Fatigue Strength Of Cruciform Joints Research Articles

Fatigue strength of cruciform joints with weld imperfections: A comprehensive numerical study

The paper presents an investigation into the fatigue resistance of load-carrying cruciform joints that exhibit weld imperfections. To accomplish this, a finite-element model of the joint is validated by a comparison to experimental investigations. The model includes both a global and a submodel that integrates the effective notch stress concept into its design. This enables the simulation of various types of weld imperfections, such as lack of penetration, lack of root fusion, undercut, excessive convexity, incorrect weld toe, excessive asymmetry of fillet welds and linear misalignment, to assess their impact on the fatigue strength of the cruciform joint. The analysis reveals that these imperfections lead to an increase in stress at the notches of the cruciform joint, which can be characterized as a function of the joint's geometrical properties. Global geometry influences on the fatigue strength of different cruciform join geometries can be regarded independently from the influence of the weld imperfections that is given by stress concentration factors. The normalised stress concentration factor enables a comparison between imperfection influences and shows, that the notch-softer design with full penetration welding at the cruciform joint is in a relative relation more strongly influenced by imperfections than the design with fillet welds. Also, the undercut represents the imperfection with the strongest effect in a relative relation within the sizes considered.Being able to evaluate the fatigue strength values of steel components with weld imperfections eliminates the need for costly repairs and new fabrications, which would otherwise result in a loss of resources and economic efficiency.

Fatigue strength of cruciform joints and longitudinal joints with laser-arc hybrid welding

This study examined the fatigue strength of cruciform joints and longitudinal joints fabricated with laser-arc hybrid welding. Load-carrying and non-load-carrying cruciform welded joints with plate thicknesses of 8, 16, and 25 mm were tested under tensile cyclic loads and out-of-plane bending cyclic loads. In longitudinal joints, four-point bending fatigue tests were performed on plate girders with flanges and a web connected by laser-arc hybrid welding. When assembling the plate girder, tack welds were installed at the flange-to-web connection to clarify their effect on the fatigue strength of the longitudinal joints. Measurements of weld toe profiles and residual stress were also conducted. The residual stress was measured using X-ray diffraction. The test results revealed that the fatigue strengths of hybrid welded joints are equivalent to those of arc welded joints and satisfy the fatigue design curves specified by the Japanese Society of Steel Construction. In addition, the effect of plate thickness on the fatigue strength was observed in hybrid welded joints as well as in arc welded joints.

Fatigue strength of laser-arc hybrid welded joints with tack welds

ABSTRACT This study examined the fatigue strength of cruciform joints and longitudinal joints fabricated with laser-arc hybrid welding, in which tack welds were installed at the connection. The cruciform joints were tested under tensile cyclic loads and out-of-plane bending cyclic loads. In the longitudinal joints, four-point bending fatigue tests were performed on plate girders fabricated with the hybrid welding. In addition, finite element analysis was performed on the cruciform joint to investigate the effect of tack welds on stress concentration at weld toes. The test results revealed that the fatigue strengths of the hybrid welded joints are equivalent to those of arc welded joints with or without tack welds and satisfy the fatigue design curves specified in JSSC recommendation. Moreover, the analysis results indicated that tack welds have little influence on stress concentration at weld toes in cruciform joints fabricated with laser-arc hybrid welding.

Fatigue strength of laser-arc hybrid welded joints with tack welds

This study examined the fatigue strength of cruciform joints and longitudinal joints fabricated with laser-arc hybrid welding, in which tack welds were installed at the connection. The cruciform jo...

Fatigue strength of cruciform joints with laser-arc hybrid welding

Fatigue strength of cruciform joints with laser-arc hybrid welding

The effect of weld bead dimensions on the fatigue strength of cruciform joints

The choice of weld bead size in the case of welded cruciform joints can be problematic, especially when the sheets forming the joint are of differing thickness. Technological standards generally recommend a weld bead thickness less than the minimum thickness of the sheets to be joined, whereas structural standards do not envisage any dependency between joint static and fatigue strength and weld bead dimensions, unless these are so reduced as to lead to failure starting and propagating in the weld bead itself rather than the base metal plates. The scope of this study is the theoretical and experimental analysis of the change in fatigue strength with varying weld bead thickness and minimum welded plate thickness.

십자형 필릿 용접부에서의 피로파괴 형상과 특성

The proportion of the welding in the production process of machinery, buildings and marine structures is increasing and the joining are mainly conducted by butt and fillet weld. In the case of fillet weld, the shape of structures is complicated depending on the constraint on the geometry of the structures, therefore, the full penetration is mostly difficult. Accordingly, it is necessary to establish safe and economical criteria of design of the structures through the strength based on the penetration state of the fillet weld. Patterns of fatigue failure in cruciform fillet weld jont appear in the form of the root, toe and mixed failure. In the case of toe and mixed failure, the fatigue strength is higher than root failure. Therefore, we have to make the enough depth of penetration or perform the welding work through improving the fatigue strength of cruciform joints in welded structures. So it is necessary to optimize the penetrated depth in the range of the possible mixed failure and find the way in the cost-effective design to lessen the amount of the welding work.

십자형 용접부 피로강도 산정을 위한 국부응력법의 비교연구

The notch effects on the fatigue strength of welded joints are both stress concentration and fatigue strength reduction. In the notch stress approach, the notch effects are usually approximated by introducing weld-bead parameters for the local detailed weld joints. In this paper, well-known notch stress approaches - critical distance method, area method and fictitious rounding method are presented for the fatigue strength of cruciform joints. The estimated results of the present methods are applied to the experiments performed in this study and reported in the references. The results of the application show that the fatigue-life scatterness of the experimental data expressed in the nominal stress is significantly reduced by introducing the effective fatigue stress of the present study.

An Effect of Finishing Welded Parts on Fatigue Strength of Cruciform Joints

An Effect of Finishing Welded Parts on Fatigue Strength of Cruciform Joints

Influence of weld and plate geometry on the fatigue strength of cruciform joints

Results of fatigue life prediction in cruciform joints are reported. Using Fracture Mechanics methods, fatigue life was computed as a function of initial flaw size, plate length and thickness, weld geometry and loading mode. The Bueckner weight function method was used for computing the stress intensity factor using a 2-D finite element program. The results have shown that plate length has little or negligible influence on fatigue strength provided that the plate length to thickness ratio is below 20 to 50 depending on the plate thickness. The attachment thickness to main plate thickness ratio also has little or no effect on fatigue strength. The plate thickness itself and the loading type (tension and bending), however, do affect the fatigue. Their effects are quantified and introduced into the SN-curve for design.

十字すみ肉溶接継手の低サイクル疲労強度におよぼすギャップ量の影響について

According to the studies on the ductile strength of cruciform welded joints, it is known that the fracture strength of the joints with comparatively small amount of gaps, does not decrease in comparison with that of the joints with no gaps, because of the increase of penetration, which is roughly proportional to the increase of amount of gap.However, such joints are frequently subjected to fatigue failure, therefore the effect of root gaps on low cycle fatigue strength of cruciform joints is investigated.The main conclusions obtained are as follows.(1) At the roots of the joints, initial microcracks are observed occasionally. The average length and the occurrence percentage of these cracks become minimum when amount of initial gaps before welding is about 2 mm.(2) As for the fillet welded joints used in this study, the penetrations are approximately equal to the amount of initial gaps before welding.(3) It is shown that the crack initiation lives can be neglected, therefore, the fatigue lives of the joints are almost regarded as the crack propagation lives.(4) It is confirmed that the well known relationship between the crack propagation rate, dl/dN and the stress intensity factor range, Δk; dl/dN=c(Δk)m are applied well to the fatigue cracks advanced toward the right angle to the loading direction.(5) The fatigue strength of the joints with actual gaps below 3 mm after welding does not decrease in comparison with that of the joints with no gaps.