Numerical simulation and experimental verification of torsion fatigue tests for material Weldox

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13th International Scientific Conference on Sustainable, Modern and Safe Transport 13th International 2019), Scientific Conference on Sustainable, and Safe Transport (TRANSCOM High Tatras, Novy Smokovec –Modern Grand Hotel Bellevue, (TRANSCOM 2019),Slovak High Tatras, Novy Smokovec – Grand Hotel Bellevue, Republic, May 29-31, 2019 Slovak Republic, May 29-31, 2019

Numerical simulation and experimental verification of torsion Numerical simulation and experimental verification of torsion fatigue tests for material Weldox fatigue tests for amaterial Weldox a, a a Mária Blatnickáa,*, Milan Ságaa, Peter Kopasa, Marián Handrika Mária Blatnická *, Milan Sága , Peter Kopas , Marián Handrik University of Žilina, Univerzitná 1, 010 26 Žilina, Slovakia University of Žilina, Univerzitná 1, 010 26 Žilina, Slovakia

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Abstract Abstract The aim of the article is to theoretically determine the stress and strain state in a critical area of the sample, based on its FE numerical The aim of the is to of theoretically theastress and strain statesample in a critical area of the sample, based on its FE numerical simulations. Onarticle the basis a series of determine simulations, load plan of a real for experiments on fatigue testing equipment was set up. The predicted loadoflevels were constant strain testing. The result will the Manson-Coffin fatigue simulations. On the basis a series of calculated, simulations,assuming a load plan of a real sample for experiments on be fatigue testing equipment was set up. Based The predicted load levels were calculated, assuming testing.value The will result be the Manson-Coffin fatigue curve. on the presented calculations, the stress state in constant terms of strain the nominal bewill predicted. curve. Based on the presented calculations, the stress state in terms of the nominal value will be predicted. © 2019 The Authors. Published by Elsevier B.V. © 2019 The Authors. Published by Elsevier B.V. © 2019 The Authors. Published byof Elsevier B.V. committee of the 13th International Scientific Conference on Sustainable, Peer-review under responsibility the scientific Peer-review under responsibility of the scientific committee of the 13th International Scientific Conference on Sustainable, Peer-review under responsibility of the scientific Modern and Safe Transport (TRANSCOM Modern and Safe Transport (TRANSCOM2019). 2019).committee of the 13th International Scientific Conference on Sustainable, Modern and Safe Transport (TRANSCOM 2019). Keywords: fatigue test; numerical simulation; torsion; Weldox Keywords: fatigue test; numerical simulation; torsion; Weldox

1. Introduction 1. Introduction Steel is undoubtedly one of the most important engineering materials in the world today, as evidenced by its wide Steel is undoubtedly one of the atmost important engineering the world today, as evidenced by its wide application, which we encounter every step. Steel is widelymaterials used in in manufacture of building structures such as application, which webuildings, encounterbut at also everyin step. Steel is widely used in manufacture building structures suchand as bridges and industrial transportation in manufacturing of vehiclesof and construction of roads bridges industrial buildings, butfor alsothe in wide transportation in manufacturing of vehiclesoccurrence and construction roads railways.and One of the main reasons application of steel is the abundant of ironof ore and and the railways. of the main reasons for the wide application of steel is the abundant occurrence of iron ore and the relatively One fast and inexpensive production. relatively fastenergy and inexpensive production. However, demands and prices are constantly increasing, causing efforts to reduce the weight of structures. However, energy and prices areenvironmental constantly increasing, causing efforts reduce the of structures. More beneficial fromdemands energy, financial and point of view is the moretoefficient use weight of omnipresent steel More beneficial from energy, financial and environmental point of view is the more efficient use of omnipresent steel

* Corresponding author. E-mail address:author. [email protected] * Corresponding E-mail address: [email protected] 2352-1465 © 2018 The Authors. Published by Elsevier B.V. Peer-review©under responsibility of the scientific committee 2352-1465 2018 The Authors. Published by Elsevier B.V. of the 13th International Scientific Conference on Sustainable, Moder n and Safe Transport (TRANSCOM 2019). Peer-review under responsibility of the scientific committee of the 13th International Scientific Conference on Sustainable, Moder n and Safe Transport (TRANSCOM 2019). 2352-1465  2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 13th International Scientific Conference on Sustainable, Modern and Safe Transport (TRANSCOM 2019). 10.1016/j.trpro.2019.07.090

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than the introduction of completely new materials. Replacing conventional structural steels with high-strength steels will result in a significant reduction in material thickness and hence the desired weight reduction with unchanged structural strength [1,2]. One common problem that limits the wide use of high strength steels in transport applications is fatigue of material and especially fatigue of their weld joints [3,4,5]. The greater is the yield strength of the material, the more notchsensitive its fatigue strength becomes. And since a notch related to the change in the cross-section of the welded joint is always present in the welded material, high-strength steel welds are considered to be sensitive to fatigue of material. However, higher fatigue strengths can be achieved by using high quality welded joints [6,7,8,9]. In the present paper, the fatigue curve of the base material Weldox 960 will be determined and will serve as a background for further research of fatigue life of various weld joints of this material. 2. Experimental procedure Experimental measurements of high strength steel samples fatigue life were carried out on built fatigue testing equipment. One part of the measurement equipment is a mechanism of torsion cyclic loading of samples. Whole mechanism is run by synchronous servomotor. Its rotational movement is transmitted by excenter on a crank that perform linear movement. This movement causes torsion loading of the sample, which is rotationally gripped at one its end and fixed at the other end (Fig. 1). [10,11].

Fig. 1. Experimental measurement equipment for torsion cyclic loading (left), excenter couple – shaft (middle) and hub (right)

Magnitude of the sample loading is set by the change of excenter shaft rotational position relative to the excenter hub (Fig. 1.). Both parts are connected by spline joint that ensures reliable connection, power transfer and fluent and precise regulation of loading by rotation of the sample gripping part. The excenter couple (shaft with hub) has thirty seven positions (teeth). One position is so called “zero position”. It is followed by eighteen gradually rising loading positions up to the maximum loading position and then the loading is gradually decreasing and repeating to the zero position. It means that the excenter couple allows setting eighteen different loading values. 2.1. Deflection calculation Currently, there are three types of excenter couples at the workplace, with maximum deflection of 2, 4 and 8 mm. The total deflection is reached as a sum of deflections (eccentricity) of both parts (shaft and hub). For example total maximum deflection of 4 mm is reached when a shaft with deflection of 2 mm is connected with a hub with deflection of 2 mm. The total deflection at individual rotational position of the shaft relative to the hub is calculated according to the Figure 2. Total deflection is equal to the distance between axis of the shaft O1 and axis of the hub O3. Axis O2 is identical for both parts in any time of their connection.



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Fig. 2. Excenter couple scheme for calculation of total deflection

Total deflection in mm depending on rotational position in number of teeth for excenter with deflection 1, 2 and 4 mm can be seen in the Figure 3.

Fig.3. Dependence of total deflection on rotational position of the shaft

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3. Stress and strain analysis of testing sample For fatigue testing of high strength steel material, sample depicted in Figure 4 was chosen. To determine stress and strain in the critical area of the sample, its model was created in FEM program ADINA (Fig. 5.).

Fig. 4. Fatigue testing sample

To analyze fatigue measurement results on individual loading levels, it is necessary to know the value of strain or stress amplitude for every loading level. Therefore, series of simulations were carried out.

Fig. 5. 3D meshed model of the sample created in program ADINA

The model of the sample was meshed using 3-D Solid tetrahedral elements with 10 nodes pre element. Density of the mesh was adjusted at the critical area of the sample by increasing the mesh density and so number of elements. Material model of the sample for simulation was created according to the real tensile test of the sample material (Fig. 6.). Material tested was high strength steel Weldox 960 with minimal yield strength of 960 MPa.



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Fig. 6. Tensile test of the sample from material Weldox 960

Boundary conditions for simulation were loading in the form of excenter deflections transformed into angles of rotation of the sample in the grip in radians and fixity of the sample in the real state. In the critical area of the sample, values of stress and strain were simulated (fig. 7.).

Fig. 7. Distribution of effective stress according to HMH theory (von Mises) on the sample loaded by cyclic torsion

A series of simulations were carried out to determine values of stress and strain in the critical area of the sample for every loading level (every tooth of the excenter couple). These results can be seen in Figure 8.

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Fig. 8. Strain amplitude (left) and nominal shear stress (right) values for torsion loading at individual load levels 4. Measurement results On the basis of abovementioned results, a number of experimental tests at various loading levels (teeth of the excenter couple) were conducted. Namely, the samples were loaded by cyclic torsion using constant strain testing at measurement equipment described in section 1. Number of cycles to the sample failure was assigned to the strain at the individual load level obtained from simulation and presented in the form of Manson-Coffin curve (Fig. 9.).

Fig. 9. Manson-Coffin curve for material Weldox 960 loaded by cyclic torsion



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As the fatigue tests ran at constant strain (controlled deformation), Wohler curve (Fig. 10) has only informative meaning and can be just used in linear area of loading (stress under the yield value) [12,13].

Fig. 10. Wohler curve for material Weldox 960 loaded by cyclic torsion

5. Conclusion Finite element model of the fatigue testing sample from high strength steel material Weldox 960 was created in program ADINA. Simulated material model corresponds to the real material used and is based on its tensile tests. Loading of the sample was applied in the form of angle of rotation (corresponding to the cyclic torsion) and series of simulations for every loading level were conducted. Values of stress and strain were gained for every load level and became a basis for fatigue experimental measurements of real samples. Measured number of cycles were assigned to the strain (stress) at individual load level and displayed in the form of Manson-Coffin and Wohler curve respectively. The next step in the research will be to conduct a series of simulations for material loaded by cyclic bending and to carry out experimental measurements on real samples to compare both gained results (torsion and bending). These results will serve as a background for further research in fatigue properties of weld joints of material Weldox 960. Acknowledgements This work has been supported by the Slovak Research and Development Agency under the contract No. APVV14-0096. References [1] Porter, D. A. 2015. Weldable High-Strength Steels: Chalenges and Engineering Applications. IIW International Conference, High-Strength Materials – Challenges and Applications, Helsinki, Finland 2015. [2] Senuma, T. 2000. Physical Metallurgy of Modern High Strength Steel Sheets. ISIJ International, Vol. 41 (2001), No. 6, pp. 520-532.

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[3] Fricke, W. 2012. IIW Guideline for the Assessment of Weld Root Fatigue. International Instite of Welding. IIW-Doc. XIII-2380r3-11/XV1383r3-11 [4] Lopez-martinez, L. 1997. Fatigue Behaviour of Welded High-Strength Steels. Dissertation. Department of Aeronautics, The Royal Institute of Technology. 1997. Report No. 97-30. [5] Schijve, J. 2003. Fatigue of structures and materials in the 20th century and the state of the art. International Journal of Fatigue 25 (2003) 679702. [6] Schijve, J. 2009. Fatigue of Structures and Materials. Springer Science+Business Media, B.V., 2009. ISBN-13: 978-1-4020-6807-2. [7] Schütz, W. 1996. A history of fatigue. Engineering Fracture Mechanics 54/2 (1996) 263-300. [8] EN 1993-1 12 (2007) : Eurocode 3: Design of steel structures – Part 1-12: General – High strength steels. The European Union Per Regulation 305/2011, Directive 98/34/EC, Directive 2004/18/EC. [9] Fricke, W. 2002. Fatigue analysis of welded joints: state of development. Marine Structures 16 (2003) 185-200. [10] Kopas, P., Blatnický, M., Sága, M., Vaško, M. 2017. Identification of mechanical properties of weld joints of AlMgSi07.F25 aluminium alloy. In: Metalurgija, Vol. 56, Issue 1-2, pp. 99-102. [11] Vaško, M., Blatnický, M., Kopas, P., Sága, M. 2017. Research of weld joint fatigue life of the AlMgSi07.F25 aluminium alloy under bending-torsion cyclic loading. . In: Metalurgija, Vol. 56, Issue 1-2, pp. 94-98. [12] Dižo, J., Harušinec, J., Blatnický, M. 2017. Structural Analysis of a Modified Freight Wagon Bogie Frame. 18th international scientific conference-logi 2017. Book Series: MATEC Web of Conferences. Vol. 134, art.no. 00010. [13] Jakubovičová, L., Ftorek, B. Baniari, V., et al. 2017. Engineering design of a test device. Procedia Engineering. Vol. 177, pp. 520-525.