Numerical analysis of residual stresses in welds of similar or dissimilar steel weldments under superimposed tensile loads

This paper presented the characteristics of residual stresses in welds of similar or dissimilar steel weldments by carrying out three-dimensional (3-D) thermal elastic–plastic finite element (FE) analyses. Moreover, residual stress behavior in welds of the weldments under superimposed tensile loads was further investigated. The materials used in this investigation were SM400, SM490, SM520 and SM570, widely used structural steels in welded structure. Results show that the maximum longitudinal residual stresses in welds of the similar steel weldments increase with increasing yield stress of the steel welded (SM400 < SM490 < SM520 < SM570). When tensile loads are superimposed to edges of the weldments, the maximum longitudinal residual stresses are increased to a higher value. In case of the dissimilar steel weldments, the difference between the longitudinal residual stresses in welds increases with increasing yield stress of the steel welded together with SM400 (SM490 < SM520 < SM570). When tensile loads are superimposed to edges of the weldments, same pattern is noted for the longitudinal stresses in welds and the difference is almost the same as that between the longitudinal residual stresses in welds.     

Through‐wall welding residual stress profiles for dissimilar metal nozzle butt welds in pressurized water reactors

This paper provides approximate expressions for through‐wall welding residual stresses in dissimilar metal nozzle butt welds of pressurized water reactors. An idealized shape of nozzle is proposed, based on which systematic elastic–plastic thermo‐mechanical finite element analyses are conducted by varying the thickness and radius of the nozzle and the length of the safe‐end. Based on the results, a through‐wall welding residual stress profile for dissimilar metal nozzle butt welds is proposed by modifying the existing welding residual stress profile for austenitic pipe butt welds in the R6 procedure.     

Crack resistance of austenitic stainless steel pipe and pipe welds with a circumferential crack under monotonic loading

This paper describes the experimental studies carried out on cracked austenitic stainless steel pipe and pipe welds under bending loads. Pipe welds were produced by gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW). Fracture resistance curves for pipe and pipe welds were compared. Results indicate that the fracture resistance of pipe and pipe weld (GTAW) is comparable but that of pipe weld (GTAW+SMAW) is inferior. Cracks do not deviate from their original plane during propagation as observed in the cases of carbon steel pipe and pipe welds. The fracture resistance of pipe welds does not depend on the loading histories to which it has been subjected prior to fracture test. Initiation and crack propagation were observed prior to the maximum moment. An existing limit load expression is applicable for the pipe base material but gives non‐conservative results for the pipe welds. Multiplication factors have been suggested for the pipe welds for evaluation of limit loads using the existing expression. Fracture resistance for the pipe and compact tension specimens have also been compared for base material and welds.     

缠绕线型对缠绕复合材料圆管轴向拉伸失效的影响

采用细观刚度模型的有限元分析（FEA）与改进的逐渐累积损伤方法相结合,建立了缠绕复合材料圆管轴向拉伸失效的分析方法与流程,以揭示缠绕线型对缠绕复合材料损伤失效的影响。对沿圆周方向分布有1个、3个和5个单胞的3种不同线型的缠绕复合材料圆管试件进行轴向拉伸破坏实验,获得其失效形式、平均拉伸强度及其随缠绕线型的变化规律。研究表明：缠绕复合材料圆管轴向拉伸失效主要以丧失承载能力的功能失效为主,缠绕线型对其拉伸强度有一定的影响;数值分析结果表明,轴向拉伸过程中,主要损伤为基体开裂与基纤剪切,纤维交叉容易引起损伤起始与扩展。     

Evolution of residual stresses with fatigue loading and subsequent crack growth in a welded aluminium alloy middle tension specimen

Neutron diffraction has been used to measure the evolution of the residual stresses in a VPPA welded Al-2024 alloy middle tension (M(T)) specimen with fatigue loading and subsequent crack growth. The measurements were carried out on the diffractometer ENGIN-X, a time-of-flight instrument, at the ISIS Pulsed Neutron Source. Fatigue crack growth was performed in situ and strain measurements averaged through the thickness of the specimen were made along two orthogonal directions as the crack grew, allowing the stresses in the specimen to be calculated assuming plane stress. 2D finite element simulation of the evolution of the initial residual stress field with crack growth, using an elastic model produced predictions that were in reasonable agreement with the experimental results. The results further indicate that some re-distribution of the residual stress field occurred due to the crack tip plasticity associated with the fatigue loading.     

Finite element analysis of stiffened laminated plates under transverse loading

A finite element model is developed to study the behavior of stiffened laminated plates under transverse loadings. Transverse shear flexibility is incorporated in both beam and plate displacement fields. A laminated plate element with 45 degrees of freedom is used in conjunction with a laminated beam element having 12 degrees of freedom for the bending analysis of eccentrically-stiffened laminated plates. The validity of the formulation is demonstrated by comparing with the available solutions in the literature. The numerical results are presented for eccentrically-stiffened layered plates having various boundary conditions and with stiffeners varying in number.     

FE analysis of residual stress relaxation in a girth-welded duplex stainless steel pipe under cyclic loading

This study intends to characterize the residual stress relaxation in a girth-welded duplex stainless steel pipe exposed to cyclic loading. FE thermal simulation of the girth welding process is first performed to identify the weld-induced residual stresses. 3-D elastic–plastic FE analyses incorporated with the cyclic plasticity constitutive model which can describe the cyclic stress relaxation are next carried out to evaluate reconstruction of the residual stresses under cyclic mechanical loading. The results unveils that considerable reduction of the residual stresses in and around the girth weld occur even after the initial few loading cycles and degree of the stress relaxation is dependent on the magnitude of applied cyclic loading.     

Interlaminar shear stresses in laminated composite plates under thermal and mechanical loading

The combined effects of thermal and mechanical loadings on the distribution of interlaminar shear stresses in composite laminated thin and moderately thick composite plates are investigated numerically using the commercially available software package MSC NASTRAN/PATRAN. The validity of the present finite element analysis is demonstrated by comparing the interlaminar shear stresses evaluated using the experimental measurement. Various parametric studies are also performed to investigate the effect of stacking sequences, length to thickness ratio, and boundary conditions on the interlaminar shear stresses with identical mechanical and thermal loadings. It is observed that the effect of thermal environment on the interlaminar shear stresses in carbon-epoxy fiber-reinforced composite laminated plates are much higher in asymmetric cross-ply laminate and anti-symmetric laminate compared to symmetric cross-ply laminate and unidirectional laminate under identical loadings and boundary conditions.     

Finite element simulation of the residual stresses in high strength carbon steel butt weld incorporating solid-state phase transformation

This paper presents a sequentially coupled three-dimensional (3-D) thermal, metallurgical and mechanical finite element (FE) model to simulate welding residual stresses in high strength carbon steel butt weld considering solid-state phase transformation effects. The effects of phase transformation during welding on residual stress evolution are modeled by allowing for volumetric changes and the associated changes in yield stress due to austenitic and martensitic transformations. In the FE model, phase transformation plasticity is also taken into account. Moreover, preheat and inter-pass temperature are included in the modeling process. Based on the FE model, the effects of solid-state phase transformation on welding residual stresses are investigated. The results indicate the importance of incorporating solid-state phase transformation in the simulation of welding residual stresses in high strength carbon steel butt weld.     

Stress intensity factors for surface fatigue crack in a round bar under cyclic axial loading

In this paper, the surface fatigue crack growth shape for an initial straight-fronted edge crack in an elastic bar of circular cross-section is determined through experiments under pure fatigue axial loading. Three different initial notch depths are discussed. The relations of the aspect ratio (b/c) and relative crack depth (b/D) are obtained, and it is shown that there is a great difference in the growth of cracks with different initial front shapes and crack depths. Further, using the three-dimensional finite element method, the stress intensity factors (SIFs) are determined under remote uniform tension loading. Since the relationship of b/c and b/D changes during the fatigue crack growth, the SIFs are determined for different surface crack configurations.     

Thermal residual stresses in metal matrix composites: A review

Recently, metal matrix composites (MMCs) have generated a considerable interest in the materials field because of their attractive physical and mechanical properties. However, during the fabrication of MMCs, thermal residual stresses are reportedly developed in the matrix as a result of the mismatch of the thermal expansion coefficients between the reinforcement and the matrix. It is well established that these residual stresses have a significant effect on the composite properties. For example, due to the presence of thermal residual stresses, it is almost never possible to achieve the maximum elastic response of the composites. In addition, yield stress and fracture toughness of the composites are significantly affected by thermal residual stresses. In this paper, a critical review of the published literature on thermal residual stresses in MMCs and their effect on composite properties are presented. Also, experimental and numerical techniques that are currently available to measure and estimate thermal residual stresses are reviewed and discussed.     

An analysis of fracture under biaxial loading using the non-singular T-stress

Finite element analysis using a two-dimensional modified-boundary-layer approach was used to model the effects of biaxial loading on crack tip stress fields. Loadings were applied corresponding to an elastic KI field, non-singular T-stress and a biaxial stress. For through-thickness cracks the T-stress inherent in the specimen geometry is augmented by the external biaxial stress. For surface-notched specimens the biaxial stress acts out of the crack plane. This effect was modelled with generalized plane strain elements. Results were analysed using the Anderson-Dodds approach for cleavage and the Beremin model in the ductile regime. Biaxial loading is predicted to have a large effect on the toughness of a through-thickness crack but little effect on a surface crack. Experimental results from a previous series of large-scale biaxial fracture tests are generally consistent with these predictions.     

Numerical evaluation of temperature fields and residual stresses in butt weld joints and comparison with experimental measurements

This paper presents a novel numerical model, based on the finite element (FE) method, for the simulation of a welding process aimed to make a two‐pass V‐groove butt joint, paying attention on the prediction of residual stresses and distortions. The ‘element birth and death’ technique for the simulation of the weld filler supply has been considered within this paper. The main advancements with respect to the state of the art herein proposed concern: (i) the development of a modelling technique able to simulate the plates interaction during the welding operation when an only plate is modelled. This phenomenon is usually neglected in literature; (ii) the heat amount is supplied to the FEs as volumetric generation of the internal energy, allowing overcoming the time‐consuming calibration phase needed to use the Goldak's model, commonly adopted in literature. Predicted results showed a good agreement with experimental ones.     

The safe-end length effect on welding residual stresses in dissimilar metal welds of surge nozzles

The effects of safe-end length and kinematic boundary conditions during welding on weld residual stresses in dissimilar metal welds are systematically investigated using finite element analyses for typical pressurized water reactor surge nozzle configurations. The study is generalized by idealizing complex nozzle geometries as straight pipes with two welds. The impact of these variables on axial residual stresses at inner surface is examined, since these are of most concern for primary water stress corrosion cracking. Possible mechanisms controlling the development of welding residual stresses are used to qualitatively explain the predicted behavior.     

Fatigue crack propagation of through cracks in thin sheets under combined traction and bending stresses

ABSTRACT Fatigue crack propagation tests of through cracks in 3 mm thick aluminium alloy 6013‐T6 plates, under combined membrane and bending stresses were carried out. Five different values for the ratio of bending to membrane stresses, SB, were examined: 0, 0.55, 1.25, 1.8 and 2.23. Firstly, the results were elaborated by taking into account only the membrane stress and the front dimension of the crack for the evaluation of the stress intensity factor range. The results relevant to the lower SB values, evaluated in this mode, show good agreement with the results obtained when only the membrane stress was applied, while the results obtained at the higher SB values exhibit a remarkable increase in the crack propagation rate. The results were successively evaluated on the basis of tabular stress intensity factor solutions available in the literature; the agreement between the predicted and the experimental data occurs when mean values of stress intensity factor, rather than local values, were used at the back face of the plate, i.e., the face where the bending produces a compressive stress, to counteract the high gradient of stress intensity factor present in this area.     

Notch fatigue life prediction considering nonproportionality of local loading path under multiaxial cyclic loading

An innovative numerical methodology is presented for fatigue lifetime estimation of notched bodies experiencing multiaxial cyclic loadings. In the presented methodology, an evaluation approach of the local nonproportionality factor F for notched specimens, which defines F as the ratio of the pseudoshear strain range at 45° to the maximum shear plane and the maximum shear strain range, is proposed and discussed deeply. The proposed evaluation method is incorporated into the material cyclic stress‐strain equation for purpose of describing the nonproportional hardening behavior for some material. The comparison between multiaxial elastic‐plastic finite element analysis (FEA) and experimentally measured strains for S460N steel notched specimens shows that the proposed nonproportionality factor estimation method is effective. Subsequently, the notch stresses and strains calculated utilizing multiaxial elastic‐plastic FEA are used as input data to the critical plane‐based fatigue life prediction methodology. The prediction results are satisfactory for the 7050‐T7451 aluminum alloy and GH4169 superalloy notched specimens under multiaxial cyclic loading.     

双轴载荷下复合材料十字型试样几何形状对中心测试区系数的影响

基于双轴拉伸载荷下复合材料十字型试样的设计特点,对比分析了不同几何形状的十字型试样在不同厚度比和载荷比条件下中心测试区应力集中系数和承力系数的变化规律,并开展了不同载荷比的双轴拉伸实验进行验证。研究表明:十字型试样中心测试区系数与载荷大小无关,与试样几何形状、厚度比及载荷比有关;等宽加载臂宽度越小、厚度比越大,应力集中系数越小,载荷比不同,应力集中系数也不同;一般而言,中心测试区承力系数随厚度比增加而增大,x向承力系数βx随载荷比增加呈非线性增大,y向承力系数βy随载荷比增加呈线性减小;在双轴拉伸载荷条件下,形状D十字型试样在载荷比f=4/1时中心测试区y向应力分量为负值,表现为压应力状态。     

Fully plastic J-integral solutions for surface cracked plates under biaxial loading

In this paper, surface cracked plates under biaxial tension are studied. Three-dimensional elastic-plastic finite element analyses have been carried out to calculate the J-integral for surface cracked plate for a wide range of geometry, biaxiality and material properties. Fully plastic J-integral solutions along the front of the surface cracks are presented for Ramberg-Osgood power law hardening material of n = 3, 5, 10 and 15. Geometries considered are a/c = 0.2, 1.0 and a/t = 0.2, 0.4, 0.6 and 0.8 and the biaxial ratios of 0, 0.5 and 1. Based on these results, the J-integral along the crack front for general elastic-plastic loading conditions can be estimated using the EPRI scheme. These solutions are suitable for fracture analyses for surface cracked plates under biaxial loading.     

复合材料π接头拉伸力学性能的试验和计算研究

采用试验和数值模拟的方法对整体化复合材料π接头在拉伸载荷作用下的力学特性进行研究。在Instron 8803电液伺服材料试验机上进行了π接头试验件的拉伸试验,记录试验过程中损伤产生及破坏过程,记录初始失效载荷和最终失效载荷。试验结果表明,填料是π接头破坏的关键部位,需要进行深入研究。提出了复合材料π接头力学性能数值模拟的基本假设和方法,基于通用有限元商用软件,建立π接头三维力学分析模型,获得π接头各部位应力分布情况;基于基本假设,对最大应力失效准则进行修正,并给出π接头各部位损伤载荷的预测值。计算预测π接头的初始损伤部位与试验吻合,初始失效载荷计算值与5个试件试验数据均值相比误差为0.53%,表明了数值分析方法的可行性。     

碳纳米管增强镁基复合材料热残余应力的有限元分析

为了探寻Ni层厚度对镀镍碳纳米管增强AZ91D镁基复合材料(Ni-CNTs/AZ91D)中热残余应力的影响, 在实验基础上, 建立不同Ni层厚度时Ni-CNTs/AZ91D复合材料的有限元模型, 模拟了Ni-CNTs/AZ91D复合材料中热残余应力的分布。研究发现: 在碳纳米管表面镀镍能够明显降低Ni-CNTs/AZ91D复合材料中的热残余应力。Ni-CNTs/AZ91D复合材料中, 热残余应力在Ni层厚度为6nm时最小; Ni层厚度由2nm增至6nm时, 热残余应力随着Ni层厚度的增加而减小; 当Ni层厚度超过6 nm时热残余应力随着Ni层厚度的增加而增大。复合材料中热残余应力的最大值随碳纳米管表面Ni层厚度的增加向Ni层与基体的界面移动。