Failure Mode and Fatigue Behavior of Friction Stir Spot Welds in Lap-Shear Specimens of Dissimilar Advanced High Strength Steels

In this study, the fatigue behavior of AZ31 magnesium friction stir spot welded joints is experimentally investigated. The friction stir spot welds employed here are representative of preliminary welds made in developing the joining process for potential use in automobile manufacturing. Load control cyclic tests were conducted on single weld lap-shear coupons and were fatigued until failure to determine stress-life properties. The fractured coupons were examined under optical and scanning electron microscopes with the intent to determine fatigue crack characteristics. Fractography analysis suggests that long crack growth accounts for a majority of the fatigue life. To predict the fatigue life of the lap-joint coupons, a long crack growth modeling approach, based on a kinked crack stress intensity solution, was employed. The fatigue model predictions compared well to the experimental stress-life results.

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The Backing Bar Role in Heat Transfer on Aluminium Alloys Friction Stir Welding

Materials Science Forum ◽

10.4028/www.scientific.net/msf.636-637.459 ◽

2010 ◽

Vol 636-637 ◽

pp. 459-464 ◽

Cited By ~ 14

Author(s):

M.J.C. Rosales ◽

N.G. Alcantara ◽

Jorge Santos ◽

R. Zettler

Keyword(s):

Heat Transfer ◽

Friction Stir Welding ◽

Aluminium Alloys ◽

High Strength Steels ◽

High Strength ◽

Advanced Materials ◽

Mechanical Degradation ◽

Great Effort ◽

Friction Stir ◽

Advanced High Strength Steels

Although new structural and advanced materials have been used in the automotive and aircraft industries, especially lightweight alloys and advanced high strength steels, the successful introduction of such materials depends on the availability of proven joining technologies that can provide high quality and performance joints. Solid-state joining techniques such as Friction Stir Welding (FSW) are a natural choice since their welds are produced at low temperatures, so the low heat input provides limited, slight distortion, microstructural and mechanical degradation. Great effort has currently been devoted to the joining of Al-Cu-Mg and the Al-Mg-Si alloys because of their high strength, improved formability, and application in airframe structures. FSW is a continuous, hot shear, autogenous process involving a non-consumable and rotating tool plunged between two abutting workpieces. The backing bar plays an important role in heat transfer from stir zone (SZ), which can influence the weld microstructure as well as the consolidation of material in the root of the join. This study aims at investigating issues concerning heat generation, within the SZ of friction stir welded aircraft aluminium alloys.

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Failure Mode and Fatigue Behavior of Ultrasonic Spot Welds with Adhesive in Lap-Shear Specimens of Magnesium and Steel Sheets

SAE International Journal of Materials and Manufacturing ◽

10.4271/2013-01-1020 ◽

2013 ◽

Vol 6 (2) ◽

pp. 279-285 ◽

Cited By ~ 7

Author(s):

Wei-Jen Lai ◽

Jwo Pan ◽

Zhili Feng ◽

Michael Santella ◽

Tsung-Yu Pan

Keyword(s):

Failure Mode ◽

Fatigue Behavior ◽

Spot Welds ◽

Steel Sheets ◽

Lap Shear

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Spot Weld Strength Determination Using the Wedge Test: In Situ Observations and Coupled Simulations

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.24-25.299 ◽

2010 ◽

Vol 24-25 ◽

pp. 299-304 ◽

Cited By ~ 7

Author(s):

Rémi Lacroix ◽

Joël Monatte ◽

Arnaud Lens ◽

Guillaume Kermouche ◽

J.M. Bergheau ◽

...

Keyword(s):

Energy Analysis ◽

High Strength Steels ◽

High Strength ◽

Spot Weld ◽

Weld Strength ◽

Spot Welds ◽

Local Loading ◽

Advanced High Strength Steels ◽

Strength Determination

This paper describes an innovative way to characterize the strength of spot welds. A wedge test has been developed to generate interfacial failures in weldments and observe in-situ the crack propagation. An energy analysis quantifies the spot weld crack resistance. Finite Element calculations investigate the stresses and strains along the crack front. A comparison of the local loading state with experimentally observed crack fronts provides the necessary data for a failure criterion in spot weld fusion zones. The method is applied to spot welds of Advanced High Strength steels.

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Investigations on the Mechanical Behavior of Advanced High Strength Steels Resistance Spot Welds in Cross Tension and Tensile Shear

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.89-91.130 ◽

2010 ◽

Vol 89-91 ◽

pp. 130-135 ◽

Cited By ~ 6

Author(s):

Sylvain Dancette ◽

Véronique Massardier-Jourdan ◽

Jacques Merlin ◽

Damien Fabrègue ◽

Thomas Dupuy

Keyword(s):

Three Dimensional ◽

High Strength Steels ◽

Complex Loading ◽

High Strength ◽

Weld Strength ◽

Tensile Shear ◽

Spot Welds ◽

Advanced High Strength Steels ◽

Cross Tension ◽

Failure Types

Advanced High Strength Steels (AHSS) are key materials in the conception of car body structures, permitting to reduce their weight while increasing their behavior in crash conditions. Nevertheless, the weldability of AHSS presents some particular aspects, in that complex failure types involving partial or full interfacial failure can be encountered more often than with conventional mild steels during destructive testing, despite high spot weld strength levels. This paper aims at characterizing the behavior of different AHSS spot welds under two quasi-static loading conditions, tensile shear and cross tension, often used in the automotive industry for the determination of their weldability. Interrupted cross tension and tensile shear tests were performed and spot welds failure was investigated with optical micrographs, SEM fractography and 3D-tomography in order to follow the three-dimensional crack paths due to the complex loading modes. A limited number of failure zones and damage mechanisms could be distinguished for all steel grades investigated. Moreover, numerical simulation of the tests was used to better understand the stress state in the weld and the influence of geometrical features such as weld size on the occurrence of the different failure types.

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Effect of Quenching and Partitioning Heat Treatment on the Fatigue Behavior of 42SiCr Steel

Metals ◽

10.3390/met11111699 ◽

2021 ◽

Vol 11 (11) ◽

pp. 1699

Author(s):

Marco Thomä ◽

Guntram Wagner

Keyword(s):

Electron Microscopy ◽

Mechanical Properties ◽

Heat Treatment ◽

Material Properties ◽

Retained Austenite ◽

Fatigue Behavior ◽

High Strength Steels ◽

High Strength ◽

Advanced High Strength Steels ◽

Scanning Electron

The manufacturing of advanced high-strength steels with enhanced ductility is a persistent aim of research. The ability of a material to absorb high loads while showing a high deformation behavior is a major task for many industrial fields like the mobility sector. Therefore, the material properties of advanced high-strength steels are one of the most important impact factors on the resulting cyclic fatigue behavior. To adjust advanced material properties, resulting in high tensile strengths as well as an enhanced ductility, the heat treatment process of quenching and partitioning (QP) was developed. The quenching takes place in a field between martensite start and martensite finish temperature and the subsequent partitioning is executed at slightly elevated temperatures. Regarding the sparsely investigated field of fatigue research on quenched and partitioned steels, the present work investigates the influence of a QP heat treatment on the resulting microstructure by light and scanning electron microscopy as well as on the mechanical properties such as tensile strength and resistance against fatigue regarding two different heat treatment conditions (QP1, QP2) in comparison to the cold-rolled base material of 42SiCr steel. Therefore, the microscopic analysis proved the presence of a characteristic quenched and partitioned microstructure consisting of a martensitic matrix and partial areas of retained austenite, whereas carbides were also present. Differences in the amount of retained austenite could be observed by using X-ray diffraction (XRD) for the different QP routes, which influence the mechanical properties resulting in higher tensile strength of about 2000 MPa for QP1 compared to about 1600 MPa for QP2. Furthermore, the transition for the fatigue limit was approximated by using stepwise load increase tests (LIT) and afterwards verified by constant amplitude tests (CAT) in accordance with the staircase method, whereas the QP 1 condition reached the highest fatigue strength of 900 MPa. Subsequent light and scanning electron microscopy of selected fractured surfaces and runouts showed a different behavior regarding the size of the fatigue fracture area and also differences in the microstructure of these runouts.

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