Fatigue crack propagation behavior in the vicinity of an interface between materials with different yield stresses

Pippan, Reinhard; Flechsig, K.; Riemelmoser, F. O.

doi:10.1016/s0921-5093(00)00703-6

Cited by 116 publications

(67 citation statements)

References 12 publications

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“…Thereby three possible critical sites that may initiate failure were identified: the interface and the two changeovers on the Al-side; firstly, between the fusion zone and the heat affected zone (3 mm from the interface) and secondly, between (primary) heat affected zone and towards the base material (7 mm from the interface). With this background fatigue crack propagation and fracture at these sites are investigated here (Part II).Additionally, crack orientation perpendicular [11][12][13][14] to the weld is also considered.Effect of temper of AA6056 on properties was studied for two conditions; welding in T4 7 followed by post weld heat treatment T6, and welding in T6 followed by defined natural ageing.As in the Part I [16] the terminology "welding" [17] has been retained, since at least one partner was melted (and thus it is not considered as brazing). The partners are also referred to synonymously by the respective side, e.g., AA6056 as the Al-side.…”

mentioning

confidence: 99%

Structure‐property investigations on a laser beam welded dissimilar joint of aluminium AA6056 and titanium Ti6Al4V for aeronautical applications. Part II: Resistance to fatigue crack propagation and fracture

Vaidya¹,

Horstmann²,

Ventzke³

et al. 2009

Materialwissenschaft Werkst

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Investigations were continued on the dissimilar laser beam welds of AA6056 and Ti6Al4V, fabricated by inserting Ti-sheet into the profiled Al-sheet and melting AA6056 alone. By using microstructure, hardness and strength as the criteria, sites exhibiting non-uniform microstructure and localized plastic deformation due to strength mismatch were investigated in two orientations:• crack parallel to the weld and• crack perpendicular to the weld for fatigue crack propagation and fracture toughness at room temperature. Effect of temper of AA6056 on these properties was studied for two conditions; welding in T4followed by post weld heat treatment T6, and welding in T6 and naturally aged for a defined period. The orientation "crack parallel to the weld" was investigated in 3 locations on the side of AA6056: the interface and the two changeovers on the Al-side.Firstly, between the fusion zone and the heat affected zone (3 mm from the interface) and secondly, between (primary) heat affected zone and towards the base material (7 mm from the interface). Although brittle intermetallic TiAl 3 had been formed at the interface, uncontrolled separation or debonding at the interface was not observed.Insofar the bond quality of the weld was good. However, the ranking of interface was the lowest since fatigue crack propagation was relatively faster than that in the fusion zone and heat affected zone, and fracture toughness was low. Therefore, unstable fatigue crack propagation is observed when the crack propagates perpendicular to the weld from AA6056 towards Ti6Al4V. The results have shown that the dissimilar joints exhibit improved performance when laser beam welded in the T6 condition. have analysed the effect of fusion weld imperfections on the fatigue life using finite element analysis method and have shown a systematic decrease in the fatigue life in the order of porosity, undercut and solidification cracks. Thus, since welds may contain defects, the crack initiation phase may be short or even absent depending on the load levels. Therefore, to be on the safer side, it is advisable to assume that the whole life shall be limited by fatigue crack propagation and fracture. 5Fatigue crack propagation is not a unique but a parameter dependent property and, hence, can be case dependent. For a crack within the weld, the resistance to fatigue crack propagation for strength overmatching in shield metal arc welded buttjoints of a low alloy high strength steel (HSLA80) is found to be superior to that for undermatching [6]. On the other hand, undermatched friction stir welded butt-joints of AA6056-T6 are found to exhibit a nearly comparable fatigue crack propagation behaviour to that of the base material or even better in the nugget region [7]. Moreover, although undermatched, butt-joints of AA6056-T6 are found to exhibit a better resistance to fatigue crack propagation when welded by friction stir than by laser beam [8]. Thus, along with the strength of the weld, the welding process (on which the occurrence of defects depends) an...

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mentioning

confidence: 99%

Structure‐property investigations on a laser beam welded dissimilar joint of aluminium AA6056 and titanium Ti6Al4V for aeronautical applications. Part II: Resistance to fatigue crack propagation and fracture

Vaidya¹,

Horstmann²,

Ventzke³

et al. 2009

Materialwissenschaft Werkst

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“…Crack path bifurcation has been observed experimentally [2,[21][22][23], it is therefore important that this possibility be investigated analytically as well. The aim of numerical analysis at this stage would be to show that conditions favouring bifurcation may develop in bi-layer and trilayer systems under fatigue loading.…”

Section: Bifurcated Crack Pathmentioning

confidence: 99%

A numerical study of crack shielding and deflection under extensive plasticity

Burke-Veliz

Reed

Syngellakis

2009

Engineering Fracture Mechanics

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Experimentally observed crack deflection events in multi-layered material systems, occurring even under pure mode-I loading, are here simulated and explained through elasto-plastic finite element modelling. The crack tip opening displacement is adopted as the crack driving force and estimated along crack paths whose deflection is predicted using the maximum tangential strain criterion. Shielding conditions that promote deflection and bifurcation are evaluated. It is shown that, under conditions of extended plasticity, CTOD evolution as a crack approaches an interface can reveal crack shielding and amplification, and that crack deflection and growth can be assessed from the variation of tangential strains around the crack tip.

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“…The opposite effect is observed as a crack approaches a more compliant layer. Bifurcation events have also been observed in bi-layered architectures in compact specimens of plastically-mismatched materials [4], especially a high levels of loading.…”

Section: Introductionmentioning

confidence: 95%

“…These multilayered systems provide the required compromise between stiffness and tribological performance through a stiff backing layer and a conformable and low-friction lining. An additional attribute of multi-layered structures is the shielding effect that reduces the growth rate as cracks approach stiffer layers [2][3][4][5], thus increasing service life. The opposite effect is observed as a crack approaches a more compliant layer.…”

Section: Introductionmentioning

confidence: 99%

Fatigue crack shielding and deflection in plain bearings under large-scale yielding

Burke-Veliz

Syngellakis

Reed

2010

Engineering Failure Analysis

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Multi-layered bearing systems used in the automotive industry show shielding and antishielding effects that reduce or amplify the crack driving force under large scale yielding conditions. Using finite element analysis, it is shown that shielding in such systems results in path deflection and bifurcation despite the absence of mixed-mode loading. As the crack approaches a stiff layer, the tangential strains measured around a blunted crack tip model show a maximum corresponding to the direction of crack propagation. The distribution of such strains indicates the effect of shielding and the likelihood of the tip to deflect or bifurcate. The suitability of bi-layer and tri-layer bearing architectures is assessed through crack path and respective crack driving force predictions.

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Fatigue crack propagation behavior in the vicinity of an interface between materials with different yield stresses

Cited by 116 publications

References 12 publications

Structure‐property investigations on a laser beam welded dissimilar joint of aluminium AA6056 and titanium Ti6Al4V for aeronautical applications. Part II: Resistance to fatigue crack propagation and fracture

Structure‐property investigations on a laser beam welded dissimilar joint of aluminium AA6056 and titanium Ti6Al4V for aeronautical applications. Part II: Resistance to fatigue crack propagation and fracture

A numerical study of crack shielding and deflection under extensive plasticity

Fatigue crack shielding and deflection in plain bearings under large-scale yielding

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