free. The second kept the load axis direction fixed and allowed the beam to deflect freely.Each configuration was repeated at 15° axis intervals and was performed twice to assure repeatability. This gave a total of 42 cantilever bending tests.The results are used to compare the beam behaviour in the transition and collapse stages between the two constraint conditions. The behaviour is also contrasted with thick-walled theory predictions, since this is the only currently available reference.     

Numerical and analytical study on deep biaxial bending collapse of thin-walled beams

The objective of the paper is to get a fundamental understanding of large rotation response of thin-walled prismatic beams subjected to biaxial bending. Square and rectangular section beams were subjected to a cantilever bending with hinge rotation up to 40°. A general purpose nonlinear FE code PAM-CRASH was used to generate results. Altogether 94 computer runs were made by changing aspect ratio, condition of the loading and bending plane with respect to principal inertia axes of the cross section. The main emphasis was placed on the determination of initial and subsequent yield loci. It was also shown that the direction of the vector of generalized strain rates obeys the normality rule. Calculated in the paper was also a critical angle defining a preferable direction of bending. The present finding can be used to better interpret results of FE calculation of automotive bodies and to develop simplified crash-oriented design tools.     

考虑旋转效应的制动盘螺栓弯矩分布规律

制动盘螺栓对保证列车制动和运行安全具有十分重要的作用，掌握制动盘螺栓弯矩分布规律对确保其使用寿命具有重要意义。采用高速动车组制动盘螺栓弯矩载荷测试技术，对国内多条实际线路的制动盘螺栓弯矩进行测试，获得了制动盘螺栓弯矩与动车组运行速度的关系。依据轮装制动盘螺栓连接结构的尺寸和工作环境开展理论分析，获得了螺栓杆弯矩分布的理论值。建立轮装制动盘车轮结构有限元模型，模拟仿真车轮高速旋转过程中螺栓杆受力情况，得到不同速度下螺栓杆的弯矩分布有限元解。研究结果表明，螺栓杆上的弯矩与列车运行速度密切相关，且运行速度越大，螺栓杆上弯矩越大。理论推导和有限元仿真结果均表明螺栓杆上各截面的弯矩大小和方向并不一致，在内外侧截面和中间截面出现弯矩极值，且方向相反。由于车轮内外结构的不对称性，导致螺栓杆上靠近轮缘一侧的截面弯矩大于外侧截面弯矩。研究工作为进一步研究制动盘螺栓的结构可靠性奠定了基础。     

计算E形截面受弯构件整体稳定临界弯距单元类型选择的探讨

本文分别采用弹性理论公式、ANSYS软件的梁单元和壳单元计算单跨简支受弯铝合金E形截面薄壁构件在不同载荷形式、不同载荷作用点位置以及不同跨距时的弹性整体失稳临界弯矩。对计算结果的分析表明,使用壳单元计算E形截面薄壁构件受弯整体稳定临界弯矩时,能达到较好的精度。     

Plain channel section struts in compression and bending beyond the local buckling load

A theoretical investigation into the behaviour of short, thin-walled plain channel section struts under compression and bending is outlined. The conditions of controlled compression (end displacement) eccentricity and controlled load eccentricity are considered and the effects of imperfections are examined. Buckling loads and post buckling reductions in stiffness are presented for a variety of channel geometries and loading conditions.     

Bending collapse of rectangular and square section tubes

The bending collapse behaviour of rectangular and square section tubes is studied theoretically and experimentally. A limit analysis technique was employed and a set of formulae relating the hinge moment and associated angle of rotation was derived. The theoretical predictions were verified by comparison with 56 quasi-static bending tests on 27 different sections having aspect ratios ( ) varying between 3.0 and 0.33 and with width to wall thickness ratios ( ) between 128 and 9.14. Very good agreement was found between the theoretical predictions and experimental results for the whole range of sections.     

Identification and prediction of cyclic fatigue behaviour in sandwich panels

The work describes the development of analytical model to identify and predict the cyclic fatigue behaviour of composite sandwich panels subjected to cyclic fatigue loading under 3-point bending conditions. Sandwich samples made from CFRP skin and Nomex core have been loaded with a mean displacement corresponding to 60% of the failure deformation, and subsequently subjected to cyclic loading under displacement control with different loading levels. The fatigue tests show that the stiffness degradation over the number of cycles is characterised by three different phases according to the loading level used. The evolution of the energy dissipated per unit volume versus the number of cycles has also been considered. The cyclic history of the stiffness degradation is developed here following an alternative approach to the one currently adopted. The approach involves the use of interpolation through empirical functions of the experimental data, with the coefficients of the interpolation based on the material properties of the sandwich structure and the type of loading. The alternative modelling approach presented in this work allows the prediction of the fatigue behaviour in sandwich structures without using a large number of test data currently needed in fatigue testing of sandwich panels.     

Evaluation on interaction surface of plastic resistance for exposed-type steel column bases under biaxial bending

Exposed-type steel column bases are used widely in low-rise building construction Numerous researchers have examined methods to identify their stiffness and strength, but those studies have heretofore been restricted to in-plane behaviors This paper presents an experimental investigation of inelastic behaviors of square hollow section (SHS) steel column bases under biaxial bending Two types of failure modes are considered anchor bolt yielding and base plate yielding Different pinching effects and interaction surfaces for biaxial bending are observed for these two modes during bi-directional quasi-static cyclic loading tests Differences are elucidated using limit analyses based on a simple analytical model     

Stress analysis of two-dimensional cellular materials with thick cell struts

Finite element analyses (FEA) were performed to thoroughly validate the collapse criteria of cellular materials presented in our previous companion paper. The maximum stress (von-Mises stress) on the cell strut surface and the plastic collapse stress were computed for two-dimensional (2D) cellular materials with thick cell struts. The results from the FEA were compared with those from theoretical criteria of authors. The FEA results were in good agreement with the theoretical results. The results indicate that when bending moment, axial and shear forces are considered, the maximum stress on the strut surface gives significantly different values in the tensile and compressive parts of the cell wall as well as in the two loading directions. Therefore, for the initial yielding of ductile cellular materials and the fracture of brittle cellular materials, in which the maximum stress on the strut surface is evaluated, it is necessary to consider not only the bending moment but also axial and shear forces. In addition, this study shows that for regular cellular materials with the identical strut geometry for all struts, the initial yielding and the plastic collapse under a biaxial state of stress occur not only in the inclined cell struts but also in the vertical struts. These FEA results support the theoretical conclusion of our previous companion paper that the anisotropic 2D cellular material has a truncated yield surface not only on the compressive quadrant but also on the tensile quadrant.     

门槛梁抗弯性能影响因素研究

以某微型车门槛梁为研究对象,分析在侧面碰撞过程中的变形模式,确定薄弱截面。为便于对抗弯性能影响因素研究,将其等效简化为单帽梁。设计三点弯曲准静态试验,采用单一变量的方法,分析单帽梁的厚度、截面长宽比和材料对抗弯性能的影响规律。结果表明:薄壁梁内板厚度对抵抗弯曲所起的作用较小,薄壁梁的抗弯性能主要由外板厚度来体现,厚度越大,薄壁梁的抗弯性能越好。截面长宽比越小,所用材料的屈服强度越高,薄壁梁的抗弯性能越好。对后期门槛梁结构设计提供参考。     

Large plastic deformation of beams of angle-section under symmetric bending

The large deflection flexural behaviour, particularly in plastic range, of beams of right-angle section under four-point symmetric bending is investigated thoroughly. Experiments were carried out for symmetric bending of aluminium alloy L-beams to observe the global load-deflection characteristics, as well as the distortion of cross-sections. The effect of supporting condition in the four-point bending on the global behaviour of the L-beams was also examined experimentally. By considering the geometrical change of beam and the plastic energy dissipations due to the global bending of beam and the angular distortion of cross-sections, a rigid, linear hardening model is proposed. The model is capable of predicting the crosssectional distortion and the structural softening behaviour observed in the experiments with a reasonable accuracy.     

Influence of spot-weld failure on crushing of thin-walled structural sections

Structural effectiveness differences have been observed in a recent study on the progressive axial collapse of thin-walled structural sections when made from different classes of steels (mild steel, interstitial-free rephosphorized high-strength steel and high-strength low-alloyed steel). A higher effectiveness was observed for spot-welded top-hat sections made from a mild steel than for similar sections made from a high-strength steel. For square sections, the structural effectiveness was not affected by the steel classes. It is anticipated that this observation applies not only for spot-welded top-hat and square sections, but for other joined and unjoined thin-walled structures as well.

The part and full failure of spot-welds, during the axial collapse of the thin-walled structural sections, is one possible explanation for the above inconsistency. This is investigated experimentally in this article using peel tests on spot-weld samples under quasi-static and dynamic conditions. Despite having a lower material strength, the mild steel spot-weld samples exhibited a higher peak force and similar energy absorption during failure when compared with a high-strength steel, both under quasi-static and dynamic loadings.

The potential contribution to the mean crushing force during progressive axial collapse is estimated from the experimental results and comparisons are made with deformed thin-walled structural sections from a recent experimental study. Possible implications for the determination of the mean crushing force from analytical and numerical models are identified and discussed.     

An experimental study on inelastic behavior for exposed-type steel column bases under three-dimensional loadings

Considerable damage occurred to steel structures during the Kobe earthquake in Japan. Numerous exposed-type column bases failed in several consistent patterns caused by brittle base plate fracture, excessive anchor bolt elongation, unexpected early anchor bolt failure, and inferior construction work. An exposed-type column base receives axial force and biaxial bending when receiving an arbitrary multidirectional earthquake motion. Up to now, numerous researchers have examined methods to identify their stiffness and strength, but those studies have heretofore been restricted to in-plane behaviors. Therefore, it is necessary to clarify the inelastic behavior of exposed type steel column bases under biaxial lateral loading and axially compressive-tensile loading, which is a closer simulation of the real seismic excitation. In this study, exposed type steel column bases with different failure types, anchor bolt yielding and base plate yielding, are tested under different loading programs, then moment resisting mechanisms and failure modes are investigated.     

Fatigue strength and fracture behaviour of CHS-to-RHS T-joints subjected to out-of-plane bending

The fatigue behaviour of six different hollow section T-joints subjected to out-of-plane bending moment was investigated experimentally using scaled steel models. The joints had circular brace members and rectangular chord members. Hot spot stresses and the stress concentration factors (SCFs) were determined experimentally. Fatigue testing was carried out under constant amplitude loading in air. The test results have been statistically evaluated, and show that the experimental SCF values for circular-to-rectangular (CHS-to-RHS) hollow section joints were found to be below those of circular-to-circular (CHS-to-CHS) hollow section joints. The fatigue strength, referred to experimental hot spot stress, was in reasonably good agreement with referred fatigue design codes for tubular joints.     

Rapid analysis of plate collapse by live-energy minimisation

An efficient method is developed for the accurate collapse analysis of thin steel plates subjected to in-plane compression. The numerical technique is based on a variational principle in which a particular energy function is minimised within a Rayleigh-Ritz type of procedure. The stress-strain behaviour of the material is calculated from a plastic flow theory. The method is presented, verified, and compared with previous theoretical work. Preliminary results for the biaxial loading case are reported.     

胶层厚度对胶接波纹板三点弯曲力学性能影响研究

三明治波纹板采用轻质化和薄壁化的结构设计方法，可以作为承载和吸能结构应用于汽车底盘前纵梁、车身Y字梁等，而现有文献缺少针对胶层厚度对波纹板性能影响的研究。通过制备胶接波纹板并开展三点弯曲工况准静态加载失效试验，分析了不同胶层厚度对三明治波纹板整体承载和吸能特性的影响规律。试验发现，不同胶层厚度下铝合金胶接波纹板结构承载能力和破坏样貌存在差异，相比于0.5 mm和1.0 mm,0.2 mm胶层厚度的三明治结构的各项力学性能和稳定性较好。随后建立胶接波纹板三点弯曲加载有限元模型，实现了对波纹板整体加载变形过程和胶层损伤的模拟，通过与试验结果对比验证了有限元建模方法的有效性，为轻质金属胶接波纹板结构设计和性能评价提供可靠方法。     

不同加载速率下PD3钢轨疲劳裂纹扩展行为研究

为研究弯矩作用下PD3钢轨的疲劳特性,在NENE-2型微动实验机上,对不同加载速率下的PD3钢轨进行了疲劳裂纹扩展性能实验研究.结果表明:PD3钢轨在弯矩作用下,随着载荷加载速率的增加,疲劳裂纹长度呈先增加,再减少的趋势.这说明该材料动态条件下断裂韧性与加载速率有较强的相关性.此时,疲劳裂纹由位错的移动速度和促进位错运动的热能共同作用与控制,当二者达到平衡时,疲劳裂纹最容易萌生与扩展.     

基于有限元法的车轮弯曲疲劳试验研究

利用SolidWorks设计软件对51/2J×15型车轮建立三维几何模型,然后将其导入到SolidWorks软件的Simulation仿真模块中进行有限元分析.根据车轮弯曲疲劳试验要求设置约束边界条件,求解计算车轮在螺栓预紧力、试验弯矩等作用下的结果分布云图,直观地查看车轮在特定载荷条件下危险点处的应力、应变等的变化情...     

冷弯薄壁C型钢梁弯曲性能的试验研究

近几年来,我国兴起了冷弯薄壁型钢结构住宅体系,冷弯薄壁型钢得到快速发展。基此,笔者采取试验、理论和有限元模拟分析相结合的方法,对冷弯薄壁C型钢梁的弯曲性能进行分析研究,从而得出冷弯薄壁型钢结构与传统的热轧钢相比,更具有良好经济性。