Influence of the radius of curvature at the weld toe in the fatigue strength of fillet welded joints

One general method for improving the fatigue strength of welded joints is introduction of compressive residual stress by peening. However, there is concern that the fatigue strength of the welded joint may decrease if excessive preloading is applied after peening. It has been found that fatigue strength decreased after applying compressive preloading to a welded joint due to cancellation of the compressive stress at the weld toe. In the present research, the influence of excessive preloading on the fatigue strength of welded joints with compressive residual stress at the weld toe was clarified by experiments using hammer peening with an improved pin. When hammer peening was applied to welded joints, increasing the radius of the weld toe reduced the decrease of compressive residual stress due to excessive preloading. As a result, the decrease of the fatigue strength of the welded joint was also reduced.

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Local strain for fatigue strength of welded structures

The Journal of Strain Analysis for Engineering Design ◽

10.1243/0309324011514746 ◽

2001 ◽

Vol 36 (6) ◽

pp. 605-610 ◽

Cited By ~ 4

Author(s):

V Dattoma ◽

C Pappalettere

Keyword(s):

Fatigue Strength ◽

Welded Joints ◽

Structural Integrity ◽

Strain Curve ◽

Local Strain ◽

Fatigue Design ◽

Curve Versus ◽

Weld Toe ◽

Stress Ratios ◽

Tip Radius

Field criteria, which are usually applied in fracture mechanics to ensure the structural integrity of cracked components, are extended to the fatigue design of welded joints, whose weld toe can be assimilated to a notch with a small tip radius. In particular, fatigue strength in terms of strain rather than of stress has been determined by applying stress cycles with different stress ratios R = σmin/σmax. Finally, for the evaluation of the fatigue strength of welded joints in structural steel, a strain curve versus different R ratios is given to be compared with the service measured local strain at the weld toe.

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Improve the Fatigue Performance of Welded Joints with Undercuts by TIG Dressing Treatment

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.472-475.1300 ◽

2012 ◽

Vol 472-475 ◽

pp. 1300-1304 ◽

Cited By ~ 2

Author(s):

Liang Chen Wu ◽

Dong Po Wang

Keyword(s):

Fatigue Life ◽

Fatigue Strength ◽

Adverse Effects ◽

Dynamic Loading ◽

Weld Joint ◽

Welded Joints ◽

Fatigue Cracks ◽

Fatigue Property ◽

Fatigue Performance ◽

Weld Toe

Undercuts often exists in the surface at weld toe. Undercuts affects the capability of weld subjected to dynamic loading greatly and fatigue cracks usually initiate from these zones with undercuts. Combining with low-alloy middle strength steel 16Mn，study of increasing the fatigue strength and the fatigue life was carried out. Compared with specimen without defects, the fatigue strength of specimen with undercuts has been increased by 10~20%. Study also shows that comparing with as-welded specimen with defects, with TIG dressing treatment, fatigue strength of cruciform weld joint of steel 16Mn has been increased by 70%, fatigue life by 5~8 times. Compared with as-welded specimen without defects, fatigue strength has been increased by 34%, fatigue life by 3~4 times. Undercuts have no adverse effects on fatigue property of welded joints under TIG dressing.

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Fatigue Strength Evaluation of the Load-Carrying Cruciform Fillet Welded Joints Using Hot-Spot Stress

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.324-325.1281 ◽

2006 ◽

Vol 324-325 ◽

pp. 1281-1284 ◽

Cited By ~ 1

Author(s):

Byeong Wook Noh ◽

Jung I. Song ◽

Sung In Bae

Keyword(s):

Fatigue Strength ◽

Welded Joints ◽

Hot Spot ◽

Plate Thickness ◽

Structural Stress ◽

Leg Length ◽

Element Analysis ◽

Hot Spot Stress ◽

Load Carrying ◽

Weld Toe

In this study, fatigue strength of load-carrying cruciform fillet welded joints were evaluated using a new method proposed by Yamada, for geometric or structural stress in welded joint, that is, one-millimeter stress below the surface in the direction corresponding to the expected crack path. Validity of the method is verified by analyzing fatigue test results for load-carrying cruciform welded specimens has different size of weld toe radius, leg length and plate thickness reported in literature. Structural stress concentration factor for 1mm below the surface was calculated by finite element analysis for each specimen respectively. When compared to the basic fatigue resistance curve offered by BS7608, the one-millimeter stress method shows conservative evaluation for load-carrying cruciform fillet welded joints.

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Research on Methods of Improving Fatigue Property of Low-Strength Steel Welded Joints

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.538.48 ◽

2014 ◽

Vol 538 ◽

pp. 48-53

Author(s):

Chun Run Li ◽

Zhen Ping Cao ◽

Zong Tao Fang

Keyword(s):

Fatigue Strength ◽

Stress Concentration ◽

Compressive Stress ◽

Welded Joints ◽

Processing Method ◽

Residual Compressive Stress ◽

Composite Processing ◽

Ultrasonic Peening ◽

Weld Toe ◽

Low Strength

TIG dressing combined with ultrasonic peening was conducted on low-strength steel Q235B in this paper, the fatigue strength of which was compared with original welding state, TIG dressing and ultrasonic peening respectively. The results indicate that fatigue strength of welded joints treated by TIG dressing is increased by 36%, composite processing method 57% and ultrasonic peening 56%, with little difference between composite processing method and ultrasonic peening in loading condition R=0.1. Stress concentration factor at weld toe treated by composite processing method is less than that by ultrasonic peening and with less residual compressive stress relief, the former is more effective in improving fatigue life at high stress level. Residual compressive stress at weld toe treated by composite processing is close to ultrasonic peening method and the effect of stress concentration is weakened, the two methods don’t appear to be much different.

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