Closed-form solution to thin-walled box girders considering effects of shear deformation and shear lag

Considering three longitudinal displacement functions and uniform axial displacement functions for shear lag effect and uniform axial deformation of thin-walled box girder with varying depths,a simple and efficient method with high precision to analyze the shear lag effect of thin-walled box girders was proposed.The governing differential equations and boundary conditions of the box girder under lateral loading were derived based on the energy-variational method,and closed-form solutions to stress and deflection corresponding to lateral loading were obtained.Analysis and calculations were carried out with respect to a trapezoidal box girder under concentrated loading or uniform loading and a rectangular box girder under concentrated loading.The analytical results were compared with numerical solutions derived according to the high order finite strip element method and the experimental results.The investigation shows that the closed-form solution is in good agreement with the numerical solutions derived according to the high order finite strip method and the experimental results,and has good stability.Because of the shear lag effect,the stress in cross-section centroid is no longer zero,thus it is not reasonable enough to assume that the strain in cross-section centroid is zero without considering uniform axial deformation.

Improved concept models for straight thin-walled columns with box cross section

This paper focuses on developing improved concept models for straight thin-walled box sectional columns which can better predict the peak crushing force that occurs during crashworthiness analyses. We develop a nonlinear translational spring based on previous research and apply such a spring element to build the enhanced concept models. The work presented in this article is developed on the basis of the publication of the author (Liu and Day, 2006b) and has been applied in a crashworthiness design issue, which is presented by the author in another paper (Liu, 2008).

Lateral static and dynamic characteristics of thin-walled box girder

To analyze the static and dynamic behaviors of the thin-walled box girder in its lateral webs in consideration of shear lag effect and shear deformation, an approach based on the minimum potential principle is introduced in this paper. Both static and dynamic response equations as well as the corresponding natural boundary conditions of the box girder are deduced. Meanwhile, three generalized displacement functions： w （x） , U（x） and O（x） are employed and their differences in the calculus of variation are quantitatively investigated. The comparison of finite shell element results with analytical results of calculation examples validates the feasibility of the proposed approach.

A comparative study on the hull strength of a ship with thin-walled box girders

Based on the Finite Element Analysis and Thin Walled-Box girder Mechanics, two design concepts of adding box girders under main deck in order to increase the hull strength of ship are presented. By comparison and analysis on the longitudinal strength, torsion strength and deck buckling between designed concepts and the original concept, it is found that by adding box girders under the main deck, the weight of hull structure is increased by lower than 10%, but the stress on the plate of the main deck is reduced by about 10%, the stress on the plating of the second deck is reduced about 20%. The shear stress on the plating of both of the main deck and second deck is reduced, but the shear stresses in several nodes are increased. Also the capability of resisting damage to ship is obviously increased by adding box girders under the main deck. The deck buckling is also increased by more than 90%. Consequently, the box girders added under the main deck are useful and effective to increase the strength of hull and ship survivability.

Powell's optimal identification of material constants of thin-walled box girders based on Fibonacci series search method

A dynamic Bayesian error function of material constants of the structure is developed for thin-walled curve box girders. Combined with the automatic search scheme with an optimal step length for the one-dimensional Fibonacci series, Powell＇s optimization theory is used to perform the stochastic identification of material constants of the thin-walled curve box. Then, the steps in the parameter identification are presented. Powell＇s identification procedure for material constants of the thin-walled curve box is compiled, in which the mechanical analysis of the thin-walled curve box is completed based on the finite curve strip element （FCSE） method. Some classical examples show that Powell＇s identification is numerically stable and convergent, indicating that the present method and the compiled procedure are correct and reliable. During the parameter iterative processes, Powell＇s theory is irrelevant with the calculation of the FCSE partial differentiation, which proves the high computation efficiency of the studied methods. The stochastic performances of the system parameters and responses axe simultaneously considered in the dynamic Bayesian error function. The one-dimensional optimization problem of the optimal step length is solved by adopting the Fibonacci series search method without the need of determining the region, in which the optimized step length lies.

THE APPROXIMATE ANALYTICAL SOLUTION FOR THE BUCKLING LOADS OF A THIN-WALLED BOX COLUMN WITH VARIABLE CROSS-SECTION

For a thin-walled box column with variable cross-section, the three governing equations for torsional-flexural buckling are ordinary differential equations of the second or fourth order with variable coefficients, so it is very difficult to solve them by means of an analytic method. In this paper, polynomials are used to approximate the geometric properties of cross-section and certain coefficients of the differential equations. Based on the energy principle and the Galerkin's method, the approximate formulas for calculating the flexural and torsional buckling loads of this kind of columns are developed respectively, and numerical examples are used to verify the correctness of the solutions obtained. The results calculated in this paper provide the basis for demonstrating the stability of thin-walled box columns with variable cross-section. This paper is of practical value.

Erosion problem in tool steel using cold box core-making process

This paper presents the erosion results of the AISI H13 steel impinged by resin-bonded silica sand, using a testing rig that closely simulates the real blowing conditions during industrial core-making. Steel specimens were heat treated to obtain hardness of 294, 445 and 595 HV200 (29, 45 and 55 HRC). Erosion tests were carried out at impingement angles from 20° to 90° and air drag pressures of 1.38, 2.07 and 2.76 bar (20, 30 and 40 psi). The main results are summarized as follows:(i) The harder material, the lower erosion;(ii) the maximum erosion rate is at 30°;(iii) Little difference in erosion rate at impact angle of 60° and 90° for a constant pressure tested regardless of the hardness level;(iv) As the pressure increases, so does the erosion rate, being more sensitive for low impact angles. Finally, a differential form of the general erosion equation is applied on a practical core-making case to evaluate the erosion rate of the H13 steel at 30° and 90° impingement angles.

回油盖隧道式二次抽芯机构注塑模设计

为解决塑件局部区域复杂特征的脱模困难问题,在注塑模具设计时首先采用局部特征分区域办法将局部难脱模特征集中分离出来,而后依据脱模方向的分布情况再进行同向集成分类,针对各集成后的脱模方向设计单次或多次抽芯机构,即脱模方向集成分类脱模设计法,从而有效地解决塑件脱模方向众多而导致的塑件整件或局部区域脱模设计困难问题。基于上述设计原理,结合润滑盒回油盖塑件的脱模设计困难问题,创新设计了一种隧道式二次抽芯机构。在该机构中,利用一根斜导柱驱动主成型块内的隧道滑块转向驱动主成型块内的另一成型活动块先完成第一次抽芯,此过程中主滑块与主成型块分离,而主成型块维持不动;然后该斜导柱再继续驱动主滑块带动主成型块完成第二次抽芯来实现塑件局部区域的脱模。结合机构运动力学分析,在该机构的结构设计中,主滑块与主成型块的闭合锁紧由楔紧块两侧不同斜角的斜面进行锁紧,其斜角分别为23°和25°,相应地,主滑块的斜导柱斜角取20°,用此参数设计的两次抽芯机构顺利地克服了塑件局部区域脱模机构设计困难难题,应用于塑件模具上,较好地实现了塑件的自动化注塑生产。塑件的模具结构为一种单点点浇口三板模具,一模一腔布局。

一种双匙联动保管箱锁的锁芯及锁匙设计分析

设计了一种双匙联动的银行保管箱锁的锁芯部件以及与之对应的锁匙,锁芯部件由10片叠放在一起的锁芯片、1个锁芯拔套、1个小圆垫和1个顶簧组成,通过大圆垫和卡簧将其装配在锁壳中。这种锁芯部件结构紧凑简单、零件数量少、加工工艺性好、装配调试方便、锁具的不相重性大、安全可靠,并且与锁芯对应的锁匙强度高、大气美观。

水夹层热芯盒热变形的防止与改进

从改进芯盒本体结构、顶芯结构及优化加热装置设计几个方面进行研究实践,结果表明开放式模框能有效缓解芯盒的受热变形,对加热装置和顶芯结构进行合理设计也是提高热芯制芯效率和砂芯质量的关键因素。

基于自动化制造复杂砂芯制芯材料的试验研究

针对缸盖等复杂砂芯在自动化制芯、组芯生产过程中存在的变形、破损、模具磨损快等问题,试验研究了烧结球形陶瓷砂、复合添加剂、新型催化剂等对砂芯及铸件质量的影响,提出了自动化生产条件下保证砂芯质量及生产连续性的解决方案。最后指出:(1)选择烧结球形陶瓷砂,有利于改善冷芯盒树脂粘模倾向及减少水套砂芯表面缺陷,解决浸涂水基涂料后的剥落问题;(2)使用复合型抗脉纹添加剂比使用单一组分抗脉纹添加剂的抗脉纹效果更好;(3)新型催化剂可以有效提高砂芯初始抗拉强度,解决砂芯初强度低造成的变形破损等问题;(4)胺催化冷芯盒自动制芯组芯工艺条件下,合适的制芯材料及组分配方是保证制芯质量的必要条件。

干式缸套缸体水套冷芯工艺开发

介绍了原来使用热芯工艺制水套芯存在的生产效率低、制芯周期长、对工装的磨损较大、发气量较大及发气速度慢等问题。详细阐述了使用冷芯工艺生产缸体水套芯的工艺过程及工装结构设计,经生产验证,冷芯水套未产生变形,铸件壁厚较为均匀,铸件内腔未发现粘砂和脉纹现象。最后指出:(1)采用冷砂芯生产的缸体铸件内腔多为松散的砂块,容易清理;(2)冷芯工艺制芯效率比原热芯工艺制芯效率提升60%;(3)冷芯工艺制芯的成本比热芯工艺制芯成本降低约10%。

三开模垂直分型全自动热芯盒射芯机研发

介绍了三开模垂直分型全自动热芯射芯机设计思路、主要组成部件、应用实例等。该整机在通用的垂直分型全自动热芯盒射芯机上增设中间模机构,实现复杂砂芯分型,减少芯盒数量,降低芯盒工装成本,且每个工位独立,可以实现多方式组合操作,并可以根据需要灵活使用设备。该设备集机、电、气一体,全程运动采用PLC精准控制,大大提高了工作效率、降低了劳动强度,已成功应用于中轴砂芯、中轴连接头、汽车轴承盖砂芯等的生产。

四气门气缸盖整体水套砂芯优化设计及模具制造

本文介绍一款新型发动机缸盖的复杂水套砂芯优化设计,及其覆膜砂制芯热芯盒模具设计制造与生产验证过程。其中水套砂芯三维模型的开发设计属于新产品开发的重点,我们通过三维模拟,3D打印实物模型修改验证,结合应用激光扫描逆向设计等技术手段,解决设计过程中遇到的各种问题,最终完成水套砂芯的优化设计。

一种缸盖热芯盒砂芯变形问题分析及改进

以一种大型单体气缸盖铸造过程中热芯盒砂芯变形问题为例,总结了热芯盒砂芯在大型单体气缸盖生产中的应用。分析热芯盒砂芯变形原因,解决了一类热芯盒砂芯浇注过程中变形导致铸件报废的问题。为有效解决热芯盒砂芯浇注过程中变形问题,除了严格控制热芯盒制芯工艺参数外,还要控制热芯盒砂芯固化层厚度一致性保证砂芯强度,采取芯撑固定工艺,为砂芯提供支撑力抵抗铁水浮力。

电控盒外壳注射模设计

根据电控盒外壳的结构特点,采用1模1腔三板模成型塑件,开模由斜导柱带动滑块,弹簧辅助,将成型塑件的倒扣位型芯抽出,合模时由定模板带动斜导柱使滑块复位,并利用SolidWorks的plastics仿真有限元分析模块,分析注射过程的压力变化、成型时间等参数,设计的模具满足注射要求,对类似塑件的模具设计具有一定的指导意义。

L型填芯箱式挡土墙结构优化研究

对L型填芯箱式挡土墙进行了结构优化研究,通过Rhino软件建立模型后,利用FLAC^(3D)有限差分软件,在挡土墙截面积保持不变的条件下,对三种不同底板高度L型填芯箱式挡土墙水平位移、竖直位移以及土压力进行了分析。研究结果表明:在保持挡土墙截面积不变情况下L型填芯箱式挡土墙稳定性随底板厚度增加而增强,为L型填芯箱式挡土墙的工程设计与施工应用提供了参考借鉴。

铝合金缸盖无机芯盒的设计与应用

无机砂应用可有效改善浇注过程的烟尘问题,基于EN31铝合金缸盖结构及无机砂芯工艺性分析,结合企业生产条件和开发成本,开展了铝合金重力倾转浇注无机砂芯盒设计和应用的研究与验证。通过对芯盒射嘴、加热油路、模块等系统设计及优化,并针对油池砂芯和冒口砂芯等复杂结构,采取交叉油路和隔板油路设计解决了模具孤岛加热不均问题,经试制验证,无机砂芯力学性能满足铝合金缸盖铸造工艺要求,为类似产品的开发试制提供参考。

Box-Behnken响应面法优选山茱萸果核提取工艺

目的:筛选山茱萸果核的提取工艺。方法:以总多酚和总皂苷为评价指标,乙醇浓度、提取次数、提取时间和溶媒用量为考察因素,采用响应面Box-Behnken设计试验,筛选山茱萸果核的提取工艺参数。结果:山茱萸果核的最佳提取工艺参数为:乙醇浓度58. 09%,溶媒用量11. 96倍,提取时间89. 64 min,提取次数1. 82次。考虑到工业大生产的实用性,把提取工艺参数设定为乙醇浓度60%,溶媒用量12倍,提取时间90 min,提取次数2次。结论:本研究筛选出的参数可为山茱萸果核的提取工艺提供依据。

Shear deformable finite beam elements for composite box beams

The shear deformable thin-walled composite beams with closed cross-sections have been developed for coupled flexural, torsional, and buckling analyses. A theoretical model applicable to the thin-walled laminated composite box beams is presented by taking into account all the structural couplings coming from the material anisotropy and the shear deformation effects. The current composite beam includes the transverse shear and the restrained warping induced shear deformation by using the first-order shear deformation beam theory. Seven governing equations are derived for the coupled axial-flexural-torsional-shearing buckling based on the principle of minimum total potential energy. Based on the present analytical model, three different types of finite composite beam elements, namely, linear, quadratic and cubic elements are developed to analyze the flexural, torsional, and buckling problems. In order to demonstrate the accuracy and superiority of the beam theory and the finite beam elements developed by this study,numerical solutions are presented and compared with the results obtained by other researchers and the detailed threedimensional analysis results using the shell elements of ABAQUS. Especially, the influences of the modulus ratio and the simplified assumptions in stress-strain relations on the deflection, twisting angle, and critical buckling loads of composite box beams are investigated.