•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.
This paper presents a novel pressure-dependent velocity boundary condition based on wear theory according to our former work, which provides an explainable perspective in understanding the physics of ...periodic time scale sliding-to-sticking transition condition and shear layer formation, as well as quality weld/void defects formation, during friction stir welding/self-reacting friction stir welding using computational fluid dynamics model. With this newly developed boundary condition, effects of welding speed and rotation speed on the weld cross-section geometry can be robustly captured. Furthermore, different cases of quality weld and void defects formation are validated with shear localization model. In both shear localization model and computational fluid dynamics model with pressure-dependent velocity boundary condition, the rationale and physical explanation of quality weld/void defects formation, as well as tool-workpiece sliding-to-sticking transition behavior, are investigated and compared: The pressure-dependent velocity boundary condition describes the relationship between weld pitch and applied velocity boundary from geometrical restrictions, and shear localization model captures transient shear layer formation within one pin revolution from one-dimensional standpoint; the pressure-dependent velocity boundary condition accounts for the time-averaged transitioning from pure sliding to full sticking during each shear layer generation and deposition cycle, whereas the shear localization model directly describes the transition from sliding to full sticking at pin/workpiece interface during each tool revolution. It is worth noting that the shear layer itself is not explicitly captured in computational fluid dynamics model due to continuity, instead the equivalent effects and movement of periodic shear layer are described and modeled. The importance of shear layer that forms during each tool revolution in periodic weld formation mechanism is emphasized in both pressure-dependent velocity boundary condition of computational fluid dynamics model and shear localization model.
Corrosion and crack defects often exist at the same time in pipelines. The interaction impact between these defects could potentially affect the growth of the fatigue crack. In this paper, a crack ...propagation method is proposed for pipelines with interacting corrosion and crack defects. The finite element models are built to obtain the Stress Intensity Factors (SIFs) for fatigue crack. SIF interaction impact ratio is introduced to describe the interaction effect of corrosion on fatigue crack. Two approaches based on extreme gradient boosting (XGBoost) are proposed in this paper to predict the SIF interaction impact ratio at the deepest point of the crack defect for pipelines with interacting corrosion and crack defects. Crack size, corrosion size and the axial distance between these two defects are the factors that have an impact on the growth of the fatigue crack, and so they are considered as the input of XGBoost models. Based on the synthetic samples from finite element modeling, it has been proved that the proposed approaches can effectively predict the SIF interaction impact ratio with relatively high accuracy. The crack propagation models are built based on the proposed XGBoost models, Paris' law and corrosion growth model. Sensitivity analyses regarding corrosion initial depth and axial distance between defects are performed. The proposed method can support pipeline integrity management by linking the crack propagation model with corrosion size, crack size and the axial distance. The problem of how the interaction between corrosion and crack defects impacts crack defect growth is investigated.
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.
•>Synthetical effect of material inhomogeneity and welding defect on fatigue behavior.•>New structure strain method including heterogeneous plasticity and stress singularity.•>Evolution of fatigue ...mode with geometric configurations and cyclic amplitudes.•>A damage tolerance-based fatigue design concept to guide manufacture of welded joints.
This paper performed experimental and analytical investigations on the synthetical effect of material inhomogeneity and welding defects on the fatigue behavior of 2205 duplex stainless steel cruciform welded joints. A series of experiments were performed, including microstructure characterization by the electron back-scattered diffraction, fatigue mechanical tests assisted by digital image correlation technique and fracture morphology observations by scanning electron microscope. Results show that fatigue life and failure location of cruciform welded joints depended heavily on their geometric configurations for lower cyclic amplitudes. However, with the elevation of loading, material inhomogeneity played a greater roles, leading to the change of fatigue failure mode with both geometric configuration and cyclic stress amplitude. To quantize the effects of welding defects and material inhomogeneity, a modified structure strain method was proposed by considering the heterogeneous plastic properties, to accurately predict both fatigue lifetime and failure location of cruciform welded joints at both low and high cycles fatigue. Lastly, a damage tolerance-based fatigue design method was discussed to guide the highly-reliable manufacture and damage detection of duplex stainless steel cruciform welded joints in the engineering.
Vortex- friction stir welding (VFSW) utilizes a stir bar made of an identical material to the workpiece to rub the workpiece's top surface, which avoids the keyhole defect in conventional friction ...stir welding. It presents great potential in the repair field of aluminum alloys. In this study, the effect of stir bar diameter, rotation speed, and welding speed on the weld formation was investigated in the VFSW of 6061-T6 aluminum alloy. The weld macrostructure, penetration, and mechanical properties were characterized. The results show that a large diameter of the stir bar can enhance the vortex material flow, increase the heat input, and eliminate the incomplete-penetration defect. The increase in rotation speed within limits can enhance the weld penetration and the mechanical properties of the weld nugget zone (WNZ). However, too high a rotation speed reduces the weld penetration and weakens the mechanical properties of the WNZ. The increase in welding speed reduces the weld penetration but enhances the mechanical properties of the heat affected zone. The incomplete-penetration defect significantly weakens the ductility of the VFSW joint. It can be eliminated by enlarging the stir bar diameter and choosing a moderate rotation speed and a lower welding speed.
A method that employs the back propagation (BP) neural network is used to predict the growth of corrosion defect in pipelines. This method considers more diversified parameters that affect the ...pipeline's corrosion rate, including pipe parameters, service life, corrosion type, corrosion location, corrosion direction, and corrosion amount in a three-dimensional direction. The initial corrosion time is also considered, and, on this basis, the uncertainties of the initial corrosion time and the corrosion size are added to the BP neural network model. In this paper, three kinds of pipeline corrosion growth models are constructed: the traditional corrosion model, the corrosion model considering the uncertainties of initial corrosion time and corrosion depth, and corrosion model also considering the uncertainties of corrosion size (length, width, depth). The rationality and effectiveness of the proposed prediction models are verified by three case studies: the uniform model, the exponential model, and the gamma process model. The proposed models can be widely used in the prediction and management of pipeline corrosion.
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.
Most directed energy deposition (DED) implementations employ a rigid end effector to deposit material layer-by-layer, which is insufficient in cases with space constraints. To enhance the ...flexibility, this paper proposes a novel soft-robotic gun (SRG) based DED technology. The ideology is to replace the rigid weld gun with a tendon-driven omnidirectional-steering continuum manipulator, which a computer can numerically control. To this end, both requirements and concepts of the SRG-DED are introduced. A prototype system is designed and implemented before dedicated kinematic modelling and trajectory planning mechanisms are presented. As demonstrated by the experimental results, the developed trajectory planning algorithm improves the computational efficiency of tendon variables and enhances the consistency of trajectory tracking. The prototype system can deposit a complex path on an inclined substrate and fabricate a thin-wall component within a pipeline. The validation work confirms the feasibility and applicability of the prototype system for metal additive manufacturing applications.
To obtain a high-quality Al/steel dissimilar joint, a micro-groove-assisted vortex-friction stir lap welding (MG-VFSLW) process was developed. Through prefabricating micro-grooves on the steel plate ...surface by laser ablation, high-quality mechanical interlock and metallurgical bonding were obtained simultaneously in the MG-VFSLW process. The weld formation, interface microstructure, mechanical properties, and failure mode in MG-VFSLW were studied by comparing them with those in VFSLW. The results showed that a line load of the AA5083/SUS304 dissimilar joint up to 485.9 N/mm was obtained by MG-VFSLW, which is 40.1% higher than that in VFSLW. Remarkable intermetallic compound layers and cracks were found in VFSLW. The cracks were closely related to the oxides on the interface. However, in MG-VFSLW, cross-riveting aluminum rivets and steel rivets were formed on the interface due to the micro-grooves and flashes made by the laser ablation. Good metallurgical bonding was also formed between AA5083 and SUS304. No remarkable intermetallic compound layers and cracks occurred. During the tensile shear tests, the aluminum rivets were cut off and some dimples and tear ridges existed on the fracture surface. In short, the high strength of the Al/steel lap joint in MG-VFSLW was attributed to the high-quality mechanical interlock and metallurgical bonding.
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