•A traction structural stress method is applied for fatigue analysis of OSD bridge.•Full-scale experimental data from independent research groups are studied.•The predicted fatigue lives match well ...with experimentally obtained fatigue lives.•The predicted failure modes agree well with the experimental results.•The results show that weld penetration affects fatigue failure mode.
In this study, a traction stress method is adopted for analyzing some of the unique fatigue behaviors observed in a series of recent experimental studies on rib-to-deck joints in orthotropic steel bridge decks. It is found that the traction-based structural stress definition is not only effective for describing the relevant stress state responsible for each of the four fatigue failure modes, but also mesh-insensitive in finite element computation. The latter attribute is essential for achieving a reliable evaluation of the most likely failure mode possible out of four typical failure modes for a given joint design (including exact weld dimensions) under specified loading conditions. As such, effective means of avoiding undesirable failure mode, e.g., Type 4 (i.e., weld root cracking), can be examined, e.g., by increasing either weld fillet size and/or weld penetration. Furthermore, the rib-to-deck joint fatigue test data investigated in this study are shown falling within the scatter band of the traction stress based master S-N curve adopted by ASME Div Code since 2007, implying that data transferability exists among these three sets of test data obtained independently by different laboratories.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This paper presents a recent study on weld residual stress relief mechanisms associated with furnace-based uniform post-weld heat treatment (PWHT). Both finite element and analytical methods are used ...to quantitatively examine how plastic deformation and creep relaxation contribute to residual stress relief process at different stages of PWHT process. The key contribution of this work to an improved understanding of furnace based uniform PWHT can be summarized as follows:(1)Plastic deformation induced stress relief during PWHT can be analytically expressed by the change in material elastic deformation capacity (or elastic deformation limit) measured in terms of material yield strength to Young's modulus ratio, which has a rather limited role in overall residual stress relief during furnace based uniform PWHT.(2)The most dominant stress relief mechanism is creep strain induced stress relaxation, as expected. However, a rapid creep strain development accompanied by a rapid residual stress reduction during heating stage before reaching PWHT temperature is shown to contribute to most of the stress relief seen in overall PWHT process, suggesting PWHT hold time can be significantly reduced as far as residual stress relief is concerned.(3)A simple engineering scheme for estimating residual stress reduction is proposed based on this study by relating material type, PWHT temperature, and component wall thickness.
•The paper clarified effects of plastic deformation and creep relaxation on weld residual stress relief during uniform PWHT.•Creep strain development is far more important than plastic strain, mostly completed even before hold time starts.•Plastic strain development is insignificant and be analytically described by a material elastic deformation capacity parameter.•An engineering estimation scheme is proposed for determining residual stress reduction resulted from furnace based PWHT.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In this study, we first present a general analytical method for calculating stress concentration factors in a cruciform connection containing either axial or angular misalignment between two ...intercostal members through an application of Castigliano's second theorem. As such, various end restraint conditions of interest in practice can be considered with ease. Such a solution method provides stress concentration factors at intersection location not only with respect to intercostal members, but also with respect to continuous members. A comprehensive set of SCF solutions, confirmed by finite element solutions, are then presented in tabular forms which can be used as supplements to the existing SCF solutions such as those given in BS 7910 and DNV-RP-C203 for performing fatigue and fracture assessment of welded connections. Some of the existing solutions are shown to be valid only under a narrower set of conditions than documented and some seem to be in significant error. As a further demonstration of the validity of the analytical approach presented in this paper, the same analytical formulation is applied for examining interaction effects between misalignments and fatigue testing conditions, resulting in significantly improved correlation of fatigue test data obtained as a part of this study.
•Presented a general analytical method for calculating SCFs resulted from joint misalignments.•Provided a comprehensive list of SCF solutions for cases of practical interest.•Demonstrated method's effectiveness in analyzing fatigue test specimens and data.•Detailed applicability of and limitations in existing SCF equations in literature.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The main objectives of the present study were the application and validation of the newly proposed Digital Image Correlation equivalent structural strain approach for assessing the low-cycle fatigue ...life of S235 welded joints. Low-cycle fatigue tests were performed at a displacement ratio of minus one. Experimental tests were performed using two different ways of controlling the displacement amplitude: applying traditional low-cycle fatigue tests at a constant amplitude and stepwise succession tests at increasing amplitudes. A comprehensive, independent experimental procedure, proposed by the authors and not yet validated for steel welded joints, was applied to assess the equivalent structural strain range using the Digital Image Correlation technique for the traditional low-cycle fatigue tests and stepwise succession tests at increasing amplitudes. It is noteworthy that the values of the DIC equivalent structural strain (ΔEs from the DIC), calculated on the external sides of the samples, were utilized to predict fatigue life in correlation with the ASME mean curve and fall within the ±3σ scatter bands (external bands). In particular, most of the tests lie within the ±2σ boundary of the design curves except for some tests at low applied displacements. Moreover, it was shown that this method is applicable to stepwise succession tests with increasing displacement amplitudes, leading to significant time savings compared to conventional experimental tests.
This paper presents a coupled shear localization model incorporating both pin/workpiece contact and three-dimensional (3D) heat flow environment generated by friction heating between tool shoulder ...and workpiece. It represents a significant improvement over an early shear localization model presented by the same authors (2014, 2015) which was focused on shear localization process in front of pin such that shear band development can be treated as a one-dimensional (1D) thermal viscoplastic problem, without considering shoulder/workpiece heating effects and contact interactions between pin and workpiece. The current model includes a novel analytical-based 3D transient heat flow solution incorporating detailed spatial resolution regarding heat generation at shoulder/workpiece interface, which provides a transient temperature environment within which shear localization process can now be examined in a greater detail. Also, contact interactions between pin and workpiece are now treated explicitly by introducing a classical contact mechanics solution for describing contact behavior between a cylinder (pin) and cylindrical cavity (surrounding base metal). This refined shear localization model has been shown capable of providing more realistic and reasonable estimations for both temperature and welding torque when compared with available experimental data. A robust numerical procedure has also been developed and implemented for determining optimum welding speed for a given combination of stir tool rotational speed and welding travel speed, which shows a good agreement with experimental results for a number of applications.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this study, the fatigue behavior of welded joints in an orthotropic steel bridge is simulated and analyzed. The traction structural stress method is proven to be more accurate and effective, and ...the predicted results agree well with the test results compared to traditional assessment methods, including the nominal stress, hot-spot stress, and effective notch stress methods. The traction structural stress concentration factor curves of welded joints under cyclic tensile and bending moment loading are obtained. The accuracy and validity of finite-element simulation methods for welded joints in orthotropic steel bridge are verified by comparing simulation results with full-scale tests results. Equivalent nominal stresses predicted by the master S–N curve method based on traction structural stress results agree well with the fatigue test results with small standard deviation. The fatigue behavior of orthotropic steel bridge analysis specifications Eurocode3 and GB50017 is combined with the traction structural stress method using unified traction structural stress concentration factor curves. This approach provides practical guidance for the fatigue behavior design of orthotropic steel bridges.
In this study, a numerical analysis model was established, on basis of the traction structural stress method, for fatigue failure mode prediction of orthotropic bridge deck (OBD) under symmetric ...three-point bending conditions. The structural stress-based criterion was validated by comparison with a collection of 64 test results. Fatigue failure modes are found to hinge on a dimensionless normalized constraint distance l/lcr that is related to specimen geometric dimensions and supporting arrangements. OBD specimens in symmetric three-point bending fatigue tests fail at toe-U-rib and external toe-deck as the actual constraint distance l is lower and higher than the critical constraint distance lcr where fatigue failure mode changed. The prediction power of the evaluation criterion is not affected by the fatigue load patch width in fatigue tests, U-rib profile shape, or weld penetrations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Adhesive-bonding has become increasingly adopted for multi-material lightweight applications (e.g., automotive structures). There is a growing interest in understanding the fatigue behaviors in this ...type of joint for supporting structural durability modeling in practice. In this paper, an analytical fracture mechanics modeling procedure is presented in the context of a generalized sandwich specimen. Its closed form stress intensity factor solutions were then derived and applied for the correlating fatigue test data obtained from the lap-shear and coach-peel test specimens with demonstrated effectiveness. Some important implications of these analytical solutions on joint design are also discussed.
A path-dependent maximum range (PDMR) cycle counting method is presented in this paper for performing fatigue evaluation of engineering components under variable-amplitude and arbitrary multi-axial ...conditions. For a given multi-axial time history, PDMR method can be used to reliably extract the following parameters that are important for modeling multi-axial fatigue damage:
(a)
Path-independent reference effective stress or strain ranges which are defined as distances in a mapped stress or strain space.
(b)
Path-dependent effective stress or strain ranges which are defined as path lengths in completing the corresponding reference stress or strain ranges in an incremental sense in the same stress or strain space.
(c)
Histogram of both path-independent reference effective stress or strain ranges and their corresponding path lengths that can be consistently used to measure out-of-phase induced fatigue damage in arbitrary multi-axial loading.
The effectiveness of PDMR method has been validated by its ability in correlating multi-axial fatigue data available in the literature. Its fracture mechanics basis is also illustrated. Under uniaxial loading conditions, PDMR method recovers exactly the same rainflow counting results.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This paper focuses on a series of new developments on analytical treatment of secondary stress concentration effects caused by the presence of angular and buckling distortions in thin plate ...structures. The distortion profiles are idealized through a simple mechanics treatment upon which the analytical solution to the stress concentration factor (SCF) induced by secondary bending is further derived. With such approach, the distortion effects on fatigue behaviors can be captured without the need for performing detailed finite element calculations incorporating measured distortions. The applications of these analytical solutions incorporating secondary bending caused by distortions and remote loading are demonstrated by analyzing existing test data obtained on small-scale thin plate butt joints containing local and global angular distortions. By considering the fatigue test data as well as measured distortion data, the use of so calculated SCFs not only enable an effective correlation among simple butt-welded specimens with various forms of angular and axial misalignments, but also between the tested specimens and the 2007 ASME master S-N curve scatter band which contain large-scale fatigue test data with plate thicknesses ranging from 5 mm up to over 100 mm.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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