Fracture mechanics parameter for the fatigue resistance of laser welds

Wang, P.C.

doi:10.1016/0142-1123(95)93047-6

Cited by 32 publications

(7 citation statements)

References 2 publications

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“…7b. This may seem to be a departure from the existing understanding of the fatigue failure of laser welds in which the failure is directly initiated from the pre‐existing crack tip due to the stress and strain singularities based on the fracture mechanics approach 9,10,16,19 . Therefore, the failure mechanism of the necking/shear for laser welded lap joints of thin sheets under quasi‐static loading conditions in the present study seems to be different from that under cyclic loading conditions.…”

Section: Failure Mechanism Of Welded Jointmentioning

confidence: 61%

Failure mode of laser welds in lap‐shear specimens of high strength low alloy (HSLA) steel sheets

Asim

Lee

Pan

2011

Fatigue Fract Eng Mat Struct

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In this paper, the failure mode of laser welds in lap‐shear specimens of non‐galvanized SAE J2340 300Y high strength low alloy steel sheets under quasi‐static loading conditions is examined based on experimental observations and finite element analyses. Laser welded lap‐shear specimens with reduced cross sections were made. Optical micrographs of the cross sections of the welds in the specimens before and after tests are examined to understand the microstructure and failure mode of the welds. Micro‐hardness tests were also conducted to provide an assessment of the mechanical properties in the base metal, heat‐affected and fusion zones. The micrographs indicate that the weld failure appears to be initiated from the base metal near the boundary of the base metal and the heat‐affected zone at a distance away from the pre‐existing crack tip, and the specimens fail due to the necking/shear of the lower left load carrying sheets. Finite element analyses based on non‐homogenous multi‐zone material models were conducted to model the ductile necking/shear failure and to obtain the J integral solutions for the pre‐existing cracks. The results of the finite element analyses are used to explain the ductile failure initiation sites and the necking/shear of the lower left load carrying sheets. The J integral solutions obtained from the finite element analyses based on the 3‐zone finite element model indicate that the J integral for the pre‐existing cracks at the failure loads are low compared to the fracture toughness and the specimens should fail in a plastic collapse or necking/shear mode. The effects of the sheet thickness on the failure mode were then investigated for laser welds with a fixed ratio of the weld width to the thickness. For the given non‐homogenous material model, the J integral solutions appear to be scaled by the sheet thickness. With consideration of the plastic collapse failure mode and fracture initiation failure mode, a critical thickness can be obtained for the transition of the plastic collapse or necking/shear failure mode to the fracture initiation failure mode. Finally, the failure load is expressed as a function of the sheet thickness according to the governing equations based on the two failure modes. The results demonstrate that the failure mode of welds of thin sheets depends on the sheet thickness, ductility of the base metal and fracture toughness of the heat‐affected zone. Therefore, failure criteria based on either the plastic collapse failure mode or the fracture initiation failure mode should be used cautiously for welds of thin sheets.

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Section: Failure Mechanism Of Welded Jointmentioning

confidence: 61%

Failure mode of laser welds in lap‐shear specimens of high strength low alloy (HSLA) steel sheets

Asim

Lee

Pan

2011

Fatigue Fract Eng Mat Struct

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“…The actual stress effect resulting from the stress concentration near the weld nugget is not sufficiently well understood, in the case of laser weld joints [12]. Earlier work [13][14][15] as well as the studies performed during this work have shown that there is extremely high stress concentration at the root of a laser weld joint and the crack initiation life could be relatively short. Therefore it makes it difficult to apply the strain life approach but also it suggests that the major portion of the total fatigue life is dominated by crack propagation.…”

Section: Accepted Manuscriptmentioning

confidence: 88%

Fracture mechanics based estimation of fatigue lives of laser welded joints

Goyal¹,

Bogdanov

El-Zein

et al. 2018

Engineering Failure Analysis

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The conventional joining methods like resistance spot welding and arc welding have several challenges during joining of thin sheets of high strength steel materials. One of the main challenge is that application of these joining methods may result in a severe distortion of welded structure. Therefore laser welding process has emerged as an alternative joining process which can help mitigate some of these challenges. Lower heat input from laser during the welding process results in a smaller size weld heat affected zone and also in lower overall distortion of the structure. The laser welding process presents an exciting opportunity in designing lighter weight structures. However, the major roadblock to application of laser welding method for large structural parts is that fatigue behavior of laser welded joints is not yet well understood. In order to study the fatigue performance of laser welded joints, detailed experimental and numerical investigations have been carried out and the results are presented in this work. The scope of experimental studies included a large set of coupons with different thicknesses and material combinations. Experimental fatigue test data has been generated for the laser welded joints produced using thin sheets of three grades of high strength steel materials (HSLA and UHSS grades) of several thicknesses (1mm, 1.6mm, 2mm and 3mm). The fatigue test data sets were obtained at R-ratios of R=0.1, R=0.2 and R=0.3. Another variable introduced into experimental studies was an orientation of laser weld joint with respect to applied loading direction. After fatigue tests were completed, detailed metallurgical investigations have been carried out to understand the failure mechanism and the crack growth behavior in laser welded joints. Based on the observed experimental and numerical studies it was concluded that the strain life based fatigue analysis method which has been successfully applied to study weld toe failures for the arc weld joints is not sufficient for the evaluation of laser welded joints. This is due to the reason that laser welded joints have unique challenges due to weld root crack failures and extremely high stress concentration at the location of crack initiation in the root of laser welded joints between the plates. The fracture mechanics based method has been developed for the fatigue life assessment of laser welded joints. In order to apply this method comprehensive three dimensional finite element studies were performed. Numerical studies show good correlation of the estimated fatigue lives obtained using proposed fracture mechanics method with the experimental data.

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“…ertragbaren Spannungsparametern bei u Èberlappenden Laserstrahlschweiûverbindungen der betrachteten Art sind mit zwei Ausnahmen nicht bekannt. Wang [3] gibt eine J-Integral-Wo Èhlerlinie fu Èr Scherzugbeanspruchung der U È berlappverbindung an. Der Mittelwert J a 0,09 Namm bei Wang ist um ein Mehrfaches gro Èûer als der Wert J a 0,015 nach Abb.…”

Section: Vergleiche Mit Schrifttumsangabenunclassified

“…Untersucht wurden der Stumpfstoû unter Zugbeanspruchung, der U È berlappstoû mit Stichlochnaht oder Kehlnaht unter Scherzugbeanspruchung, die Doppel-L-Probe unter Scha Èlzugbeanspruchung, die Doppel-U-Probe mit Stumpfnaht und die Hutprofilprobe mit Stichlochnaht unter Schubbeanspruchung der Na Èhte. Eine spa Ètere Untersuchung von Wang [3] aus der amerikanischen Automobilindustrie befaûte sich mit dem U È berlappstoû mit Stichlochnaht unter Scherzugbeanspruchung und lieferte eine Wo Èhler-Linie auf Basis des zyklischen J-Integrals. Einzelne weitere Untersuchungen geben konstruktive Hinweise [4], vergleichen mit konkurrierenden Fu Ègeverfahren [5 ± 8] oder beziehen sich auf Aluminiumlegierungen [9].…”

Section: Introductionunclassified