Residual stress measurement in an extra thick multi-pass weld using initial stress integrated inherent strain method

Residual stresses existing in a multi-pass butt joint with a thickness of 70 mm, using a flux-cored arc welding process, were measured by an inherent strain method (ISM). Since such a thick plate before welding contains a large amount of initial residual stresses (−300 to +100 MPa), the initial stresses were integrated with conventional ISM in order to determine the total residual stresses in a welded joint. Two methods named as initial stress integrated ISM and initial inherent strain integrated ISM were suggested for the consideration of the initial stress distributions through the thickness of base plates. The results show that there is a significant difference between the integrated ISM with initial stresses or initial inherent strain and the conventional ISM without initial stresses. The residual stresses measured by any of the initial stress integrated ISM and initial inherent strain integrated ISM agreed well with the neutron diffraction measurement. Thus, the proposed initial stress integrated ISM is a proper destructive measurement method in the case of thick weld joints.     

基于ANSYS的刚性悬挂振动特性分析

通过对刚性悬挂的简化,在一些基本假设的基础上,建立了刚性悬挂的有限元模型。进行了静力分析和模态分析,得到了悬臂长度大小对汇流排整体变形的影响,合理选择可改善汇流排终端几跨的跨中挠度,并分析了悬臂的大小、之字值和悬挂刚度对刚性悬挂振动特性的影响。     

基于固有应变理论的船体焊接变形仿真研究

大型船舶构件尺寸大、焊缝分布广,传统的有限元焊接仿真方法难以满足其大尺寸结构计算的要求。基于热弹塑性有限元法对T型局部接头进行焊接变形计算,获取焊缝处平均固有应变值,然后将其作为初始载荷施加在全尺寸壳单元分段模型上进行弹性计算,最终得到大型分段的整体焊接变形。仿真结果表明,结合小模型的热弹塑性法和大结构固有应变法,能准确高效的预测大型结构的焊接变形。     

公路超限超载治理的宏微观经济学分析

在分析公路超限超载运输的经济学性质、发生发展的一般内在机理与中国特性的基础上,结合公路超限超载问题解决的经典经济学思路与中国国情提出了相应长效治理机制。     

An efficient FE computation for predicting welding induced buckling in production of ship panel structure

In a Thermal-Elastic-Plastic (TEP) FE analysis to investigate welding induced buckling of large thin plate welded structure such as ship panel, it will be extremely difficult to converge computation and obtain the results when the material and geometrical non-linear behaviors are both considered. In this study, an efficient FE computation which is an elastic FE analysis based on inherent deformation method, is proposed to predict welding induced buckling with employing large deformation theory, and an application in ship panel production is carried out. The proposed FE computation is implemented with two steps:(1) The typical weld joint (fillet weld) existing in considered ship panel structure is conducted with sequential welding using actual welding condition, and welding angular distortion after completely cooling down is measured. A TEP FE analysis with solid elements model is carried out to predict the welding angular distortion, which is validated by comparing with experimental results. Then, inherent deformations in this examined fillet welded joint are evaluated as a loading for the subsequent elastic FE analysis. Also, the simultaneous welding to assemble this fillet welded joint is numerically considered and its inherent deformations are evaluated.(2) To predict the welding induced buckling in the production of ship panel structure, a shell element model of considered ship panel is then employed for elastic FE analysis, in which inherent deformation evaluated beforehand is applied and large deformation is considered. The computed results obviously show welding induced buckling in the considered ship panel structure after welding. With its instability and difficulty for straightening, welding induced buckling prefers to be avoided whenever it is possible.     

Numerical prediction and mitigation of out-of-plane welding distortion in ship panel structure by elastic FE analysis

As an application to predict and mitigate the out-of-plane welding distortion by elastic FE analysis based on the inherent deformation theory, a panel structure of a pure car carrier ship is considered. The inherent deformations of different types of welded joints included in this ship panel structure are evaluated beforehand using thermal elastic plastic FE analysis. Applying idealized boundary condition to focus on the local deformation, elastic FE analysis shows that the considered ship panel structure will buckle near the edge and only bending distortion is dominant in the internal region. In order to mitigate out-of-plane welding distortion such as buckling and bending, straightening using line heating is employed. In the internal region, only inherent bending with the same magnitude as welding induced inherent bending is applied on the opposite side of welded joints (fast moving torch). On the other hand, only in-plane inherent strain produced by line heating is introduced to the edge region to correct buckling distortion (slow moving torch). The magnitude of out-of-plane welding distortion in this ship panel structure can be minimized to an accepted level.     

Prediction of steel plate deformation due to triangle heating using the inherent strain method

In a shipyard, line heating and triangle heating are two major processes carried out by skilled workers to form curved plates in various shapes under various heating conditions. There have been many studies on line heating, but triangle heating has rarely been studied owing to its complicated heating process with irregular multiheating paths and highly concentrated heat input. Triangle heating is the most labor-intensive job. Hence, it is essential for most shipyards to study the automation, as well as the improvement, of the triangle heating process in order to increase hull-forming productivity. In this study, a pioneering attempt to simulate triangle heating was made. A circular disk-spring model is proposed as an analysis model for the elastoplastic procedure of triangle heating, and the inherent strain method is also used to analyze the deformation of plates. The results of the simulation were compared with those of experiments and showed good agreement. It is shown that the present approach and the model used in this study are effective and efficient for simulating triangle heating for the steel plate forming process in shipbuilding.     

20000TEU集装箱船抗扭箱结构的焊接变形预控

抗扭箱作为20000TEU超大型集装箱船的关键结构,由于其组成的板材较厚且与集装箱直接接触,因此需严格控制该结构的面外焊接变形。采用基于固有变形理论的弹性有限元分析,预测抗扭箱的焊接变形,且与实际测量结果比较吻合;通过设计大厚板的非对称X型坡口来控制面外变形,结果表明：采用非对称设计的X型焊接坡口更有利于减小变形,仅需一次翻身、提高生产效率。在不考虑装配间隙时,基于高效的热-弹-塑性有限元计算归纳出超厚板(40mm~85mm)的最佳正反面坡口深度比;而考虑实际生产中的装配间隙时,最佳正反面坡口深度比与板材厚板呈非线性关系。最后将考虑装配间隙时,优化的非对称坡口焊接接头应用到抗扭箱结构中,面外焊接变形减小明显,有利于指导船厂的实际生产。     

焊接结构变形分析系统(Weld_Sta)的开发及其应用

为使现场工程人员方便进行焊接结构变形分析,开发了一个能简单地对焊接变形有限元分析所需的数据进行前处理,对焊接变形进行计算机分析并对仿真结果进行后期处理的软件-焊接结构变形分析系统。该软件操作简便,具有自动寻找焊缝,通过固有变形数据库自动导入焊接参数,自动施加约束条件,计算模块兼容性强等多项实用功能,从而满足现场工程人员要求。并以某大型船体分段焊接变形预测为例,验证了本软件系统的实用性和可靠性。     

Recent research on welding distortion prediction in thin plate fabrication by means of elastic FE computation

Elastic FE simulation with inherent deformation and interface element is an ideal and practical computational approach for predicting welding distortion in production of thin plate structures. In this study, recent researches on inherent deformation theory and welding induced buckling investigation of ship panel were sequentially introduced. Taking bead-on-plate welding as research objective (plate with 2.28 mm in thickness), integration approach with inherent strain was proposed to accurately and conveniently evaluate magnitude of inherent deformation. Also, average temperature to clarify the mechanism of influential effect of plate width on magnitude of inherent deformation was presented and examined. With the mechanism investigation of welding induced buckling by elastic FE analysis using inherent deformation, an application for predicting and mitigating the welding induced buckling in fabrication of ship panel with thin plates by employing different welding procedure patterns was carried out. Examined intermittent zigzag welding procedure is effective to reduce the magnitude of in-plane inherent shrinkages and control the possible welding induced buckling.