Mitigation of welding distortion and residual stresses via cryogenic CO2 cooling - a numerical investigation

Fusion welding remains the most common and convenient fabrication method for large, thinplate welded structures. However, the resulting tendency to out-of-plane distortion exacts severe design and fabrication penalties in terms of poorer buckling performance, lack of fairness in external appearance, poor fit-up and frequent requirements for expensive rework. There are several ways to mitigate welding distortion and this study concentrates on the use of cryogenic CO2 cooling to reduce distortion. A feasible combination of welding process and cooling parameters, was investigated computationally and the resulting effects on final deformation were predicted. Three different computational strategies were developed and applied to butt-welding and fillet-welding processes, with and without the inclusion of cryogenic cooling. In the first method, a fully transient, uncoupled thermo-elastoplastic model was investigated. This method is comprehensive but not readily applicable to predict welding distortions in complex, industrial-scale, welded structures, due to the large computational requirement. More computationally efficient models are needed therefore and two further models of this type are suggested in this study. The results show good agreement between the different models, despite substantial differences in computational budget. In butt-welded plates, a significant decrease in out-of-plane distortion is obtained when cryogenic cooling is applied. In fillet-welded plates, cooling had much less effect on welding distortion. This was largely due to the size and configuration of the test case assemblies and the fact that the attached stiffener greatly increased the overall stiffness and resistance to contraction forces

Stress analysis of corner welded joints structure by modern numerical-experimental approach

Otvoreni i zatvoreni tankozidi preseci imaju široku primenu u industrijskim aplikacijama za dizajn mnogih mašina i strukturnih komponenti. Ove komponente su često fabrikovane zavarivanjem, a ne livenjem ili kovanjem. Tankozidi profili su obično povezani pomoću ugaonih zavarenih spojeva. Takvi spojevi su takođe korišćeni u drugim inženjerskim aplikacijama kao što su građevinske mašine, mostovi, ramovi, šasije vozila i dr.. U ovoj disertaciji ponašanje zatvorenih profila (kutija, okrugla cev) i otvoreniih profila (L, Z, C i K profili) šavnih profila, proučavani su tako što su izlagani statičkim opterećenjima i numeričko-eksperimentalnim pristupom. Sa tačke gledišta strukturne analize, uprkos široko rasprostranjenim ugaono zavarenim spojevima koji efikasno nose opterećenja na elementima, ne postoji praktičan, jednostavan i precizan pristup za njihov dizajn i analizu. U tu svrhu , inženjeri često moraju pripremiti relativno komplikovan model konačnih elemenata ploče ili zapremine. To je zato što navedeni eleementi izloženi opštim opterećenjima proizvode koncentracije napona u blizini spojeva. Jedan od doprinosa ovog istraživanja je bolje razumevanje ponašanja ugaono zavarenih spojeva izloženi naprezanju savijanja i naprezanja savjanja sa uvijanjem. Primena metode konačnih elemenata predstavlja osnovni numerički pristup. Posmatrani profili su medelilrani različitim konačnim elementima (greda, ploča i zapremina) i sa različitim slučajevima opterećenja. Primećuje se da na kratkom rastojanju od spoja putem ugaono zavarenih spojeva struktura nosećeg elementa pod izloženim opterećenjem ponaša se kao greda. Zavareni spojevi su generisani različitim tehnikama modelrianja sa primenom različitih tipova i veličina konačnih elemenata elemenata. Kompletni rezultati deformacija su, takođe, eksperimentalno dobijeni pomoću tehnike primene korelacije digitalne slike (DIC). Eksperimentalni testovi se izvode za proveru numeričkih simulacija u cilju ispitivanja mehaničkih performansi zavarenh spojeva izloženi kombinovanim opterećenjima. Rezultati numeričkog prroačuna pokazuju dobro slaganje sa eksperimentalnim rezultatom .Hollow and non hollow section members are widely used in industrial applications for the design of many machine and structural components. These components are often fabricated by welding rather than by casting or forging. For example, in agricultural machinery, the hollow tubes are typically connected together through welding to form a corner welded joints. Such joint connections are also employed in other engineering applications such as construction machinery, offshore structures, bridges, and vehicle frames. In this dissertation, the behavior of tubular (box and circle profile) and non tubular (L, Z, C and X profiles) joint connections profiles, subjected to static loads were studied both experimentally and numerically. From a structural analysis point of view, despite of the wide use of corner welded joints as efficient load carrying members, there is no available practical, simple and accurate approach for their design and analysis. For this purpose, engineers must often prepare relatively complicated and time consuming Finite Element models made up of shell or solid elements. This is because unlike solid-section members, when hollow section members are subjected to general loadings, they may experience severe deformations of their cross-sections that results in stress concentrations in the connection’s vicinity. One of the objectives/contributions of this research work is the better understanding of the behavior of the corner welded joint connections under out-of- plane bending and torsion loading conditions. Through a detailed Finite Element Analysis (FEA) using shell and solid elements, the stress distribution at the connection of the tubular and non tubular corner welded joints were obtained for different loading conditions. It is observed that at a short distance away from the connection of the corner welded joints, the structure behaves similar to beams when subjected to loadings. Finite element models with different modeling techniques and meshing with various size and types of elements were created and analyzed. The full displacement field results were obtained experimentally by using the digital image correlation (DIC) technique. Experimental tests were performed to validate numerical simulations in order to investigate the mechanical performance of a series of fillet-welded connections under combined loading. The full displacement field results show good agreement comparing with the experimental results..

On the use of the Peak Stress Method for the calculation of Residual Notch Stress Intensity Factors: a preliminary investigation

Residual stresses induced by welding processes significantly affect the engineering properties of structural components. If the toe region of a butt-welded joint is modeled as a sharp V-notch, the distribution of the residual stresses in that zone is asymptotic with a singularity degree which follows either the linear-elastic or the elastic-plastic solution, depending on aspects such as clamping conditions, welding parameters, material and dimension of plates. The intensity of the local residual stress fields is quantified by the Residual Notch Stress Intensity Factors (R-NSIFs), which can be used in principle to include the residual stress effect in the fatigue assessment of welded joints. Due to the need of extremely refined meshes and to the high computational resources required by non-linear transient analyses, the R-NSIFs have been calculated in literature only by means of 2D models. It is of interest to propose new coarse-mesh-based approaches which allow residual stresses to be calculated with less computational effort. This work is aimed to investigate the level of accuracy of the Peak Stress Method in the R-NSIFs evaluation

On creep-fatigue endurance of TIG-dressed weldments using the linear matching method

This paper is devoted to parametric study on creep-fatigue endurance of the steel type 316N(L) weldments at 550◦C identified as type 3 according to R5 Vol. 2/3 procedure classification. The study is implemented using a direct method known as the Linear Matching Method (LMM) and based upon the creep-fatigue evaluation procedure considering time fraction rule for creep-damage assessment. Seven configurations of the weldment, characterised by particular values of a geometrical parameter ρ, are proposed. Parameter ρ, which represents different grades of TIG dressing, is a ratio between the radius of the fillet of the remelted metal on a weld toe and the thickness of welded plates. For each configuration, the total number of cycles to failure N⋆ in creep-fatigue conditions is assessed numerically for different loading cases defined by normalised bending moment ˜M and dwell period t. The obtained set of N⋆ is extrapolated by the analytic function dependent on ˜M, t and parameter ρ. Proposed function for N⋆ shows good agreement with numerical results obtained by the LMM. Therefore, it is used for the identification of Fatigue Strength Reduction Factors (FSRFs) effected by creep, which are intended for design purposes, and dependent on t and ρ

Seismic Performance of Steel Pipe Pile to Cap Beam Moment Resisting Connections

INE/AUTC 13.0

Finite element analysis of fillet welded joint

T-joint fillet welding is the most common welding in engineering applications. Transport vehicles, marine ships, mobile plant equipment are few examples where fillet welding are used extensively. Analysis of welded structures are still remains a challenge for the designer to produce desired output results. In welding process rapid heating and cooling introduced residual stress and geometrical deformations. Heat effected zone play pivotal role in determining the strength of a welded joint which changes the properties of parent material and reduce the strength after welding operation. There are many case which structures are continuously under cyclic loading when the fatigue life of the welded joints are a major design consideration. The aim of this project is to analyse the normal stress and fatigue life of fillet welded joints using computer modelling and experiments. Finite element based tool ANSYS Workbench 15.0 was been used to analyse the normal stress and the fatigue life under cyclic loading. Computer model of the joint developed using three different types of material which was parent metal, heat affected zone metal and weld metal. Experimental tests were carried out at USQ laboratory on double side welded T-joints. Grade 250 Structural steel was used to prepare specimen and gas metal arc welding (GMAW) process applied to welding the joints. The ultimate purpose of the project has been achieved with developing techniques of the finite element analysis of fillet welded joint. The experimental investigation validate the performance of the FEA analysis results were found 1.2% error on tensile test. The experiment yield stress was found 263.4 MPa and simulation yield stress at the same location appears 266.7 MPa. In order to calculate fatigue life of welded joint used iterative process to define stress at one million cycle. The analysis found 274 MPa stress and 7740 cycle fatigue life applying yield load. After reduced load at 12kN and found the fatigue life one million cycle where shows 88 MPa stress which is 35% of yield stress. So that designer can consider 35% of yield strength when design structure for fluctuating and repeated loading conditions

Review of recent advances in local approaches applied to pre-stressed components under fatigue loading

Fatigue strength of mechanical components in the high cycle regime depends on both the applied loading and the intensity of any residual stress field induced by either non-homogeneous plastic deformation or the solidification of a local portion of material due to welding operations. In presence of geometric variations that are amenable to being modelled as a sharp V-notch, the residual stress distribution near the notch tip is singular and follows the same form as the solution obtained by Williams in 1952 where the intensity of the asymptotic stress field is quantified by the notch stress intensity factor (NSIF). However, the residual stress varies during fatigue loading and a stable value may be reached. Numerical models have been developed for the calculation of the residual NSIFs and their variation under fatigue loading. Taking advantage of these models, new local approaches have also been recently developed which are able to predict the fatigue strength of pre-stressed notched components. The present paper provides a brief review of such recent advances

Symmetrical couple f-shaped notches with high rejection c-band of uwb patch antenna

The ultra-wideband (UWB) antenna is developed to cover a broad bandwidth. ‎The UWB radio systems are interfered ‎by the ‎same ‎spectrum ‎that shared with the local bands. In this paper, two F-shaped slots on a hexagonal patch UWB antenna are demonstrated ‎‎ to realize a high band rejection. The symmetrical couple F-slots is ‎notched on the hexagonal UWB ‎ ‎patch antenna to avoid the interference ‎and ‎‎enhance the notching results at C-band. The demonstrated ‎antenna employs a coplanar waveguide ‎(CPW) technique to meet a fractional bandwidth of 126%. The proposed method validates ‎several ‎‎reconfigurations of the F-slot location on the demonstrated design. Six steps ‎parametric study are considered to test the slots location. The results of the proposed antenna with slots are introduced based on analytical, simulation, and ‎measurement. The total design size ‎‎28 mm × 43 mm × 1.6 ‎mm is simulated by ‎using CST Microwave Studio. The two F-slots are achieved the antenna gain of -6 dB, ‎return loss of -1.2 ‎dB, and ‎VSWR of 15.2 at the rejected band of 4 GHz. The ‎measurement results are compared with the simulation results between the three ‎prototypes. The current ‎distribution on the design is discussed at 2.88 GHz and 4 GHz frequencies. The radiation patterns illustrate ‎omnidirectional of H-plane and bidirectional of E-plane. This paper validates the slots locations to enhance the notches performance and reduce the interference