Gusset Welded Joints Research Articles

Cyclic elastoplasticity and XFEM based fatigue life assessment of out-of-plane gusset welded joints

Conventional design methods for high-cycle fatigue failure of engineering components often assume a linear-elastic material behaviour. The different driving forces of crack initiation and propagation fail to be considered, resulting in less accurate predictions of fatigue life. To address this issue, the present study proposes a novel method to predict the fatigue life of out-of-plane gusset welded joints based on cyclic elastoplasticity and extended finite element method (XFEM). Incorporating the welding residual stress simulated by thermal–mechanical analysis, the cyclic stress–strain response of out-of-plane gusset welded joints was assessed by Fatigue SS (FSS) constitutive model. The crack initiation life was therefore predicted by the local strain approach considering the mean stress correction. Based on the converged cyclic stress–strain response, the crack propagation behaviour and life were predicted by XFEM in combination with Virtual Crack Closure Technique (VCCT). The influence of mean stress, mixed-mode crack and residual stress on crack initiation and propagation life was also investigated. The results show that the proposed method can predict the fatigue life of out-of-plane gusset welded joints under the pure tension loading with high accuracy against experimental results.

Local MIL-HDBK-5D equivalent stress based fatigue assessment of the gusset welded joint improved by Portable Pneumatic Needle-Peening treatment

This study proposes a local MIL-HDBK-5D equivalent stress (LMES) based approach to investigate the fatigue lives of Portable Pneumatic Needle-Peening (PPP) treated gusset welded joints made of SM490. The LMES range is identified by the elastic–plastic local stress cycle simulated by the muti-process finite element analysis, including welding, PPP, and fatigue loading processes. Using the LMES, Fatigue test results of as-welded (AW) and PPP treated joints are consolidated into a single S-N curve. This LMES based S-N curve can be used for evaluating fatigue life comprising the influence of residual stress, cyclic stress relaxation, and local weld toe geometry for welded joints studied in this work.

Experimental investigation of fatigue strength of out-of-plane gusset welded joints under variable amplitude plate bending loading in long life region

Experimental investigation of fatigue strength of out-of-plane gusset welded joints under variable amplitude plate bending loading in long life region

Fatigue Life Assessment of Welded Joints by Combined Measurements Using DIC and XRD.

The existing methods of assessing the fatigue life of welded joints fail to consider local strain ranges and mean stress at the weld toe. The present work proposes a novel approach to assessing the fatigue life of welded joints by conducting measurements with digital image correlation (DIC) and X-ray diffraction (XRD) in combination. Local strain ranges at the weld toe of gusset welded joints were measured by DIC. Hammer peening was conducted on the welded joints to introduce different initial stresses. The influence of mean stress was investigated by considering initial residual stress measured by XRD and a perfect plastic material model. The fatigue experiment was carried out on specimens with and without hammer peening. The results showed that hammer peening could offset adverse welding deformation effectively, and introduce significant residual compressive stress. The fatigue failure life increased by more than 15 times due to hammer peening. The fatigue initiation life assessed by the proposed method was close to that based on nominal stress, indicating that the proposed method is reliable for predicting the fatigue initiation life of welded joints.

Generalized SCF Formula of Out-Of-Plane Gusset Welded Joints and Assessment of Fatigue Life Extension by Additional Weld.

The existing S-N curves by effective notch stress to assess the fatigue life of gusset welded joints can result in reduced accuracy due to the oversimplification of bead geometries. The present work proposes the parametric formulae of stress concentration factor (SCF) for as-welded gusset joints based on the spline model, by which the effective notch stress can be accurately calculated for fatigue resistance assessment. The spline model is also modified to make it applicable to the additional weld. The fatigue resistance of as-welded and additional-welded specimens is assessed considering the geometric effects and weld profiles. The results show that the error of SCFs by the proposed formulae is proven to be smaller than 5%. The additional weld can increase the fatigue life by as great as 9.4 times, mainly because the increasing weld toe radius and weld leg length lead to the smaller SCF. The proposed series of S-N curves, considering different SCFs, can be used to assess the welded joints with various geometric parameters and weld profiles.

Improvement of fatigue strength of out-of-plane gusset welded joints by controlled-additional weld bead shape and toe grinding

Improvement of fatigue strength of out-of-plane gusset welded joints by controlled-additional weld bead shape and toe grinding

Paper Review of “Fatigue surface crack growth behavior in flat plate and out-of-plane gusset-welded joints under biaxial cyclic loads with different phases”

Paper Review of “Fatigue surface crack growth behavior in flat plate and out-of-plane gusset-welded joints under biaxial cyclic loads with different phases”

Enhancing fatigue strength of welded joints made of SBHS700 by hammer peening with ICR apparatus and HFMI treatment

This paper investigates the fatigue strength enhancement of two types of peening techniques: hammer peening with impact crack-closure retrofit apparatus and high-frequency mechanical impact (HFMI) treatment on out-of-plane gusset-welded joints made of SBHS700. In this work, fatigue tests were continuously carried out using plate specimens that were removed from a previously tested girder specimen. The results showed that the fatigue strength enhancement of these peening techniques on the welded joints was expected to be at least three classes higher compared with as-welded details with similar dimensions. Unexpectedly, the improvement effect of the hammer peening on one specimen was slightly lower than that of the other specimens. According to SEM observation, the cause of the slight reduction was that due to its weld shape, the distance between the crack initiation point and the treatment edge became greater than 2 mm. Finally, evaluations were performed on available data, including the test results from this study, based on an extended Modified Goodman model to estimate the fatigue limits of HFMI-treated joints. Consequently, the estimation results by the model indicated a good agreement with the fatigue strength enhancement of HFMI treatment and a possibility to be able to assess the enhancement of the hammer peening.

Fatigue surface crack growth behavior in flat plate and out-of-plane gusset-welded joints under biaxial cyclic loads with different phases

Although many in-service welded built-up structures, which contain many welded joints as fatigue crack initiation sites, are subjected to many types of loading, their structural integrities are evaluated according to design codes based on theoretical and experimental investigations under uniaxial loading conditions. Additionally, most of these codes implement the S–N curves approach. This study highlights the biaxial cyclic loading with different phases. The fracture mechanics approach toward fatigue life evaluation can obtain the fatigue crack growth history. This paper confirms the applicability of the previously proposed numerical simulation method for obtaining the fatigue crack propagation histories of a cracked plate subjected to biaxial loads with a phase difference for each loading component. A fracture mechanic approach was used to establish the proposed method. The fatigue surface crack growth behavior of a flat plate and an out-of-plane gusset-welded joint under biaxial cyclic loadings with different phases was investigated by extending the applicability of the proposed method to a through-thickness crack. Comparisons between the measured crack evolution and the numerical simulation results were carried out to validate our fatigue crack growth simulation for flat plane and welded joints.

Fatigue Strength Improvement and Fatigue Crack Closure by Portable Pneumatic Needle-Peening Treatment on Welded Joints

This study experimentally investigates effect of fatigue strength improvement of the Portable Pneumatic Needle-Peening treatment (PPP treatment) as a needle peening on out-of-plane gusset welded joints by using plate bending fatigue tests. This study also examined effect of the travel speed and the number of treatment passes of the PPP treatment with regards to its fatigue strength improvement. After the fatigue tests, the observation of the fracture surface with Scanning Electron Microscope was carried out in order to clarify the crack initiation. From those test results, it may be concluded that the effect of fatigue strength improvement might be governed by treatment passes with sufficient travel speed. In addition, this study carried out additional fatigue tests that focus on fatigue crack closer by using the PPP treatment. As a result of additional fatigue tests for fatigue crack closure, it might be said that the effect of fatigue crack closure is effective when the distance between fatigue cracks and treatment area is less than 2.0 mm.

Fatigue Strength Improvement of Welded Joints of Existing Steel Bridges by Shot-Peening

Shot-peening recently can be applied to existing steel bridges due to the development of new vacuuming techniques of shots after peening in the construction site. This study experimentally investigates effects of fatigue strength improvement of shot-peening on welded joints. Bending fatigue tests using out-of-plane gusset welded joints specimens were carried out and three type specimens were compared: as-welded, grit-blasted, and shot-peened. In addition, this paper examines differences of fatigue strength improvement effects in case of applying shot-peening to inside of scallop where shots might be difficult to hit perpendicularly to weld toe of welded joints because of narrow space, and the residual stress measurement in order to clarify introducing compressive residual stress were carried out. As a result, it may be concluded that shot-peening can improve fatigue strength of welded joints and its mechanism was identified as extension of crack initiation life and delay crack propagation due to beneficial compressive residual stress in the vicinity of surface layer.

Effect of blast treatment on fatigue strength of out-of-plane gusset welded joints under compressive bending stresses

Effect of blast treatment on fatigue strength of out-of-plane gusset welded joints under compressive bending stresses

09.06: Continuous fatigue test of welded joint taken from SBHS700 girder specimen

ABSTRACTSteels for bridge high performance structures (SBHS) have high strength, good weldability and workability. SBHS700 of 780MPa class must particularly clarify with respect to fatigue problems. At the previous study, the fatigue test with the SBHS700 girder specimen was carried out and fatigue strength improvement methods to introduce compressive residual stress were used on its out of plane gusset welded joints. However, the previous study did not quantitatively show the fatigue strength improvement because these out of plane gussets have not failed.In this study, in order to clarify the effects of the fatigue strength improvement methods, these out of plane gussets are taken from the girder by gas fusion cutting and made as small fatigue specimens. If there is enough compressive residual stress left at the weld toe, the fatigue tests are carried out.Before the fatigue tests, residual stress at 2mm from treatment edge of centre gusset was measured by the X‐ray diffraction method and compared with previous studies. The target of fatigue test was UIT (Ultrasonic impact treatment). At first, nominal stress range is 100MPa under the same condition of the previous study. If fatigue crack does not appear after 2 million cycles, nominal stress range is increased, such as 150MPa, 180MPa, 200MPa.As a result, enough compressive residual stress was confirmed at the weld toe from the X‐ray diffraction method. UIT specimens reached 2 million cycles in 200MPa stress range. Fatigue test results were considered based on an equation which modified Goodman's diagram applies to the weld toe due to estimate the fatigue limit. Therefore, high fatigue strength can be expected.

Fatigue Behaviour of CFRP Strengthened Out-of-Plane Gusset Welded Joints with Double Cracks

This paper investigates the fatigue behaviour of out-of-plane gusset welded joints strengthened with carbon fibre reinforced polymer (CFRP) laminates. Two notches were introduced at the weld toes adjacent to longitudinal plate ends to simulate the initial damage. Variables including the stress range, single- or double-sided strengthening and modulus of CFRP materials were considered. It was found that both cracks propagated under fatigue loading. All the specimens fractured along one predefined notch when the fatigue crack reached a certain length while the other crack also grew to some extent. Test results showed that the addition of composite materials significantly prolonged the fatigue life of specimens by as much as 1.28 to 8.17 times. Double-sided bond and ultra-high modulus CFRP materials led to a better strengthening efficiency. Thereafter, a series of numerical analyses were performed to study the stress intensity factor (SIF) and crack opening displacement (COD). Local debonding around the crack tip at the adhesive-steel interface was taken into consideration. Finally, the fatigue life of all the specimens was evaluated based on the linear elastic fracture mechanism (LEFM) theory and the predicted results agreed well with the experimental data.

Fatigue behaviour of out-of-plane gusset joints with one-side fillet weld

In previous studies, many fatigue tests have been performed to investigate the fatigue behaviour of out-of-plane gusset welded joints. However, fatigue behaviour of out-of-plane gusset joints with a one-side fillet weld has not yet been clarified sufficiently. In this research, in order to quantitatively clarify the behaviour, welding residual stress at the weld toes of the joint was measured by a cutting method. In addition to this, fatigue tests were carried out on the joints with a one-side weld and turn-around weld. The plate thickness is 9 mm and the weld size is 10 mm. Moreover, finite element stress analyses were conducted on the test specimen models and parametric models with different main plate and gusset plate thickness. Their results show that fatigue cracks for out-of-plane gusset joints with a one-side fillet weld initiate from both weld toes at the start and end points of weld beads and non-penetration weld of the gusset side. Also, the crack initiation points are different depending on the weld arrangement; however, their fatigue strengths are almost same.

Effects of ultrasonic peening on fatigue strength of out-of-plane gusset joints

Effect of high frequency peening treatment with a small radius tip pin, which is less than 3mm radius tip pin, still remains unclear, although the effect of ultrasonic impact treatment on fatigue strength has been investigated. The objective of this study is to investigate the effect of ultrasonic peening with a 1.5mm radius tip pin on fatigue strength of out-of-plane gusset welded joints. Plate bending fatigue tests of those joints carried out. The results show that the peening can improve fatigue strength, when mean stress does not change or already changes before the peening is carried out. It also shows that the effect of the ultrasonic impact peening become less with increasing mean stress after the ultrasonic peening was carried out, and when the ultrasonic peening is not sufficient for the weld toe.

An analytical and experimental study on the thickness effect of fatigue strength in large-scale-welded models

Although “thickness effect” has long been considered to be a weakening factor with respect to fatigue strength, it is still somewhat unclear as to which factors dominate this effect as well as how it is influenced by different structural or joint types and different loading patterns. Using geometric specimens cut from a steel plate, it was confirmed, both through experimentation and the resulting analysis, that not only the stress concentrations but also the stress gradients at weld toes were the dominant factors relevant to thickness effect. These experimental results were verified by fatigue tests of cruciform-welded joints and out-of-plane gusset-welded joints as well as associated analysis (Yamamoto et al. 2012). In addition, the thickness effect in large-scale structural models was investigated through structural model fatigue tests and associated analysis, and it was found that the thickness effect in such large models was quite small in comparison to that observed in fatigue tests of small specimens.

Fatigue Crack Growth Behaviour of an Out-of –Plane Gusset Welded Joints under Biaxial Tensile Loadings with Different Phases

Most of in-service welded built-up structures, which contain many welded joints as fatigue crack initiation sites, are subjected to many types of loading and these loadings have different axial components with different phases. However, the structural integrities are evaluated according to design codes based on theoretical and experimental investigations under a uniaxial loading condition. Most of these codes are based on the S-N curves approach. On the other hand, authors proposed the numerical simulation method of fatigue crack propagation histories of a cracked plate subjected biaxial loadings with phase difference of each loading component. Fracture mechanics approach is applied to establish our method. In this study, fatigue crack growth behaviour of an out-of-plane gusset welded joint under biaxial loading with two different phase conditions were investigated. The phase difference effect for fatigue crack shape evolution under biaxial loading was confirmed by measured ones. Besides, comparisons of measured crack evolution with the numerical simulation results were performed to validate of our fatigue crack growth simulation for welded joints.

Fatigue strength improvement of out-of-plane welded joints of steel girder under variable amplitude loading

This study investigates improvement effects of fatigue strength by the postweld treatments, which are hammer peening treatment and additional welding with low-temperature transformation welding material. High cycle fatigue tests with constant and variable amplitude loadings are performed on out-of-plane gusset-welded joints of girder specimens. Test results indicate that this treatment can improve fatigue life under both the constant and variable amplitude loadings. The damage accumulations (D) of as-welded and cleaning obtained by Miner’s rule with the mean curve of constant amplitude loading are conservative (D > 1.0). However, since the beneficial effects of the compressive residual stress on fatigue life should decrease due to the relaxation of compressive residual stress, the D in specimens prepared by cleaning plus pneumatic peening, cleaning plus electric peening, and additional welding with low-temperature transformation welding material are extremely nonconservative (D ≈ 0.2–0.6). The modified Miner’s rule based on the results of fatigue test with constant maximum stress, which is the same as the maximum stress in the variable amplitude loading, is appropriate to the improved welded joints.

Fatigue strength improvement of welded joints by blast cleaning for subsequent painting

In the fabrication of steel bridges, prior to painting, blast cleaning is performed to clean the surfaces and to increase the adhesive properties of the surfaces for the subsequent painting. In addition to these objectives, blast cleaning can improve the fatigue strength of welded joints, as a result of the impact of forcibly propelled abrasive materials on the welded joints. A series of fatigue tests were carried out on the five different types of welded joints: one-side out-of-plane gusset fillet welded joints, both-side out-of-plane gusset fillet welded joints, non-load-carrying rib fillet welded cruciform joints, butt welded joints, and a large-scale model beam with out-of-plane gusset welded joints, and under the three different types of load conditions: uniaxial tension, out-of-plane bending, or in-plane bending stress cycles. Drawing on previous fatigue test results that include unpublished data, this paper presents the beneficial effects of blast cleaning for the subsequent painting applications on the fatigue strength improvement of welded joints and also presents a simple quality control method for the blast cleaning process that improves the fatigue strength.