scholarly journals Mismatch effect on fatigue crack propagation limit curves of GMAW joints made of S960QL and S960TM type base materials

2020 ◽  
Vol 10 (1) ◽  
pp. 28-38
Author(s):  
Haidar Mobark ◽  
János Lukács
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Structural Steels ◽  
Cyclic Loading Condition ◽  
Strength Category ◽  
Crack Propagation Resistance ◽  
Base Materials ◽  
Propagation Limit ◽  
Mismatch Effect

Welded structures cannot be produced without imperfections, cracks or crack like defects. Among the structural steels, 960 MPa strength category represents a reliable application possibility. Consumables are also available, but the behaviour of mismatch types under cyclic loading condition is not yet clear. In order to know the fatigue crack propagation resistance of 960 MPa strength category steels and their gas metal arc welded joints fatigue crack growth tests were performed. The tests results were analysed and fatigue crack propagation limit curves were determined.

Fatigue Crack Propagation Limit Curves for S690QL and S960M High Strength Steels and their Welded Joints

2018 ◽  
Vol 1146 ◽  
pp. 44-56 ◽  
Author(s):  
János Lukács ◽  
Ádám Dobosy ◽  
Marcell Gáspár
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Welded Joints ◽  
High Strength Steels ◽  
High Strength ◽  
Base Materials ◽  
Propagation Limit

The objective of the paper is to present the newest results of our complex research work. In order to determination and comparison of the fatigue resistance, fatigue crack growth tests were performed on different grades of S690QL quenched and tempered, and S960TM thermomechanically rolled high strength steels.15 mmand30 mmthick base materials were used for our investigations. Welded joints were made from these base materials, using gas metal arc welding with matching, overmatching, and undermatching filler metals. In the paper, the performance of the welding experiments will be presented, especially with the difficulties of the filler material selection; along with the results of the fatigue crack growth examinations executed on the base materials and its welded joints. Statistical aspects were applied both for the presenting of the possible locations of the cracks in the base materials and the welded joints and for the processing of the measured data. Furthermore, the results will be compared with each other, and the possibility of derivation of fatigue crack propagation limit curves will be referred.

Two Methods for Determination of Fatigue Crack Propagation Limit Curves and their Application for Different Materials

2007 ◽  
Vol 345-346 ◽  
pp. 395-398 ◽  
Author(s):  
János Lukács
Keyword(s):  
Fracture Toughness ◽  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Research Work ◽  
Stress Intensity Factor Range ◽  
Crack Propagation Resistance ◽  
Threshold Stress Intensity Factor ◽  
Propagation Limit

There are different documents containing fatigue crack propagation limit or design curves and rules for the prediction of crack growth. The research work aimed to characterise the fatigue crack propagation resistance of different materials using limit curves and determination of limit curves under different loading conditions, based on statistical analysis of test results and the Paris-Erdogan law. With the help of the characteristic values of threshold stress intensity factor range (Kth), two constants of Paris-Erdogan law (C and n), fatigue fracture toughness (Kfc) or fracture toughness (KIc) two reliable method can be proposed. The limit curves calculated by both methods represent a compromise of rational risk (not the most disadvantageous case is considered) and striving for safety (uncertainty is known).

scholarly journals Mismatch effect on fatigue crack propagation limit curves of S690QL, S960QL and S960TM type base materials and their gas metal arc welded joints

2020 ◽  
Vol 65 (2) ◽  
pp. 75-86
Author(s):  
János Lukácsa ◽  
Haidar Mobarkb
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Welded Joints ◽  
Steel Structures ◽  
High Strength ◽  
Structural Elements ◽  
Base Materials ◽  
Propagation Limit

Nowadays, one of the basic trends in the industry is the environmental impact reduction, in other words the weight decreasing of structural elements and structures, which can be approached by applying different high strength steels. In case of different steel structures, the main manufacturing and joining technology is the welding, the conventional and advanced methods of fusion and pressure welding processes. Beside the weight decreasing, the reliability and safety requirements according to steel structures have significant grown. During the welding process, the welded parts are affected with heat-effect and mechanical loads, which result in inhomogeneous welded joint. The inhomogeneity of the welded joints appears both in microstructural (local) and in geometrical (both local and global) aspects. The changes in microstructure and geometry appear in deflections (basically acceptable), or rather in failures (basically unacceptable); and these influence both the behaviour and the loadability of welded joints. Discontinuities in base materials and their welded joints have especially high danger in case of cyclic loading conditions, which are typical for different structures and structural elements (e.g. bridges, vehicles). There are different standards and prescriptions containing fatigue crack propagation limit curves and rules for the prediction of the crack growth; simple and two-stage crack growth relationships can be found in the literature, most frequently based on the Paris-Erdogan law. The paper summarizes and presents the results according to our fatigue crack growth investigations on Weldox 700E and Weldox 960E quenched and tempered (Q+T) and on Alform 960M thermomechanically treated (TM) high strength steel base materials and their gas metal arc welded joints. The mismatch effect has also been studied; matched, overmatched, undermatched and matched/overmatched (mixed-matched) welded joints were investigated. 15 mm thick plates were used for the investigations, statistical aspects were applied both for presenting the possible crack locations in the real plates, as well as for processing the measured data. Furthermore, the results will be compared with each other, and fatigue crack propagation limit curves will be derived using simple crack growth relationship.

scholarly journals On the Fatigue Crack Propagation in Structural Steels (1st Report)

1969 ◽  
Vol 38 (11) ◽  
pp. 1243-1248 ◽  
Author(s):  
Kin-ich Nagai ◽  
Masaki Watanabe ◽  
Susumu Hioki ◽  
Katsuya Kajimoto
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Structural Steels

Enlarged Zn, Mg Contents with a same Zn/Mg Ratio Improve Fatigue Crack Propagation Resistance of Al-Zn-Mg-Cu Alloys with T7651 State

2020 ◽  
Vol 1003 ◽  
pp. 3-10
Author(s):  
Kai Wen ◽  
Bai Qing Xiong ◽  
Hua Zhou ◽  
Xi Wu Li ◽  
Zheng An Wang ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Aging Treatment ◽  
Fracture Morphology ◽  
Precipitate Size ◽  
Propagation Resistance ◽  
Crack Propagation Resistance ◽  
Cu Alloys ◽  
The Difference

The fatigue crack propagation of Al-Zn-Mg-Cu alloys could be influenced by the content of main alloying element. In the present work, two Al-Zn-Mg-Cu alloys with a same Zn/Mg ratio were treated by two stage over-aging aging treatment and typical T7651 states were extracted via mechanical properties. Fatigue crack propagation of the two alloys were tested and the related precipitation characteristics and fracture morphology were observed. The results showed that the alloy with higher Zn, Mg contents possessed a better fatigue crack propagation resistance compared with the alloy with lower Zn, Mg contents. The corresponding fracture morphology also showed the difference of fatigue striation, which provided an additional support. The precipitation observation demonstrated that the both alloys possessed GPII zone, η' phase and η phase while the alloy with higher Zn, Mg contents had a larger average precipitate size and a larger proportion of large size precipitates compared with the alloy with lower Zn, Mg contents. Cut and bypass mechanisms of dislocation-precipitate interactions were used to explain the difference of fatigue crack propagation between the two alloys.

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