Study on the preciseness of hot spot stress of web-stiffened cruciform welded joints derived from shell finite element analyses

A new simple and accurate shell FE-based structural Hot Spot Stress (HSS) determination method for web-stiffened cruciform joints has been proposed. Local stress of welded joints in full-scale bulk carrier (BC)’s lower stool models subject to bending and pressure loadings are examined. HSSs determined by the proposed method are compared with those derived by Lotsberg’s method and the conventional 0.5t-1.5t extrapolation. As results, following are found:

(1)

The local stress of full-scale BC lower stool models with various stool angle and plate thickness can be calculated accurately solely from shell FE results by means of the proposed method.

(2)

HSSs of welded joints in full-scale BC lower stool models subject to bending and pressure loadings derived by the proposed method show good agreement with the target HSSs determined from fine solid models. This demonstrates the validity of the proposed method for actual ship structures under the real load.

(3)

The excessive safety allowance of HSS determined by the conventional 0.5t-1.5t extrapolation can be reduced substantially by adopting Lotsberg’s method or our proposal. The proposed HSS determination method gives more accurate estimates compared to Lotsberg’s method under the conditions chosen, and the application range of the proposed method is equal to or wider than Lotsberg’s method.

     

Modeling and analysis of thin-walled Al/steel explosion welded transition joints for shipbuilding applications

The study presents an analysis of S355J2+N steel and AA5083 aluminum alloy welded structural joints using explosion welded transition joints of reduced thickness. The transition joint thickness reduction significantly hinders the welding of the joints due to the risk of damage to the Al/steel interface as a result of the high temperatures during welding. Numerical modeling of the welding process is performed to determine safe welding parameters for the transition joint. The numerical analysis is supported by measurements of the temperature areas by a thermographic method. Welded structural joints are analyzed to determine the welding influence on the mechanical properties and microstructure of the transition joints. On this basis, a number of tests are carried out, including microhardness distribution measurements, strength tests of joints in two welding configurations and strength tests of the microspecimens of transition joints. Moreover, an experimental and numerical analysis of strain and stress distributions is carried out in combination with the use of the finite element method and digital image correlation, which allow us to identify the critical areas of the joints with regards to their strength. The results of the microstructural and strength tests carried out using macro- and microspecimens show softening of the aluminum alloy layers. However, the AA5083 and AA1050 layer softening as a result of welding did not reduce the load capacity of the transition joints, which could determine the strength of the dissimilar Al/steel welded structural joints.     

T型焊接结构的角变形控制

T型焊接在船舶结构中的应用是非常广泛的.T型接头附近局部的加热及冷却使被焊结构产生残余应力及角变形.目前在船厂精度控制中,通常采用构件焊接后对某些部位进行火工校正的方法来控制残余角变形.论文提供了另外一种有效控制结构残余角变形的方法:对结构焊前施加弹性的反向角变形.文中首先利用热弹塑性有限元来模拟未施加反变形的结构的焊接过程,以估算残余角变形;然后模拟施加了弹性反变形的结构的焊接过程,并计算此时结构的残余角变形,以最终确定构件所需要的弹性反向角变形值.施加了弹性反向角变形的构件在焊接后无需进行火工校正.     

大型核电厚壁结构X射线衍射法残余应力测试

采用X射线衍射法（ XRD）对大型核电厚壁结构堆芯板端面、堆芯板与吊篮筒体环焊缝焊前焊后残余应力进行无损测量。研究堆芯板端面、环焊缝焊前焊后残余应力的分布情况及变化规律。结果表明：堆芯板焊前残余应力主要是机加工应力,且焊接过程对其残余应力影响不大;1＃和2＃堆芯板环焊缝轴向残余应力分布趋势明显,呈现焊缝为压应力,母材为拉应力;测试的环向应力在各区域分布不一致;焊接对远离焊缝区域的应力没有影响,远离焊缝区域呈现较大的加工应力。     

Fatigue crack growth behaviour of A5083 series aluminium alloys and their welded joints

We investigated the difference in fatigue behaviour between the aluminium alloys A5083-O and A5083-H321, which are used as structural components in ships and high speed craft. We obtained S–N curves for the base materials and the welded joints made of A5083-O. The relationships between the fatigue crack propagation rates and the stress intensity factor ranges ΔK, ΔK _eff and ΔK _RPG (Toyosada et al. in Int J Fatigue 26(9):983–992, 2004) were determined. Additionally, the evolution of fatigue crack growth for the base materials and the welded joints made of A5083-O was measured. We also carried out numerical simulations of fatigue crack growth for both base metals and their welded joints made of A5083-O. The difference in fatigue crack growth behaviour for each alloy and the validity of the numerical simulations of fatigue crack growth based on the RPG stress criterion (Toyosada et al. 2004) in the base materials and their welded joints was investigated.     

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.     

Numerical simulations of fatigue crack initiation and propagation based on re-tensile plastic zone generating load criterion for in-plane gusset welded joints

Many accidents are caused by fatigue in welded built-up steel structures, and so it is important to estimate the fatigue lives of such structures quantitatively for safety reasons. By assuming that fatigue cracks cannot grow without an accumulation of alternating tensile/compressional plastic strain, one of the authors identified an improved effective stress intensity factor range ΔK _RPG based on the re-tensile plastic zone generating (RPG) load, which represents the driving force for fatigue cracks, and suggested that ΔK _RPG should be used as the parameter to describe fatigue crack growth behavior. The “FLARP” numerical simulation code in which ΔK _RPG is implemented as the fatigue crack growth parameter, was developed in order to predict fatigue crack initiation and propagation behavior. In this paper, it is demonstrated that FLARP gives accurate estimates for fatigue life by comparing the estimated fatigue crack growth curves and S–N curves with the experimental results for in-plane gusset welded joints, which are used in many welded steel structures. Moreover, the effect of induced bending moment due to the linear misalignment in the out of plane direction on the fatigue strength of in-plane gusset welded joints is investigated through numerical simulations.     

预测船体分段焊接变形方法概述

船体分段在焊接过程中产生的焊接变形会使船体结构强度降低,精确预测和控制焊接变形是现代造船工艺的要求.焊接变形分析方法包括实验法、解析法、数值分析法、等效载荷法等,常用的是后两种方法.数值分析法采用热弹-塑性有限元模型精确模拟焊接现象,但计算工作量大;等效载荷法计算焊接区域的固有应变,并将其转化为等效载荷,进而应用弹性有限元分析求得整个结构的焊接变形.     

船用脱硫装置特种不锈钢管焊接工艺设计

通过研究船用脱硫装置设计及材料特性,结合项目产品特点及现有资源,设计3种船用脱硫装置特种不锈钢管焊接工艺.为确保新焊接工艺满足设计要求,体现实用性和经济性,对焊接方法、焊材种类进行遴选,并进行焊接试验以优化各项焊接参数.试验结果表明,管材焊接接头的各项性能满足设计及规范要求,新焊接工艺通过评定并得到船级社认可.经实船应...     

厚钢板焊接线能量和板厚与CTOD之间的回归分析

依据相关规范对海洋平台用EQ70、EQ56低合金调制高强度厚钢板焊接接头进行低温(-10℃)裂纹尖端张开位移(CTOD)韧度试验,对试验结果CTOD值与线能量和板厚进行回归分析,建立相应的回归数学模型,得到线能量、板厚对CTOD值的影响规律,对三者进行预报和控制,给出了焊接不同板厚所用线能量的上限值。     

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.     

等效热点应力法结合临界面法评估焊接接头多轴疲劳强度研究

基于焊缝本身引起的非线性分布应力自平衡的性质,在板厚方向应力峰值零点位置定义等效热点应力,结合基于临界面法的MWCM法建立评估复杂焊接接头多轴疲劳强度的方法。采用数值计算分析零点位置的变化规律,建立零点位置拟合方程。利用公开发表的试验数据以及现有的热点应力法有限元计算结果对等效热点应力法进行精度验证。结果表明,等效热点应力法和现有的热点应力法具有很好的一致性,能在一定程度上考虑厚度效应对疲劳强度的影响,可以评估多轴疲劳强度。     

船用不锈钢管道焊接技术研究

本文通过对船用不锈钢管道的使用环境及特殊要求的分析,提出了船用不锈钢管道焊接的技术、方法和焊接的工艺参数,实践证明这些方法可获得高质量的焊接接头,能够满足焊接工程质量。     

铜管路件焊缝致密度检验方法研究

铜管路件主要由铜管及三通接头焊接而成,焊接的质量对水冷系统有很大的影响。本文研究了铜管路件焊缝致密度的检验方法,介绍了铜管路件焊接方法、影响焊接质量的各种因素及焊接工艺过程。提出了铜管路件焊缝致密度检验方法,该方法首先对检验样本进行制备,接着通过由光学显微镜与计算机组成的成像系统对样本焊缝位置进行显微图像采集,对采集到的焊缝显微图像在图像软件中进行处理,获取焊缝缺陷的长度,从而计算焊缝位置的致密度。     

12毫米厚铝合金板的搅拌摩擦焊研究(英文)

Most of the investigations regarding friction stir welding(FSW)of aluminum alloy plates have been limited to about 5 to 6mm thick plates.In prior work conducted the various aspects concerning the process parameters and the FSW tool geometry were studied utilizing friction stir welding of 12 mm thick commercial grade aluminum alloy.Two different simple-tomanufacture tool geometries were used.The effect of varying welding parameters and dwell time of FSW tool on mechanical properties and weld quality was examined.It was observed that in order to achieve a defect free welding on such thick aluminum alloy plates,tool having trapezoidal pin geometry was suitable.Adequate tensile strength and ductility can be achieved utilizing a combination of high tool rotational speed of about 2000 r/min and low speed of welding around 28 mm/min.At very low and high dwell time the ductility of welded joints are reduced significantly.     

Prediction and mitigation of out-of-plane welding distortion of a typical block in fabrication of a semi-submersible lifting and disassembly platform

Out-of-plane welding distortions of block structures during fabrication of offshore structure will significantly influence its dimensional accuracy and production schedule. Taking a B514 block of a semi-submersible lifting and disassembly platform as research object, typical welded joints and their welding conditions were summarized based on actual welding procedure specification (WPS). Effective thermal elastic plastic (TEP) finite element (FE) analysis with parallel computation technology was carried out to examine thermal-mechanical response. Welding inherent deformations, which are considered as the elementary cause of welding distortion, were then evaluated. With welding inherent deformations as mechanical loading, elastic finite element (FE) analysis was then employed to predict dimensional accuracy of examined B514 block, which has a good agreement with measurement data. In order to ensure the fabrication accuracy with less out-of-plane welding distortion, inverse deformation approach was applied to reduce the out-of-plane welding distortion, and influence of welding sequence on out-of-plane welding distortion was also examined. Both mitigation practices have obvious effect on dimensional accuracy of examined B514 block, while corresponding mechanical mechanisms were also clarified.     

F550Z海洋平台用钢SAW焊接接头低温韧性研究

为研究大热输入条件下埋弧自动焊（ submerged arc welding ,SAW）对海洋平台用550 MPa钢焊接接头组织与低温韧性的影响,采用50 kJ＆#183; cm-1的焊接热输入,测定接头各区域冲击吸收功,并观测各区断口形貌及显微组织．结果表明：焊接接头韧性从焊缝到母材,呈现先降低后升高的趋势,最低处在熔合线及熔合线2 mm处．焊缝处组织为针状铁素体加细小弥散的碳化物,断口形貌为韧窝和解理台阶,-60℃冲击吸收功为110 J．熔合线及熔合线2 mm处断口形貌基本相同,只由放射区组成,无纤维区,微观特征为大面积的解理面,没有韧窝;微观组织为粗大粒状贝氏体,冲击吸收功非常低只有25 J．熔合线5 mm处断口纤维区面积较大,微观形貌含有大量的韧窝,微观组织为细小的铁素体、碳化物及粒状贝氏体,该区为焊接接头的正火区,具有优异的低温韧性,-60℃冲击吸收功为202 J．     

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.     

Influence of the welding sequence on residual stress and distortion of fillet welded structures

T-joints are one of the most common welded joints used in the construction of offshore structures, including ships and platforms. In the present study, a sequentially coupled thermo-mechanical finite element model that considers temperature-dependent material properties, high temperature effects and a moving volumetric heat source was used to investigate the effect of welding sequence on the residual stresses and distortions in T-joint welds. The parameters of Goldak's double ellipsoidal heat source model were predicted using a neural network. The numerical models were successfully validated by the experimental tests. The results show that the welding sequences have significant effects on the residual stresses and distortions, both in the magnitude and distribution mode. The optimization of the welding sequences should be investigated numerically or experimentally before the construction welded structure.     

固有变形计算方法及其在船舶焊接结构变形中的应用

采用基于固有应变法的弹性有限元分析预测大型复杂结构的焊接变形的前提是必须已知焊缝附近的固有变形。结构的焊接残余应力与焊接变形取决于其接头的固有变形大小及分布,因此开发精确计算接头固有变形的方法,并依此建立一个完善的固有变形数据库对于大型复杂结构焊接变形的预测有重要意义。文中提出了几种计算固有变形的方法包括公式法、热弹塑性有限元法、实测法,并分别采用这几种方法对典型T型接头的横向固有收缩与纵向固有收缩进行计算,三种方法得到的结果比较一致。在此基础上,进一步以典型船体结构为研究对象,采用依照这三种方法建立的固有变形数据库对其焊接变形进行预测,并与实测数据进行比较,验证了该数据库的有效性。