Fatigue Crack Propagation Limit Curves Research Articles

The influence of the base material - filler metal pairing on the fatigue crack propagation of 700 MPa strength category welded joints

In the field of welding of high-strength structural steels, the 700 MPa strength category represents a kind of boundary. Overmatched (OM) consumables are also available, but the behavior of various mismatch types under cyclic loading condition is not yet clear. In order to know the fatigue crack propagation resistance of 700 MPa strength category steels and their gas metal arc welded joints fatigue crack growth tests were performed on statistically representative samples. Matching/overmatching (M/OM) mismatch type was tested, the tests results were analyzed and fatigue crack propagation limit curves were determined. The different mismatch types, our and previous results were compared. It can be concluded that M type is the optimal and M/OM type is more beneficial than simple OM type.

Uticaj neusklađenosti na granične krive širenja zamornih prslina osnovnih materijala tipa S690KL, S960KL i S960TM i njihovih, elektrolučno u zaštiti gasa, zavarenih spojeva

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.

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

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 high strength steels based on two-stage relationship

Nowadays, the environmental impact reduction and the reliability enhancement of operating structures are basic trends in the heavy industry, which can be achieved using advanced materials and technologies. Metal structures are often operated with microstructural failures (e.g. cracks), and under cyclic loading conditions. The research work has focused on the high strength steels from the world of materials, on the welding technologies from the manufacturing processes, and on the fatigue cracks from the material failures. In order to determine and compare the fatigue resistance of different high strength steels grades and their gas metal arc welded joints, fatigue crack growth tests were performed on S690QL, S960QL and S960M steel grades. Statistical aspects were applied both for the presenting of the possible locations of cracks in base materials and welded joints and for the processing of the measured data. Fatigue crack propagation limit curves were derived based on two-stage crack growth relationship, using probability methods. The determined limit curves can be applied for engineering critical assessment and structural integrity calculations.

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

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.

Fatigue Curves for Aluminium Alloys and their Welded Joints Used in Automotive Industry

Our research work has focused from the materials world on the aluminium alloys, from the manufacturing processes on the welding technologies, and from different loads on the cyclic loads. The article aimed (i) to demonstrate the behaviour of the friction stir welded (FSW) joints under cyclic loading conditions; (ii) to determine fatigue (limit) curves for two aluminium alloys and their welded joints. Experiments were performed on 5754-H22 and 6082-T6 aluminium alloys and their FSW joints. Both high cycle fatigue (HCF) and fatigue crack propagation (FCG) tests were executed on both base materials and their welded joints. Statistical behaviour of the base materials and welded joints was represented by the cutting of the specimens and the using of different crack paths. HCF limit curves were determined based on staircase method and FCG limit curves can be determined by own developed six step method. The investigations and their results were compared with each other and with the results can be found in the literature.

Behaviour of AlMg3 Base Material and its Friction Stir Welded Joints under Cyclic Loading Conditions

The friction stir welding (FSW) is a dynamically developing version of the pressure welding processes. Nowadays, the knowing of the properties and the behaviour of the welded joints is an important direction of the investigations, especially under cyclic loading. The research work aimed (i) to demonstrate the behaviour of the FSW welded joints under cyclic loading conditions; (ii) to confirm the applicability of the used friction welding technology. Experiments were performed on 5754-H22 aluminium alloy and its welded joints; both high cycle fatigue (HCF) and fatigue crack propagation (FCG) tests were executed. HCF limit curves were determined based on staircase method. Statistical behaviour of the base material and the welded joints under FCG was represented by the cutting of the specimens, in other words by the using of different crack paths. FCG limit curves can be determined by own developed six step method. The investigations and their results were compared with each other and with the results can be found in the literature.

Fatigue Crack Propagation Limit Curves for High Strength Steels and their Application for Engineering Critical Assessment Calculations

There are different prescriptions containing fatigue crack propagation limit curves and rules for the prediction of the crack growth. The research work aimed (i) to determine fatigue crack propagation limit curves for high strength steels and their welded joints, based on the Paris-Erdogan law; (ii) to use the determined limit curves for engineering critical assessment (ECA) calculations. Experiments were performed on different high strength steels and their welded joints; and the propagating cracks in the specimens represent the different possible locations of the real cracks in the structural elements. Fatigue crack growth tests were executed by ΔK-decreasing and constant load amplitude methods. The evaluation process consists of six steps, and by means of the selected values a statistical method can be proposed for determination of the limit curves. Engineering critical assessment calculations were performed on a welded structural element having crack like defects.

Behaviour of Friction Stir Welded Joints Made out of Two Aluminium Alloys under Cyclic Loading Conditions

The friction stir welding (FSW) is a dynamically developing version of the pressure welding processes. Nowadays, the knowing of the properties and the behaviour of the welded joints is an important direction of the investigations, especially under cyclic loading. The research work aimed (i) to demonstrate the behaviour of the friction stir welded joints under cyclic loading conditions; (ii) to determine fatigue limit or design curves for aluminium alloys and their welded joints made by FSW process. Experiments were performed on 5754-H22 and 6082-T6 aluminium alloys and their welded joints. Both high cycle fatigue (HCF) and fatigue crack propagation (FCG) tests were executed on both base materials and their welded joints. Statistical behaviour of the base materials and welded joints was represented by the cutting of the specimens and the using of different crack paths. HCF limit curves were determined based on staircase method. FCG limit curves can be determined by own developed six step method. The investigations and their results were compared with each other and with the results can be found in the literature.

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

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).

Fatigue Crack Propagation Limit Curves for Different Metallic and Non-Metallic Materials

Fatigue Crack Propagation Limit Curves for Different Metallic and Non-Metallic Materials