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This work analyses the effect of residual stress shakedown and corrosion degradation on the ultimate strength assessment of a steel welded plate. The analysis is performed in several steps by the finite element method. In the first step, the heat source is defined as a moving heat source in order to simulate the welding processes and consequently t...
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Generation of residual stress and structure deformation are the most important problems in the process of structure welding. Residual stresses inside and around the welded joints are harmful for integrity and proper functioning of the welded part. Tensile residual stresses near the weld zone may cause in developing brittle fracture, reduction of fa...
High frequency mechanical impact (HFMI) is a post-weld treatment method for improving fatigue strength of welded joints. Much of the experimental research on fatigue performance of HFMI treated welded joints has concentrated on the beneficial compressive residual stresses created by the treatment and the fatigue strength of these joints under const...
Friction welding is a solid-state bonding process that presents itself as an interesting option as it generates less residual stress, less distortion, and crack formation when compared to the fusion welding process. The characteristics of this process also allow satisfactory welding of dissimilar materials, with good results in terms of mechanical...
Numerical simulations are powerful tool for analyzing and research in domain of mechanical constructions. In welded joints is very important to determine residual stresses and temperature distribution in sample, apropos, element of construction. For welded construction that are in exploitation is not possible doing experiments, so numerical simulat...
In this paper a numerical analysis of a T-joint fillet weld is performed to investigate the influences of different preheat temperatures and the interpass time on the longitudinal residual stress fields and structure deflections. In the frame of the numerical investigations, two thermo-mechanical finite element models, denoted M2 and M3, were analy...
Citations
... However, the plate ultimate strength can be reduced in intact conditions [36]. It was shown in [37] that, when the plate is subjected to multiple loading cycles (as it is in ship structures over a couple of years of operation), the residual stresses are released. This phenomenon is known as a shakedown effect. ...
The work presented here investigates the structural response of cleaned corroded plates, subjected to compressive load in the presence of a locked crack, where the change of mechanical properties as a result of corrosion development and the cleaning process is also accounted for. A Finite Element model for assessing the compressive strength, considering geometric and material nonlinearities, is developed, and the analysed plates are compared with the available experimental data. An experimental design plan is generated using the Design of Experiments techniques, which quantifies the influence of the governing variables and their interactions with respect to the plate's ultimate compressive strength. With a limited number of observations, the most significant effects are identified. The corrosion degradation is revealed to be the most crucial effect leading to an effective strength reduction. It was found that, in the case of a corroded plate with a locked crack subjected to a compressive load, the most severe case is when the crack is transversely oriented. The strength reduction is slightly lower than when the corrosion degradation and the presence of a crack are considered to be a simple summation of these two effects but acting separately. The outcome of the analysis is the development of several empirical formulations that allow a fast estimation of the ultimate strength of a corroded plate, subjected to compressive load in the presence of a locked crack, accounting for different cleaning.
... It should be pointed out here that the DoD, initial imperfections and material properties are not the only parameters that govern the strength reduction of the stiffened plate when corrosion degradation is present. The corrosion plate surface roughness [14] and residual stresses [6,22,23] can also significantly influence the reduction of the ultimate strength. ...
The objective of this work is to investigate numerically (using the non-linear FEM and the approach stipulated by the Common Structural Rules) the severe nonuniform corrosion degradation effect on the ultimate strength of stiffened plates and compare the results to the already published experimental works. Different factors governing structural behavior of corroded stiffened plates are investigated, such as corrosion degradation level, material properties, initial imperfections and boundary conditions. The numerically estimated ultimate strength demonstrated to be very close to those observed during the experimental test. A sensitivity analysis with respect to the most important governing parameters of the numerical estimation of the ultimate strength is also performed and several conclusions are derived. The applied calculation procedure avoids using of a pitted surface of the corroded plates and instead of that an equivalent thickness is applying leading to a relatively fast and practical approach for ultimate strength assessment of corroded stiffened plates.
... Instead of imposing the residual stresses in the numerical models, an indirect method of changing the material properties was used in the ultimate strength analysis of welded plate structures, in order to account for the residual stresses and corrosion degradation. 43,44 A similar strategy was also employed in the thick surface layer model proposed by Bäumel and Seeger, 45 which is able to estimate the stress-strain relationship and fatigue life of surface-strengthened cylinder components. It assumes that, with sufficient accuracy, the behaviour of the component can be described by only 2 parts, a case and a core cylinder. ...
... The approach introduced here is inspired by the work done by Tekgoz et al 43,44 and the thick surface model. 45 If a uniform residual stress exists in a specimen used in tensile tests, the stress-strain curve obtained from the specimen is different from that from a specimen without residual stress. ...
The impact of residual stresses on the fatigue crack initiation life of welded joints is evaluated by the finite element method. The residual stresses of nonload‐carrying cruciform joints, induced by welding and ultrasonic impact treatment, are modelled by initial stresses, using the linear superposition principle. An alternative approach of using modified stress‐strain curves in the highly stressed zone is also proposed to account for the residual stress effect on the local stress‐strain history. An evaluation of the fatigue crack initiation life of welded joints based on the local strain approach is carried out. The predicted results show the effect of residual stresses and agree well with published experimental results of as‐welded and ultrasonic impact treated specimens, demonstrating the applicability of both approaches. The proposed approaches may provide effective tools to evaluate the residual stress effect on the fatigue crack initiation life of welded joints.
... The time when the plate ultimate strength curve crosses the curve of hull girder stresses represents an optimal time for inspection [22]. The example shown in Fig. 2 is based on the actual thickness measurements of ships in service given in Ref. [23]. Other studies have been performed [22e24] to identify the most appropriate stress-strain curves accounting for the initial imperfection, corrosion degradation and residual stresses by modifying the stress-strain curve of perfect intact non-corroded material. ...
... It has to be pointed out here that the DOD is not the only parameter that governs the strength reduction when the non-uniform corrosion is present, but also many other factors such as initial imperfection (Tekgoz et al. 2012), boundary conditions and load effect (Garbatov et al. 2011), corrosion plate surface roughness (Silva et al. 2013), residual stresses (Tekgoz et al. 2013aTekgoz et al. , 2013bTekgoz et al. , 2014) and material properties change (Garbatov et al. 2014b) due to the corrosion degradation have an adverse effect on the ultimate strength. It is considered, for the tested stiffened plate specimens, that the remaining residual stresses after two pre-loading cycles are negligibly small and are not accounted for in the present analysis . ...
The objective of this work is to investigate experimentally and numerically the severe non-uniform corrosion degradation effect on the load carrying capacity of stiffened plates. Eight stiffened plates, which are initially corroded in real open sea conditions with different corrosion degradation levels, have been tested under compressive load. Different factors leading to a reduction of structural capacity have been investigated, including the material properties, degree of degradation, equivalent thickness and testing support conditions. The experimental results also showed to be very close to those estimated by the existing guideline procedure for a numerical evaluation of the ultimate strength, adjusted to be used for the severe corroded stiffened plates.
... The implementation of this approach to the finite element analysis has been discussed in detail in [24][25][26] (see Fig. 2). To find out the shape of the modified stress-strain curve an iterative procedure is developed. ...
This work analyses the effect of residual stress on the ultimate strength of a thin rectangular stiffened and single plate. The analysis is performed by the finite element method employing commercial software. The heat source is defined as a moving heat one in order to simulate welding processes and consequently the corresponding residual stresses. Three types of welding sequences have been conducted for the stiffened panel. A sensitivity analysis is performed accounting for the plate thickness, heat source, speed and level of residual stresses. Modified material stress strain curves have been developed accounting for the plate thickness that can be directly used in the non-linear finite element analyses of ultimate strength of thin plates.
... There exist today several commercial FE-codes that may be employed for detailed nonlinear simulations of the development of the temperature and stress fields present during welding. Lindgren (2001), Runesson et al (2003), Dong (2005) and Tekgoz et al. (2013) discussed methods for numerical simulation of the welding process taking into consideration actual thermal, mechanical and microstructure developments. The focus is on material modelling, coupling effects between thermal, mechanical fields and microstructure, numerical techniques and modelling aspects. ...
As-built welded ship structures retain internal residual stresses after being manufactured that affect the structural performance of ship's components like plates, stiffened plates or more complex structures. The operation of the ship subjects the structure and its components to alternate loading that releases these residual stresses, total or partially, under certain conditions. The objective of this work is to analyse the stress relief process under in-plane alternate loading and to establish a formulation suitable for application on simplified methods of ship's structural analyses. The residual stresses relaxation on unstiffened and stiffened plates is formulated and the correction to material stress-strain curves is presented for any stage of the relaxation process. The balance of energy during the relaxation process is estimated in order to allow the evaluation of initial residual stresses level. Finally it is presented the impact of residual stresses relief in the structural response of box girders under bending moment due to the application of several cycles of loading and unloading.
Ship structures are subjected to complex sea loading conditions, leading to a sophisticated structural design to withstand and avoid structural failure. Structural capacity assessment, particularly of the longitudinal strength, is crucial to ensure the safety of ships, crews, the marine environment, and the cargoes carried. This work aims to overview the ultimate strength assessment of intact ship structures in recent decades. Particular attention is paid to the ultimate strength of plates, stiffened panels, box girders, and entire ship hull structures. A discussion about numerical and experimental analyses is also provided. Finally, some conclusions and suggestions about potential future work are noted.
The objective of this work is to investigate the structural compressive response of plates with locked cracks accounting for all relevant factors and correlation between them. The nonlinear FE model considering both geometric and material nonlinearities is employed herein, and the FE model of the structural response of intact plates is validated with the available experimental data. In the common studies, based on One Factor at a Time analysis, some of the parameters and interactions between them are excluded. In the present study, the numerical investigations are conducted with the use of the Design of Experiments techniques, where all essential parameters and their interactions are adequately considered. With a total of 32 numerical analyses, the most influential factors and their interactions are identified. As a study outcome, empirical formulations, which allow for a fast estimation of the ultimate compressive strength of intact plates, plates with locked cracks, and repaired cracked plates, are derived. The developed formulations represent a fast and practical tool for estimating the ultimate compressive strength of intact, cracked, and repaired plates, which can be easily employed in the reliability analysis.
Biodiesel has recently received increasing attention because of many advantages such as higher cetane number and flash point compared to diesel fuel. However, corrosion of engine parts exposed to biodiesel or biodiesel-diesel fuel blends is still a critical challenge in the biodiesel industry. In the existing literature, there is still a lack of systematic studies including corrosion process in light alloy and changes in mechanical and fuel properties of engine parts (such as brass) after exposure to biodiesel. Therefore, in this study, (1) waste sunflower oil biodiesel (WSOB, B100) was supplied and blended with diesel fuel (B0) at the volume ratios of 10%, 20%, and 40 , which are called as B10, B20, and B40, as usual. The important fuel properties of the biodiesel-diesel fuel blends were also analyzed using ASTM test methods. (2) Corrosion characteristics of brass exposed to the biodiesel-diesel fuel blends were determined by means of a static immersion method at room temperature. (3) Mechanical properties of brass were investigated before and after the corrosion test. Finally, (4) variations in surface morphologies of the brass coupons were researched. According to the experimental results, the corrosion rate (0.3810 mpy) of brass exposed to B100 was found to be higher than that of brass exposed to B0 (0.1330 mpy) for the exposure duration of 960 hours. The Brinell hardness numbers (BHN) were determined as 406.265, 477.713, 541.983, 579.448, and 636.602 N/mm² while the tensile strengths (TS) were 1381.30, 1624.22, 1842.743, 1970.13, and 2164.45 MPa for B0, B10, B20, B40, and B100, respectively. BHN and TS values of B10 were closer to that of B0. Therefore, B10 was found to be a more suitable alternative to diesel fuel in terms of fuel property and corrosion characteristic. The results of this study can promote thermo-physical property collection for biofuels and guide for corrosion studies related to the industrial applications of diesel-biodiesel blends and pure biodiesel.
